ae I en I oe oe oe wee oe ome

TABLE 5-3 (cont.)

a nate 1 Soe

{camp IE snowy EE cng (NEE Conera BEE sore JERE Gone TE conse TEE owen TEE oxo }

53+

. Summary of Key Logistics Constraints —
, Logistics Category Break-up (July) Freeze-up (October)
, Conventional Marine- .
- small work boats (<50 ft) ¢ high ice concentrations, «slush ice clogging jet dnves
particularly under any and/or outboards ‘
pressure .
: , + |e limited or no icebreaking
© Inmited oily water storage in » ability
any high volume discharge
scenano ‘ ‘
Air Cushion Vehicles ;
. * + no known limitations over * spray icing build-up on decks,
rotting fast ice (potential intakes and props
. soccenpayioad or up to 80 problems offshore with rubble (manageable but need to allow
: 5 fields and/or ridging over four for down-time and have back-
Note: mobilization time for more | feet high) oP).
than one machine to arrive m oy .
Prudhoe Bay at any time of year * ice adfreezing to hull can add
. | could exceed five days substantial deadweight and
cut into payload (avoid |
__ Prolonged shutdowns in the
water in freezing
temperatures)
. + potential downtime in October
due to strong winds >25 kt ~
' (avg 10% of the time)
an
' ,
' :
aa



Ny eee eee oone tt) Sep saee ae ian 2 bi; Geass

jooene AFR sane JET ome TERE weno FE tae DR ony JR omen) BE oso BE ore J rome BEE we

aoe

oOo moe ci

| oa)

The ISB operations targeting the oil on ice floes would continue until all the available oil had been
ignited. Delays in operations due to response time and environmental factors would not affect the
overall removal effectiveness. The estimate of on-ice ISB effectiveness for the 15-day period,
expressed as a percentage of the total blowout flow: .
Oil volume removed from ice byISB= . 3024 bbi/day + 12,000 bbi/day
: = °25%

“ The total oil removed by ISB operations both on water and ice is:

Total oil removed by ISB operations = . 14%+25%
= 39%


jue a ne 7

} ooo]

[oe TE oan J omen SE oney BE my TT sane SR ou SE ne

ae Pe CEES Canes anaes 1 ees snail abil mci nosto-eoemanntn .ee a ooo A

direction which remains relatively unrestricted is to the northwest where ice floes at break-up have
been observed or tracked moving as fara as Harrison Bay within a few days of leaving the Prudhoe
Bay area. : : . .

Open-Water Wake. An open water wake has frequently been observed when close pack ice qi 10
or more) moves past gravity based drilling structures and artificial islands in the US and Canadian
Beaufort Seas. This wake may extend for adistance of? to 3 island diameters or approximately 1000
to 1500 feet and will be as wide as the island diameter or about 500 feet.

New ice will start to form almost immediately in the open water wake, with the grease ice and nilas
moving with ‘wind to build up a slush dam against the i ice floes at the downwind side of the wake.

This wake effect is accounted forin developing the freeze-up scenario with 7/10 ice at Northstar. In
lighter concentrations, individual floes are free to close in quickly behind the island as the ice drifts
past; consequently, a wake as such does not exist in those cases. At break-up, the scenarios are
located to the east of West Dock which forms an extension from the shore. By defimtion, with open
water already present to the west of West Dock in July, there is no ice upstream to create a wake ‘
effect, even if the configuration of the drilling pad allowed ice flow on both sides.

_ Fast Ice Nearshore. While the freeze-up broken ice scenarios are applicable to the Northstar

production island, logistics for any oil spill response will undoubtedly be based at West Dock. It is
anticipated that freeze-up storms (greater than 20 kts) in October, when the ice thickness is less than
. 12 inches, can create a broken ice condition at the Northstar production island but retain a 1-2 mile
wide zone of landfast ice around West Dock. Response vessels will have to negotiate a solid ice
cover (6"-12" thick) over a distance of 1 to 2 miles in order to reach the broken i ice described in the
simplified scenarios presented below. so 5

-19-


ee

—

Aamo om oo o.oo

TABLE B-3
Wind Direction Occurrence at Northstar and Pt. McIntyre

wn Per Cent Occurrence of Wind Directions =" nae
‘| Mar ’| Apr | May | Jun :| Jul ‘| Aug ‘| Sep _:| Oct ~| Nov "| Dec’
Ni 3 4 3 5 ‘6 7.7 6 7 3 3
NE} 21| 23{ 24] 28] 16] 224722] 18] 16 22| 20
Ej 18] 19{ 21] 22) 34] 384:*28{ 32] 31 26] 18
SE| 6 4 5 4 6 3] °:-5 6 8]. 6 5
S| 5 4 3 5 3 2 4 5 5 5
SW| 22 20 19 1B 7 4 > 6 9]- 14} 21
Wl 15] 18] 16) 12} 124 10] *: 13] 101. 12] 15
_NW| 4 4 3 4 6 8 10 81% 3 4
Calm 6 4 6 9| 10 6 5 6 9 9
; " ‘TABLE A-4 .
Cumulative Frequency Distribution of Monthly Air Temperatures

at Northstar and Pt. McIntyre

RLCLOLOC/[SC/OILoOl[o|~—

w

WlSOlOlO[SClololol[oi4njin

w

Note: The notation ** indicates less than 0.5 per cent but greater than zero.”



8661 UNV ‘eoNno0g

vas

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RBeownrwmoeanpnonpNnomtwoOooLD



moo co

~ Executive Summary ©

| owant TER dane TRS couse TERE canes EE mene BEE ones JEG ones SER ote TE neon TER concn JE sowe B oorey BE poe |

Co Co

1. Background

This study was performed for Alaska Clean Seas and the U.S. Minerals Management Service, acting

« on behalf of the North Slope Spill Response Project Team (NSSRPT)', a task group formed to

develop comprehensive oil spill response plans for petroleum operations on the North Slope of
Alaska. The objective of the study was to evaluate the capabilities to recover spilled oil from very
large oil well blowouts occurring during broken ice conditions in the southern Beaufort Sea. The
study team was to consider six well-defined oil well blowout scenarios and determine quantitatively:

¢ whether the mechanical cleanup systems that are currently available on the North Slope are
adequate to satisfy Alaska State requirements for cleaning up spills from blowouts in broken .
ice conditions;

+ whether additional resources would significantly improve the existing mechanical recovery
capability, and to what extent; and

* what the maximum cleanup capabilities might be for dealing with blowout spills in brokeni ice
if all possible cleanup techniques ‘were considered

The scenatios cover two locations (Point McIntyre and Northstar Island) in three ice concentrations
(30, 50 and 70% respectively). For Point Mclntyre the scenarios are 12,000 barrel-per-day spills
during spring break-up | a The Northstar Island scenarios are 15,000 barrel-per-day spills
that occur during fall freeze-uj : :

The study describes in detail the behavior and fate of the six blowout scenarios and the likely
effectiveness of countermeasures in recovering the resulting spills on water and ice. First, the
effectiveness of the mechanical recovery systems that exist on the North Slope is assessed. Then the
possible benefits are evaluated of adding more mechanical systems to the response, and of adding
the countermeasures of dispersant use and in situ burning to the mix of response options available.
Also discussed is the potential benefit of igniting and burning the blowout at source and thus
Preventing a major marine spil from occurring in the frst instance. The results are summarized as _
follows.

1 ‘The NSSRPT members include* Alaska Clean Seas, Alaska Department of Environmental
Conservation, Alaska Department of Natural Resources, Alyeska Pipeline Service Company,
British Petroleum Exploration (Alaska) Inc , North Slope Borough, US. Environmental Protection
Agency, and ‘US Minerals Management Service we

‘ Executive Summary - Page 1


> Gen

’Estimate of Recovered Fluids per 24-hr Time Period

TABLE 6-16 .

2 Item Calculation Volume °
total fluids per 24 hours 560 bbl/hr x 24 hours x 40% 5376 bbl
total free water 373 bbl/hr x 24 hours x 40% 3581 bbl
volume that can be decanted total free water x 80% . 2865 bbl |
total fluids stored per 24 hours total fluids less decant 2511 bbl .

foil 112 bbl/hr x 24 hours x 40% ~ 1075 bbl
"emulsified water 75 bblfbr x 24 hours x 40% 720 bbl
free water total free water x 20% ‘716 bbl |

aI mmo otro oO

oa oO Oo oO

an equivalent average oil thickness. The following table summarizes those calculations.

The above calculations were for one system which could encounter the entire width of the thick
slick.’As in the previous break-up scenario, additional systems could be used to attempt to recover
oil from the thick slick that is missed by the first system. The target for the additional systems is the
oil that escapes containment due to inefficiencies associated with the ice conditions, assumed to be
60% for the 50% ice condition. Using the same calculation procedure as in the previous break-up
scenario, ’a total of three additional systems are considered in sequence. For each system, the
encounter rate is estimated by subtracting the oil recovered by the previous system and estimating

r Estimate of Slick Conditions and Fluid Recovery for Four Systems Operated Sequentially
i «System Encounter Encounter Oil recovered Total fluid
. thickness Tate per 24 hours per 24 hours
fi - #1 2.1mm , 112 bbi/hr 1075 bbl 2511 bbl
fi ‘ #2 * 126mm ~ 67 bbV/hr . 643 bbl 1503 bbl |
#3 0.76 mm 40 bbl/hr 384 bbl 899 bbl
fi #4 0.46 mm + 24 bbi/hr * 230 bbl + §38 bbl |
f total - : - 2332 bbl 5451 bbl |
Tl : . -113-


jee TR one SR coe rooms ER ce J oe Ee vores BE roe mee coy DE oes I coe BE ones BE oes EE we DE naan DT coe DO ce |

ee ey See ee CS _ “ ae 0) a Bs) Oa see

maneuverability is required, they are very useful. This is exactly the situation that exists for the
blowout spills at Northstar and Pt. McIntyre considered in this study. The fields are close to land and
the spraying of dispersant product onto oil slicks scattered among broken ‘ice will require

maneuverable aircraft, such as helicopters, and skilled operators, both of which are found on the
“North Slope serving the petroleum industry on a regular basis.

. The helicopter-based units are self-contained systems that are slung beneath the helicopter. They are

made up of a dispersant reservoir, a pump-motor assembly and a spray-boom. ‘The system has the
advantage of not requiring any modification to the helicopter before use. Despite their higher
cruising speeds (50 to 75 kt with external slung loads), the helicopter is limited by its limited
operating range and very small payload, which ranges from 240 to 600 gallons for those systems
available in the U.S. With a small payload, many sorties are required to deliver significant quantities
of dispersant. Also, because of their high speed and low pumping rate, helicopter systems arelimited ~
to application rates of about 10 gallons per acre, and therefore require multiple passes to provide
higher doses to the thick oil patches. 5

The general strategy for dispersant use for the blowout spills in this study would be to have two
helicopter/spray bucket systems during daylight hours spray both the oil that is escaping mechanical
operations at the time and the oil that escaped during the previous night. The details of this operation
are described in Chapter 6 for the appropriate spills.


8 ee a ee pas 05) pala on +.) aaa a ale

“TABLE Bl
Exceedence Probability Distribution Of Ice Drift Speeds at Northstar and Pt. Melntyre

_ TABLE B-2
Cumulative Frequency Distribution Of Monthly Wind Speeds
' . at the Northstar and Pt. McIntyre Developments



avant } Reenter reeTNitE-— eerie es i — ale tmantoctee

Aor rr Or MoO MOM SOOO Ooo eo

, Barges : | Endeavor working platform and storage for skimming operation

+] Containment boom | Ro-Boom 36x43 | concentrate oil for recovery
Skimmers _ | Transrec 250 oil recovery

Given that the majority of the oil in these blowout scenarios is concentrated in a relatively narrow

» Slick, a large number of systems would not be required to encounter all of the thick portions of oil.
_ In fact, two containment systems, each involving 360 feet of boom deployed in a J-configuration,

could encounter the entire 240-ft thick slick width (using a gap ratio of 1:3). For the moment, the
effectiveness of two such systems will be evaluated, although the possible effectiveness of additional
systems will be estimated later in the analysis Oil recovery would be carried out using a skimmer
operated from the barge and deployed at the apex of the ‘Y’, There are several weir-type skimmers
stockpiled by ACS that would meet the estimated encounter rates in these scenarios, which will be

-in the range of 50 to 100 bbl/hour. (Alternatively, oleophilic skimmers such as the LORI brush

skimmer or the Foxtail could be used, but weir-type skimmers are used in the evaluation to illustrate

the greater fluid handling concems of weir-type devices. ‘The resulting estimate of system

effectiveness would be the same in either case.) Table 6-4 summarizes the key equipment that would
be used for the initial containment and recovery response for this scenario. ;

. | “TABLE 6-4
Key Equipment for the Initial Containment and Recovery Response for Scenario 1

Equipment Type | Examples ~ ‘ Function

Beaufort 20

Tugs . Pt. Barrow tow equipment to site and position on-scene. -
° Pt. Thompson , oe .

Arctic Tern a
Sag River
Toolhk River
Kavik River

- | Desmi Ocean
Desmi Harbor

173


mo co

a _ ES ee ae as Coane s nee seabed dn abenmces po i Semen so

ice concentrations fixed over the duration of each scenario; and keeping oil discharge rates
constant over the period of the blowout. These are not realistic, but they serve the purposes of
the study. ,

7. . Finally, the issue of spill probability is not addressed, although this is surely a very important
consideration for both regulators and industry. The maximum spill size in the study, 225, 000
barrels (15,000 barrel-per-day blowout x 15 days), is close in size to the Exxon Valdez spill.

_ Despite the still-fresh memory of this spill, it should be understood that oil well blowouts are
far less probable than tanker spills. To help put this into perspective, Appendix G has been
prepared; this is a quick analysis of the probability of blowout spills of the size considered in
this study. :

1.8 Addendum to this Report

When the first draft of this report was completed in April 1998 it became clear to members of the
North Slope Spill Response Project Team (NSSRPT) and other reviewers that one of the terms of
reference for the study (detailed in Section 1.5 above) was particularly unrealistic. This was the
requirement that wind and ice conditions for each scenario remain fixed over the entire 15-day
blowout period. To explore the significance of this restriction, NSSRPT requested that the scenarios

_ bere-analyzed using realistic conditions instead of the unvarying winds and ice concentrations that

_ were used originally. The spring break-up and fall freeze-up situations were examined separately by

“two different study teams. The spring break-up situation at Pt. McIntyre was re-analyzed by the
original study team; the results are presented in Appendix H of this document. The fall freeze-up_

situation at the Northstar location was studied by a task group set up within NSSRPT; the results of
this study are available in a separate report. Except for Appendix H, no other references to this
additional work is made in the following chapters or appendices.

5 ”


i _— — vo ere hire GN miles: a eh be be

S come a eaten TRIE wrens |

m en

: | 500-foot range.
July 15 _E 15 3 {0 5/10 move to the NW past the island at rates up to
Day 12 “ . 0.5 kt.

Table H-1: .
- Sequence of Wind Events Corresponding to a 15 day Break-up Scenario at Northstar

Anticipated Ice Conditions
Vicinity of Northstar (Seal Island)

deteriorated fast ice, 4 to 5 feet thick, starts to shift and

Dayl : i . | fracture - concentrations remain at 9 to 9.5/10 all day
’ but leads and cracks open up and large floes (>1,000
feet) start to become visible. Movements at this stage
“| limited to 100's of feet.
JulyS - E 15; | ice starts to open up around the island with movements
Day2 - of up to 1,000's of feet. Concentrations 8 to 9/10 fairly
{ homogeneous. .
July 6 | OE 10 concentrations in the 7 to 8/10 range move steadily
Day 3 . past the island at about 0.3 kt. .
July7to9 * SE calm to 10 kt | 5 to 6/10 concentrations wallow around the island with
Days 4to6 . (variable) no consistent drift pattern.
July 10 to 14 -N $ 3 to 5/10 {highly in homogeneous) concentration drift
Days 7 to 11 (variable) > ~ | slowly in the vicinity of the island with no particular

pattern and speeds less than 0.1 kt. Large (1,000's of

feet of open water interspersed with belts and patches
of ice up to 5/10) Floe sizes more likely in the 100- to

July 16 to 18 , | concentrations in the 1 to 3/10 range move
Days 13 to 15 sporadically in patches past the island with stretches of
‘ open water for up to 4 mile.

3. Spill Behavior a : ‘

An uncontrolled blowout occurs in early July at the Northstar artificial island releasing 15,000 -

-barrels of oil per day (BOPD) and 33 x 10° standard cubic feet (scf) of natural gas per day (a Gas-to-

Oil Ratio [GOR] of 2200 scf/bbl). Over the 15-day period of the incident, the air temperature ranges
from a nighttime low of 35 °F to a daytime high of 45 °F. Daylight exists for 24 hours. The
surrounding water is initially covered by 9+/10ths deteriorating fast ice that is 3 to 5 feet thick. At
the beginning of Day 3 the ice sheet breaks up and begins to move under the influence of the wind.
Ice concentrations decline continuously after this and reach 1/10th to 3/10ths by Day 15. Table H-1

“shows the wind and ice conditions assumed for this scenario. The ice floes are initially 500 to 1000

feet in size; however, as breakup progresses the floes fracture and reduce to 50 to 500 feet in size
for Days 4 through 15. The ice is drifting at the same speed as the water (both wind-driven at 3% of

ak ee coe tet


PS Ey ene He Sees - bhi Sis ae een as is) Sons

; : TABLE 6-18. ,
Slick Conditions and Fluid Recovery for Four Systems Operated Sequentially in Scenario 6

Encounter Oil recovered Total fluid
rate per 24 hours per24hours  .
59 bbl/hr - 283 bbl * 660 bbl 1
#20 0.88 mm 55 bbI/hr . 226 bbl 525 bbl
#3 0.70 mm 52 bbI/hr 178 bbl 416 bbl
#4 056mm . 48 bbl/hr 144 bbl 336 bbl |
total - - *831 bbl 1937 bbl

aa nrnmt a cc

Unlike the previous ‘two breakup scenanos, the oil recovered per system does not decline
substantially. This is related to the very low effectiveness of each system due to inefficiencies
associated with the 70% ice concentration. Because each of the systems tecovers only a fraction of
the available thick slick, the slick is essentially unchanged by each successive system. One might

~ above recovers only about 1% of the blowout volume, and subsequent systems would accomplish
even less.

Predicted Effectiveness of Existing Mechanical Systems in Recovering 15-Day Discharge .

This final step in this section is to use the above calculations to assess the effectiveness of existing
systems to deal with the total volume of oil discharged over the 15-day blowout period. The
assessment includes the effects of response-time delays, and the environmental derating factors of
visibility, VFR flying conditions, and wave heights. As for all the break-up scenarios, the response
time is estimated to be 12 hours, so for the 15-day period the effect is to reduce effectiveness by 3%
qs -%) + 15 = 0.97). Also for all break-up scenarios, the combination of the three environmental
factors are such that, on average, mechanical containment and recovery will be effective 66% of the

time. The following is the estimate of effectiveness for the 15-day period, expressed asa percentage
” of the total blowout flow: ‘

S122. |

aor o ate oO OOOO

be tempted to suggest adding even more systems, but it should be noted that the lastof the fournoted - .


i

ao wo

6.10 Summary of Countermeasures Effectiveness

6.10.1 Existing Countermeasures

In this chapter, six blowout scenarios were examined to determine the potential effectiveness of

existing countermeasures, that is, excluding any possible use of dispersants or in-situ burning; the

results are summarized in the table below. Effectiveness is defined here as the percentage of the

blowout flow over the 15-day period that could be recovered by existing response systems. A second

effectiveness number is also shown: it takes into account the reduction in blowout volume due to

evaporative losses - fixed at 20 % for all scenarios ~ and losses due to tiny-particle drift - estimated

to be 10 % of the total blowout flow. This second effectiveness number is therefore the percentage

recovery of the oil that is estimated to land in the marine environment, that is, 70 % of the total

blowout flow.

TABLE 6-19
Summary of Recovery Effectiveness for Six Scenarios

| . Freeze-up - | Break-up '
| Scenario Parameters Ice Coverage Ice Coverage
30% | 50% | 70% | 30% | 50% | 70%
Estimated 15-day recovery, 5.9 '2.2 0.6 18 12 44
percentage of total blowout |
Estimated 15-day recovery, :
percentage of total blowout that 85 3.1 0.8 25°-| 18 63 |
| reaches ice/water surface ,

The results are discussed below according to the major variables in the analysis.

“ 128-



Loman TERS cae TE conve TRE coves FE oman» FREE cxnen TE mee EEE crews A overs EEE cove BE sere SE veseee JE oven ites one TE ouane BE ene TE wena FE smn TE so |

Table G-1 ‘

Historical Large Oil Spills from Offshore Oit-well Blowouts
Area : Reported Spill Date Operation Underway
Size (bbl)
Mexico (Ixtoc 1)  * | 3,000,000 1979 “Exploratory Drilling
Dubai . 2,000,000 1973 Development Drilling
Iran' —— 2 1983 Production
Mexico . « 247,000 "1986 Workover .
Nigeria . - 200,000 1980 Development Drilling
North Sea/Norway . 158,000 , . 1977 Workover
Irn’ 100,000 . 1980 Development Drilling
U.S.A., Santa Barbara 77,000 1969 ‘ Production
Saudi Arabia ‘ 60,000 - 1980 Exploratory Drilling
. Mexico . 56,000 1987 Exploratory Drilling
U.S.A., S. Timbalier 26 53,000 . -1970 .
’ ,U.S.A,, Main Pass 41 30,000 1970 Froduetion
. US.A,, Timbalier Bay/Greenhill 11,500 1992 Production ,
Trinidad . 10,000 . 1973 Development Drilling
L ' The Iranian Norwuz oil-well blowouts in the Gulf of Arabia, which started in February 1983,
were not caused by exploration or drilling accidents but were a result of military actions during
the Iraq/Iran war.

Blowouts during Production and Workovers. Table G-1 shows the occurrence of two extremely
large (>150,000 bbl) and five very large (>10,000 bbl) oil spills from blowouts during production
and workovers. Developing an exact risk exposure for these events is not easy because of lack of
data, but it is estimated that the total oil produced offshore on a worldwide basis up to the end of
1995 is about 100 billion barrels, and that the total producing oil well-years is 200,000 well-years
(SL Ross 1998). Generally, in analysing accidents in the oil and gas industry the exposure variable
of "well-years" is used to normalize data for the continuous operation of production. This exposure

is also convenient to use for workovers inasmuch as these maintenance activities, although not being -
continuous operations, usually occur with regularity, say, every five to seven years or so during the
lifetime of a well. .

On this basis the worldwide frequency of extremely large oil spills (>150, 090 bbl) from oil-well
blowouts that occurred during production or workovers is 2/200, 000 = 1.0x 10° blowouts/well-year.
For very large spills (>10,000 bbl) the number is 2.5 x 10° blowouts/well-year.

Finally, it is emphasized that the spill frequencies derived above for extremely large spills, however -

~ low, are based on spills in countries (except Norway) that do not generally have regulatory standards

as stringent as those existing in the USA. For example, the largest oil spill in history, the Ixtoc I
oil-well blowout in the Bay of Campeche, Mexico, that occurred in 1979, was caused by drilling
-2- '

3


pe Seanan a —

co .co

a a eo

r

Skycrane to sling the North Star offshore. Once on location in broken thin i ice, these smaller
boats could work locally to support the skimming systems. .

"New 42.8 (1998) X2
870 hp

Northstar - 32 ft

38-55 ft (5 in total

14 to 28 ft (~45 in total)

Caribou and Lemming (2) .

60 X 160 ft

flexa float barge (2)
- 40X140f

Mop King (Landing Craft)

Annika Marie
14X43 ft

Alaska Clean Seas (ACS).

2.5 ft draft, with push knees to handle

, 200 series barges. Unknown potential in ice but

. in early October

expect good utility in 3 to 6/10 at break-up and
some applications offshore

Usually last boat out of the water in mid-October.

‘ Straight shaft, twin screw. Could be used offshore
-, for part of October.

All jet drive (assume no capsbiliy under freezing
conditions)

mix of jet drives and outboards skifts, inflatables,
N hull, flat bottom, and landing craft (see ACS
listing) .

Deck barges (non ice strengthened)

One at East Dock, one at West Dock. These
barges are ex-ARCO with no current USCG
certificates. Useful to support spring operations in
shallow water - not recommended for offshore use
at freeze-up. .

Ice Services - TJ Borden

Shallow draft, 250 ton capacity

“Self propelled hinged out drive

Expect limited capability in ice over 3/10.
Most applicable to shallow water response and in

, Support of shoreline clean-up in July.

. ane FV.
‘Twin screw w/5 ton crane ‘ ;
. QO . R Ss . ‘
3.5-ft draft research/work boat, fibreglass hull

Expect limited ice capability up to about 5/10
(summer only) . . .

» Be ‘ :

ach -herdrenmt


ee ee ee ee itetate we ths ae ee we oede commenents

the 120 foot release height to the surface ts shown in the fourth column. The largest droplets (ie,
the largest 10%) fall fastest and, on average, fall out of the plume nearest to the blowout; the
smallest droplets (i.e., those with a diameter that 90% of the droplets are bigger than) fall very
7 slowly and will drift downwind for long distances. .

TABLE 6-2

Predicted Near-source Dimensions of the Oil Spray Footprint from a Blowout ©
“During Freeze-up at Northstar in 3/10ths Ice Cover

Droplet Distance | widih of Average oil '

Size range
of oil drops | diameter used | downwind for | footprint for thickness
(by volume) | ~ to represent 99.7% of the 99.7% of across width
size range drops in the * drops (mm)
(mm) . ° | given size range (fy |
- to settle to the
surface (ft)
. 1 largest 10% 1.55 500 90 . 0.4
2 20% 135 530 - 100 0.7
3 30% 115 | 590 115 09
4 40% 0.95 * 660 ~ 130 “Ld
3 ‘VMD" 0.75 - 920 180 . 09
6 . 60% 0.55 . 1,200 230 0.9
7 70% «0.35 1,600 360 0.7 {
8 80% ” 015° 6,600 1000 03 -
“9 90% 0.05 33,700 6,600 0.05

* Volume Median Diameter . : . _

The fifth column gives the width of the footprint at the given downwind distance created by the

falling oil droplets. This number is strictly a function of atmospheric turbulence parameters. It is ,
calculated by mulnplying the standard deviation of atmospheric turbulence in the horizontal plane
at the given distance downwind by 2.67 to account for 99.7 % of the drops falling out in that width.
’ The final column gives the average thickness of the footprint created by the. falling oil droplets if all
the oil accumulated to the given downwind distance was spread evenly across the width of the

oo ‘ 68.


an oe) es sens Ngaaeas

' . References to Chapter 2

A Climatic Atlas of the Outer Continental Shelf Waters and Coastal Regions of Alaska (1988), Volume
Ill, Chukchi- Beaufort Sea, AEIDC, Anchorage, Alaska.

* 2. Coastal Frontiers Corporation (1996a) Personal observations by P. Gadd or C. Leidersdorf during

yearly summer trips to the Seal Island-Northstar area from 1982 through 1995. '
3. Cornett, S. and R. Kowalchuk (1985), Statistical Analysis of Ice Movement in the Beaufort Sea
Using ARGOS Buoy Data, APOA Proj. 222, Canadian Manne Drilling Ltd., Calgary, Alberta.
4. Cox, G. (1976), Sea Ice Conditions Along the North Coast of Alaska, Cape Halkett to Camden Bay,
June through Oct., 1953-75, AOGA Project 35, Amoco Production Company, Tulsa, Oklahoma.

"5. St. Martin, J. (1987), Arctic Drifting Buoy Data 1979-85, US Coast Guard Report No. CG-D-10-87,

Washington, DC (AD-A182 967)
6. Tekmarine, Inc , Polar Alpine Inc., and OCTI (1985) 1984 Beaufort Sea Multiyear Ice Floe Tracking +
» Study, AOGA Project 280, Sierra Madre, CA.

7. Thorndike, A. and J. Cheung (1977a), AIDJEX Measurements of Sea Ice Motion, 11 Apni 1975 to

14 May 1976, AIDJEX Bulletin No. 35, Seattle, Washington.

8 Thorndike, A. and J. Cheung (1977b), Measurements of Sea Ice Motion Determined from OCS Data
Buoys, October 1975 to December 1976, Polar Science Center, University of Washington, Seattle,
WA.

9. Vaudrey, K. (1981), 1980 Freezeup Study ‘of the Barrier Island Chain and Harrison Bay, AOGA

Project 129, Vaudrey & Associates, Inc., Missouri City, TX.

10. Vaudrey, K. (1982), 1981 Breakup Study of the Barrier Island Chain and Hamson Bay, AOGA
Project 148, Vaudrey & Associates, Inc., Missouri City, TX.

11. Vaudrey, K. (1982a), 1981 Freezeup Study of the Barner Island Chain and Harrison Bay, AOGA °
Project 160, Vaudrey & Associates, Inc., San Luis Obispo, CA.

12. Vaudrey, K. (1983), 1982 Breakup Study of the Barrier Island Chain and Harrison-Smith Bays, ©
AOGA Project 191, Vaudrey & Associates, Inc , San Luis Obispo, CA.

13. Vaudrey, K. (1983a), 1982 Freezeup Study of the Barrier Island Chain and Harrison Bay, AOGA
Project 200, Vaudrey & Associates, Inc., San Luis Obispo, CA.

14, Vaudrey, K. (1984), 1983 Breakup Study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA’
Project 224, Vaudrey & Associates, Inc., San Luis Obispo, CA.

15. Vaudrey, K. (1984a), 1983 Freezeup Study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA
Project 246, Vaudrey & Associates, Inc., San Luis Obispo, CA.

16. Vaudrey, K. (1985), 1984 Breakup Study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA °
Project 274, Vaudrey & Associates, Inc., San Luis Obispo, CA.

17. Vaudrey, K. (1985a), 1984 Freezeup Study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA
Project 282, Vaudrey & Associates, Inc., San Luis Obispo, CA.

-_ 18. Vaudrey, K. (1986), 1985 Breakup Study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA

Project 319, Vaudrey & Associates, Inc., San Luis Obispo, CA.

19, Vaudrey, K. (1986a), 1985 Freezeup Study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA
Project 327, Vaudrey & Associates, Inc., San Luis Obispo, CA.

20. Vaudrey, K. (1987), 1985-86 Ice Motion Measurements in Camden Bay, AOGA Project 328,
Vaudrey & Associates, Inc., San Luis Obispo, CA.

21. Vaudrey, K. and D. Dickins, 1996 Oil Spill Tracking at the Northstar Development During Break-Up
and Freeze-Up Using Satellite Tracking Buoys. Report prepared for BP Exploration (Alaska).

: -26- ; ' ‘


mc oc

cu

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oon m

| om

jeune TE ome TAR cucy BEE come EEE owen ER vase |

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' . ,

drifting at 0.7 knots. Although a containment and recovery system could not be deployed in the

‘wake, due to the potential exposure to oil mist concentrations in the plume, an i situ burning

operation could be mounted there that consists of 500 feet of fire boom held by two tugs’ using 350
feet of rope each. This would place the tugs 200 feet from the plume centerline (using a gap ratio of -

1:3), a distance sufficient at this location to reduce airborne oil mist concentrations to below the

target 5 mg/m’. A helicopter carrying a Hel1-torch would support the burn operation.
The encounter rate of the ISB unit, deployed to encounter the entire width of the thick slick, is:

~  ISBencounter rate (max) "= (180 feet) x (0.6 mm) x (0.7 knots) = 267 bbi/hr —
Unlike the containment and recovery system, the ISB system is envisioned as being used ina "batch"
mode. In the eight hours of daylight available in this scenario the system would collect oil °
continuously for 7 hours (capturing some 1869 bbl of oil, enough to cover only the back 18 of the
pocket of the boom) then maneuver sideways and remove the oil with one bum at the end of the day.

. It is potentially slightly more efficient to collect and burn simultaneously. However, the oil slick

thicknesses emanating from the source would be close tothe minimum ignitable for weathered crude
(ca. 2 mm) meaning there would be a risk of the fire burning back to the spill source.

. The estimated daily recovery rate for this ISB operation is 1869 bbl. . : .

The weathered oil on the ice floes is too thin to ignite.

Asimilar overall reduction in in situ burning effectiveness to that determined above for mechanical
containment and recovery, can be estimated using the same response time and environmental factors

” as for mechanical containment and recovery. For ISB operations the additional factor of the |

percentage of time that winds are less than 20 knots (80%) is also taken into account. The estimate
of ISB effectiveness for the 15-day period, expressed |as a percentage of the total blowout flow:

‘

. Oil volume removed by ISB = 1869 bbl/day x 0.83 x 0.77 x 0.80 + 15,000 bbi/day = 6.4 %

on .


on =

aC

5 canna |

ee Ee oe oe es ns on oD ore oe

emulsification i is briefly discussed first.

[oven eames |

2 — Seas pe aes mens a pareve ens eremmeneneh tbat mde atsirevemmen me ui Sceee o

underside of the ice cover. Such scenarios are not possible i in the present study, so this aspect of
oil/ice interaction is not dealt with here.

3.6.1 The Effect of Ice on the Four Main Oil Spill Processes

The effect of broken ice on the four main spill processes of spreading, evaporation, ‘dispersion and

=

Oil spill spreading can be dramatically curtailed because of the presence of broken ice and brash
ice. In high concentrations (greater than 5/10), oil spreading tends to be limited to the spaces between
the floes. There are a number of models that predict the spreading of oil as a function of ice
concentration. These are based largely on the results of a field trial off the east coast of Canada (SL
Ross and DF Dickins 1987) ‘ '

yo

Oil spill evaporation is not greatly affected by the presence of ice unless the oil is trapped under or ;
within the ice. Evaporation of volatile components occurs whether the oil rests on water or onice. .
Laboratory testing of oils from the ‘North Slope indicates that the initial evaporative loss, by volume, *

within the first 48 hours can be expected to range between 16 and 30% depending on the oil (SL
Ross 1994) ‘ - :

Oil spill dispersion and emulsification rates for oil spills on water depend on the mixing energy
available at the sea surface, and since the presence of ice tends to dampen the effects of wind on sea

state, both dispersion and emulsification rates in broken ice conditions would be expected to be less _,

than the case in open water conditions, all other factors remaining the same.

3.6.2 Oil Spilled Within Broken Ice, Spring through Fall « *

‘

During the primary period of spring break-up, oil spilled in broken ice conditions would be contained

in the openings between floes and would coat the surrounding ice surfaces. As spring melt proceeds
the area of contamination would correspondingly increase. >


aan rr oO MO OPO oO oO eel ee lL

Appendix D

Properties of Point McIntyre and Milne Point Crude Oils

and

, Comparison of Properties between Milne Point and Northstar Crude Oils


ES ae ey Caen etait tien me 0h) Gee iguee et ealéusemetin

| onme His ame 3 nse TEE coe TE wove BE come TEE emmee BE somes Te omen EL trove Ira owe TE vow FE eon TEE eae |

aan

* anoticeable decrease in burn efficiency with water contents above 12.5%, the decrease
being more pronounced with weathered oils; and oo

¢ zero bumefficiency for stable emulsion slicks having water contents of 25% ormore. Some

‘crudes, like Milne Pt. used as an analogue for Northstar crude in this report, form meso-

. stable emulsions that can be ignited and burn efficiently without emulsion breaker addition.

The primary objective of this study, as stated in the terms of reference for the study, is to evaluate
the mechanical Tecovery capability that exists on the North Slope for dealing with blowout spills in
* broken ice conditions. Insitu burning is to be considered a back-up method, that is, a ‘method to deal

’ with any oil that cannot be handled by existing mechanical systems. Although the following

scenarios and analysis of ISB conform to this directive, it should be understood that ISB techniques
could be used as a first option in a number of spill situations with good results.

5.6 Dispersant Use

.5.6.1 General Considerations os

. When oil is spilled on water, it exhibits a cohesiveness or resistance to break up. This cohesive

strength is due to the interfacial tension between the oil and water. A chemical dispersant acts at the
oil-water interface to greatly reduce this interfacial tension. This action promotes the break-up of the
oil film into droplets | that disperse into the water phase. If the droplets are small enough they will
have little buoyancy and will be carried away and diluted bys normal ocean current and movement.

Despite the great decrease in interfacial tension, some mixing energy is still needed to promote
movement and dispersion of the fine oil droplets into the water column. This energy can be supplied
either by the natural motion and currents of the sea or by mechanical means such as work boats. The

more energy that is available, the less dispersant that is required.

Dispersants will not be effective on highly viscous spills, either spills that are viscous to begin with
such as Bunker C spills or spills that become viscous through water-in-oil emulsification. The exact
cut-off point is not fully understood and i it certainly varies with oil type. The general rale-of- thumb

‘ - 58."


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ae ipa ae 6 eee se ene Ot. eee

Figure H-7

Area of Blowout on ice
~ afer 12 hours

Schematic view of one of two areas of oiled ice on Day 2 ©



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: Appendix A ~
“Background on Petroleum Activities in the Alaskan North Slope
The following was abstracted from MMS 1998 and ADNR 1998. .

The North Slope of Alaska contains the largest petroleum field discovered in North America,

‘ namely, Prudhoe Bay. It also contains many satellite fields with over 100 million barrels in reserves

(see Figure A-1). Production from North Slope fields, including both onshore and offshore fields,
peaked in 1988 at just over 2.0 million barrels per day. Present troduction is 1.4 million barrels per
day.

a Exploration ‘began on the North Slope in the 1920s. The first lease sale was held in 1964, and the ”

next few years saw a series of major discoveries: Prudhoe Bay (1968), Kuparuk (1969), and Milne
Point (1970). Estimated reserves from these discoveries totaled 12 billion barrels. Oil Production
began in 1977 after the trans-Alaska oil pipeline was constructed.

Eight of the post-Prudhoe Bay discoveries are currently producing oil because of the Prudhoe Bay
infrastructure and their relatively close location to the Trans-Alaska Pipeline. Six of these, Lisbume,
Kuparuk, Milne Point, Endicott, Niakuk, and Point McIntyre are major fields (Table A-1). While

. initial production on the North Slope was from onshore areas, four fields produce at least some of

their reserves from offshore areas, these fields are Endicott, Point McIntyre, Milne Point and Niakuk.

Table A-1: Major Producing Fields on the North Slope and in the Beaufort Sea

f Field Name

Estimated Original
Economically Recoverable
Oil (MMBBL)*

Estimated Original
Economically
Recoverable

* Gas (BCF)

12,219

28,203

145

362

2,627

998

395

23

622

66

34

Sources ADNR 1998



, Cee eee ee ae i ae i ei el ae

«

(1984) reports that the rate of oil slick movement may be increased by a factor of 3 percent of the
wind speed measured 10 m above the water surface. However, the final vector of oil movement
depends on the combined influences of residual currents and wind-induced surface currents. Over
relatively long distances, Coriolis ‘forces (due to the earth's rotation) cause the direction of
wind-induced slick motion to deviate some 10 to 15° to the right of the wind direction (in the
Northern Hemisphere). In nearshore marine waters, the movement of oil slicks is also affected by
tidal currents, river outflows and longshore currents. , oO

Oil Spreading. Numerous models of oil spreading behavior have been developed over the past 25
years. All relate the properties of the oil (density, viscosity and interfacial tension) to its spreading
on calm water. Most models today use the model developed by Mackay et al. (1980) which includes
the assumption that as the slick spreads, it forms thick patches that contain most of the oil volume
in a small portion of the area. These patches are surrounded by thin sheens (in the 0.001 mm range)
containing a small portion of the total oil volume over a wide area. The feature is consistent with
observed spill behavior. , . ,

Some oils do not spread on water as described above. This category includes oils that have a pour
point (i e., the temperature below which the oil does not flow) that exceeds the ambient temperature.
The pour point of an oil can be naturally high or may be high as a result of evaporative losses of
hydrocarbons during exposure to the environment. * “ot
Evaporation. Evaporation is the most predictable oil spill process (Mackay 1984). The evaporation
rate of an oil slick is controlled or affected by: 1) the temperature of the oil and the air; 2) the surface
area of the oil in contact with air; 3) the thickness of the oil; 4) wind speeds; and perhaps most
important 5) the concentration and vapor pressure of the individual components of the oil. The most
- useful studies of oil slick evaporation rates were conducted by researchers at the University of
Toronto in the late 1970s and early 1980s (e.g., Nadeau and Mackay 1978, Stiver and Mackay 1983).
In these studies, the volume or mass fraction of oil evaporated is related to an exposure coefficient
> (combining time, oil volume and area, and the "mass transfer coefficient” to the atmosphere) and to
the vapor pressure-concentration relationship for the oil. The unique aspect of this approach is that

a ‘ | -29-


mane 00) SS A Sooo om etin dumenmomon

a ee

: [ Type of System

TABLE 5.4

Dispersant Application Platforms in Alaska

Payload ; Location ]

- Number
Vessel spray system 2 1000 gallons” Valdez, AK
Vessel spray system 1 1000 gallons Valdez, AK
Helicopter bucket 2 _ 240 gallons ~ Valdez, AK
ADDS pack 2 _. 5500 gallons Anchorage, AK

TABLE 5.5
2 . Specifications on Dispersant Application Vessels in Alaska

C-130/ADDS pack ° Vessel Helibucket

Payload
"Max. Speed
Min. Speed:
Max. Pump Rate
Min. Pump Rate

Swath Width
Reposition Time

‘

Volume (gallons)

"5000 gallons min. 1000 gallons ~ 240 gallons
150 knots > 10 knots 54 knots
-130knots |S 3 knots 27 knots.

800 gallons/min. ‘12 gallons/min. 120 gallons/min.

100 gallons/min. ‘~~ 12 gallons/min. 79 gallons/min.
150-200 feet 90fet + 100 feet
4.25 min. Omin. _ 225 min,

: TABLE 5.6 .
Corexit 9527 Dispersant in Alaska Owned by or Available to Alyeska ‘

itorage

60000
"4700

: 11275 ~
: 9405

* bulk

_ 55-gal. drums ‘

_ 55-gal. drums

-61-


meen m cs ci

coo oe: co

procedures (used by PEMEX, Mexico’s national oil company) that are not practiced in U.S. waters
and which are contrary to U.S. regulations and to the accepted practices within the international oil
and Bas industry.

Calculated Frequencies for the Northstar Project .

The exposure numbers for Northstar (wells to be drilled, well-years of operations, et) are shown in
Table G-2.
“Table G-2 .
Drilling and Production Plans for Northstar =.

Years of Production
Oil Producer Well-years

Total Oil Production (Million barrels)
Well Statistics

- Development Oil Producers
- Development Gas Injectors
- Drilling Time Frame

Using the above worldwide spill frequency s statistics as a basis for fio the spill frequencies
estimated for the projects would be: “

ot “Predicted frequency of extremely large oil spills ¢l 50, 000 bbl) from blowouts during a

drilling operation, based on an exposure of wells drilled: 21 x 3.9 x 10° = 8.2 x 10. This

*, represents a 0.082% chance over the two-year drilling period, or an average annual
probability of one in 2400.

. Predicted frequency of very large oil spills ergy 000 bbl) from drilling blowouts based on
“+ an exposure of wells drilled: (14+7) x 7.8 x 10° = 1.6.x 10° or a 0.16% chance over the
Grilling period. On average, the annual probability is one in 1300. ~

. ~ Predicted frequency ° of extremely large’ oil -spills 150, 000 bbl) from

production/workover blowouts, based on an exposure of well-years: 266 x 1.0x 10°=2.7

- x10? or a 0.27% change over the project's lifetime (20 years) or a one-in-7400 chance

” per year. This means that if the project continued forever at the same, fixed conditions,
“* one could expect an oil spill larger than 150,000 barrels once every 7400 years.

” Predicted frequency of very large oil spills (>10,000 bb!) from productign/workover
blowouts, based on an exposure of well-years: 266 x 2.5 x 10° = 6.7.x 10° or a 0.67%
chance over the project's lifetime (20 years) or a one-in-3000 chance per year.

7 . Be


’

=

_ Air temperature (day)
;Air temperature (night)
_ Floe ice thickness

Daylight
Floe Size
‘ MeltPonds © |

"Tee Drift Rates*

— Ice Drift Direction :

Sea State

‘Visibility
Ceiling

an en SENS lt neha as al Oy ee

s

_ The table below lists the other environmental conditions that will apply throughout the scenario:

" 45°F

35°F

3 to 5 feet, Days 1 to3
1.5 to 4 feet, Days 4 to 15

24 hours _

500 to 1,000 feet, Days 1 to 3 ~
50 to 500 feet, Days 4 to 15

40 to 50%, Days 1 to 3
60 to 70%, Days 4 to 15

* use 3% of the wind for average (may

be double this average f for periods of
hours)

use 30° to the right of the wind typ.

N/A for Days 1 to 3
98% <3 feet for Days 4 to 15

22% <'2nm

M% <1, 500 feet with vis, om

*Note: ony eply sped rl fm Day 3 ones oo confined to move fely Day and.

2.2 Descriptive Oil in Ice Scenario: Suggested Pattern of Wind Events

The following description attempts to paint a temporal picture of what might happen to the ice cover
around Northstar during a typical break-up sequence. It should be noted that there are literally
hundreds of credible combinations of ice, winds and temperatures that could lead to different

outcomes.

The table below summarizes the weather patterns and anticipated ice conditions around the island.
The sequence is not intended to represent any particular year, but was created as a composite of
observed patterns of ice deterioration in the vicinity of Seal Island between 1981 and 1985 (Ref.

Vaudrey individual reports). —


Reon |

Se ae andi aks aah one acadp sammsmmasie

6.5 Scenario 4. Pt. McIntyre in 3/10ths Ice Cover During Break-up

6.5.1 Blowout/Spill Behavior (Scenario 4. Pt. McIntyre, 3/10ths Ice, Break-up)

An uncontrolled blowout occurs in mid July at the Pt McIntyre drill site releasing 12,000 barrels
of oil per day (BOPD) and 9 x 10° standard cubic feet (scf) of natural gas per day @ Gas-to-Oil Ratio
[GOR] of 750 scf/bbl). Over the first 72 hours of the incident, the air temperature ranges from a
nighttime low of 35 °F to a daytime high of 45 °F. The wind speed averages 11 knots from the west.
The water to the east of the causeway is covered by 3/10ths melting ice floes. The ice is 3 to 4 feet
thick and its surface is 40% to 50% covered by melt ponds. The floes are fifty to five hundred feet

in size. The ice is drifting at the same speed as the water (both wind-driven at 3% of the wind speed)

-at 0.3 knots to the east. These conditions do not change over the time period of the scenario; as well,

the ice concentrations do not change as it drifts away from the spill site (i.c., no convergence or

divergence of the pack).

As the oil and gas exits the 4-inch inside diameter tubing at the wellhead the high velocity of the gas
atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces and
the droplets agglomerate. The kinetic energy of the gas jet from the wellhead carries the droplets to
a height of 70 feet above the release point. From this point the oil droplets begin to fall as they are

a

carried downwind by the wind. -

In this scenario, the slick is 100 feet wide and 17 mm thick at the starting point of the surface slick
modeling. This is at a distance of some 500 feet downwind of the blowout. At this point, the oil slick
is assumed to be evaporated to 20% loss. * . .

For the purposes of this scenario, it is estimated that 70% of the oil spray lands on water and 30%
lands on the ice surface. The spray that lands on ice floes coats the surface and is slowly flushed by

_ melt water into the melt pools on the floes. The range of oil thicknesses initially deposited on the

floe surfaces ranges from 3 mm near the center-line of the oiled strip to 0.01 mm at the edges. The

-98-


5 Ge ae eee peas Ab) Oib aes aan ims inn espana ae

y ,

North Star and Milne Pt. Comparison - .7
1.0 TYPE Crude
Fresh Fresh 479% 416%
North Star_Milne Pt North Star Milne Pt.
20 DENSITY (g/mL)
: 25°C ud 0818 0 829 0 876 0.885
30 VISCOSITY ; ; 7
31 DYNAMIC VISCOSITY (mPa s) . oe
25°C 29 62 1140 ° 733
’ 32 KINEMATIC VISCOSITY (mm*isec) .
25°C - 3575 1301-828
40 INTERFACIAL TENSIONS @ 20°C (mN/m) 7
41 AIR-OIL: 299 © 252 ~ 329
42 OIL-SEAWATER 25 171 249
30 POUR POINT (°C) <:9<-9 21 12



Ultimately, the rotting ice will release any oil still remaining in the form of thin sheens trailing the
drifting floes.

TABLE 6-17

Summary of Slick Characteristics froma Blowout During Break-up |
at Pt. Mcintyre in 7/10ths Ice Cover over 72 Hours

Time Thick oil lefton | Emulsification Slick Thick slick | Thick slick
Qh). water (% of total | (% water vol.) viscosity thickness width
released) (cP @ 30 ‘F) | |_(mm) (ft)
Initial , 12 Oo. 25000 ° - 11. 100
| 3 |. 2 0 26000 11 100
6 12 , 0, 26000 11°} 100, |
12° 12 0 27000 11 100 |
24 12 0 29000 11 100
48 12 0 33000 11 100
72 12 0° 36000 © {> 1.1 100

6.7.2 Existing Methods (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up)

Compared with the previous two scenarios during break-up, the greater ice concentration in this
scenario limits the amount of oil on the water and available for containment and recovery, as well
as severely limiting the applicability of containment and recovery countermeasures. The slick
conditions are roughly the same as the other two break-up scenarios allowing the same general
approach and equipment for containment and recovery. However, the encounter rate, when reduced
to account for the 70% ice concentration, will be much less than the available skimming capacity. |
Given the 100-foot slick width, 1, 10 mm slick thickness, and the 0.5 knot rift Tesults in an encounter
rate of only 59 bbl/hour.

~ 120- Jes


- = Ey a ee See apie eS ae a lt lesen be

surface of the ice can be successfully ignited and burned even after ‘weathering for several weeks,
Wind herding of the oil in small pools enables much thinner oil films to be burned than would
otherwise be possible (Dickins and Buist 198 31). ‘Fresh crude mustbe approximately 0.04 inches thick
for ignition to take place, and weathered crudes i in the range of 0.1 to 0.2 inches are readily ignitable.
Weathering of the oil is not as critical as once thought. Ongoing work in Canada and Norway ech
et al. 1993, Guenette etal 1995, SL Ross 1995 and 1998) has demonstrated that it is possible to
effectively burn fresh crudes with up to 25 to 40 percent emnulsification (water in oil), albeit at a
reduced efficiency. ACS has conducted similar studies i in ‘the last few years concentrating on ©
emulsions made of Alaskan risk oils and seawater. During these studies bench testing was conducted
utilizing various emulsion breakers and gelled fuel mixtures to enhance ignition of emulsions.
Promising techniques from the laboratory were then re-evaluated during both small scale and meso-
scale testing, producing similar results to the SINTEF studies (Buist et al. 1995 and 1997) |

Work in Alaska and elsewhere has proved that the Heli-torch is a highly effective tool in igniting
multiple oil pools over large areas (Allen 1987) Slung beneath a helicopter, the Heli-torch is safe

. and efficient. Approved hand-held igniters can still be used by helicopter-transported field crews to

ignite isolated pools of oil. Burning efficiencies of approximately 97 percent have been achieved in
numerous large scale and meso-scale experiments. °

In practical applications, values tend to be lower because a proportion of the oil is contained in pools
too small and numerous to burn, and not all of the oil is available in sufficiently thick films. As a
general rule it is considered practical to burn 80 percent of all oil present in pools greater than 50
square feet, amounting to 68 percent of the total oil exposed on the surface (Norcor 1975; Buist and
Dickins 1981, Gulf Canada 1990). Manual recovery of any burn residue or thin unburned oil films
on the ice might i increase the overall recovery effectiveness by up to 10 percent. Realistic estimates
for the amount of residual oil remaining at the point of final ice break-up range from 10 to 20
percent. With appropriate safety precautions anda helicopter or amphibious vehicle in attendance,
surface operations to collect residue could continue until within a few days of break-up. Once

" collected the residue could be transported to shore with helicopter buckets.


Anaetnamanmin deepens re 0h) Sp ni aeee _— 1} Comeenee

ones

ee I me os oe ee oe oe rn es oe nn Bn Bre om ER ovo Doce Boe oe oe

The above analysis shows that the 2500 barrels of escaped oil can be treated with dispersant ina

" dispersant-to-oil ratio of 1:20. Now the question is: How effective will the treatment be in actually

dispersing the oil? If the ice were not present and dampening the waves, one could estimate that the
dispersant effective could be in the 50 to 80 % range, the range estimated for spills of Alaskan North

- Slope crude treated with Corexit 9527 (SL Ross 1997) No one can say with any certainty what the
» value would be in this case; there is simply no relrable knowledge on the subject of dispersant use
in an ice situation like this. To be conservative, we will estimate that only 25% of the treated oil in .

this scenario will be dispersed. Continuing the conservative thinking, we will further assume in the
next two scenarios involving 50% and 10% ice, that dispersant effectiveness will be essentially zero.

‘Ih summary, for this scenario it is assumed that the dispersant operation will disperse 25% of the

2500 barrels of oil that escaped the mechanical recovery operation. :

6.2.5 In situ Burning (Scenario 1. Northstar, 3/10ths Ice, Freeze-up)

‘Itis recognized that insufficient vessels exist to conduct an in situ buming(ISB) operation in addition

to the containment and recovery operation described above. However, a description and assessment

1

of such an operation is given below for assessment purposes.
‘The in situ burning unit that would make sense for this scenario consists of 360 feet of fire boom and
two tugs. A helicopter carrying a Heli-torch would support the burn operation. The ISB unit, as with
the containment and Tecovery system, would be deployed to encounter as much as possible of the
thick slick. The encounter rate of each bum unit for this scenario is thus the same as for the recovery
unit at:, ‘ . . :

ISB encounter rate (max) = (360 feet x 0.33 gap) x 0.7 mm x 0.4 knots x (1 ~ 30% ice)

, “= 83 bbl/hr , ,

Unlike the containment and recovery system, the ISB system is envisioned as being used ina "batch"
mode. Oil is collected in the back of the boom for a certain period of time, then the system is moved

away from the heavy concentrations of oil anid the accumulated oil is burned off. For the sake of .

‘

an : 81.

:


aononnmnonm mo.

ma cl

me BE name SR vee | ou saame TR oven ms oe some ove om |

i i a 2 ee ee eee el pont abit mr sensu ones mtiedmtoremuhe

@ Develop an efficient Slope-wide response capability, including, but not limited to, efficient and
effective use orintegration of response personnel, communications or logistical needs to support
spill response for North Slope operations; ‘

@ Develop an ACS Response Plan, the design of which would meet, to the extent possible, the .
format and substance requirements of the federal/state sub-area plan;

@ Use the ACS Response Plan as abase document to support the individual facility contingency

plans of North Slope operators; : ’ -

© Develop a sufficient number of generic oil spill response scenarios, whether located on land,
near shore or offshore; ooo , : ,

@ Develop as a first priority oil spill scenarios necessary for State approval of contingency plans
for the Pt. McIntyre and Badami fields (Endicott, Naikuk and Milne Point facility plans are also
affected); and “ : - oy

. Identify additional spill response equipment needs as a product of developing the spill response
scenarios. This is to be done sufficiently 3 in advance to ensure tumely approval of contingency
plans for new fields. ‘

1.3 Past Regulations regarding Broken Ice: Tier 1 and Tier 2

’ The difficulty of the NSSRPT mission is complicated by the problem of “broken ice”, a marine

situation in which ice floes are scattered and in motion on the water surface. The cleanup of oil spills
in broken ice conditions has been a concern in Alaska ever since oil exploration and production *
began to move into the nearshore and offshore areas of the Alaskan North Slope. Although oil spill
cleanup methods are well established for spills in open water and for spills on solid, landfast ice, it
has been recognized for some time that spills in broken ice conditions are more problematic. .

Oil drilling restrictions during broken ice conditions in the Alaskan Beaufort Sea have been the
subject of debate for over twenty years. The main environmental concer is that a large oil well
blowout might occur and have a serious impact on the bowhead whale, an endangered species whose
fall migration route north of the barrier islands is close to drilling sites. In 1978, the State of. Alaska
restricted drilling to the ice-covered period from November 1 through March 31 each year, and in
May 1982 a complex two-tiered restriction became effective. Tier 1 kept intact a prohibition on

+22.


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4. Alternative Countermeasures . - : a

For each of the six ‘blowout scenarios the potential effectiveness of alternative countermeasures was
also examined. This includes the use of dispersants, in situ burning, and igniting the well to burn off

- the oil as it is emitted from the well. The results are summarized in Table S-2. In each case,
~ effectiveness is defined as the percentage of the blowout flow over the 15-day period that could be —

dealt with by the particular technique.
" TABLE S-2
Summary of Recovery Effectiveness for Alternative Countermeasures
(as a percentage of total blowout flow)

Existing Countermeasures

Dispersant - Use

In-Situ Burning! - on-water 4°] 22. ; 14

- on-ice ‘0 ‘|. 25

Well Ignition 7 ; 99. 74

‘11. Note that ISB on-water effectiveness is for comparison with existing containment and recovery

‘effectiveness; ISB on-ice effectiveness would be in addition to either containment and Tecovery or
ISB on-water effectiveness. ~

« The use of dispersants is an attractive option for dealing with blowout-type spills, particularly those

that are relatively close to centers of logistic support, as are the spills in these scenarios. The modest
daily spill rate combined with the ability to deliver the required quantities of dispersant while the oil
is relatively thick means that there are good opportunities for application. Also, a dispersant
operation as described here could be mounted relatively quickly, within 12 hours as opposed to the
60 hours estimated for containment and recovery in the freeze-up scenarios. Unfortunately, the
presence of ice tends to dampen any wave action which is required for effective dispersion. In this

- . Executive Summary - Page 4


require up to 35 miles of pipeline to link up with the Badami field to the west.

0 eee See siremerrmnanindtedithi: athe ste —_ eethamnqmemmpunenans

Offshore lands in the Beaufort Sea were first offered in 1979 in a sale that included State lands
(within 3 miles of shore) and Federal lands (beyond 3 miles). Since then, several large, offshore oil
fields have been discovered, including: Endicott/Duck Island, Point McIntyre, Seal Island/Northstar,
Niakuk, and Tern/Liberty (in appraisal phase as of early 1998). These fields lie close to shore,
beneath State lands or on the boundary between State and Federal lands. So far, only one offshore
field, Endicott/Duck Island, has been developed, and it began producing in 1987. Northstar is the -
second offshore field scheduled for development; production is proposed to start in 1999.

The first Federal-only offshore lease sale in the Beaufort Sea was held in 1982. Since then, four more
Federal sales have been held. A total of 28 exploration wells have been drilled. Nine wells are
considered capable of producing oil in paying quantities. All these discoveries, however, remain
undeveloped. Three presently non-commercial fields (Sandpiper, Hammerhead, and Kuvlum) have
been unitized for possible future development.

In addition to Northstar, several fields have been proposed for development, including Badami,
Alpine, Liberty, Tarn, and West Sak. The onshore Badami field, discovered in 1991, is estimated to
contain 145 million barrels of economically recoverable oil, and is expected to come on-line in the
fall of 1998.

_ The Liberty field is located on federal leases appooaiintty five miles offshore i in the Beaufort Sea,

northwest of the Badami field It is estimated to contain 120 million barrels of recoverable oil.
Production is proposed to begin in 2000. The Tarn prospect is located southwest of Kuparuk and
contains estimated proven and potential reserves of 50 million barrels. Production is expected to

. begin by late 1998 or early 1999.

The Sourdough field discovered in 1997 could contain 100 million barrels of recoverable oil. Further
exploration is needed before determining whether to develop the field. The Sourdough Project would

Finally, in February 1998, two newoil accumulations, Sambucca and Midnight Sun, werediscovered -

-during the drilling of a Prudhoe Bay “satellite” prospect. Test production from the discovery i is
‘ planned for the first half of 1998.


aan aoe

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‘

It is often difficult for cleanup systems to reach tanker spills quickly because such spills can occur
virtually anywhere along the world’s marine transportation corridors. Although cleanup equipment

‘can be stockpiled and made ready in particularly high risk areas, such as ports and other high traffic

areas, this does not guarantee that spills will conveniently occur within easy striking distance. An
effective 2 Fesponse with mechanical systems must involve several ocean-going vessels working in
tandem, some to manage the equipment and others to accept and store recovered oil, so the time to

reach a spill and begin operations is limited to the time needed for all systems to arrive on site. This
can take many hours depending on the spill location.

These problems expan traditionally why mechanical systems have done poorly of on most historical
spills, aside from any lack of preparation on the part of the responders. The number mentioned often
by experts is that mechanical systems responding to historical spills have recovered at sea about 5
to 10 percent of the oil spilled. This number applies to the situation generally, but perhaps not to the ‘

* Prince William Sound area today, because of the build-up of; mechanical recovery capability that has

taken place following the Exxon Valdez tanker spill in 1989.

Blowout Spills. The general capability for dealing with oil spills from offshore oil well blowouts
is believed to be much better than for tanker spills. In these situations the contingency planner knows '
beforehand the exact location of the potential oil discharge and so is able to expend considerable
effort in developing a site-specific preparedness to deal with the problem. Protection priotities,
currents, wind patterns, spill movement predictions, etc. can all be studied before the event.
Furthermore, although the total quantity of oil that can be released is large, the amount of oil
discharged per day is relatively low and it can be recovered or treated with a modest amount of
equipment or materials. Finally, the oil slick at the blowout site generally is in a concentrated, fresh
and non-viscous state which benefits the’ main control techniques of skimming, burning and
dispersing. All these factors put the: contingency planner and oil it spill responder ina relatively good
Position to deal with the problem. :

a

For the specific case of an oil blowout from a gravel island in the Beaufort Sea, the situation is even

_better for several reasons. First, the oil is discharged at or above the island’s surface where it can be

easily removed by ignition and burning. Second, the island may be used as a base from which to

ro, wo 36-


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anmoanmonp

* ~

Oil Fallout Percent vs Distance
from Source (4inch ID pipe)

10000

Distance from Source (m)

Ss

10 20 30 40 50. 6 70 8 90
Percent of Oil on “Ground”

je 2 ae 5 8 = 12s mmscfiday

Figure 3 : Oil Fallout Percent vs Distance from Source (4 inch ID pipe)

. Oil Fallout Percent vs Distance
from Source (6.3 inch ID pipe)
10000 3 - - -
e 7
of 4
-B 1000 4
a 3
€ q
& 4
i 100 4

10
1 30 40 50 60 70
Percent of Oil on “Ground”

2 -— 5 -e 10-— 20-8- 32 mmscf/day

Figure 4 : Oil Fallout Percent vs Distance from Source (6.3 inch ID pipe)


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filsec. If there were no turbulence in the wind, in the 16 seconds required for a 0. 75 mm diameter
droplet to fall 120 feet, it would be carried more than 360 feet downwind. In real wind conditions ,
considerable amounts of turbulence exst and must be accounted for in determining the trajectory
of the oul. spray. If the oil spray generated by: the blowout were imagined to be all one drop size (ue,
0.75 mm diameter), the drops would still fall at different distances from the blowout because of the
turbulence in the wind. As the spray of oil drops falls, it is being spread horizontally and vertically
by air turbulence, or meandering of the wind. In the tume required for 99.7% of the 0.75 mm droplets

. to fall to the surface the wind has carried the final few 0.75 mm droplets 920 feet from the blowout.

The air turbulence also spreads out the droplets laterally as they fall, with the width of the

"footprint" of the oil on the surface increasing with distance. from the source in a parabola-like

' shape.

In reality, the spray of oil droplets is made up of many different droplet sizes. In determining the
footprint of the oil spray on the surface, this must also be taken into account. This is accomplished
by dividing the full range of oil drop sizes produced by the blowout into nine smaller ranges, each
representing 10% of the total volume of all the oil droplets. Only nine drop-size ranges are used

_ because 10% of the volume of oil released is assumed to be in droplets so small (much less than 50

Em) that they remain suspended in the atmosphere and never settle out, Each range is characterized

bya droplet diameter that is representative of the droplets in the same range. For example the
~ largest 10% of the volume of oil spray droplets is represented bys a 1.55 mm diameter oil | droplet;

the smallest 10% that will settle is represented by a 0.05 mm diameter droplet. The dimensions of ‘

. the oil spray footprint on the surface is calculated by determining the distance downwind and width .

for 99.7% of the representative droplets in each range to settle to the surface.

* Table 6-2 shows the estimated width and thickness of the oil spray footprint as a function of the
”. percentage of the volume of droplets that have fallen out of the plume and the distance downwind

of the blowout in the 13 5 knot wind and 0.4 knot current of this scenario. The second column gives

“the size range of the droplets being modeled (ie e., the first row is calculated using a drop diameter

representing the largest 10% of the oil drops, or 1.55 mm) and the third column gives the droplet
diameter representing the size range. The distance downwind for 99.7% of | these se droplets to fall, from

-67-


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mod

A possible limitation in operating ‘the described systems over a period of time is that of storage
space. Given that there are a Timited number of tugs/barges applicable to the freeze-up season, it

would be a serious loss of effectiveness if a barge system were to have to shut down recovery

« operations in order to shuttle fluids back to storage at West Dock. Based on the above fluid recovery

rates this would have to occur about every 8 days, translating into a loss in overall effectiveness of
roughly 13% (1 day in 8 spent shuttling fluids). An alternative would be to consider the use of
hovercraft to transport fluids from the spill scene in order to extend the use of the barge storage
space. As described in detail in Appendix F, two hovercraft could be on scene within the same
response time as the tug/barge combinations. The two machines, operating in tandem, could provide
a shuttle throughput of up to 2600 bbl/day, which would extend the use of barge storage almost
indefinitely: (14,000 + 12,200 bbl) + (3250 - 2600 bbl/day) = 40 days available storage.

Predicted Effectiveness of Existing Mechanical Systems in Recovering 15-Day Discharge

This final step in this section is to use the above calculations to assess the effectiveness of existing
systems to deal with the total volume of oil discharged over the 15-day blowout period. The
assessment includes the effects of response-time delays, and the environmental derating factors of
visibility, VFR flying conditions, ‘and wave heights. The response time for the freeze-up Scenarios
is estimated to be 60 hours, so for the 15-day period the effect is to reduce effectiveness by 17% ((15

* ~2.5) + 15 = 0.83). As discussed in Chapter 5, the combination of the three environmental factors

is such that mechanical containment and recovery will be effective, on average, 77% of the time. The
following is the estimate of effectiveness for the 15-day period, expressed as a percentage of the total

“blowout flow: , .
Recovered oil volume = 1394 bbl/day x 0.83 x 0.77 + 15,000 bbl/day 4
= 59%
5
__ “
-76-


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ate
’

Evaluation of Cleanup Capabilities for Large Blowout Spills
in the Alaskan Beaufort Sea During Periods of Broken Ice

‘for

* Alaska Clean Seas .
Anchorage, AK

; and
: Department of the Interior
Minerals Management Service.
Anchorage, AK
on behalf of the

North Slope Spill Response Project Team

: by

S.L. Ross Environmental Research Ltd.
, Ottawa, ON

DF. Dickins and Associates Ltd.
Salt Spring Island, BC ‘

Vaudrey and Associates, Inc. 5
San Luis Obispo, CA

, June 1998 -


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. : TABLE 6-12
Key Equipment for Containment and Recovery in Scenario 4

Equipment Type Examples « Function

Barges _ | Endeavor . _ working platform and storage for

‘ Beaufort 20 . . | skimming operation
BG 210/211/213

Tugs Pt. Barrow tow equipment to site and position
. Pt. Thompson . on-scene

Arctic Tern

Sag River

Tooltk River . 5

Kavik River ’ : -

} Other boats « "| 42'work boats (2#) boom handling and deployment
a : Northstar ; .
38-55' work boats - jet drive (5#)

‘

y

Containment boom | Ro-Boom 36x43. concentrate oil for recovery |

Skimmers Transrec250 °° ‘ oil recovery
LORI ss

Desmi Ocean
Desmi Harbor

~ The slick conditions of interest are those estimated for 3 hours down drift of the blowout. This
corresponds to a distance of about 5500 feet, which is judged to be a safe operating distance based
on hydrocarbon-in-air concentrations. At this point the thick slick is 100 feet wide and averages 4.2
mm thick. Unlike the previous scenarios and because of the different oil, it is predicted that the oil
will be somewhat emulsified at this point and contain 55% water. This emulsified water, therefore,
will haye to be taken into account in the calculations. For a containment system positioned
downstream of a blowout, the encounter rate is calculated by multiplying the encounter width of the
system by the slick thickness and the slick drift rate of 0.3 knots. In addition to this one must account

’ for the fact that, on average, 30% of the slick width would be covered by ice. Thus the encounter rate
for oil on water and available for recovery would be reduced by 30%. So, for each containment .
system employing 150 feet of boom, the encounter rate is:

“102. ,


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_ October, with 12 hours of natural light for operating, a daily throughput of 2,600 barrels is

considered achievable (amounting to 17% of the blowout flow rate). It should be noted that

“with searchlights and GPS navigation, hovercraft are capable of operating safely in

conditions of darkness and poor visibility which would ground all but the most sophisticated
IFR helicopters.

Depending on the encounter rate and 4 throughput efficiency of the skimming systems, it
appears that the air cushion vehicle is an effective means of lightering recovered product
while allowing the tug and barge systems to stay on location for as many hours as possible.
Given the shortage of capable tugs to manage barges offshore, the air cushion vehicle option
offers significant advantages, particularly in the 5/10 and 7/10 ice concentrations.

ACV Attachments: LACV-30 and AP.1-88 spec sheets, photographs of hovercraft over
broken ice (SAS, Canadian Coast Guard, British Hovercraft Comp. )

Summary of Logistics Effectiveness

Logistics options can be divided according to three broad effectiveness factors: transport
from a shore-based staging area to and from the spill site, on site support for the response
operation, and mobilization times. ., ‘

1. Transport: payload (weight and volumetric constraints), transit time, ability to
deal with the ice, and weather limits (expected worst-case downtime).

2. On-site support: deck area, internal or deck tank storage for recovered product,
‘weather and ice limits, maneuverability in ice, and accommodation.

“3. ‘Mobilization: factors include a combination of crew travel time and time needed
for equipment preparation and warm-up. Personnel may have to flown-up to the

* slope, and equipment may have to be taken out of storage and/or de-winterized.
These factors are particularly acute in October as the heavy marine equipment is
normally prepared for winter lay-up by the end of September. Crowley estimates

about 48 hours for a cold ie start-up depending on weather and ice conditions at the * -

time.

Table F-1 summarizes these effectiveness factors for each <ipmet category.

oo OS


| aaa |

’ : . .

The ISB operations targeting the oil on ice floes would continue until all the available oil had been
ignited. Delays in operations due to response time and environmental factors would not affect the
overall removal effectiveness. The estimate of on-ice ISB effectiveness for the 15-day period,

+

expressed as a percentage of the total blowout flow:

‘Oil volume removed from ice byISB= = . 4000 bbl/day + 12,000 bbl/day
= 33%

The total oil removed by ISB operations both on water and ice is:

anaonntn a oo

Total oil removed by ISB operations = ° 711%+33%
‘ . = 40%

‘

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systems. The reason for this is unknown, but, since this is the only data available, it
is used in the final modeling with one modification. The volume median drop
diameter of the subsea release was around 1050 um. This is somewhat higher than
the 750 zm diameter identified for above sea oil blowouts This would seem

~ reasonable since the gas flow would be reduced somewhat due to the over-pressure
provided by the water above the submerged discharge point. This will reduce the
gas exit velocity and result in reduced droplet shearing and larger drop diameters.-
To account for this, the measured drop size distribution in Figure 1 has been shifted
so that the volume median diameter of the new curve is 750 um, but the slope of the :
curve has been preserved. The resulting drop-size distribution has been used in our *
modeling to identify the oil fallout rate as a function of distance from the release
location. Due to the lack of supporting data we were unable to identify different
drop size distributions as a function of the gas and oil flow rates and discharge pipe
diameter. .

Measured Oil Drop Size Distribution
Dome Subsea Oil & Gas Release

Cumulative Volume %

’ 50 350 650 950 1250 ~ 1550 . 1850
Drop Diameter (micrometers) ‘

Figure 1 : Oil Drop Size Distribution from Subsea Oil & Gas
Release

Pneumatic atomization equations, for predicting the VMD as a function of blowout
parameters, have not given results that match the information available from field
’ observations so they have not been used in this study.

Modeling Results °
The input conditions considered in the modeling were as follows: ,

Oil Flow: Barrels of Oil per Day(BOPD) 5,500 8,000 12,000 15,000
Gas-to-Oil Ratio (GOR)(f° gas/barrel oil) 400 750 2,200

Wind Speed (knots) > $101520
_ Discharge Pipe Internal Diameter (in) 4&63 ->
Atmospheric Stability Class , D


i So SO Se Ee OOD SS SES ae meh) hee ‘2S 1 eee a

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atmosphere. In total, an estimated 70% of the blowout flow will eventually reach the ice/water
surface. This means that only about 40% of the total blowout flow (60% x 70%) will reach the
surface and form a thick slick. About 30% of the total blowout flow (40% x 70%) will reach the
surface, but in a relatively thin slick for which a containment and recovery response would be
relatively ineffective, whether in broken ice or open water conditions.

Daylight Ho ,

It was assumed that recovery operations would be conducted only during daylight hours, for reasons
of worker safety and due to difficulties in positioning containment equipment relative to the slick.
For the freeze-up scenarios, with daylight hours ranging from 8 to 12 hours, this causes a decrease
in effectiveness to only one-third to one-half what it otherwise could be. There is no such reduction
in effectiveness in the spring break-up scenarios given the 24-hours of daylight at that time of year.

Delays inR Juring F ;
The ice conditions during freeze-up at West Dock, where the primary equipment and marine logistics

‘are located, means that the response time would be 60 hours as opposed to the 12 hours used in the

break-up scenarios. Over the 15-day period, this translates into a loss in effectiveness of 17%.

We i l eae . ;
Considering the negative effect of weather (mostly sea state and visibility) on countermeasures
effectiveness, it was calculated that containment and skimming equipment could be operated 77% _

~ of the time during freeze-up and 66% during break-up.

"3. Advantages of Adding More Recovery Equipment and Vessels

In all spill cases, the entire width of the thick slick could be encountered using one or two systems
with a total boom length of no greater than 720 feet. Similarly, there are a number of skimmers
stockpiled with (derated) recovery rates that exceed the rate at which oil would be encountered in
the thick slick, so the capability of. recovery equipment should not limit the operation. Finally, there
is adequate logistical systems to support the containment and recovery operation, including the
storage and transfer of recovered fluids.

- In each of the scenarios, consideration mn was given to the possible effectiveness of additional

containment and recovery systems. In each case it was found that any such equipment would be
limited to chasing relatively thin slicks of oil ~ either that which originally landed outside the thick
portion of the slick or that which was lost past ¢ containment due to ice problems — and would
contribute little more to the overall effectiveness. - 5

a . . : Executive Summary - Page 3


‘

Now, considering the period of broken ice only, assuming that the total period as a worst case is
approximately eight weeks (3 in break-up and 5 in freeze-up), the above blowout probability
numbers should be divided by 6.5 that is, 52 weeks /8 weeks). The final numbers are shown in Table
G-3 below. ~ ,

Itis seen that for the first two years of the project, while virtually continuous drilling is occurring,

the probability per year is one in 16,000 that an extremely large blowout oil spill (>150,000 bbl)
would occur during either the freeze-up or the break-up periods Once development drilling is
completed, the equivalent annual probability drops to one in 48,000. This means that if the
production operation were to continue forever at the given rates, one could expect an extremely large
spill during broken ice conditions once every 48,000 years.

One final note: In the scenarios it was assumed that the blowouts flowed unabated for a period of
15 days. One of the main reasons that oil spills from historical blowouts have been relatively small
is that most have been brought under control quickly either through mechanical procedures or
because of the tendency of a blowing well to "self-bridge” and stop naturally. As discussed in SL
Ross 1998, for 145 blowouts in the U.S. Gulf of Mexico from 1956 to 1986, 60% were controlled
in less than one day, 81% were controlled in less than a week, and 91% within one month.


4

45 Days4,5,and6  - : Ce . a

See |}! + i a =a ss esteteeenhe

The estimated daily removal rate for one ISB unit is thus: :
ISB unit daily removal rate from the water surface = (22 bbV/hr x 24 br) x 0.5 = 264 bbl

If three units were deployed to encounter the entire thick slick available the total daily ISB removal
rate from water would be 792 bbl. This would be slightly higher than the potential effectiveness of
three containment and recovery units because it is envisioned that burning, then maneuvering theISB °
unit back into the thick oil will take less time than for the conventional boom and skimmer system.

The oil that falls on the ice floes in this scenario is ideal for in sttu burning operations. After
allowing the surface oil to concentrate in melt pools, about 75% of the surface area of the pools
would be covered with 10 mm-thick oil. Taking into account an average oil-removal-by-burning
efficiency of 80%, and conservatively estimating that only oil in melt pools greater than 50 ft? (90%
of the total) would be ignited by Heli-torch operations, the overall oil removal by burning becomes:

daily oil removed from floes by buming = 15, Od bbl x 50% onice x 80%x 90%
4 ~ = 5400 '

The ISB operations targeting the oil on ice floes would continue until all the available oil had been

ignited. Delays in operations due to response time and environmental factors would not affect the

overall removal effectiveness. The estimate of ISB effectiveness expressed as a percentage of the
total blowout flow and including operations on both water and ice for Day 3 of the scenario, is:

(792 + 5400 bbI/day) + 15,000 bbi/day

Oil volume removed by ISB
' vO MG

‘

Similar tactics would be employed for Days 4 through 6 as the ice concentration decreases to 5 to
6/10ths. At a distance corresponding to 12 hours downwind of the spill source, the thick slick width

_ is 760 feet and the thickness is 1.0 mm. The ice and the slick are drifting at a rate of only 0.1 knots. °

Using this as an encounter speed would result in a very slow operation. Rather, it is likely that the

* operation would proceed at a greater speed, say 0.4 knots, in a downwind direction to maximize the

encounter rate of oil. (Selecting 0.4 knots as the encounter speed allows two units, each with an
encounter width of 100 feet, to effectively encounter the entire width of the thick slick: 2 units x 100
feet x 0.4 knots is approximately equal to 760 feet x 0.1 knots.) Using two in situ burn units, each
comprising 300 feet of fire-resistant boom and two tugboats and supported by one Helitorch, the
following estimates can be made for effectiveness of “on-water” burning. The encounter rate of each
system would be:

ISB encounter rate = (300 feet x 0.33 gap) x 1, 0 mm x 02 4 knots x a- 50% ice) *
= 71 bevhr

As for the Day 3 scenario the ISB systems would be used in a “batch” mode. The estimated daily
removal rate for one ISB unit is thus: :

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2 ee eae mae 05) Sy es one 4) Doane oe

encounter rate = ‘ (150 feet x 0.33 gap ratio) x 4.2 mm x 0.3 knots x (1 - 30% ice)
_=  156bbY/hour (emulsion) a
= Wbblhour ~*~ (oil only) st

Both the emulsion encounter rate and the "oil only" encounter rate must be considered: the first is
of concern when taking into account the derated recovery rate of the skimmer and when calculating
the total fluid volumes; the latter is of concern when calculating the actual amount of oil recovered.

The emulsion encounter rate is within the derated recovery rate of several of the offshore skimmers
that could be used; therefore, the encounter rate will be the limiting factor and will be used in
subsequent calculations. Using this as the recovery rate, and using the guideline of 20% oil recovery
efficiency (the actual emulsification of 55% water-in-oil emulsion in storage is used instead of the
40% guideline used in other scenarios), the total fluid recovery rate can be estimated as shown in the
table below: . .

: ‘ . TABLE 6-13 .
Fluid Recovery Rates for Scenario 4 _

Fluid , ° Calculation ' Recovery rate ]

| emulsion . | lesser of system encounter rate and derated recovery rate | 156 bbl/hr |
oil oil content in emulsion = 45% . 70 bb\/hr
free water oil content in recovered fluid (recovery efficiency) = 20% | 624 bbl/hr
emulsified water | emulsified water content in recovered fluid = 55% 86 bbl/hr |
| total fluids emulsion + free water 780 bbi/hr

\

As in the previous scenarios, there will be inefficiencies when operating containment and recovery
equipment among broken ice. These inefficiencies will be due to having to reposition containment
boom to avoid large ice features and to rid the contained area of accumulations of small floes. As

described previously, this containment efficiency is estimated to be 70% for the 30% ice

-103-


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TABLE 1

Typical Environmental Parameters for Northstar during Freeze-up

-24-

5 "Ice Concentration (tenths) * Wee
sk E wee MPG hee G ye Gate TT,
Local variability Oto 0.4 at island, but | 0.2 to 0.6 at island, but 03 to 0.8 at island, but
in concentration 10/10 landfast ice near | ~ 10/10 landfast ice 10/10 landfast ice
‘ West Dock within 1to2NMof | within 1 to2NM of
. West Dock West Dock
| Date (from-to) 10/10 through 10/12 10/19 through 10/21 10/29 to 10/31
Daylight hours 12 10.5 8
(incl. twilight) ,
Floe ice thickness (ft) 041006 0600.8 1.0 to 1.2
| Floe size (ft) 100’s to 1000’s 100’s to 1000’s 100’s to 1000’s
Snow thickness (in) 1to2 2to4 5to6
on top of the ice . a ]
Ice drift speed (kt) 0.3 to 0.4, up to 1.0 °° | 0.7 to 1.0, upto 1.5 0.8 to 1.2, up to 1.8
Ice direction (to) ‘NW E NE
Wind speed (kts) 12 to 15 " 18 to 20 20 to 25
Wind direction E WSW SW
(from) : ~
Air temp. (day) -°F 23 18 13
: | Air temp. (night) - °F © 13
Precipitation (snow) ‘ ‘1. 1 1
(inches)
Sea state ; 84% of time < 3 ft NA N/A.
height (ft)/period with periods of 6 to 8 s
(sec) : : ]
Visibility (NM) , 5% of time <%zNM 5% oftime<¥24NM | 5%oftime<%2NM |
(helo ops) (=3 to 4 hr in 3 days) (=3 to 4 hrin3 days) | (~3 to 4 hr in 3 days)
Ceiling height (ft) 3% of time 3% oftime 3% of time ]
(fixed wing ops) ceiling ht. < 1500 ft with | | ceiling ht. < 1500 ft ceiling ht. < 1500 ft
‘ visibility < 1 NM with visibility < 1 NM _ | with visibility < 1 NM
Atmospheric icing - - 3% of the time 3% of the time 3% of the time
(helo ops) (~2 hr in 3 days) (~2br in3 days) (~2 hr in3 days) :



» Helitorch, the following estimates can be made for effectiveness of “on-water” burning. The

encounter rate of each system wouldbe:

ISBencounter rate = (300 feet x 0.33 gap) x 0.8 mm x 04 4 knots x a- - 40% ice)
. = 68 bbV/hr

Using the same assumptions used previously regarding a batch-bum process effectively using 50%

. of a 24-hour day, the estimated daily removal rate for one ISB unit is:
ISB unit daily removal rate from the water surface = (68 bbVhr x 24 hr) x 0.5 = 816 bbl

If two units were deployed to encounter the entire thick slick available the total daily ISB removal
rate from water would be 1632 bbl.

As in Days 3 through 6, the oil that falls on nthe ice floes could also be dealt with by in situ burning.
After allowing the surface oil to concentrate in melt pools, about 75% of the surface area of the pools
would be covered with 10 mm-thick oil. Taking into account an average oil-removal-by-burning
efficiency of 80% and conservatively estimating that only oil in melt pools greater than 50 ft? (90%
of the total) would be ignited by Heli- torch operations results in an overall a removal by burning
of:

daily oil removed from floes by buming - “5 15.000 bel x 28% on ice x 80% x 90%

The ISB operations targeting the oil on ice floes would continue until all the available oi] had been
ignited. Delays in operations due to response time and environmental factors would not affect the
overall removal effectiveness. The estimate of ISB effectiveness expressed as a percentage of the
total blowout flow and including operations on both water and ice for each of Days 7,8,9,10, and 11
of the scenario, is: .

” Oil volume removed from ice by ISB = “(1632 +3024 bol/day) + 15,000 bbI/day |
so = 31%

4.7 Day 12 . ‘ '

The cleanup tactics would be essentially the same as those employed for the previous eight days,

except that a third in situ burning system would be required to encounter the entire thick slick width
~ at the prevailing drift speed of 0.45 knots. At a distance corresponding to 12 hours downwind of the

spill source, the thick slick width is 290 feet and the thickness is 0.4 mm. Using three in situ burn

units, each comprising 300 feet of fire-resistant boom and two tugboats and supported by one

Helitorch, ‘the following estimates can be made for effectiveness of “on-water” buming. The

encounter rate of each system would be:

. ISBencounterrate = (300 feet x 0.33 g2p) x04 mm x04 knots x( 30% ice)

= 45 bbV/hr '

_+19-


6.3 Scenario 2. Northstar in 5/10ths Ice Cover During Freeze-up

6.3.1 Blowout and Spill Behavior (Scenario 2. Northstar, 5/10ths Ice, Freeze-up)

An uncontrolled blowout occurs in mid October at the Northstar artificial island releasing 15,000
barrels of oil per day (BOPD) and 33 x 10° standard cubic feet (scf) of natural gas per day (a Gas-to-
Oil Ratio [GOR] of 2200 scf/bbl). Over the first 72 hours of the incident, the air temperature ranges
from a nighttime low of 8 °F to a daytime high of 18 °F. The wind speed averages 19 knots from the
‘WSW. The surrounding water is covered by 5/10ths new ice floes. The ice is 0.6 to 0.8 feet thick and
covered by 2 to 4 inches of snow. The floes are hundreds to thousands of feet in size. The ice is
drifung at the same speed as the water (both wind-driven at 3% of the wind speed) at 0.6 knots to
the ENE. These conditions do not change over the time period of the scenario; as well, the ice
concentrations do not change as it drifts away from the spill site (i.e., no convergence or divergence
of the pack). The water will be covered with newly growing ice crystals and slush.

As the oil and gas exits the 63-inch inside diameter tubing at the wellhead the high velocity of the
gas atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces
and the droplets agglomerate. The Kinetic energy of the gas. jet from the wellhead carries the droplets
toa height of 90 feet above the release point. From this point the oil droplets begin to fall as they

are carried downwind by the wind.

In this scenario, the slick is 180 feet wide and 0.7 mm thick at the starting point of the surface slick
modeling. This is at a distance of some 920 feet downwind of the blowout. At this point, the oil slick
is assumed to be evaporated to 20% loss. . : mo

For the purposes of this scenatio, is estimated that 50% of the oil spray lands on water and 50%

lands on the ice surface. The spray that lands on ice floes coats the surface and is absorbed by the © *’

snow. The range of oil thicknesses on the floe surface ranges from 0.9 mm near the center-line of


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wellhead, the deposition rate, averaged over the width of the plume, i is high enough to exceed the
holding capacity (or equilibrium thickness, defined by McMinn 1972 as 38.1 mm for an assumed
effective roughness height of 0.5 feet) and the oil spreads away from the initial deposition zone.

Farther from the blowout the deposition rate declines and the width of the plume increases until the

point is reached where the slick thickness generated over the scenario time period does not exceed

the equilibrium thickness and the oil does not spread from where it was initially deposited. '

Over the 24 hours of Day 1 of the scenario (see Table H-1) 10,800 bbls of oil are deposited on the
ice: (15,000 bbl/day x 0.8 x 0 9). Figure H-1 shows the thickness of the slick on the ice downwind
of the blowout after the first day, when it is assumed that the ice moves and carries this oiled area
away to the NE. The first droplets of oil hit the ice surface some 50 m downwind of the blowout. A
short distance downwind of this the oil is deposited in amounts sufficient to exceed the equilibrium

thickness; this rate of deposition continues until a distance of 210 m from the blowout. In this area

the oil spreads laterally away from the deposition zone. Figure H-2 shows the width of the oiled area
as a function of distance downwind of the source after 24 hours deposition. The zone where
additional spreading occurs is apparent. Figure H-3 shows a schematic “bird’s eye” view of the oiled .
ice after 24 hours deposition. The total oiled area is 31 ha (0.12 sq. mi.).

Figure H-4 shows the cumulative percentage of the 10,800 bbls of oil deposited per day that falls to
the ice as a function of distance downwind: 50% of the oil falls within 100 m; 75% falls within 220
m and 90% falls within 540 m. .

3.2 Day 2 ,
On Day 2 of the scenario two major ice movements occur: one at midnight and one at noon, dividing
the oiled area into two equal portions. Figure H-5 shows the thickness of each of the two equal areas
as a function of distance from the location of the source and Figure H-6 shows the corresponding
width. Figure H-7 shows a pictorial view of one area; the total area oiled in each portion is 30 ha,
for a total of 60 ha oiled on Day 2.

3.3 Day 3 .

The dimensions of the slick on water or ice floes as they pass under the blowout plume on Days 3

through 15 were estimated as in the six “average” scenarios described in the text of the main report
(width and distance defined as those for 99.7% of a given droplet size to settle - thickness a function
of current speed). For the purpose of further predictive modeling of the fate and behavior of the
surface oil slicks, we use the footprint thickness at the point where all (99.7%) of the droplets of a
diameter representing 50% (by volume) have reached the surface. This thickness, and the
corresponding width, are used to define the starting dimensions of the “thick” portion of the oil slick.

On Day 3 the wind is 10 kt from the east and the current is 0.3 knots to the west. As such, the thick
slick is 180 feet wide and 1.3 mm thick at the starting point of the surface slick modeling This is at,
adistance of approximately 920 feet downwind of the blowout. The thick slick at this point contains
about 60% of the oil that will eventually settle to the surface. As noted, at this point the oil slick is .

- assumed to be evaporated to 20% loss About 40% of the oil that eventually settles to the surface

falls beyond the 920 foot mark. Because most of these droplets are very small, they travel far

"55° a


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operations are assumed not to take place at night. The following analysis assumes that there are’

environmental incentives for using dispersant and that government approvals are in place.

+ The analysis focuses first on the logistics of the operation, that is, determining how much of the oil

can be treated with dispersant using the proper dispersant-to-oil ratio (DOR). Once this is done an
attempt will be made to assess how effective the dispersant might be in actually dispersing the oil
from the water’s surface. The program will use helicopter/spray-bucket systems for the operation.
These are ideally suited for this kind of operation because spills are close to land, high

, maneuverability is required of the spray platforms, and there already is much helicopter experience

in the area. The specifications of the helicopter/spray bucket systems were provided earlier in Table
5.5 in Chapter 5. These are summarized below.

| Item . Capacity

Payload 240 gallons
-  [Max.Speed © S4knots °° |
Min.Speed = -—«-—-.-« 27 knots
Max. Pump Rate": - 120 gallons/min. | :
Min. Pump Rate‘, 79 gallons/min,
Swath Width © ——*100feet_ =:
Reposition Time (360°) 2.25 min.

. The slicks that are the target for dispersant spaying in this scenario, as noted in Table 6-3, are in the

range of 0.5 to 0.7 mm. In order to treat slicks of this thickness using a dispersant-to-oil ratio (DOR)

. of 1:20, an application rate of about 30 gallons per acre would be required. The helicopter system
specified in the above table has the capability of spraying about 10 gallons per acre, on average. So,
each targeted slick would have to be sprayed about three times to achieve the properdosage. Current ‘

_ expert opinion is that a DOR of ‘only about 1:50 or ‘even 1:60 may be sufficient for effective


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x

* whether the mechanical cleanup systems that are currently available on the North Slope are
adequate to satisfy Alaska State requirements for cleaning up spills from blowouts in broken ice

conditions; , _

¢ whether additional resources would significantly i improve the existing mechanical recovery
capability, and to what extent, and ‘

¢ what the maximum cleanup capabilities might be for dealing with blowout spills i in broken ice
if all possible cleanup techniques were considered

The scenarios cover two locations (Point Mclntyre and Northstar Island) in three ice conditions. For.
Point McIntyre the scenarios are to consider spills during spring break-up conditions with ice
concentrations of 30, 50 and 70% respectively. For the Northstar Island scenarios, the spills will
occur during fall freeze-up during i ice concentrations of 30, 50 and 70% respectively. The parameters

- for the six spill situations or scenarios are in Table 1-1.

< - x ‘

- TABLE 1-1 ;
Parameters for Six Blowout Scenarios in Broken Ice _

Ou! volume. Northstar- 15,000 BOPD for 15 days minus 20% evaporative loss

Pt McIntyre - 12,000 BOPD for 15 days minus 20% evaporative loss
Type of blowout: - Oil is exiting the casing under high pressure and being sprayed i into the

rhage atmosphere .

Oil type. Alaska North Slope (ANS) crude oil .
Ice concentrations ‘© - Assumes 1" year ice only, with no multi-year incursions. Ice

. concentration will not vary during the scenario duration. For example, a
30% ice concentration will remain constant throughout the 30% ice

scenario.
Weather conditions: _The mean weather conditions for the North Slope, based on historical
, information, will be used during the applicable time periods for both
_ freeze-up and break-up
Equipment recovery Lori brush skimmer - 217 barrels per hour
efficiencies! - Oleophilic skimmers ‘ 20% of nameplate capacity
“ Weir skimmers . 20% of nameplate capacity

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Thick oil Emulsification Slick
remaining on .} (% water vol.) viscosity
water (% of total tay (cP @ 30 °F)

- 3.4 Days 4,5 and 6 . ,

On Day 4 the wind drops to 3 knots from the south-east and the current is 0.1 knots to the north-
‘west. As such, the thick slick is 180 feet wide and 4.2 mm thick at the starting point of the surface
slick modeling ,

Table H-3 summarizes the predicted characteristics of: the thick slick on Days 4, 5 and 6 over a time '
period of 24 hours. The oil that forms the thick slick on the water has a viscosity of 120 cP anda .
Pour Point of 10 °F at the point where the on-water modeling is started. For the first 24 hours after
its creation, the thick portion of the slick on water continues to spread laterally as it drifts with the —

ce, reaching a width of 1000 feet and a thickness of 0.7 mm. °

The presence of ice climinates the wave action that would normally exist with a 3 knot wind and
suppresses natural dispersion and emulsification of the oil slick.

The thick oil slick continues to evaporate slowly throughout the 24 4 hour modeling period. It loses
a total of 32% of its volume to evaporation after 24 hours. The viscosity of the unemulsified oil
increases to 140 cP after 12 hours and reaches 160 cP at 24. The Pour Point of the thick oil after 24
hours has increased to 22 °F.

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__ helicopter blade i icing, air cushion vehicle icing through freezing spray, internal ice build-up within

barge tanks, and rapid consolidation of shipping channels broken through fast ice At the same time,
the air temperatures are low enough to rapidly generate large volumes of ice crystals and slush ice
in any open areas and leads between the floes. This slush seriously affects small boat operations and
may complicate oil recovery. Sea state is not usually a key operating issue with the presence of
broken ice and, in October, the ice effectively dampens most swell and wind waves. '

The rapidly diminishing daylight in October and frequent strong winds are also important operational
constraints affecting flight operations, and reconnaissance effectiveness. Ice motion can carry the
oiled ice away from the spill source at initial rates of over 10 miles per day, leading to a rapid

~ increase in the contaminated area and in the logistics of coordinating the response over increasing

distances. Safety of personnel and equipment offshore in October under worsening weather -

conditions will be one of the fundamental issues in selecting transport systems. Transport options , .

will need to consider search-and-rescue and back-up equipment in the event of an emergency.

At break-up, the overall environmental setting is more moderate, with ice rapidly melting overtime,
24 hours daylight, warmer temperatures and generally light winds. Major operational constraints are

associated with maneuvering marine equipment through the floes in shallow water, and i in some ©

years with getting marine equipment away from West Dock through heavy ice in early July. Flight ,
operations are more likely to be curtailed to some extent in July due toa lack of VFR conditions Gow
ceiling and visibility in fog) _ ‘

Table’ 5-2 provides an overview of the : logistics inventory on the North Slope and Table 5-3 Table
5-3 summarizes the general operating capabilities and limitations of each equipment group when
operating within the environmental settings representative of the two main scenario groups of break-
up nearshore and freeze-up offshore (refer to Tables 2-1 and 2-2 at the end of Chapter 2 fords detailed
climate and ice descriptions). vos :

<

Specific pieces of equipment are further described i in ‘Appendix F in terms of their ability to provide .

transport and on-site support, as well as expected mobilization times. Additional information and
the results of past experience are added where possible to appreciate how different vehicles can be

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” Appendix F ~

Background Information and Details on Logistics

This section provides background information and details on the different types of aviation and
marine support equipment available at Prudhoe Bay and in Alaska to support an oil spill response
in broken ice during the months of July or October.

Acknowledgments

The authors wish to express their appreciation toall of the individuals and companies who provided
information and took the time to answer difficult questions needed to complete this section. (see

“ Contact List at end of Appendix)

Contents -- . _

@ Aircraft and Helicopters -

© Marine Equipment

@ Air Cushion Vehicles

© Summary of Logistics Effectiveness

© Options to Improve Logistics Capabilities .

@ Contacts. , :
© References :

Aircraft and Helicopters

This heading is subdivided into: ,

. Helicopters (Light Lift): 800 to 1,200 lb sling load, 4 to 6 passengers
. : Examples: Bell 206B/L, BO-105
e Helicopters (Light to Medium): ~ 2,200 to 10,000 Ib sling load, 12 to 21 pass.
Examples Bell 212/214, Vertol 107, Super Puma,

5

"Fixed Wing (Reconnsissance): Example: ARCO Twin Otter
© Fixed Wing (Freight): Examples: Northem Air Cargo (NAC) DC-6 (24,400

Ib); Lynden Airfreight Electra and L382 Hercules (up

to 46,000 Ib)

_ The focus here i is twofold: (1) obtaining immediate mobitiy in terms of transport from the Prudhoe

Bay support base to the spill site and/or barges on location; and (2) reserving the heavy lift capacity

, to move additional response equipment from southem staging points as needed.


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involving 5/10ths i ice. The logistical “tu would be identical to that described i in the previous

scenario.

‘The major question about dispersant use in this scenario is whether there would be enough oceanic
mixing energy to effect good dispersion. This is difficult to say. To be conservative, we will assume

that dispersant effectiveness in this situation will be close to zero, and will not "remove" any oil from”

the surface. However, in the real event it seems that it would make reasonable sense to try to disperse

. the escaping oil slicks. This may prove to be effective under the circumstances.

6.3.5 In situ Burning (Scenario 2. Northstar, 5/10ths Ice, Freeze-up)

As in the first scenario it is recognized that insufficient vessels exist to conduct an in situ burning
operation in conjunction with the containment and recovery operation described above, but if there
were, the i in situ buming unit would consist of 345 feet of fire boom and two tugs. -Ahelicopter/Heli

torch system would Suppor th the bum operation.

The encounter rate of each bum unit for this scenario would be the same as for the Tecovery unit at:

(345 feetx 0. 33 BP) x05 mm x 0. 6 knots x (1- - 50% ice)

ISB encounter Tate (max)
: 61 bbY/hr

Asin the first scenario the ISB system is envisioned as being used in a "batch" mode. Oil is collected
in the back of the boom for a certain period of time, then the system is moved away from the heavy
concentrations of oil and the accumulated oil is bumed off. For the sake of simplicity, i s assumed
that the thick slick is encountered and collected for 50% of the time, and the remainder of the time
is spent burning off the accumulated oil and maneuvering the unit back into the thick oil slick. This
equates, over a 10.5-hour day, to collecting oil for 5.25 hours and burning and maneuvering for 5.25
hours. Each individual burn would take about 1.2 hours from ignition to extinction. After each day’s
operations, the section of fire boom would have ‘to be replaced. Iti is potentially twice as efficient to

: _ collect and burn simultaneously however, because the oil slick thicknesses emanating from the

-90-


: 3 ee eee ~ hn tmiueda a) ee 2

_ © Shortage of ice capable barges and tugs. This deficiency is most critical for the
« October scenarios; in most years there are only two tugs (Point Barrow and ..
Thompson) with sufficient power to move conventional barges through more than *
a few inches of ice, and maintain a channel between West Dock and an offshore ..
location such as Northstar (only one of these tugs was on the Slope through the
. winter of 97/98). Lynden's ice strengthened tug the Arctic Bear may be operating
out of Prudhoe Bay from 1998 on. There is only one barge, the Endeavor,
_ capable of transporting deck cargo and recovered liquids through more than about
6 inches of ice, a condition which is often reached by October 10. Other barges _
are capable of operating in broken ice offshore until later; the limiting condition
becomes one of gaining access to and from West Dock through the new fast ice
‘ beginning to extend out from shore. Regardless of the type of barge or tug, .
"marine operations will eventually have to cease as the ice builds up in late
. October or possibly early November in a favorable year.

. ’ Possible solution(s): (1) contract for an additional powerful tug capable of
’ supporting and moving barges in broken ice; (2) contract for an additional
icebreaking barge capable of maintaining offshore logistics resupply withheavy  -
loads and recovered liquids through October and into early November (ideally -
capable of routine operations in 1.2 to 1.5 ft of solid ice); (3) utilize hovercraft
‘as the primary method of transportation to and from shore, leaving the barges
primarily as offshore storage, response platforms and accommodation support.
Two LACV-30's are capable of lightering over 1,800 bbl of recovered fluids in
a ten hour day over the 8 mile run between West Dock and Seal Island
(Northstar)

@ Mobilization times for heavy marine equipment, particularly i in October when
_ tugs and barges presently on the slope are already i in a state of winter lay-up.
* Minimum time from first call to arrival on-site (e.g., Northstar) of a fully
equipped response barge would be between 48 and 72 hours. Minimum time to
obtain a single operating air cushion vehicle would be 24 hours.

Possible solution(s); (1) contract to maintain critical equipment such as the

_ Endeavor, both Point Class tugs and an LACV-30 hovercraft in a state of "hot

* standby” in October - that is delay the winterization; (2) conduct regular

icebreaking around West Dock and along a channel leading to open water and

broken ice further offshore for as long as possible through October; (3) maintain

. a dedicated ice breaking, or ice strengthened oil response barge with the most

appropriate equipment to deal with a broken ice condition onboard in a state of
operational readiness for as long as the ice allows.

.A sustained offshore operation may depend on having the icebreaking barge
available as a shuttle to and from West Dock. In that case it would be logical to
ts use the ex - SATCO ice strengthened barges with conventional bows (operated
by Lynden), as a dedicated oil spill response platform(s), and the non-ice
strengthened series 200 barges as back-up on site storage for as long as they are
able to operate. The Endeavor would be left as the primary means of lightering -

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Clearly the efficiency is sensitive to both ice concentration and the average floe size that is assumed.
Recognizing that the broken ice field will contain a mix of floe sizes, the results of the above table
can be averaged to provide an estimate of containment efficiency of 70% in 3/10ths ice, 40% i in
5/10ths ice, and 20% in 7/10ths ice.


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footprint and was evaporated 20%. This value inutially increases with distance from the blowout,
reaches a maximum and then decreases as the spray gets farther from the blowout This decrease
is partly due to the large widths predicted for the large downwind distances for all of the smallest
droplets to settle to the surface. For the purpose of further predictive modeling of the fate and
behavior of the surface oil shck, the footprint thickness at the point where all (99.7%) of the droplets
of a diameter representing 50% (by volume) have reached the surface is used. This thickness, and
the corresponding width, are used to define the starting dunensions of the "thick" ‘portion of the oul
slick that is the focus of further modeling and the countermeasures assessments. In this case, the
thick slick is 180 feet wide and 0.9 mm thick at the starting point of the surface slick modeling. This
is at a distance of approximately 920 feet downwind of the blowout.

For the purposes of these scenarios it was assumed that all of the oil landed past the perimeter ofthe -
island. This is a reasonable assumption for the prevailing westerly winds, but it is acknowledged that

a small percentage of the oil could be deposited on the island particularly with wind from the east.
Takang nto account the fact that many of the drops in Range 6, about half of the drops in Range 7
and a few of the drops in Range 8 settle out in this (920 ft) distance the thick slick at this point
contains about 60% of the oil that will eventually settle to the surface. As noted, at this point, the
oil slick is assumed to be evaporated to 20% loss. About 40% of the oil that eventually settles to the

surface falls beyond the 920 foot mark. Because most of these droplets are small (some of Range 7
and virtually all of Ranges 8 and 9) they travel far downwind and spread widely before settling out.
These droplets form a very thin slick on either side of the thick oil. This very thin slick is a long,
narrow triangular area with an average thickness that can be shown to be on the order of 35 um.

The approximate mass balance for the oil released from the blowout is: 20% evaporates from the

drops i in the air; the smallest 10% of the volume of the weathered droplets are so small that they ~

remain suspended in the atmosphere; about 60% of the remaining oil (or about 40% of the total- -

0. 6x0. 7, composed of mostly the larger droplets) settles to the surface within 920 feet and, if it
. lands on water, forms a slick 0.9 mm thick and 180 feet wide; and, 40% of the remaining oil (or

* -69-




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it permits the results from a variety of laboratory evaporation experiments to be easily extrapolated
to actual environmental conditions with a high degree of confidence. .

‘

With an above-surface blowout, evaporation also occurs as the oil droplets from the blowout rain
down onto the surface. The amount of oil that evaporates in this situation is controlled by the size
of the droplets, the volatility of the oil, the length of time they are in the air, and the air temperature.
“Rather than use the model to estimate an initial evaporative loss for the droplets i in the air, a fixed
value of 20% initial volume loss to evaporation was used in the study, as requested in the terms of
reference for the study. This leads to an under-estimate of evaporative loss for one of the oils used _
in the study ( Milne Point as surrogate for Northstar) and an over-estimate for the other (Pt.

McIntyre).

Emulsification. When most crude oils are spilled at sea, they tend to form water-in-oil emulsions.

Emulsification occurs in the presence of mixing energy suchas that provided by wave action. During
emulsification, seawater is incorporated into the oil in the form of microscopic droplets. This water
intake results in two undesirable changes to the oil. First, there is a significant increase in the bulk

‘ volume of the oil (usually up to a 4-fold increase), greatly expanding the amount of oily material that

must be dealt with. Secondly, there isa marked i increase in fluid viscosity (upt to 100- -fold). The much
higher viscosities greatly inhibit the natural dispersion of oil and make the application of chemical
dispersants useless.

Mackay (1983) and Mackay and Zagorski (1982) developed preliminary models for the -

emulsification process, and these are often used to describe the phenomena in quantitative terms.

Natural Dispersion. In conjunction with evaporation, the process of natural dispersion reduces the
volume of oil on the water surface, thereby influencing the potential extent of surface and shoreline
contamination. Dispersion rates are determined by oil/water interfacial tension, oil viscosity, oil
buoyancy and slick thickness. Environmentally, sea state is the most important factor controlling the

- rate and amount of dispersion. Even the heaviest, emulsified oils can an disperse over a period of time

in heavy seas with frequent breaking ‘waves

30."


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to arrival at Deadhorse from Anchorage are: 5 days for the first, 10 days for the second, and ~
one month for the third and fourth machines

In addition to the LACV-30, Lynden has two AP.1-88's certifi ied for 88 passengers or up to
8 tons internal small package type loads. One of these craft is in Anchorage and could also "'
be moved by road to the North Slope in an emergency within one week. Although not °
optimized for freight, Lynden's AP.1-88 would be the safest and most effective way of
moving large numbers of people to and from the Northstar spill location in October.

Both of these designs have proven themselves with extensive over-ice experience under ice
conditions often more severe than expected off Prudhoe Bay in October. When icebreaking
is not the primary mission, the LACV-30 can cruise at over 40 knots over young ice while
causing only superficial cracking. While the load center must be kept within prescribed c.g.
limits while on cushion, the craft can also act as a stable self propelled barge in the
displacement mode with skimmers and equipment over the side (taking care to lift up on
cushion periodically to break the ice around the skirts and underneath). :
Although ice needs to be cleared periodically from exposed surfaces under freezing

conditions, hovercraft have not experienced any significant problems with propeller icing
even over thin breaking ice. SAS avoided operating at low speed on cushion over open water

. in freezing conditions to limit ice build-up on the superstructure (another altemative is to

drop into the water and move forward on partial cushion with the skirt in the water to trap
spray). Other procedures included hot water/glycol spray at base (similar to aircraft deicing
rigs at airports), and operating at lower cushion settings to reduce air flow and associated
spray in freezing conditions. As ice concentration increases the severity of superstructure
icing rapidly decreases. The worst areas tend to be close to the ice margin where there is a
greater opportunity of wind waves and spray. Dickins (1983) provides a detailed summary
ofall known ACV cold climate operating experiences, along with operational measures taken
to deal with specific conditions.

During October, strong winds over 25 knots persist for 10% of the time on average Ref
Table A-2 in Appendix A). These winds are close to the operating limits for the LACV-30,
especially in conditions of freezing spray. There are no known limitations in operating over
broken ice in the spring. Winds are much more moderate at that time of year, with situations
over 25 knots occurring less than 3% of the time.

Example ACV Lightering Scenario: The LACV-30 operated by Lynden (Alaska Hovercraft)
was designed as a ship to shore lighter. This machine could transport 5,000 gallon (119

* barrel) loads from a spill site at Northstar to West Dock in less than 18 minutes travel time

tegardless of ice conditions (assuming a conservative 25 knot block speed). With two

, machines operating in parallel during daylight/wilight hours averaging 10 hours in October

(allowing sufficient time for repairs and maintenance at night) the LACV-30's could lighter

: aminimum of 1,800 barrels per day based on one return trip every 70 minutes (36 minutes

travel, and 34 minutes transfer), and allowing for at least two craft refueling.

With high volume transfer pumps at each end and a typical cruise speed of 30 knots, it
would be possible to achieve a return time of less than one hour. ‘For the first half of

“ll . a os


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CI

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de ss Sy ay eee en ne as bs) See te ai epee 2

The contaminated area would be located through visual observation of surface oiling and boring
‘holes in the ice on a grid pattern to locate sub-surface accumulations of oil. Handheld global-
positioning-system (GPS) units would be used to record the exact locations of both surface and sub-

> .

surface pools.
Recovery operations on early-season, landfast ice would be similar to remote terrestrial spill response
actions once the oil is brought to the surface. Logistics constraints may demand that in situ buming

* be utilized as the primary recovery option.

Despite all efforts, however, the oil recovery efficiencies for spills i in the fall freeze-up Period would
be expected to be low. ,

~42-


i gmeeene

as EE:

~ TABLE 6-14

5/10ths ice cover over 72 hours

Ultimately, the rotting ice will telease any oil still remaining in the form of thin sheens trailing the
* drifting floes.

Summary of slick characteristics from a blowout during break-up at Pt. McIntyre in

Wa

”

Time ~ Thick oil left on Emiulsification Slick Thick slick | Thick slick
‘(h) water (% of total | (% water vol.) viscosity thickness | width
: released) | (cP @30°F) | (mm) (ft)
Initial 22 0 25000 21 100
3 22 0 26000 21 100
6 22 0 26000 2.1 100
| 12° 2 0 26000 21 100
24 22 0 27000 21 100
48° 22 0 28000 2.1 100
22 0 30000 21 100

6.6.2 Existing Methods (Scenario 5. Pt. McIntyre, 5/10ths Ice, Break-up)

As in the previous break-up scenario, the relatively narrow slick of thick oil means it can be

encountered in its entirety by one or two containment and recovery systems. For the moment the

evaluation will consider one system operating ata fixed location down drift of the blowout site, with
the potential effectiveness of additional systems analyzed later.

” ‘The slick conditions of interest are similar to the previous break-up scenario except that the oil does

not emulsify due to the dampening effect on the wave energy of the higher ice concentration. At a

, . point 3 hours down drift of the blowout, the thick slick is 100 feet wide and averages 2.1 mm thick.

Combining this with the drift rate of 0.3 knots, and accounting for the ice concentration of 50%, the

encounter rate for oil on water and available for recovery is estimated as:

1

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Free water pickup is expressed as the oil recovery efficiency, defined as the percentage of water-free

_oil of the total volume of recovered fluid This is particularly important for weir-type skimmers

which are known to recover large volumes of water along with the recovered oil. Weir-type
skimmers are defined as having a recovery efficiency of 20% Oleophilic-type skimmers (e.g., the
LORI brush skimmer and ‘the Foxtail rope mop type device) recover relatively water-free oil.

As recovered fluid is pumped to storage iti is assumed t that some of the free water is mixed with the
oil to form a water-in-oil emulsion. The ‘assumed water content i is 40%; thus the emulsion volume
in storage is 1 / (1 - 40%) = "1.67 times the recovered oil volume. ° :
For planning purposes it canbe assumed that 80% of the free water in storage can be decanted at the
spill site. This water would be pumped from the bottom of the storage tank or barge, and would
typically be discharged within the boomed area where containment and recovery equipment is

_ operating. * 1 . ' . :

5 - vay

5.4 Logistical Constraints | -

Compared with the Tesponse to spills during open water periods, the response during break-up ‘and

~ freeze-up will be limited to some extent by the availability of tugs and barges that are capable of

operating in broken ice conditions. The following are summaries of the inventory and applicability
of the response platforms and support vessels that are available and of the logistical restraints
associated with these. ;

The presence of broken ice narrows the logistics options considerably, compared with either a solid
ice or open water situation. Unlike the mid-winter or mid-summer periods, there is no one piece of
equipment which can provide reliable access to and/or support at the spill site (e.g., ice roads and
barges). ‘

At freeze-up, the primary problem i is rapidly forming new ice under freezing air temperatures.
Although not severe when compared with conditions in January or February, the freezing potential
and wind chill i in October/N lovember still Tepresent considerable Spprtionsl challenges, such as

‘-47-


downwind and spread widely before settling out. These droplets forma very thin slick on either side

of the thick oil. This very thin slick is a long, narrow triangular area with an average thickness that
is on the order of 35 jm (0.035 mm).

The approximate mass balance for the oil released from the blowout i is: 20% evaporates from the
drops in the air; the smallest 10% of the volume of the weathered droplets are so smal] that they
remain suspended in the atmosphere; about 60% of the remaining oil (or about 40% of the total - 0.6
x 0.7, composed of mostly the larger droplets) settles to the surface within 920 feet and, if it lands
on water, forms a slick 1.3 mm thick and 180 feet wide; and, 40% of the remaining oil (or about 30%
of the total - 0.4 x 0.7, composed of mostly small droplets) settles out farther downwind and forms
a thin (35 ym) slick bordering the thick slick on both sides.

For the purposes of this scenario, it is estimated that 30% of the oil spray lands on water and 70%
lands on the surface of ice floes. The thickness of this oil coating ice floes is estimated by summing
the amounts of oil of the various size ranges that settle onto the floes as they drift under the plume
from the lee side of the island to the point at which oil droplets finish settling. Directly in the lee of
the island, over the distance required for 97.7% of the average size drops to settle out (920 feet), it
is assumed that the ice floes are coated evenly over a width equal to the plume width (in this case
180 feet). Further down drift, the oil coating is incremental. The average oil thicknesses on the floe
surface ranges from 1.7 mm near the center-line of the oiled strip to 0.007 mm out near the edges.
The spray that lands on ice floes is slowly flushed by melt water into the melt pools on the floes. The
flushing process results in wind-herded oil thicknesses on the melt pools of 10 mm. The oil covers
up to 60% of the surface area of the melt pools; the largest slicks are on floes near the center-line of
the oiled strip. This oil will evaporate at a rate negligibly different from the oil that falls on the water,

reaching a total evaporative loss of 29% after 24 hours.

Table H-2 summarizes the predicted characteristics of the thick slick over a time period of. 24 hours.
The oil that forms the thick slick on the water has a viscosity of 120 cP and a Pour Point of 10 °F
at the point where the on-water modeling is started. For the first 18 hours after its creation, the thick
portion of the slick on water continues to spread laterally as it drifts with the ice, reaching a width
of 410 feet and a thickness of 0.5 mm. After 21 hours, the oil has evaporated to a point (28%) where
it’s Pour Point (30°F) exceeds the: ambient water temperature and the thick portions of the slick cease
to spread on water.

The presence of ice eliminates the wave action that would normally exist with a 10 knot wind and
‘suppresses natural dispersion and emulsification of the oil slick.

The thick oil slick continues to evaporate slowly throughout the 24 hour modeling period. It loses
a total of 29% of its volume to evaporation after 24 hours. The viscosity of the unemulsified oil
increases to 170 cP after 12 hours and reaches 190 cP at 24, The! Pour Point of the thick oil after 24
hours has increased to 32 °F.

-10-


mealtimes — oe

. Freeze-up Break-up
io P te
Scenario Parameters . Ice Coverage ~ Ice Coverage
30% | 50% | 70% }.30% | 50% | 70%
| _ Existing Countermeasures 59 |°22 | 06 | 18 | 12 | 44
Dispersant-Use. | 42 ] 0 | 0 .| O | 0 0
In-Situ Burning? - on-water 3.4 22 6.4 0 14 7A
_ on-ice ‘ 0 0 0 15. 25 33
Well Ignition ‘ 99 : 74 .
| to” |
1. All figures expressed as a percentage of total blowout flow. « : ,
2. Note that ISB on-water effectiveness is for comparison with existing containment and -
recovery effectiveness; ISB on-ice effectiveness would be in addition to either
containment and Tecovery OF ISB on-water effectiveness.

TABLE 6-20

Summary of Recovery Effectiveness! for Alternative Countermeasures

Q

Dispersant Use. The use of dispersants is an attractive option for dealing with blowout-type spills,
particularly those that are relatively close to centers of logistic support, as are the spills in these

. scenarios. The modest daily spill rate combined with the ability to deliver the required quantities of

dispersant while the oil is relatively thick mean that there are good opportunities for application.

. However, the fact that there is broken i ice has two major impediments to the overall effectiveness of

a dispersant operation. First, the presence of ice tends to dampen any wave action which is required
to allow dispersants to be fully effective. In this evaluation, it is assumed that dispersants would be
“ineffective in the 50% and 70% ice scenarios due to the limited wave energy, although dispersant
application might be attempted. The second limitation is that, with the blowout spills in these
scenarios, a fixed percentage of oil lands not on the water surface but on the ice as it drifts past the
spill source (a percentage that matches the average ice concentration) and this oil would not be

oe ABB


. 51 Overview of Tactics

oe pemee hderenah vhentes-serte-tadnereaeneine — oe Bit ee eee a abdedeeteeneets

5. Existing Spill Response Approaches and Systems

In this section the systems that currently exist for dealing with spills in ice will be described. -

Included will be an overview of current cleanup approaches and plans, and a description of the key

* equipment available to implement these plans. The description ‘of the equipment will include a

discussion of their operational capacities and hmitations and will set the stage for the subsequent
evaluations for each of the blowout scenarios. :

. The chapter focuses on countermeasures for physically recovering spilled oil, but two short sections

are written (in Sections 5.5 and 5.6) on the countermeasures of in situ burning and dispersant use.

3

_ The tactics for dealing with the spills in the specified scenarios will depend on the degree of ice

concentration, the ability to use containment boom to safely and effectively concentrate spilled oil
for recovery or for in situ burning, and logistical considerations.

‘
'

For spills in light ice conditions it will be feasible to use containment boom and skimmers to
concentrate and recover oil. Short lengths of boom, up to 400 feet depending on ice concentrations,
would be deployed in a J-configuration from a barge that would be used as a skimming platform and
for storage of recovered fluids. High-strength boom would be required for this application to
withstand contact with ice. Skimmers for this mode of operation could include either weir-type

_ devices or oleophilic Tope-mop skimmers. Overall effectiveness of this type of deployment would

depend primarily on two factors: the rate at which oil is encountered and concentrated for recovery,
and any inefficiencies resulting from encountering various ice forms.

The encounter rate, that is, the volumetric rate at which the boom/skimming system encounters the

< ilslick, is a function of the swath width of the booming system, the slick thickness, and the speed

of advance of the system. The swath width of the booming system is a function of the length of boom
deployed, which must be limited to a few hundred feet depending on ice concentrations. For the

-43- J


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This encounter rate is less than the derated recovery rate of several of the offshore skimmers that
could be used, so the encounter rate is the limiting factor and is used in the calculations of recovery
effectiveness. Following the same calculation procedure and guidelines for oil recovery efficiency,
the total fluid recovery rate can be estimated as shown below:

_Table H-7: Fluid Recovery Rates for Days 13-15
Calculation

96 bbV/br
384 bbV/hr
64 bbl/hr
320 bbY/hr |

lesser of system encounter rate and derated recovery rate

oil content in recovered fluid (recovery efficiency) = 20%
emulsified water content in recovered fluid = 40% ,
total water less emulsified water

oil + emulsified water + free water

Compared with the previous scenarios in the main report, the main difference here is the lesserice ._
concentration and its effect on containment efficiency. For the 10% ice condition, the containment
efficiency is assumed to be 90%; that is, the containment operation is effective for 90% of the time
accounting for interruptions related to clearing ice from the containment and repositioning the system
when avoiding large floes. Given the 24-hours of daylight at this time of year, the total fluid volumes

efficiency.

Item

Table H-8: Estimate of Recovered Fluids

Calculation

per 24-hr Time Period

* per day are calculated in the following table, combining the hourly rates and the 90% encounter

Volume ;

j total fluids per 24 hours ©

480 bbW/hr x 24 hours x 90%

10368 bbl

total free water

320 bbV/hr x 24 hours x 90%

6912 bbl

volume that can be decanted

total free water x 80%

» 5530 bbl

total fluids stored per 24 hours

total fluids less decant

4838 bbl

96 bbi/hr x 24 hours x 90%

2074 bbl

64 bbV/hr x 24 hours x 40%

* 1382 bbl

total free water x 20%

1382 bbl

- The above calculations were for one system which could encounter half the width of the thick slick.

A second system could be used, with identical recovered oil and fluid volumes. As in the previous
break-up scenario, additional systems could be used to attempt to recover oil from the thick slick that

, is missed by the first system. The target for the additional systems is the oil thatescapes containment -

due to inefficiencies associated with the ice conditions, assumed to be 10% for the 90% ice

er) ne


Se 5): ee omeds abi: teeneans

+e

Thick oil ‘ | Emulsification | . Slick Thick slick
remaining on (% water vol.) viscosity | thickness
water (% of total : (cP @ 30 °F) (mm)
released : ~_ |

* takes emulsification ito account

4. Countermeasures
4.1. Overview .

The selection of countermeasures will vary according to the ice concentrations. As described in the
main text of this report, in a break-up scenario the two main tactics of in situ burning and
containment and recovery are comparable in their effectiveness at dealing with oil amongst broken
ice floes. This is because the slicks that result from blowout spills are not thick enough for effective
skimming or burning unless the oil is first concentrated and thickened. Jn situ burning does have an
advantage over skimming when it comes to buming oil that lands on ice. Given the above-freezing
temperatures, oil that lands on ice will accumulate and thicken somewhat in melt pools on the
surface of the ice. This thickening process allows for in situ burning of oil that would otherwise be
present in only thin sheens and thus difficult to recover. As well, at the start of the break-up period
the ice is relatively motionless for a few days, during which time the oil from the blowout will
accumulate downwind of the source in burnable thicknesses. In this situation, in situ burning would
be the primary response option, although for safety reasons, it would not take place until the oiled

ice moved away from the blowout source.’ :
42 Day1 , 2 4 >
The oil that is deposited on the ice in the first two days of the blowout is ideally suited for removal
by in situ burning. Approximately 75% of the oil that hits the ice is located within 700 feet of the
blowout (some 8100 bbls), in very thick slicks (about 40 mm). Another 20% of the oil that hits the
ice is located up to 3300 feet from the blowout (some 2160 bbl) in thinner slicks (as thin as 0.6 mm).
When the ice containing the first day’s oil deposits moves away from the island on Day 2, the oil
would be burned. Igniting the thick oil near the source-end of the area would result in a burn of 95%
removal efficiency (or 7700 bbls), leaving behind a residue of about 2 mm (or 400 bbls). The thinner

; oil, concentrated in melt pools, could be bumed with an average removal efficiency of 80% (or 1730 ~

’

-15-


A - Cana ogy enanee +e Gees tetera ann: Ot Snes tmeas bl} ap ee

condition. Using the same calculation procedure as detailed in the main report, two additional -
systems are considered. For each system, the encounter rate is estimated by subtracting the oil
recovered by the previous system and estimating an equivalent average oil thickness. The following
table summarizes those calculations.

Estimate of Slick Conditions and Fluid Recovery for Two ‘Additional Systems -

System | Encounter -|: Encounter , Oil recovered > Total fluid
thickness rate per 24 hours per 24 hours

#1 0049 mm 9bbVhr * “194 bbl 972 bbl
#2 ~~ 0.049mm . 9 bbV/hr 194 bbl
_|_-

Note that the slick remaining after these two systems would be an average of only 0.007 mm thick,
with an encounter rate of less than 1 bbl/hour and a daily recovery volume of much less than 1% of

the daily blowout volume.

The following is the estimate of effectiveness for each of Days 13 through 15, expressed as a
percentage of the total blowout flow: °

Recovered oil volume = (2X 207442 19 bbVday ~ 15,000 bbl/day
, . > = 30% ‘

In situ burning could be considered as an option for dealing with the small fraction of the oil that
lands on ice floes. In this instance, in situ burning would supplement the containment and recovery
operation. Using the same calculation procedure as for the previous Days 3 through 11:

daily oil removed from floes by buming = 15,000 bbl x 7% on ice x 80% x 85%

‘= 714 bbl -
= 48% of 15,000

4

The total oil removal for Days 13 - 15 is thus (30% + 4.8% = 35%). ue

49 Summary of Effectiveness ; oo

Table H-9 summarizes the estimated effectiveness for each of the 15 5 days of the scenario. The
highest effectiveness values are for Days 1 and 2 when oil that pools in a thick layer on the relatively
stationary ice and can be removed through in situ buming. The lowest values is for Day 12 where
the moving broken ice reduces the effectiveness of cleanup operations. The average effectiveness
over the 15-day period is 38% of the total 15,000 barrel/day blowout flow, and 53% of the oil that
lands on the ice and/or water surface.


tle sremnnnen

” TABLE 6-3 .
Summary of Slick Characteristics from a Blowout During Freeze-up _
at Northstar in 3/10ths Ice Cover over 72 Hours

eee
takes emulsification into account

Time _ Thick oil left on | Emulsification Slick Thick slick | Thick slick
(h) water (% of total | (% water vol.) viscosity’ "| thickness width
released) __ (cP. @ 30°F) (mm) (ft)
Initial 26% 0 Y + 420° 09 180
3 25 0 145 0.7 240
6 24 0 "160 06 250 |
12 22 0 180 05 280
| 24 21 75 7000 - 1 300
48 19 75 8700" * 16. 300 |
72 18 75 9300° 15° 300

6.2.2 Existing Mechanical Methods (Scenario 1. Northstar, 3/10ths Ice, Freeze-up)

This section evaluates the likely effectiveness of a containment and recovery operation in response

to the scenario. The ice conditions at West Dock, more than the ice concentrations at the spill site,

will govern the marine equipment that can be used for the operation and the speed of the response.

The primary issue becomes one of breaking out the frozen-in vessels and moving them offshore =

through a band of newly forming fast ice which could easily extend a mile or more to the north of
~ West Dock. Barly i in the freeze-up scenario, when 3/10ths ice concentration is assumed, up to four
tugs and two ice-strengthened barges could be mobilized and used for offshore support of
containment and recovery. Smaller boats could be used for boom handling on site; however, these
vessels are not ice-strengthened and would need to be transported to the site as deck cargo on a.
barge. It is estimated that mobilization time for this marine support would be a minimum of 48

__ hours, and 60 to 72 hours until it arrived on-site. (ti is noted that since the draft report was prepared,

a decision was made to locate response equipment on Northstar Island. This change i in capability was
not addressed in this analysis.) - .

-72-


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" slick.)

In this scenario the weathered oil on the ice floes is too thin to ignite.

on : . 2

. simplicity, it is assumed that the thick slick is encountered and collected for 50% of the time, and

the remainder of the time is spent burning off the accumulated oil and maneuvering the unit back
into the thick oil slick. This equates, over a 12-hour ‘day, to collecting oil for 6 hours and burning
and maneuvering for 6 hours. Each individual burn would ‘take about 12 hours from ignition to
extinction. After each day’s operations, the section of fire boom would have to be replaced. It is
potentially twice as efficient to collect and burn simultaneously; however, because the oil slick

a thicknesses emanating from the source could be close to the minimum ignitable for weathered crude
‘ (about 2 mm) there would be a danger of the fire buming back to the spill source. (The thickness is

only 0.7 mm at 3 hours down current and this i is the average thickness across the width of the thick

The estimated daily removal rate for one ISB unit is thus:

ISB unit estimated daily removal rate = (83 bbl/hr x 12 m3 x0.5 = 498 bbl
If all the vessels capable of operating i in this scenario were used for ISB operations, a total of two
ISB units could be deployed, removing an estimated 996 bbl of oil from the water surface per day.
If more vessels were available, four ISB units could be operated to remove 1992 bbl per 12- ‘hour day.

A similar overall reduction in in situ burning effectiveness to that determined above for mechanical
containment and recovery, can be estimated using the same response time and environmental factors
as for mechanical containment and recovery. For ISB operations the additional factor of the
percentage of time that winds are less than 20 knots (80%) is also taken into account. The estimate
of ISB effectiveness for the 15-day period, expressed as a percentage of the total blowout flow:

Oil volume removed by ISB 996 bbl/day x 0. 83 x0.77 x 0.80 + 15,000 0 bbl/day

34%

-82-


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mount an oil spill control operation during open water conditions And third, the presence of a solid
ice cover for most of the year leads to the situation where an oil blowout from a gravel island is
usually little different than a blowout on land That is, most oil can be ignited and the remainder
simply recovered by mechanical means from the landfast ice surface.

In summary, relative to other offshore oil spill situations, oil well blowouts and spills from gravel
islands in the Alaskan Beaufort Sea are considered to be straightforward to clean up, particularly

or burned, and open water when the oil on the water near the island can be dealt with by
conventional containment and recovery devices. - : ‘ .

Nevertheless, broken or unstable ice conditions exist for short periods during fall freeze-up and
spring break-up in the Alaskan Beaufort Sea. The presence of the ice will inhibit spreading of the
oil, however, with the blowout conditions considered in this study (ie., open orifice blowouts with
high gas-to-oil ratios), the initial slick thicknesses are too thin to allow for in situ burning without
concentrating the oil in some manner. The other approach, using conventional booms and skimmers,
also has serious problems because the oil is often too thin and widespread for cleanup systems to
operate efficiently, if at all, among the ice floes

, In summary, spills from blowouts in open-water and complete-ice-cover situations are much more
amenable to cleanup than instantaneous tanker spills. However, the capability in a broken-ice
situation is generally not good regardless of spill type, as discussed below. ‘

4.2 Review of Cleanup Capabilities for Spills in Various Ice Concentrations

The following sections are abstracted from Dickins and Glover 1996. These describe industry’s -

proposed strategies and techniques for dealing with oil spilled in different combinations of ice and
open water off the North Slope, drawing on experience with past spills (both accidental and
experimental) and | knowledge of the expected fate and behavior of oilinice.

-37-

: during the predominating periods of complete ice cover when the oil can be removed mechanically

vs


SS eee r ee nN aa me 0h) i oe onan Gakpemmmnain

'

Recovered oil volume= 831 bbI/day x 0.97 x 0.66 + 12,000 bbl/day
= 44% ‘

6.7.3 Additional Systems (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up)

The above analysis described the potential effectiveness for four containment and recovery systems.
Although one system can encounter the entire width of the thick slick, itis assumed that a substantial
amount of oil is lost due to having to maneuver around ice floes and clear smaller ice from the
containment configuration. Three additional systems were then analyzed for their ability to
sequentially recover oil missed due to these inefficiencies. As noted above, any additional systems
would have a daily Tecovery volume of less than 1% or less of the daily blowout volume.

6.7.4 Dispersants and Burning (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up)

The viscosity of the oil and the ice conditions are too formidable in this scenario to consider the use

of dispersants.

If it were necessary to implement in situ burning in this scenario 300 feet of fire boom and two
workboats would again be needed. A helicopter carrying a Heli-torch would support both the on-
water and ice floe bum operations. The encounter rate of each burn unit would be: ;

ISB encounter rate (max) = (300 feet x 0.33 gap) x 1.1 mmx 0.5 knots x (1 - 70% ice)
‘ = 59 bbV/hr

The ISB system, used ina "batch" mode, would encounter thick slick 50% of the time; the remainder
of the time would be spend burning off the accumulated oil and maneuvering the unit back into the
thick oil. This equates, over a 24-hour day, to collecting oil for 12 hours and burning and
maneuvering for 12 hours. Each individual burn would take about 1.2 hours from ignition to
extinction. Twice each day, the section of fire boom would have to be replaced. It is potentially twice
as efficient to collect and burn simultaneously; however, because the average oil slick thickness

123.


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6.5.4 Dispersant-Use and Burning (Scenario 4. Pt. McIntyre, 3/10ths Ice, Breakup)

:

Dispersant Use. The strategies and good opportunities for using dispersants on this spill in 3/10ths
" ice would be similar to those discussed for the 3/10th ice freeze-up situation at Northstar (Scenario

1) except for one problem - the very high viscosity of the oil. After just a few hours on the water the
oil is predicted to have a viscosity of over 100,000 cP. This is well beyond the viscosity limitations

~ of even the most effective dispersant products today. If another production area involving a less

viscous oil had been chosen for this spring break-up scenario, the dispersant results would have been
similar and even better than to those calculated in Scenario 1. A springtime dispersant operation
would likely be far more successful than an operation during freeze-up because the oil is not

contaminated with slush ice, the air temperatures are higher, and, of greatest importance, there are |
24 hours of daylight in which to conduct operations.

In situ Burning. At the safe distance for operations downwind of this blowout, the thick slick has
emulsified to 55% water content. This prevents ignition. The use of "emulsion breaking" chemicals
to promote ignition will not work with Pt. McIntyre crude oil that is weathered to this extent.

Ignition of the thick slick among the floes before it emulsifies is not recommended; the average slick
thickness is greater than the minimum ignitable thickness for weathered oil on water and the fire

- could spread, uncontrolled, over the entire thick slick and back to the spill source.

The oil that falls on the ice floes in this scenario is ideal for in situ burning operations. After
allowing the surface oil to concentrate in melt pools, about 60% of the surface area of the pools
would be covered with 10 mm-thick oil. Taking into account an average oil-removal-by-burning

efficiency of 80% and conservatively estimating that only oil in melt pools greater than 50 ft? (90%

of the total) would be ignited by Heli-torch operations results in an overall oil removal by burning
of: : .

daily oil removed from floes by burning = (12,000 bbl) x (21% on ice) x 80% x 90% = 1815 bbl

 107-


aoanmtmo moO

— = am re me tt ela ns ol GF

If two units were deployed to encounter the entire thick slick available the total daily ISB removal
rate from water would be 2688 bbl. This is slightly higher than the case of containment and recovery
because i it is envisioned that burning, then maneuvering the ISB unit backi into the thick oil will take
less time than for the conventional boom and skimmer system. .
The oil that falls on the ice floes in this scenario is ideal for in situ burning operations. After
allowing the surface oil to concentrate in melt pools, about 75% of the surface area of the pools
would be covered with 10 mm-thick oil. Taking into account an average oil-removal-by-burning
efficiency of 80% and conservatively estimating that only oil in melt pools greater than 50 ft? (90%
of the total) would be ignited by Heli-torch operations results in an overall oil removal by buming
of: / ‘ . . ‘
daily oil removed from floes by buming = 12,000 bbl x 35% onice x 80% x 90%
‘ = 3024 bbl :

A similar overall reduction in on-water in situ burning effectiveness to that determined above for

- mechanical containment and recovery, can be estimated using the same response time and

environmental factors as for mechanical containment and recovery. For ISB operations the additional
factor of the percentage of time that winds are less than 20 knots (95%) is also taken into account.
The estimate of ISB effectiveness for the 15-day period, expressed as a percentage of the total
blowout flow: . 5

Oil removed from waterbyISB | = 2688 bbl/day x 0.97 x 0.66 x 0.95 + 12,000 bbi/day
: = 14% :

6


a = seme as eee 3 as 4 $e ae ee oumede ai See

CI

- 43 Day2

- melt pools that would form on ice floes.

rma OOO oO Oo

ma oe

oom

bbls), leaving behind a 1 mm thick residue on the melt pools (or 430 bbls). In total, of the 10,800

‘bbls of oil deposited on the ice surface on Day 1, 9430 bbls, or 87%, could be removed by in situ

burning. This corresponds to 63% of the total blowout flow of 15,000 barrels.

)

On Day 2 two ice movements occur creating two individual oiled ice areas, which for these purposes
are assumed to be identical. Approximately 70% of the oil in each of the two areas that hits the ice
is located within 560 feet of the blowout (some 7600 bbls in total), in very thick slicks (about 40 -
mm). Another 25% of the oil that hits the ice is located upto 3300 feet from the blowout (some 2700
bbl) i in thinner slicks (as thin as 0.3 mm). When the ice containing the second day’s oil deposits
moves away from the island on Day 3, the oil would be burned. Igniting the thick oil near the source-
end of both areas would result in a bum of 95% removal efficiency (or 7200 bbls), leaving behind
aresidue of about 2 mm (or 400 bbls). The thinner oil, concentrated in melt pools, could be burned

. With an average removal efficiency of 80% (or 2160 bbls), leaving behind a 1 mm thick residue on

the melt pools (or 540 bbls). In total, of the 10,800 bbls of oil deposited on the ice surface on Day
2, 9360 bbls, or 87%, could be removed by i situ burning. This corresponds to 63% of a total
blowout flow of 15,000 barrels.

44 Day3

In ice concentrations greater than 5/10ths, i in situ burning would likely be the response tactic of
choice. Although in situ burning offers little theoretical improvement in effectiveness compared with
containment and recovery, the lesser logistical requirements will likely lead to greater effectiveness
in an actual spill incident. As well, in situ buming offers the potential to bum oil contained in the

The requirements for in situ burning in this scenario would be three ‘barn systems, each using 300
feet of fire boom and two tugs. A helicopter carrying a Heli-torch would support the burn operation
The encounter rate of each burn unit for this scenario would be:

» ISBencounterrate = (300 feet x 0.33 gap) x 0. 7 mm x 0. 3 knots x a 70% ioe)
; = 22 bbV/br ;

The ISB system would be used in a “patch” mode. Oil would be collected in the back of the boom
for a certain period of time, then the system would be ‘moved away from the heavy concentrations
of oil and the accumulated oil would be bumed off. It is assumed that the thick slick is encountered
and collected for 50% of the time, and the remainder of the time is spent burning off the accumulated
oil and maneuvering the unit back into the thick oil slick. This equates, over a 24-hour day, to
collecting oil for 12 hours and burning and maneuvering for 12 hours. Each individual burn would
take about 1.2 hours from ignition to extinction. Twice each day, the section of fire boom would
have to be replaced. It is potentially twice as efficient to collect and burn simultaneously; however,
because the average oil slick thickness emanating from the source is close to the minimum ignitable

_ thickness for weathered crude (ca. 2 mm) there would be a danger of the fire burning back to the spill

source. ‘ 2 . . ‘


oe eng ee Ss as - Et) Tepe gees _ i) Goes

5 ce |

ma Co

jeens FRE] vane TEE 0000 TEE owomy TEE nee FE onan BE oe BE cen BE core EE von |

As well, the greater ice concentration drastically affects the containment efficiency. For the 70% ice
condition, the containment efficiency is estimated to be only 20%, that is, the containment operation
is effective for only 20% of the time due to interruptions related to clearing ice from the containment
and repositioning the system when avoiding large floes.

In all, using the same calculation procedure as in the first two break-up scenarios, only a small
fraction of the blowout volume could be expected to be recovered given the 70% ice concentrations.
The following is an estimate of the fluids recovered by a single containment and recovery system

in a 24-hour period. |

Estimate of Fluids Recovered by One System per
24-hour Time Period

24-hr period
total oil recovered 283 bbl
total fluid recovered ‘ 660 bbl

As in the two other break-up scenarios, additional systems could be used to contain and recover
portions of the thick slick that escape containment. As noted above, the containment system is

_ estimated to be effective only 20% of the time, so although all the slick can be encountered

theoretically, an estimated 80% is lost due to inefficiencies associated with the ice conditions. ,

-Following the same | calculation procedure as in the other two break-up scenarios, a total of three

additional systems are considered i in sequence. For each system, the encounter rate is estimated by

* subtracting the oil recovered by the previous system and estimating an equivalent average oil

thickness. The following table summarizes those calculations.

121


[a ee ee ae 0) ele eee a a. Ses

Appendix B

Supplemental Data on Ice and Climate

To assess the potential variation from the established scenarios described in Tables 1 and 2 in the
main text and the resulting effects on the oil spill response, Exceedance or cumulative probabilities
for selected parameters are discussed below and presented in following tables.

© Ice Drift Speed. The cumulative frequency distributions of ice drift speed for freeze-up and
break-up are presented in Table B-1, based on daily ice movement rates computed from ARGOS
buoy records collected in the eastern Beaufort Sea during 1979-1987 and from three site-specific
ARGOS buoys deployed between Northstar and West Dock during the 1996 break-up season.
For example, the table can be read to show that on average, ice drift can be expected to exceed
‘ one knot at freeze-up for 1.9% of the time. It should be noted that ice drift can exceed the values
shown for short periods in response to local winds and currents.
e Wind Speed. The cumulative frequency distribution of, monthly wind speed is presented in Table
B-2, along with a plot of monthly wind speed exceedence for four wind speeds (10, 15, 20, and
25 knots) in Figure A-1. During freeze-up, November is the windiest month, but October runs
a close second with winds blowing harder than 15 knots 37% of the time. The winds tend to
subside throughout the spring and early summer. July is the calmest month when winds are
greater than 15 knots only 19% of the time.

@ Wind Direction: The cumulative frequency distribution of monthly wind speed is presented in
Table B-2, along with a plot of monthly wind speed exceedence for four wind speeds (10, 15,
20, and 25 knots) in Figure B-1. During freeze-up, November is the windiest month, but October
runs aclose second. For example, the table can be read to show that winds in October will be less
than 15 knots 63% of the time. The winds tend to subside throughout the spring and early
summer. For instance, in July, the calmest month, winds are less than 15 knots for 81% of the
time. The seasonal trend in wind strength is shown clearly in Figure B-1 with the troughs in the

* curves corresponding to the summer period (July to August) and the peaks corresponding to the
fall and early winter (October to January).

© Air Temperature. The cumulative frequency distribution of monthly air temperatures is given
in Table B-4 for the entire year. Air temperature data are based on approximately 29 years (1957-
85) of data recorded at Oliktok and 37 years (1949-85) of data recorded at Barter Island,
respectively located approximately 40 nautical miles west and 90 nautical miles east of Northstar
and West Dock. Except for a 1% chance that the air temperatures in October will be below
—20°F, it is unlikely that air temperatures will play any Significant role in the development of oil
spill response scenarios. .

© Visibility. Visibilities from less than 0.25 nautical miles to greater than 10 nautical miles are

presented in Table B-5 as cumulative probabilities of occurrence for each month. It can be seen
.that the break-up season during July has the most fog, with visibilities less than 0.5 miles

- occurring about 22% of the time. By contrast, the freeze-up season during October experience
the least fog, with visibilities less than 0.5 miles occurring only 5% of the time.


TABLE B-5

Cumulative Probability of Visibility by Month at Northstar and Pt. McIntyre ;

«'_Cumulative

Probability of Visibility

<2 =.

Ve] po

<2

egy t

113

16.6

20.6

29.5

72.2:

89

13.6

17.7

26.2

69.6

7.0

11.8

16.2

24.0

67.0

5.7

96

14.2

22.8

65.1

77

13.7

19.8

304

112

9.2

143 -

18.0

24.6

65.8

TW21.6 + | 26.05 7

7:28.8-' 5

34.52. °

1 69.1

17.8

23.1

27.1

31.6

66.9

11.6

17.8

23.3

33.6

79.3

EPs ase

317.3 re

530.1 "1

R578.

12.5

17.0

286

72.3

11.1

15.8

25.0

70.8


jeanen BE end J Succ SO way SE nee TR cures BE oa |

tr _— SOs SE NO LS TED ONS ME be ne be th Sans

2. Effectiveness of Existing Mechanical Countermeasures _ _ a

* Results are summarized in the Table S-1. Effectiveness is defined as the percentage of the blowout

flow over the 15-day period that could be recovered by existing response systems. A second
effectiveness number is also shown; it takes into account the reduction in blowout volume due to
evaporative losses — fixed at 20% for all scenarios — and losses due to tiny-particle drift - estimated
to be 10% of the total blowout flow. This second effectiveness number is therefore the percentage
recovery of the oil that is estimated to land i in the marine environment, that is, 70% of the total
blowout flow.

_TABLE S41
‘Summary of Recovery Effectiveness for Six Scenarios

Estimated 15-day recovery as a
percentage of total blowout

Estimated S-day § recovery asa
i percentage of t lowol
! Feaches iee/water surface

Major factors affecting the results are discussed below.

Effects of Ice '

The major effects ofthe ice are that (a) a certain percentage ofthe blowout lands on ice and is thus
unavailable for containment and recovery based countermeasures; and (b) as the ice coverage
increases, it becomes more and more difficult to operate containment boom to concentrate oil for
recovery. Particularly for the spills in 70% ice coverage, attempting ¢ a containment and Tecovery
response would be almost Pointless. ‘

Initial Stick Conditi
Each blowout produces a thick, relatively narrow band of oil directly down drift of the blowout
source, with a much wider relatively thin slick on each side of the thick slick. It is estimated that |
about 60% of the oil that eventually reaches the surface will land in the thick portion of the slick. It
‘was also estimated that (a) 20% of the total blowout flow would evaporate from the droplets in the
air; and (b) 10% of the droplets would be so small that they would remain suspended in the

Executive Summary - Page2 :


De eS ee eS we Ot) Ge eles —_ Cae

mc

Dickins, D.F. and 1.A. Buist. 1981. Oil and gas under sea ice study. Report to the Canadian Offshore
Oil Spill Research Association, Calgary -

Dickins, D. and I. Buist. 1997. Oil spill countermeasures for ice covered waters. Invited chapter for
spill control and recovery review commissioned by the International Union of Pure and Applied
. Chemistry (UPAC), London, 1997 (in preparation)
Fingas, M.F., B. Fieldhouse and J.V. Mullin. 1997, Studies of water-in-oil emulsions: Stability
studies. Proceedings of the Twentieth Arctic and Marine Oilspill Program Technical Seminar,
Vancouver, BC. Envrironmnet Canada Ottawa. pp 21-42.

Fraser, John, Ian Buist, and Joseph Mullin, 1997. A review of the literature on soot production
. during in-situ buming of oil. Proceedings of the Twentieth Arctic and Marine Oilspill Program
Technical Seminar, Edmonton. 1997.

Gill, S.D., C. Bonke, and J. Carter. 1985. Management of the Uniacke G-72 incident. Proceedings
of the 1985 Oil Spill Conference. American Petroleum Institute, Washington, D.C.

- Guenette, C.C. and P. Sveum. 1995. In situ burning of uncontained crude oil and emulsions.

Proceedings of the Eighteenth Arctic and Marine Oilspill Program Technical Seminar,
“ Edmonton.

Gulf Canada Resources Limited. 1990. Kulluk drilling program 1990 - 1992; Submission to the
Environmental Impact Review Board. Inuvik, NWT

Laursen, Krista K, Ronald J. Ferek, and Peter V. Hobbs. 1992. Emission factors for particles,
elemental carbon, and trace gases from the Kuwait oil fires. Journal of Geophysical Research,
vol. 97, no. D13. . .

* Lewis,A, A Crosbie and L. Davies. 1998a. The AEA’97 North Sea Field Trials on Oil Weathering
and Aerial Application of Dispersants. Proceedings of the Conference: Dispersant Application
in Alaska: A Technical Update, Anchorage, AK, March 18-19, 1998.

Lewis, A., A. Crosbie, L. Davies and T. Lunel. 1998b. Large Scale Field Experiments into Oil
Weathering at Sea and Actual Application of Dispersants. Proceedings of the Twenty-First
Arctic and Marine Oilspill Program Technical Seminar, Edmonton, June 10 to 12, 1998.

MMS. 1998, Alaska Outer Continental Shelf, Beaufort Sea Planning Area, Oil and Gas Lease Sale
170, Final Environmental Impact Statement. U.S. Department of the Interior, Minerals _
management Service, Alaska OCS Region. Report No. OCS EIS/EA MMS 98-0007.

Mackay, D., I.A. Buist, R. Mascarenhas, and S. Paterson. 1980. Oil spill processes and models.

Department of Chemical Engineering, University of Toronto. Environmental Protection Service
Publication no. EE-8. Environment Canada, Ottawa. | .

39.


aa —<==

ae

—s

sels seems

‘

TABLE 6-11

3/10ths Ice Cover over 72 Hours

_ capability which is largely focused on near-source slick behavior and Tesponse.)

emulsified oil slicks on the water between floes. The ice floes that were sprayed with oil as they
passed under the blowout plume contain melt pools with 10 mm thick slicks of oil covering up to
60% of the pool’s surface. The larger pools of oil are on the floes near the center-line of the oiled
strip. (Note that for the purposes of these scenarios, barriers to spill movement such as the Endicott

causeway were ignored. The main objective of the scenarios was to address the countermeasures

Ultimately, the rotting ice will Telease any oil still remaining in the form of thin sheens trailing the
drifting floes.

~ Summary of Slick Characteristics from a Blowout During Break-up at Pt. McIntyre in

-100-

‘ 6.5.2 Existing Methods (Scenario 4. Pt. Mcintyre, 3/10ths Ice, Break-up)

slick. The key differences in the breakup scenarios are the following:

[time | ‘Thick oitlefton | Emulsification | Slick ~ | Thickslick | Thick slick |
(bh). | water (% of total | (% water vol.) | viscosity thickness width .
released) ’ ‘| (P@30°F) | (mm) (ft)
Initial « 31 0° 25000 ' 21 100
3, 31 55 200000 42 100
| 6 31 - 69 600000 62 100
‘yy °12 31. 74 1000000 1A 100
| 24 31 15 1000000 TA 100
48° 31 75 1100000 TA 100°
72 ‘30 75 1200000 14 100

The response approach here is essentially the same asin the previous freeze-up scenarios: using one
or two barge-based containment and recovery systems to encounter the entire thick portion of the °



be Denes ae

Cl

, Corexit 9527 is stockpiled in the PWS area and elsewhere in Alaska.

Ne Ee en mS 0h) See eee 4 ade ceaamamn ten

«” A few of the scenarios (Scenarios 4, 5 and 6) involve very viscous oil slicks. For these,

~ dispersant use could be tried, but the results would likely not be good.

+ _ Intelligent dispersant use involves environmental trade-off decision making, where the potential

impacts of the untreated oil are compared to the potential impacts of the treated oil. Dispersants
should not be used in the Alaskan Beaufort Sea until these trade-offs are sorted out. In 1985 a
dispersant use decision making system was developed for the Canadian portion of the southem
‘ Beaufort Sea (Trudel et al. 1988), but this has yet to be done for the Alaskan portion. In the.
Canadian study it was found that dispersant use made good environmental sense in many
scenarios, but it remains to be seen if that would be the case off the North Slope. - ‘

In any case, environmental impact issues are beyond the scope of this study. When dispersant use
is discussed in the scenarios in Chapter 6, the discussion is limited to the issue of effectiveness.

5.6.2 Platforms and Supplies in Alaska
The State of Alaska has one of the best dispersant-use capabilities in the world. The spray systems
and their specifications, and the amounts of dispersant available in Alaska, mostly owned by Alyeska .

Pipeline Services, are summarized in Table 5.4, Table 5.5 and Table 5.6. The total volume of

dispersant is 100,000 gallons. Note that the product is Corexit 9527. There are dozens of dispersant
products available globally, but only four products are approved for use in U.S. waters, by virtue of

’ the fact that they are listed on the EPA NCP Product Schedule. These are: Corexit 9527, Neos AB

3000, Mare Clean 200, and Corexit 9500. In practical terms, however, only Corexit 9527 and the
recently developed product, Corexit 9500, are stockpiled in North America in large quantities. Only

As noted in Table 5.4 there are three types of systems available in Alaska for applying dispersant to
oil slicks: helicopter systems, vessel systems, and large fixed-wing aircraft. The aircraft system that
currently has the largest delivery capacity is the C-130/ADDS pack which holds 5000 gallons of
dispersant. Generally, helicopter systems are not considered appropriate for response to large
offshore spills because of their limited range and payload. But when spills are close to land and good

-60-


ao

&

_ When operating containment and Tecovery systems among broken ice there will be inefficiencies
Telated to the avoidance of large ice floes and the accumulation of floes within the containment

boom. There has been little experience or field studies to quantify this, although it is believed that
conventional boom and skimmer operations would be effective at least in light ice concentrations
(say, up to 3/ 10ths coverage), somewhat applicable i in 5/ V Oths coverage with effectiveness declining
rapidly as concentrations approach 7/10ths or greater. For the purposes of this evaluation it is
necessary to quantify this in some manner. A proposed approach for this is detailed in Appendix C,
and described briefly as follows. -

4

Canying out containment operations ina broken i ice field could involve maneuvering around large
floes, periodically reorienting the boom, and perhaps emptying the contained area of brash ice, slush,
and smaller ice pieces. If the ice field could be idealized as being of equally spaced floes of equal
sizes, one could develop a simple mathematical relation between the ice concentration and the
average distance between floes. Given an average ‘Speed of advance, one could then calculate the
amount of time that a containment system could advance through open water. This could then be
combined with a given amount of time to reposition the system to calculate an estimated percentage
of time that the containment system i is able to advance and effectively contain and concentrate oil
for recovery. Clearly an ice field is not made up of equally spaced floes of equal size, but doing this
calculation for a range of floe sizes and averaging the results should provide a reasonable estimate
of the effectiveness of containment operations in an ice field. Based on average floe sizes of up to
1000 feet in diameter, and an average speed of advance of 0.4 to 0.6 knots, an estimate of the
containment efficiency in ice is 70% in 3/10ths i ice concentrations, 40% in 5/10ths, and 20% in

7Noths. ’ : . .

Additional factors that will be included in the evaluation relate to the storage aspects of ‘the
operation. These include the amount of free water that is recovered along with the oil, the amount
of this water that is emulsified as it is pumped to storage, and the amount of free water that can be
decanted from storage. The values used here are taken from the Guidance Document for Marine On-
Water Response Strategy Plans developed by the North Slope Response Project Team (3/10/98).

~46-


hae we sneeae oemenreeree-emumrennmndinhht be sath-wes _ atte eenoninc

4 +

‘ initial mapping pass over an incident is 2,000 ft. Swath widths are variable with 10: 1 zoom. For

example, from 1,000 ft, coverage would range from 150 to 1,500 feet.

The most favorable conditions for IR detection tend to be thin oil films on water at night. Surface
temperature discrimination has been tested to 0.2 °C. Airborne video will see discoloration of oil
on snow but there could be confused targets with dirt on the ice in July. Fine oil mist mixed with
snow and/or slush ice (expected to be a common condition in most broken ice spills) is probably the
most difficult situation for detection (Parrish pers. comm.)

With the reconnaissance package onboard, the Twin Otter is certified VFR, which sets the operating

limits as three miles and/or 500 ft ceiling at Deadhorse and anywhere in the Prudhoe Bay Unit (PBU)
atnight. During daylight hours, ARCO has FAA Clearance to file VFR with forward visibility down
to one mile

There is no shortage of med:um fixed wing utility aircraft i in Alaska (e.g , Caravan, King Air,
Navaho etc.). A wide variety of machines could be in Prudhoe within four hours of a call out.
Heavy lift freighters are available through operators in Anchorage, principally Northem Air Cargo
(NAC) and Lynden, with payloads ranging from 12 to 23 tons (e.g., DC-6, Electras, L382 Hercules).
Given the time needed to order and assemble any heavy loads for supplemental spill response gear,

, the availability of aircraft in this category is not expected to be the critical path. ACS has an existing

MOU with NAC which calls for a dedicated DC-6 aircraft to be ready to to load in Anchorage for
example within 2 hours.

Aviation Attachments: tefer to selected spec shoots ACS Aviation Support Guide, company/agency
contact lists.

Marine Equipment

All vessels presently known to be at Prudhoe Bay and having some © potential to support a : response
operation in broken ice are described below.

Tugs and barges are the most important pieces of offshore marine equipment, with demonstrated
capabilities in a wide range of broken ice conditions; barges provide a stable, safe working platform
as well as the necessary storage volume to support skimming operations. A wide mix of smaller
vessels are also available from various sources to support a spring break-up operation; only a few
of these have any significant application during freeze-up. :

_ Ice strengthening is a definite advantage, but not essential in the spring or in the early stages of

freeze-up. Non ice strengthened equipment can operate effectively in high concentrations of broken
ice with careful handling, as demonstrated by the oil industry and sealift operators in the US and
Canadian Beaufort offshore areas over the past 30 years or more.

The most serious operating concems relating to the freeze-up scenarios are: (1) breaking out from
West Dock and reaching the Northstar spill site; and (2) maintaining a channel through the new fast
ice along shore to allow lightering of recovered product to shore; and (3) managing a number of

barges offshore in moving ice with only one or two powerful tugs (Note: from 1998 on, it is

expected that two Point Class tugs will be available again). An additional concern involves the


5 a as Sede ie oe 0h) ee ei ee —_< ++) Geen ee

a a ao oo eo

| oy TE oan |

mo co

pone FEE eae 3 vores TEE oon BE owe BE ewe BE vend BE one HE roe |

642 Existing Mechanical Methods (Scenario 3. Northstar, 7/10ths Ice, Freeze-up)

Compared with the previous two scenarios during freeze-up the preater ice concentration in this
scenario limits the amount of oil on the water and available for containment and recovery, as well
as severely limiting the applicability of containment and recovery countermeasures. The slick
conditions are roughly the same as the other two freeze-up scenarios - a slick of 230-foot width and
0.5 mm thickness - allowing the same general approach and equipment for containment and
recovery. However, the encounter rate, when reduced to account for the 70% ice concentration, will
be much less than the available skimming capacity. Given the slick conditions and using the same
approach as in the previous scenarios results in an encounter rate of only 43 bbl/hour.
As well, the preaterice concentration drastically affects the containment efficiency. For the 70% ice
condition, the containment efficiency is estimated to be only 20%, that is, the containment operation
is effective for only 20% of the time accounting for interruptions related to clearing ice from the
containment and repositioning the system when avoiding large floes.
In all, using the same calculation procedure as in the first two freeze-up scenarios, only a small
. fraction of the blowout volume could be expected to be recovered given the 70% ice concentrations.
The following is an estimate of | the fluids recovered for two systems per 8-hour period (hours of
daylight at the latter end of freeze-up):

’

‘

Estimate of Fluids Recovered by Two Systems per Day
8-hrperiod = 1
total oil recovered , 138 bbl

[total fluid recovered ° 322 bbl |



‘cee — NN a eee oi pane nee aim =

boone TE weno Sk coven Tn meen UR cone J one |

“27 Simplified Models for Freeze-Up and Break-Up Scenarios

Simplified models are developed here to define ice break-up and freeze-up conditions for the
purposes of spill response evaluation. : ,

: . ‘

Introduction. The terms of reference or parameters for this study, as stated in Chapter 1, focus on
='six blowout scenarios, each of which is to take place in an given ice coverage, either 30% 50% or
70%, which is to remain constant throughout the blowout scenario period of 15 days. The ultimate
objective is to determine what capability exists for cleaning up spills in these broken ice conditions,
however long the conditions last. It is clear from the discussions in this chapter that such ice
concentrations might occur, but only for a relatively short period, in the order of hours for most
situations. Regardless of this, it remains important to know whether or not a reasonable capability
exists for dealing with spills in such broken ice conditions.
In terms of satisfying 1 the objective of the study, and at the same time remaining reasonably true to
the reality of the situation, the following i is proposed. First, the oil spill cleanup capability that exists
when operating in fixed, "broken ice" ' conditions will be calculated. Then it will be assumed that
these conditions last a full 15 days. This i is a less reasonable thing to do, but it will be done

nonetheless. Because the spills are continuous discharges, the spill characteristics at and near site

should be the same at the beginning stages of the blowout as at the end, for constant broken-ice and . '

environmental conditions. Therefore, once the daily spill cleanup capabilities for a given broken ice
condition are established, it becomes simple to calculate the overall 15-day capability for that
* blowout situation. ; . : "

In summary, the following approach rwill be taken in conducting the “evaluation of spill

countermeasures.

26 4


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Lye |

romero wr oon oO

a _ _ SEE Ee ED SRN Eee = ha ee ie i eee

Stump Island and to the east between the coast and Stump Island) and over-floods the ice along the

» entire west side of the WDC. During years of heavy flooding, the water can extend to a portion of

the east side of the WDC by coming around the north end of WDC and by flowing through the 650-ft
breach. -

The overflood water on top of the floating landfast ice in water ‘depths of 6 to 20 feet) quickly drains
through holes and cracks The overflood water on top of the bottom-fast ice (frozen to the sea floor)
loosens it and allows the ice to pop up to the surface. In both cases, the top of the ice in the overflood
zone is usually covered with a thin layer of silt deposited by flood water. Within a period of 2 to 3
weeks after the flooding has ceased, most of the landfast ice within the overflood zone will have -
melted in place from a combination of the fresh, relatively warm, water and the increased heat

absorption by the dirty ice.

’ Thus, by early aly when break-up typically occurs, there may be little or no ice in eastern Simpson

Lagoon and along the west side of the WDC; in contrast, it is likely that a completely intact, 10
tenths ice cover will exist on the east side of the WDC. Of course, the sheet ice along the east side
of the WDC and around PM2 pad will be very deteriorated, with approximately 40% to 50% of its
surface covered by melt ponds

At this time in late June or early July, any 20-knot wind that begins to blow will probably initiate
break-up If break-up is caused by an easterly wind, the broken ice will stack up along the eastern
shoreline of the WDC and will remain 10 tenths coverage for a distance of a few miles offshore. In , .
outer Prudhoe Bay and south of Reindeer I. and Cross L., it is likely that open water will exist. If
break-up is caused by a westerly wind, then open ‘water will probably exist at the eastern shoreline
of the WDC, with 5-6 tenths ice in outer Prudhoe Bay and 8-9 tenths ice near the barrier islands. As
the winds shift from one direction to the other, the broken ice floes and pans will move back and .
forth across the lagoon in belts and patches of varying concentrations, all the while melting rapidly.
The broken ice inside the barrier islands moves at about 0.3 to 0.5 knots during the short break-up

-_~ season, but peak rates may reach 0. 8 to 1 £0 kao. Usually, within2to3 weeks of break-up, the region

around the WDC and most of the bays and lagoons, such as Prudhoe Bay and Stefansson Souid, will
become open water a tenth or less ice concentration).

-16-


flushing process results in wind-herded oil thicknesses on the melt pools of 10 mm. The oil covers

up to 60% of the surface area of the melt pools; the largest slicks are on floes near the center-line of
the oiled strip. This oil will evaporate at a rate negligibly different from the oil that falls on the -
water, reaching a total evaporative loss of 22% after 72 hours.

Table 6-11 summarizes the predicted characteristics of the thick slick over a time period of 72 hours.
The oil that forms the thick slick on the water has a viscosity of 25,000 cP and a Pour Point of 68
°F at the point where the on-water modeling is started. As such, the oil slick does not spread on
water. For the duration of the scenario (72 hours) the slick moves with the oiled ice floes anddoes ,
not spread further, although the thick slick may meander among the widely-separated floes in the

pack ice field due to oceanic eddies or large-scale turbulence.

The presence of ice dampens the wave action that would normally exist with an 11 knot wind and
reduces natural dispersion of the oil slick compared with open water conditions. The slick is .

, Predicted to begin to form a water-in-oil emulsion immediately after the oil had been deposited on .

the water surface. If emulsification rates are the same in loose pack ice as in open water under
identical winds, the slick would be fully emulsified (75% water content by volume) after12 hours
on the water. By this time the slick thickness has increased proportionately to the volume of water
in the emulsion, reaching about 7 mm for the 75% water emulsion.

The oil slick continues to evaporate and naturally disperse slowly throughout the 72 hour scenario.

- Itloses 21% of its volume to evaporation and an additional 0.01% to dispersion after 24 hours; 21%

to evaporation and 0.06 % to dispersion after 48 hours; and, 22% to evaporation and 0.15% to
natural dispersion after 72 hours. The viscosity of the emulsion increases to 1,000,000 cP after 24
hours; 1,100,000 cP at 48 hours and 1,200,000 cP at 72 hours. The Pour Point of the oil after 72
hours has increased to 71 °F. :

At the end of the 72 hour scenario period, 30% of the oil released at the beginning of the scenario
still remains in thick slicks on the water surface between floes and 21% on the surface of ice floes.
The oiled area is a Jong (24 nautical miles), narrow (100 feet) strip that ‘contains 7 mm thick

¥ -99- : ‘ a


eidh inmmeestin

Figures 5 and 6 can be used to determine the width of the plume at the

location downwind. . . .

‘Fallout Width vs Percent on Ground
(4 inch ID pipe)

1000

Fallout Width (m)

10 +20 30 40 50. (60 70 80 86090
Percent of Oil on “Ground”

2 + 5 -e 8 12 | mmscf/day

Figure 5 ; Fallout Width vs Percent on Ground (4 inch ID pipe)

‘

Fallout Width vs Percent on Ground
(63 inch 1d prpe) - 7A

” 1000

Fallout Width (m)

1 _— —j

Percent of Oil on "Ground"

e-2 + 5 -e 10+ 20 = 32 =~ mmscf/day

10. 20 30 40 50 6 70 80 99°:

Figure 6 : Fallout Width vs Percent on Ground (6.3 inch ID pipe)


5 a en FF) Sse ae - .} SRaneee

aan moO OO OT oO OM ee oe eo lo hl

OIL NAME: Point Mcintyre

10 TYPE Crude
WEATHERING (Volume %)
; 0 98 179
20 DENSITY (gimL) ;
wc . - +0911 | 0920 0932
15°C 089s oot 0920
30 VISCOSITY
31 DYNAMIC VISCOSITY (mPa s) ‘
°C 7563 0 | 19000, 119125
15°C 442° 1251 4413
32 KINEMATIC VISCOSITY (mm/sec) . ;
“48 8302 2065 2 «127817
15°C : 494 1373 4797
40 INTERFACIAL TENSIONS @ 15°C (mN/m) °
41 AIROL ; 335 350 347
42 OIL-SEAWATER 219 287 292
5.0 POUR POINT (°C) -4 3 4
60 FLASH POINT (°C) 6 12 36
"70 EMULSION FORMATION TENDENCY AND STABILITY
7.1 TENDENCY
15°C 100 100 100
7.2 STABILITY : tos .
16°C 093 100 1.00
0 DISTILLATION DATA (°C) '
VOLUME LIQUID VAPOR
% EVAPORATED TEMPERATURE __ TEMPERATURE
1BP - 888°C 596°C
5 , * 4096 927
10> 1672 9214
- 15 ' 2448 1060
' 20 2843 1293
30 ; 3358 ; 1920
40 _ 3798 2366
: 45 3981 2073

90 WEATHERING

Fv= In(1+7401 @ exp(6 3- 3910/TkVTk)
(7401/Tk)

where Fv ts fraction of oil weathered by volume
In ts natural log
@ ts evaporative exposure
exp is exponental base e
Tk is environmental temperature (Kehn)



es es Se ee ms bi Se ae ns i) Sane oe Eee oe

aot oO eee eee ere lL

ice area = 34 x (60°+360)x xR?

= nR/2 | ,
totalarea = %x(X)x(Xsin 60°) .

= (sin 60°/2) x (X2) a
Ice area—total area = 30% = (xR) ~(X’sin 60°)

X = RxV x x03xsin60°
for diameter = 1000 feet, R = 500 feet, X = 1740 feet

separation distance = X-2R
= ‘740 feet

At an average speed of advance of 0.4 knots, the open water separation would be traversed in:

time = 740 feet + 0.4 knots °

“= 18 minutes ro

In light ice concentrations such as 3/10ths, assume 5 minutes downtime to release contained ice or

* reposition equipment, thus the operating efficiency is estimated to be:

efficiency = 18minutes + (18+5)
= 19% -

Similar calculations can be performed for floe sizes ranging from 100 to 5000 feet in diameter, but
increasing the “repositioning time” to 10 minutes for 50% ice and 15 minutes for 70% ice, as
follows:

Average Floe . , Average Floe * Estimated
Diameter, feet Separation, Efficiency
feet of open water

Ice Coverage 30% | 50% | 70% | 30% | 50% | 70%
100 ao - | 74 35 14 | 27 | 7.9 | 22 ‘
500 370 | 174 | 69 | 65 | 30 | 10 .
1000 ‘ 739 | 347 | 139} 79 | 46 | 19
2000 ‘+ "11479 | 694 | 277 | 88 | 63 | 31
5000 ‘| 3696 | 1736 | 693 | 95 | 81 53 -



point is determined by atmospheric dispersion and the settling velocity of the oil particles.
Atmospheric dispersion potential can be characterized by using an atmospheric stability
classification system developed by Tuer (1970). Stability classes are determined by the turbulent
structure of the atmosphere and by wind speed. Stability is quantified using a six-part scale with
categories being labeled A through F. A is the most turbulent class and F is the most stable. Class
D is typical for offshore conditions (Turner 1970) and it is this class that is selected for drilling
- locations in the Alaskan southern Beaufort Sea.
The oil particles discharged into the air will eventually "rain" down, with the larger droplets falling
close to the release point and the smaller droplets falling further downwind. The width and thickness
of resulting slicks of oil can be calculated using a step-by step procedure developed by Belore et
al.(1998). The procedure, presented in Appendix C, is used in Chapter 7 to describe the behavior of
_ the blowouts and the initial characteristics of the resulting slicks for the six scenarios considered. It
should be noted that there is a large uncertainty associated the modeling results because of certain,
key assumptions used in the model. The main assumption is that the average diameter of the droplets
discharged in the blowouts is 0.75 mm ‘The rationale for using this number is explained in Appendix
“Corin Belore et al. 1998.

3.3 General Behavior of Oil Spilled on Open Water ~
Once the oil from a blowout reaches the ocean surface it is swept away by winds and currents and
undergoes a number of so-called "weathering" processes. This section provides an overview of the
processes that have a major influence on the potential cleanup and impact of the oil. In broken ice
’ conditions the oil will fall on both oil and ice. The behavior of the oil on open water is discussed in
. this section. The behavior of oil on ice and among ice floes is discussed in Section 3.6.
~~ The most important phenomena that influence spill impact and control are movement, evaporation,
natural dispersion, and emulsification. Each of these processes is discussed briefly below.

Oil Movement. Surface slicks may be trarisported away from the site of a spill by water currents.
These currents usually combine residual movement and wind-induced surface movement. Mackay

¥

-28- oy oo


an aes 6S ee are poe EE) Ge cee ee o nt>tadentenen

The greatest uncertainty surrounds the question of whether or not marine equipment could be broken
free at West Dock and moved offshore through solid ice over about 8 to 9 inches ie., two of the
freeze-up scenarios considered here (Sawin pers comm.). :

Only the Endeavor and Challenger (presently in Seattle) have true icebreaking bow forms and a
flared hull to clear ice while under way. The Endeavor demonstrated her ability to break well over
a foot of new ice during sea trials in the fall of 1982 and she has operated in much thicker ice for
short periods. Other barges will break some solid ice but rapidly become limited by the power
available to overcome the resistance of the blunt bow which tends to plough ice and snow ahead of
the vessel. Slush ice build-up can quickly become the limiting condition, even in very thin ice (less
than 4 inches). Hatfield and Dickins (1981) estimated that a conventional barge shape would have
great difficulty breaking over 6 inches of new ice in freshly broken channel. Multiple passes along
a single channel may increase this limit to about 9 inches temporarily, but the enhanced ice growth
from overturning cold ice blocks will begin to seriously affect vessels progress after a relatively
small number of passes. It may be necessary to transit with the Endeavor back and forth to West
Dock every 48 hours just to maintain the broken ice channel in a partially consolidated state.

Shallow draft tugs such as the Sag River also have a barge like bow shape and tend to stop moving
forward as they ride up on the ice. This problem can be overcome by mobilizing the less capable
tugs and barges as a convoy behind the Endeavor. Once offshore among broken floes, the River
Class tugs could still operate effectively for part of October. These smaller tugs would be most
useful in a July broken ice condition when they could push barges i in shallow water through rotting
floes (see below).

Broken ice at break-up usually presents a much easier case for ‘conventional marine equipment. The
exception would be if the ice becomes pressured through wind packing. Regular tugs and barges
can push their way (slowly) over long distances through rotting floes in high concentrations (up to

~ 9/10), as demonstrated in past operations and trials. The industry Task Group carefully documented

the July 1983 trips with the barge Endeavor and two Point class tugs from Barter Island to Prudhoe
Bay, and with the barge Satco 10 and tugs Fox and Bear from Flaxman Island to Prudhoe. Even
without an icebreaking bow, the Satco barge was able to cover 55 nautical miles at an average speed

‘of over 2 knots in over 7/10 ice. In a return convoy from Barter Island, some 15 conventional (non

ice strengthened) barges and ten tugs made it back to Prudhoe without mishap though 106 miles of
heavy ice.

> It was concluded from these experiences that non-ice-breaking tugs and barges can operate

effectively in close pack ice (7 to 9/10) when the ice is an advanced stage of melt, and is not under
significant pressure. In their "Evaluation of Industry's Oil Spill Countermeasures Capability in
Broken Ice", SL Ross (1983) concluded that an ice strengthened barge with two tugs could negotiate
substantial stretches of broken ice in concentrations of 8 to 9/10 in the spring. High power is not
essential under these conditions, and a much wider variety of smaller work boats under 1,000 hp can
still provide useful support for spill response (including moving the large 200 series (60 X 200 ft)
barges short distances).

Primary Inventory: covering mostly heavy equipment with substantial capabilities in most broken -
ice scenarios .


Ss aoe o ee ees || ee See cats 1 ooo

6.6 Scenario 5. Pt. McIntyre in 5/10ths Ice Cover During Break-up —

6.6.1 Blowout/Spill Behavior (Scenario 5. Pt. McIntyre, 5/10ths Ice, Break-up)

An uncontrolled blowout occurs in early July at the Pt. McIntyre drill site releasing 42,000 barrels ~
of oil per day (BOPD) and 9 x 10° standard cubic feet (scf) of natural gas per day (a Gas-to-Oil Ratio
[GOR] of 750 scf/bbl). Over the first 72 hours of the incident, the air temperature ranges from a ,
nighttime low of 34 °F to a daytime high of 45 °F. The wind speed averages 9 knots from the NW.
The water to the east of the causeway is covered by 5/10ths melting ice floes. The ice is 3 to 4 feet
thick and its surface is 40% to 50 % covered by melt ponds. The floes are fifty to five hundred feet

- insize. The ice is drifting at the same speed as the water (both wind-driven at 3% of the wind speed)

at 0.3 knots to the SE. These conditions do not change over the time period of the scenario; as well,
the ice concentrations do not change as it drifts away from the spill site (Le., no convergence or
divergence of the pack). .

As the oil and gas exits the 4-inch inside diameter tubing at the wellhead the high velocity of the gas

. atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces and -

the droplets agglomerate. The kinetic energy of the gas jet from the wellhead carries the droplets to.
a height of 80 feet above the release point. From this point the oil droplets begin to fall as they are
carried downwind by the wind. : .

In this scenario, the slick is 100 feet wide and 2.1 mm thick at the starting point of the surface slick
modeling. This is at a distance of some 500 feet downwind of the blowout. At this point, the oil slick
is assumed to be evaporated to 20% loss. ,

4

For the purposes of this scenario, it is estimated that 50% of the oil spray lands on water and 50%
lands on the ice surface. The spray that lands on ice floes coats the surface and is slowly flushed by

- melt water into the melt pools on the floes. The range of oil thicknesses initially deposited on the

floe surfaces ranges from 3.7 mm near the center-line of the oiled strip to 0.01 mm at the edges. The

‘

-109-


ca oo en

nor |

4.6 Days 7 through 11 .

* 4.8 Days 13,14 and15 ..

aoe Oo mea Oe Oa Ol

HE = _— Saas joe Oe eee = mien pa ee

* : Page
Introduction......... cece eee e cence ees eeeveseesens Santen eecneeeeeceeeeeees 1
Description of Environmental Conditions .........sssceeeeeecceceeceescees "eee
2.1 Assumptions and Background ..........+-+ occeaenececccnes .

2.2 Descriptive Oil in Ice Scenario: Suggested Pattern of Wind Events

Spill Behavior
3.1 Day! .
3.2 Day2.
3.3 Day3 ........
3.4 Days 4,5and6 ...

3.5 Days 7 through 11 . 12
3.6 Day 12 .......44- sence eeeeeeneeeerees -13
3.7 Days 13, i4end 15 tence eeeeeeeeeees rere errrrerys se eneeeeeeseeces «ee 14

45 Days 4,5 and6 .
4.7 Day 12 ........5.


EE SS ee eee CTE us ~ ae 05) pe oe —_ +o) Seen

amon oaenmommre

aan mM OO OOo lL

the surface, but in a relatively thin slick for which a containment and Tecovery response would be
relatively ineffective, even in open water conditions. The slick thickness in these thin portions is :
estimated to be 0.035 mm, meaning encounter rates would be on the order of 5 to10 bbi/hour, and
daily recovery volumes would be less than 1% of the blowout flow.

an

Daylight Hours. It was assumed that containment and recovery operations would be conducted only
during daylight hours, for reasons of worker safety and due to difficulties in positioning containment
equipment relative to the thick portions of the slick. For the freeze-up scenanios, with daylight hours
ranging from 8 to12 hours, this causes a decrease in effectiveness to only one-third to one-half what
it otherwise could be. There is no reduction in effectiveness in the break-up scenarios given the 24-
hours of daylight at that time of year. .

Other Problems During Freeze-up. In addition to the limited number of daylight hours, there are
two additional concerns during the freeze-up period that cause a reduction in effectiveness for the

_ first three scenarios. The first is that the ice conditions at West Dock, where the primary equipment

and marine logistics are located, will limit the speed of the initial response. In the freeze-up
scenarios, it was estimated that the response time for containment and recovery would be 60 hours
as opposed to the 12 hours used in the break-up scenarios. Over the 15-day period, this translates into
a loss in effectiveness of 17% ((15 days - 60 hours) + 15 = 83%).

Weather Limitations. In the calculations of effectiveness, the first step was to estimate a daily
recovery volume for the specified number of systems. This number was then used to calculate a 15-

day recovery percentage, incorporating the effects of response time and the effects of weather

limitations. For the freeze- -up scenarios 5 this latter factor was estimated to be 77%; that is, operations
would be effective 77% of the time, combining suitable conditions of waves less than 3 feet (84%),
visibility greater than %-mile (95%), and ceiling height greater than 1500 ft (97%). Similarly, for
the break-up scenarios, operations would be effective 66% of the time, combining waves less than

3 feet (95%), visibility greater than ¥%-mile (78%), and ceiling height greater than 1500 ft (89%).

‘

-130-


co

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a as ooo

rf _ ae ee 2 2 nee meal abit: mabeante

Foy

Beaufort 23 : ‘ so »
34X147f | ‘ Deck cargo: West Docks 2 and 3
Chartered to ACS - 1997 , (600 tons) at draft of ~5.9 ft.
for use with the Trans Rec (light draft 1.8 ft) :

Ice Class ABS 1A (second highest)

~ Probable ice limit in October: 5 to 6 inches in a
‘previously unbroken sheet or up to 9 in broken —

a channel
~ * . - ‘
Beaufort 20/21 “Deck cargo: West Dock 3 (1,500 tons)
60 X 202 ft at draft of 7 ft (light draft = 2.8 ft)
~ . Fuel: 12,200 bbl in 8 tanks at 7.8 ft
Ice Class ABS 1AA (highest)
Probable ice limit in October: 5 to 6 inches in a
4 previously unbroken sheet _ “
ae . - .
Arctic Bear ‘51,000 Ib bollard, twin screws in nozzles

1,700 hp Min draft 6 ft (8 ft icebreaking)

. Icestrengthened, est. icebreaking capability similar to’
. Point Class Crowley tugs (~6-8 inches).

Arctic Tern 20,000 Ib bollard, twin screw shallow 730 hp draft
_ G.5 ft). Most useful for break-up scenarios
- . @ significant icebreaking capability)

* presently i in Seattle with the Beaufort 21 - possible tow to
Prudhoe summer 1998 - no decision has been made on over-
wintering this equipment at the present time (Lynden, pers
comm )

There are numerous smaller work boats and barges available in the Prudhoe Bay area (see .

‘ general list below and attachments). Most of this equipment could be used locally in

Prudhoe Bay during break-up but, few if any of these vessels have sufficient power to break
more than a few inches of solid ice nearshore after freeze-up.

As described above, the main problem in October is being able to make passage through the
band of thin fast ice separating West Dock from the broken ice offshore. Jet drives and
outboards are not considered useful i in a freezing environment with slush i in the water (acs

pers. comm.).

Work boats with screws (e.g., North Star and new 42 f. vessels being delivered to ACS in

- 1998), could potentially operate offshore for part of October by being transported out to the

spill site as deck cargo on one of the barges. Previous demonstrations have used aheavy lift

:
x


ae tf) Sen eee se ot) Ciena

TABLE §-3

* Summary of Key Logistics Constraints
Logistics Category Break-up (July) Freeze-up (October)
‘| ~ helicopters ice unsafe for shutdown and ~ | ’ ice unsafe for shutdown and
parking parking offshore -
* shng loads hmited to 800 to
1,200 Ib with equipment in © luted visibility 2% < < In + icing potential (3% of time)
Prudhoe (2 h), up to 7,900 Ib mile) ’
~ with Bell 214 from Barrow ¢ daylight starting to become
(2.5 h), or up to 10,000 Ib ¢ Inmited commercial Iumited (may require IFR)
with equipment in Alaska a availability in July (most ‘ .
to 2 days) ” commercial machines in +” only one or 2 machines
Alaska are under long-term _ (BO105 and/or Bell 206L) in
contract at this time of year) Prudhoe area on short notice
> . (eg, 2 hours) :
ae ¢ high frequency of strong
winds over 25 kt (10%)
Air Support 7 :
= fixed wing (reconn) © Iumited visibility (26% <1 i} oil in slush/snow may give
mile) ARCO system not + Inmited discrumination in IR or
certified for IFR operation visual ' .
Conventional Manne.
~ tugs and barges ¢ high ice concentrations limit |* limiting solid ice thickness of
. speed & maneuvering ~6 inches for conventional
Deck cargo - . of (blunt bow) barges, or up to
650 to 2,700 + tons depending on} draft limits (4 to 5 ft) may 1.2 ft for icebreaking barge
barge and water depth . prevent vessels from reaching Endeavor
oiled ice driven into shallow .
Liquid products (total capacity) water ¢ fast ice between West Dock
12,200 bbl ice strengthened (1) ‘ . and offshore (will become the
16,000 bbl ice breaking (1) * ice packed into W. Dock early | * limitmg factor by mid-
12,000 bbl non ice str. (2) July may delay vessel October in determining barge
operations access to an offshore site)
+ feasibility of breaking-out
frozen-in equipment from
‘West Dock unknown in ice
over six to eight inches
«freezing of oily water in tanks
n , Geparate first 1f possible)
+ risk of becoming trapped or
beset offshore without
7 additional marine support as
1 back-up (shortage of tugs)
* need minimum 48 hours to
. mobilize wintenzed vessels i in
, October
-52-



ee eee Ce ae mee 0h) Se eae wee Gas

Estimate of Fluids Recovered By Four Systems per 24-hr Period

. total oil recovered . : 3309 bbl
' 'T total fluid recovered «13,244 bbl

— a ems toa

, Predicted Effectiveness of Existing Mechanical Systems in Recovering 15-Day Discharge

This final step in this section is to use the above calculations to assess the effectiveness of existing

. Systems to deal with the total volume of oil discharged over the 15-day blowout period. The

assessment includes the effects of response-time delays, and the environmental derating factors of
visibility, VFR flying conditions, and wave heights. The response time for the break-up scenarios
is estimated to be 12 hours, so for the 15-day period the effect is to reduce effectiveness by 3% ((15-
¥2) + 15 = 0.97). As discussed in Chapter 5, the combination of the three environmental factors are
such that, on average, mechanical containment and recovery will be effective 66% of the time. The
following is the estimate of effectiveness for the 15-day period, expressed as a percentage of the total

blowout flow:

Recovered oil volume= * 3309 bbl/day x 0.97 x 0.66 + 12,000 bbl/day
: = 18%

ms

6.53 Additional Systems (Scenario 4, Pt. Mcintyre, 3/10ths Ice, Break-up)

The above analysis described the potential effectiveness for two containment and recovery systems

that could encounter the entire width of the thick slick, as well as two additional ‘systems to

; sequentially recover oil missed due to inefficiencies associated with ice conditions. Any additional

systems would be limited to chasing thin sheens outside the area of thick oil, or attempting to recover
oil missed by the first four systems. In either case, the encounter rate for these additional systems
would be less than 10 bol/hour, and the daily necvery volume would be less than 1% of the daily
blowout volume. °

-106-


NS 8 ee ee on tn a: ES) ow ee es oh Gaueen on

about 30% of the total - 0.4 x 0.7, composed of mostly small droplets) settles out farther downwind
and forms a thin (35 um) slick bordering each side of the thick sick.

For the Purposes of this scenario, it is estimated that 70% of the oil spray lands on water and 30%
lands on the surface of ice floes. ‘The Spray that lands on ice floes coats the surface and is absorbed
by the snow. The thickness of t this oul coating is estumated by summing the amounts of oil of the
vartous size ranges that settle onto the floes as they drift under the plume from the lee side of the
island to the point at which oil droplets finish settling. Directly in the lee of the island, over the

, distance required for 97. 7% of the VMD droplets to settle out (920 feet - see Table 6-2 above), itis

assumed that the ice floes are coated evenly over a width equal to the plume width (in this case 180

7 feet). Further down drift, the oil coating is incremental. The average oil thicknesses on the floe

surface ranges from 1.2 mm near the center-line of the oiled strip to 0.005 mm out near the edges.
This oil will evaporate at a rate negligibly different from the oil that falls on the water, reaching a

‘total evaporative loss of 33% after 72 hours.

” Table 6-3 summarizes the predicted characteristics of the thick slick over a time period of 72 hours.
” The oil that forms the thick slick on the water has a viscosity of 120 cP and a Pour Point of 10 °F

at the point where the on-water modeling is started. For the first 15 hours after its creation, the thick
portion of the slick on water continues to spread laterally as it drifts with the ice, reaching a width
of 300 feet and a thickness of 0.5 mm. After 15 hours, the oil has evaporated to a point (28%) where
its Pour Point (30 °F) exceeds the ambient water temperature and the thick portions of the slick cease
to spread on water. For the duration of the scenario (72 hours) the thick slick generally moves with
the oiled ice floes and does not spread further, although it may meander among the widely-separated

floes in the ice field due to oceanic eddies or large-scale turbulence.

The presence of ice dampens the wave action that would normally exist with a 13.5 knot wind and
reduces natural dispersion of the oil slick compared with open water conditions. The thick slick is
predicted to begin to form a water-in-oil emulsion some 18 hours after the oil had been deposited
on the water surface. If emulsification rates are the same in loose ice as in open water under identical —
winds, the slick would be fully emulsified (75% water content by volume) after 27 hours on the

-70-


aan Om SS

4

moots

i —_— NO ee eS: Se eee oS ee Le be

through 19 and extensive personal experience in the area during break-up and freeze-up (Ref. 9

through 20).

Ice Drift Speeds: Realistic ice drift speed and direction values are derived from a combination of a
percentage of wind speed and actual nearshore ARGOS buoy measurements (References 3, 5 through
8, and 20, 21) where applicable. As explained below, wind speeds used in the scenarios are not
necessarily Tepresentative of the means. : :

oy

Metocean Conditions (winds, air temp, precipitation, sea state, visibility, ‘and ceiling height): mean

values for these parameters are extracted from Reference 1, with atmospheric icing estimated by ~

ERA Helicopters who are the only operator to have maintained an operations base in the Prudhoe
Bay area continuously for ‘the last 25 years. . .

Wind Speed And Ditestion: During break-up, the scenarios for 3 and 5 tenths (30% and 50%) ice
coverage are defined by average wind speeds of 8-12 kts. However, the 7 tenths ice concentration
scenario is assumed to occur sometime during or immediately after the initial break-up event, when
the landfast ice undergoes arapid transition from 10 tenths to a broken ice condition; therefore, the

wind speed in this case is represented by a moderate “storm” wind (15-20 kts) which would be .

necessary to initiate the break-up event.

« During freeze-up, the scenario for 3 tenths ice coverage represents the median wind speed (12-15
kts) for October. The other scenarios are represented by higher wind speeds, reflecting the frequent .

occurrence of storms during freeze-up (scenarios with higher concentrations are more likely to occur
during or on the tail of a storm event). The logic here is that over a72-hour period spill response
teams will hkely encounter moments of sustained above average winds. Based on the frequency

- distribution of wind speeds shown in Table B-2 in Appéndix B, the winds shown in Table 1 will be

exceeded 20-30% of the time for the 50% ice concentration scenario and 10-20% of the time for the

-22-


rane we es or we woe we cee onc Doses conn mo Joos vom wees J woe ome De

: . TABLE 6-9 ‘
* Estimate: of Recovered Fluids per 10%4-hr Time Period For Scenario 2

Item - ~ Calculation =~ Volume
| total fluids per 10% hours >‘) 305 bbI/hr x 10% hours x 40% 1281 bbl
total free water ~ ‘ 203 bbi/hr x 10% hours x 40% 853 bbl
volume that can be decanted ‘ total free water x 80% “| 682 bbl
total fluids stored per 10% hours total fluids less decant 599 bbl
oil so 61 bbi/hr x 10% hours x 40% 256 bbl
emulsified water . 41 bbl/hr x 10% hours x 40% 172 bbl

_[ free water < total free water x 20% ‘ 171 bbl

The above calculations were for one system so the above numbers canbe doubled to account for the
two systems that would be deployed at the site:

: ‘ Estimate of Fluids Recovered by Two Systems per Day
oo | total oil recovered j 512bb1
» | total fluid recovered - 1198 bbl |

Asin the first scenario, hovercraft could be considered to shuttle fluids and make most effective use
of the available storage within the barges on-site. In this instance, the maximum hovercraft

throughput of up to 2600 bbi/day exceeds the w dally recovery of fluids and would extend the use of
barge storage indefinitely. ‘

Predicted Effectiveness of Existing Mechanical Systems in Recovering 15-Day Discharge’

" ‘This final step in this section is to use the above calculations to assess the effectiveness of existing
__ Systems to deal with the total volume of oil discharged over the 15-day blowout period. The
1 assessment includes the effects of Tesponse-time Selays, and the environmental derating factors of

4 4 oa

-88-


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drilling activity below a predetermined threshold depth during: 1) periods of broken ice; 2) outside

the barrier islands during the open water period; and 3) during the fall bowhead whale migration
Tier 2 of the decision would allow drilling during periods of broken ice, and during periods of open
water outside the barrier islands once a lessee “demonstrates compliance with applicable laws and
regulations, including the theoretical and physical capability to detect, contain, cleanup, and dispose

_ of spilled oil in broken ice conditions”.

In February, 1982, a joint agency/industry Steering Committee and Technical Committee were
formed to address the criteria for Tier 2 approval. In February 1983, the oil companies notified the
State that they were ready to demonstrate their capabilities. After consultations with State, Federal
and North Slope Borough officials, the companies prepared a document entitled “Oil Spill Response
in the Arctic” summarizing their views on the current state-of-the-art for cleaning up spills in broken
ice (Industry Task Group, 1983). The regulatory agencies agreed with many of the views but
questioned others, particularly those claiming an adequate capability in about 3 to 5 oktas (3/8ths to
5/8ths or 37.5 to 62.5%) ice coverage. On the basis of these questions, field tests were designed to
demonstrate cleanup capability in this ice cover range. These demonstrations were conducted by the
oil companies during June and July of 1983 in the Beaufort Sea area, and witnessed by a team of
State, Federal and local officials and technical consultants. The field trials included demonstrations
of: .

¢ In-situ burning of oil in scattered ice

¢ Burning of oil in fire containment boom

* Operation of the ARCAT ( purpose-built skimming vessel) in broken ice

* — Operation of tugs and barges in broken ice :

© Operation of rope mops from a barge in broken ice and open water

+ Boom deployment in moving broken i ice ,
Based on these demonstrations and the recommendations of the consultants’ report (SL Ross 1983),
the State issued its “Tier 2 Decision” in June 1984 which stated that adequate capability exists to
clean up spilled « oil in broken ice and during open v water outside the barrier islands for exploratory
drilling if: woos

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water. By this time the thickness of the thick portion of the slick has increased proportionately to the
volume of water in the emulsion, reaching about 1.5 mm for the 75% water emulsion.

The thick oil slick continues to evaporate and naturally disperse slowly throughout the 72 hour
scenario. It loses 29% of i its volume to evaporation andan additional T%to dispersion after 24 hours;

“32% to evaporation and 9 % to dispersion after 48 hours; and, 33% to evaporation and 11% to
' natural dispersion after 72 hours. The viscosity of the unemulsified ou! increases to 180 cP after 12

hours; when the thick slick emulsifies, the slick viscosities are 7000 cP at 24 hours, 8700 cP at 48
hours and 9300 cP at 72 hours. The Pour Point of the thick oil after 72 hours has increased to 44 °F.
At the end of the 72 hour scenario period, 18% of the oil released at the beginning of the scenario

. Still remains in thick slicks on the water surface between floes and 18% (0.9 x 0.3 x [1 - 0.33})

remains on the surface of ice floes. The remainder of the oil discharged has evaporated or naturally

. dispersed, never settles, or is in very thin slicks surrounding the thick slick. The oiled water area is

a long (29 nautical miles), narrow (300 feet) strip that contains relatively thick (1.5 mm) emulsion

_ Slicks on ‘the water surrounded by thin oil. The ice floes that were sprayed with oil as they passed

under the blowout plume are coated with 0.005 mm to 1.2 mm of oil on the snow on their surface.

’ The thicker coatings are on the floes near the center-line of the oiled strip.

Over time, the oil remaining on water will be incorporated into the surface layer of the growing ice *
and the oil remaining on floes will be covered by snow. A portion ‘of the oiled ice will likely be

. formed into ridges and rubble fields during November and December as the thin ice deforms under
_ Pressures from wind and heavier pack ice to ‘the north. Any oiled ice which escapes being

incorporated into the fast ice will gradually drift west, and in many years could end up in the
Chukchi Sea by spring. During the spring (late May to early June) any oil still remaining near the
surface of level ice will rise to lie in melt pools; the oil incorporated into ridges and rubble fields will
be released more slowly. Ultimately, rotting ice will release any oi still remaining at breakup in the

- form of thin sheens trailing the drifting floes.

-71-


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6.23 Additional Recovery Systems (Scenario 1. Northstar, 3/10ths Ice, Freeze-up) |

Iti is interesting to note the possible effectiveness of an additional system for this scenario. Given that
the two identified systems can encounter the entire width of the thick slick, a third system would be’
limited to chasing relatively thin sheens. The thickness of oil outside of the thick portion is estimated
to be 35 um, or 0.035 mm. This is only 1/20th (or 5%) of the thick slick thickness. This would
correspond to an encounter rate of only 6 bbl/hr, and based on the above calculation procedure, a

_ daily recovery volume of only 70 bbl (i.e., less than 1% of the ally blowout volume). °

‘Consideration could also be given todeploying a third system to attempt to recover: oil from the: thick
slick that i is missed by the first two systems: although the two systems encounter all of the thick
slick, they lose an estimated 30% of it due to inefficiencies associated with the ice conditions. More
serious consideration will be given to this possibility in the break-up scenarios, and a calculation
procedure is described for estimating the potential effectiveness of additional systems. However, in
the freeze-up scenarios, given the other limiting factors (percentage of oil on ice, encounter
efficiency, limited daylight hours), the effectiveness of each of the first two systems is only about

_ 3%. Additonal systems would recover only a Portion of this, in this scenario, perhaps an additional

1%. Finally it is noted that there would be a limited time period with which to use additional

. systems: the freezing temperatures mean that the oil will be mixed with slush ice and soon

incorporated into ice forming on the water surface.

6.2.4 Dispersant-Use (Scenario L Northstar, 3/10ths Ice, Freeze-up)

’ Inthis scenario the amount of oil that falls on water to form relatively thick slicks (> 0.5 mm) ~ after

unavoidable losses due to evaporation, tiny-particle drift, and oil falling on ice - is 3900 barrels per
day (15,000 BOPD x 0.26 ~ see Table 6-3). According to the above analysis of mechanical recovery
capability the amount that can be physically recovered is 1394 barrels of oil per day. This leaves
2506 barrels of oil per day as a target for a dispersant program. This is the oil that has been lost

because of inefficiencies of the recovery operation, mainly due to ice intrusions, and losses because


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1, Introduction

Table of Contents uo .

1.1 Industrial Setting .............206
1.2 NSSRPT Goals .........-++- sec eeceeeneeeeeees
* 1,3 Past Regulations regarding Broken Ice: Tier 1 and Tier 2
1.4 Current Regulatory Situation and Related Questions . .
1.5 Terms of Reference of Study .......seseseeeees
1.6 Structure of Report ...........-00
1.7 Limitations of Study ..... “ .
1.8 Addendum to this Report ..... see eeeeeeeeeees
2. Ice and Other Environmental Conditions..........+
2.1 Introduction .: 0... ccc ccceeceneceeeneneeeenes
2.2 Overview of Ice Conditions in the Alaskan Beaufort Sea .
2.3 Descriptions of Freeze-up at Northstar ........
2.4 Descriptions of Break-Up at Pt. McIntyre .
2.5 Persistence of Broken Ice .........seeeeceserere
2.6 Other Ice Features Affecting Broken Ice Spill Response and Logistics
2.7 Simplified Models for Freeze-Up and Break-Up Scenarios
3. General Behavior of Offshore Blowouts and Oil Spills in Ice .
3.1 Introduction .....2...0..ee08 sence enceeeeveeees
3.2 Behavior of Above-Surface Blowouts :

3. 4 SL Ross Oil Spill Model ...........seeeeeee

3.5 Modeling of Pt. McIntyre and Northstar Crude Oils ..... .

3.6 Behavior of Oil Spilled on Ice and in Broken Ice... ......eseeceeees
3.6.1 The Effect of Ice on the Four Main Oil Spill Processes .....
3.6.2 Oil Spilled Within Broken Ice, Spring through Fall... se .sseeeeeeeeeeeeeee
3.6.3 Oil Spilled on Top of the Ice 1.0.0... fc ce cece eee c et eeceeenesesenceee

4. Overview of Spill Countermeasures ........cecceccecceeeccececscenscesceencens

4.1 Differences between Fighting Blowout Spills and Tanker Spills ......

4.2 Review of Cleanup Capabilities for Spills in Various Ice Concentrations ........... 37
4.2.1 Mid-winter Response (January to April) ........ccceeeeeseeesceceeenees
4.2.2 Spring Response (May to June) ........... eet ee eenee

, ‘4.2.3 Summer Response (August and September)

5. 2 Booms and Skimmers and
+ 5.3 Operational and Safety Considerations ...........sseeeeeeeeeseees
5.4 Logistical Constraints .........-. : :

5.6 Dispersant Use ...
5.6.1 General Considerations ..... .

5.6.2 Platforms and Supplies in Alaska ......0..0sceeeee UE 60

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« The potential effectiveness of an additional system is now evaluated for this scenario. Attempting

to recover oil outside the "thick slick" would be telatively ineffective. As discussed previously, the

oil thickness outside the thick slick is estimated to be 35 pm, or 0.035 mm, corresponding toan .”
* encounter rate of only 6 bbl/hr. Additional systems could be considered to attempt to recover oil

from the thick slick that is missed by the first two systems: although the two systems encounter all’
of the thick slick, they lose an estimated 30% of it due to inefficiencies associated with the ice
conditions. oe . .

The amount of oil remaining on the water is estimated by subtracting the amount recovered by the
first two systems from the original slick. -

original slick volume/hour 4.2 mm x 100 feet x 0.3 knots x (1 - 30%) - | 313 bbI/hr _
(on water) | ‘

: emulsion recovered/hour 2352 bbl (oil) + 45% emulsion + 24 hours 218 bbl/hr

equiv. thickness of remaining | 95 bbl/hr + (100 feet x (1-30%))+0.3 knots |1.27mm -
emulsion slick : . :

4

* It is acknowledged that the remaining emulsion would not be a continuous slick of constant

thickness, but the for the purpose here of estimating the average encounter rate of a containment
System over a 24-hour period, the discontinuities will tend to average out over time. Following the
same calculation procedure as for the first two systems, but using a wider swath width of 100 feet
to compensate for the thinner slick, a third system could recover an additional 739 bbl of oil, and
2933 bbl of total fluids. Similarly, reducing the slick by the amount recovered and applying afourth

effectiveness drops rapidly, ‘with daily recovered volumes of about 1% of the spill rate. In all,
applying four systems to fight the spill in this scenario, the following are the estimated volumes of
recovered oil and total fluids. oe a . :

~ .105-

. system, an additional 218 bbl of oil and 877.bbl of total fluid can be recovered. After this, °


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. Obviously, there will be inefficiencies when operating containment and recovery equipment among

broken ice. These inefficiencies will be due to having to reposition containment boom to avoid large
ice features and to rid the contained area of accumulations of small floes. As described previously,

“this containment efficiency is estimated to be 70% for this scenario; that is, due to interruptions

related to the broken ice the containment operation is effective for 70% of the time.

Using these figures one can then estimate the total oil, emulsion, and free water that could be
recovered per unit time period. Assuming that operations are restricted to daylight hours, the total

* fluid volumes per day are calculated by combining the hourly rates, the 70% encounter efficiency,
“and the 12 hours of daylight available at this time of year (see Table 6-6).

TABLE 6-6 :
- Estimate of Recovered Fluids per 12-br Time Period

Item * — Calculation . Volume
| total fluids per 12hours =~ * | 415 bbl/hr x 12 hours x 70% * 3486 bbl
total free water 277 bbl/hr x 12 hours x 70% 2327 bbl
[Volume that can be decanted total free water x 80% 1861 bbl ‘|
| total fluids stored per 12 hours total fluids less decant 1625 bbl |
oil . ‘ 83 bbl/hr x 12 hours x 70% 697 bbl
emulsified water , . | 55 bbl/hr x 12 hours x 70% . 462 bbl
, [free water : : total free water x 20% . 466 bbl_|

The above calculations were for one system operating for only the 12 daylight hours. There is
adequate equipment and marine support to provide for two systems, so the above estimates per
system can be multiplied by two, resulting in the following estimates of oil and fluid recovery per
12-hr time period. —_ se -

| Estimate of Fluid Recovered by Two Systems per Day

: total oil recovered. "1394 bb1
: * [total uid recovered 3250 dbl

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Appendix G -
. Probability of Very Large Blowouts During Broken Ice Periods -

- It must be recognized that the oil well blowouts i in this study, involving up to 225,000 barrels of oil

spilled, are extremely rare events That they would occur during the brief periods of broken ice adds
to their extreme improbability. The purpose here is to work through some calculations to
demonstrate how truly remote the possibilities are.

“Astudy for BP Exploration (Alaska) Inc. was recently completed on the probability of blowouts and

oil spills from the planned Northstar and Liberty oil development projects in the Beaufort Sea (SL
Ross 1998). The following analysis was drawn from that study. We restrict ourselves to blowout
probabilities associated with the Northstar venture. The situation for Point McIntyre would be
similar. We also restrict ourselves to what we call “very large” oil spills, defined as being larger than
10,000 barrels and “extremely large” oil spills, defined as being larger than 150,000 barrels, a size
that corresponds to the ones considered in this broken ice study. The following analysis is based on
the assumption that drilling and production operations are equivalent in safety terms to offshore
drilling elsewhere. The analysis can be considered conservative given that the drilling is actually
taking place on land (artificial, eravel islands), which is known to be safer than drilling offshore. -

Historical Statistics ne ' -
In the US. only two moderate-size oil-well blowouts involving oil spills greater in size than 50,000
barrels have occurred since offshore drilling began in the mid-fifties. One must look beyond the U.S.
to find a reasonable database on very large and extremely large offshore oil-well blowouts. Table G-
1 lists all worldwide blowouts involving the spillage of more than 10,000 barrels each. For our
definition of "extremely large" spills, that is, oil spills 150,000 barrels in size or greater, it is seen
that there have been five such spills in the history of offshore drilling, two of which occurred during

' development drilling and two of which occurred during Production or workover activities. The fifth —

was from exploration drilling.

Blowouts during Drilling. ‘Spill frequencies are best expressed i in terms of a risk exposure factor
such as number of wells drilled. On a worldwide basis approximately 36,633 offshore wells were
drilled from 1955 to 1980 of which 24,896 were development wells (Gulf 1981). The total number

_ ofdevelopment wells drilled up to 1988 has been estimated to be 51,000 (Sharples et al. 1989). Thus

the frequency of extremely large spills from oil-well blowouts during development drilling up to
1988 becomes 3.9 x 10° spills per well drilled (2/51,000) or one such spill for every 25,500 wells ©
drilled. A similar analysis can be done for so-called "very large” spills, that is those larger than
10,000 barrels. Referring to Table G-1 it is seen that, up to 1988, four development drilling blowouts
have produced spills in this category, so the spill frequencies for these become 7.8 x 10° spills per
well drilled (4/51,000)

The number of wells drilled worldwide since 1988 is not readily available, but the literature
indicates that only one large oil well blowout larger than 10,000 barrels occurred since that time (this
was the Timbalier Bay production-well blowout occurring in state waters of the U.S. Gulf of Mexico
in September, 1992). This means that estimates based on more current statistics would be even lower

‘ than those noted above because no drilling-related blowouts have occurred since 1988.


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Compared with the freeze-up scenarios there is a wider variety and greater number of marine
systems that can be mobilized for the Tesponse. As well, initial mobilization should be much
faster, with equipment on site within 12 hours as opposed to the 60 to 72 hours estimated for

mobilization and transit for the freeze-up scenarios.

At this time of year there are 24 hours of daylight, which should allow effective containment
and recovery operations during "night-time", .
In the previous scenarios, although the systems could encounter all of the thick Slick, a
significant portion of the oil was lost due to inefficiencies associated with booming «
operations among broken i ice. Some of these. inefficiencies can still be expected in the break-
up scenarios, but unlike the freeze-up scenarios, there may be significant benefits to using

» additional systems to attempt to contain and recover oil that is missed the first time. The

prime difference here is the 24-hours of daylight and the resulting increase in per-system

~ effectiveness. . ae?

As in the freeze-up scenarios, s, the relatively narrow slick of thick oil means it can be encountered in

_ its entirety by two containment and recovery systems. For the moment the evaluation will consider

” two systems operating at a fixed location down drift of the blowout site, with the potential .
effectiveness of additional systems analyzed later. The following summarizes the major pieces of
equipment that could be mobilized in response to this scenario. "


* fluid recovery rates. ;

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mobilized and used for offshore support containment and recovery. As in the first scenario it is

_ estimated that 60 to 72 hours would elapse before these arrived on-site.

The slick conditions are similar to those in the first scenario, with heavy concentrations of oil in a

relatively narrow slick, surrounded by a thin sheen. Asin the first scenario, two containment systems _

could encounter the entire 230-foot slick width. Overall, a similar set of equipment -- tugs, barges,
“ booms, and skimmers -- would be employed. ‘The main difference in this scenario is the increased

amount of ice, which lowers the effective encounter rate of the system (the system cannot access the
oil that is distributed on the ice) and the lower containment efficiency associated with operating in

the increased i ice concentration.

‘In this scenario, the slick conditions at a point 3 hours down drift of the blowout are a thick slick of

230-foot width and 0.5 mm thickness. Combining this with the slick drift rate of 0.6 knots and the
50% ice concentration results i in an encounter rate per system of:

encounter rate = (345 feet x 033 gap ratio) x05 mmx 0, 6 knots x(1- - 50% ice)
"8 61 bblhour .

This is less than the derated recovery rate of several of the offshore skimmers that could be used, so

again the encounter rate is the limiting factor and i is used i in subsequent calculations. Following a
similar calculation process as in the first scenario, the following table shows the calculations for total

-86-


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are strong winds (>25 kt) and the possibility of skirt damage in very rough ice. As to be
expected with a hybrid vehicle combining marine and aeronautical technologies, the older
designs of ACV's (represented by the LACV-30 presently on the Slope) tend to require ahigh
level of maintenance. One machine cannot be expected to operate continually without blocks

of time each day set aside for maintenance. This is taken into account in estimating a

conservative lighter rate for ACV's used as part of the logistics solution.

Air cushion vehicles have a long history of arctic trials and operations dating back to 1966.

Dickins (1989) provides details of many of these experiences in Canada the United States
and Scandinavia. Examples include: a pioneering 4,000 mile trip from the UK to Sweden
in 1972 by the BH.7 (including 1,100 miles over a mix of solid and broken ice); a year-
round freight operation with two SR.N6 machines over ice and open water in the Mackenzie

- Delta from 1974 to 1977, and trials with the Jeff(A) at Prudhoe Bay from November 1983

to July 1984 (including a test run from East Dock to Challenge Island and back in mid-July
over rough rotting ice with a 75 ton load). A review of air cushion vehicle applications for
spill response on the North Slope for the Alaska Oil and Gas Association (AOGA) concluded
that, for a large part of the year, ACV's offer the only reliable means of carrying heavy loads
safely to offshore sites in the Beaufort Sea (Dickins, 1979). “-

The Canadian Coast Guard used a Bell Voyageur (less powerful prototype to the LACV -30
presently available in Alaska) on routine icebreaking operations, spill response, and aids to

navigation maintenance on the St. Lawrence River from 1974 to 1988. Every spring, this ~

craft prevented millions of dollars in flooding by breaking up the river ice and preventing ice
jams; typical ice thickness’ broken at about 10 knots ranged from 19 to 20 inches. At a
slower speed (2 to 4 knots), the Voyageur broke about 10 inches of ice by introducing an air
cavity under the sheet. The AP.1-88 replacement for the Voyageur (a cargo version of the
craft in Lynden’s fleet in Anchorage) has performed similar duties, including icebreaking,
for the past ten years (1988 to 1998). A newer more powerful AP.1-88 derivative is about
to enter service with the Montreal Coast Guard hovercraft unit (1998). ©

From 1984 to the early 1990's Scandinavian Airlines System contracted for up to three AP.1-
88 passenger hovercraft (100 seats) to operate between Denmark and Sweden over a variety
of ice conditions, often encountering rough broken floes and ice rubble. Even in the most

> severe winters (temperatures down to -8 °F) these craft still managed a reliability of 80 to

85%. Over 27 months between 1984 and 1986, two craft carried 310,000 passengers.

At present, Lynden Incorporated (Alaska Hovercraft) maintains the only fleet of air cushion
vehicles in Alaska. Of primary interest for the oil spill response role are the LACV-30 (ex
US Army ship to shore lighters) with a 30 ton payload capacity and a large open working

_ deck (32 X51 ft). This vehicle can carry bladders or the standard intermodal 5,000 gallon

(20 ft long) fuel tanks on deck One of these craft is stationed at Prudhoe Bay on cold stand-
by, with an estimated 24 hours required to mobilize with a crew out of Anchorage.

A further 6 machines are kept in Anchorage in different states of readiness. With special
road clearances for a 30 ft width, it would be possible to transport one of these hovercraft by

’ trailer to Prudhoe over a 2 to 3 day period. Expected total mobilization times from first call .

" -10-


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» ” TABLE F-1°
~ Logistics Effectiveness Summary
“| Category Transport On-site Support | { Mobilization Time
: (hours)
Fixed Wing: light NIA ARCO Twin Otter one hour from call
for remote sensing ‘
Fixed Wing: heavy | Anchorage to Prudhoe {| N/A 2 hours to loading
‘ Seattle to Prudhoe . . 9 hours to loading -
24,400 Ib (DC-6) to °
‘ 46,000 Ib (Hercules) : :
Helicopter: light 4-6 persons or helitorch, surface July - 2/3 machines in
- samples, reconn , ice 2 hours
Bell 206/B0105/Astar | 800-2,200 Ib tracking beacons pet + 1/2 machine n2
Ours .
° additional machines
from Anchorage m 6
: L “| hours .
Helicopter: medium July - non available
12 persons or 3,000 1b reconn + freight transfer
Bell 212 : Oct - 2+ 1n 6 hours
Helicopter: heavy | 9- 22 persons July (107) 1 m 15h
. 7,900 - 10,000 Ib sting | freight transfer July (214)2in25h
214ST, BV107, . Oct (107) 1+ in24h
Super Puma Note. 107 not cert. for Oct (214) 2+ in 2 Sh *
passengers :
Marine Tugs/Barges ’ manine base for Oct - 48 h to start-
«| 600 to 2,700 tons + helicopter operations, up, estimate 60-72 h to
‘ capacity on deck cargo | accomm barge, spill arrival on-site
barges * . | response barge, .
recovered liquids July - 2-4 h or less.
Total Barges 4-5 storage notice after July 5 (typ )
tank/deck combination > expect 12 to 16 h to on-
barges, and 3-4 deck . | Offshore storage as site with equip loaded
cargo only (# m any Ice Str. Barges
given year dependon | . 1 @ 12,200 bbl
dry-docking schedules) | Non ice str. barges
ne . + 2-3 @ 5,500 bbl ,
Total Tugs 5-6 Icebreaking Barge .
vt = 1@ 16,000 bbl ,
Support Boats , ‘ .

. a light freight + Spring break-up July -6 to 8 hours ©
ACS fleet + other - personnel (July) + skimmer platforms on-site depending on
Prudhoe Contractors & i . ~ boom tending we.

BP , | No significant ice ~ temporary storage “
- ‘ capability in Oct . ‘ October - limited utility
except Northstar & 2
: new ACS boats (1998)
- -13-



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§.5 In situ Burning

> +e

. The main job in this study isto evaluate the countermeasures approach of mechanical recovery. The
“ secondary job is to determine whether the cleanup approaches of in situ burning and dispersant use

can be useful in supplementing the mechanical recovery capability. This and the following section

‘provide summaries on these two alternative spill cleanup techniques

Research and actual spill experience have demonstrated that in situ burning (ISB) can be very
effective when used on oil spills in ice conditions. This is because oil spilled i in waters that are
largely covered by ice will remain relatively thick and contained. The current interest in in situ

_ burning for spills on open water started in the early 1980s with the development of fire-resistant oil

containment boom. The petroleum companies operating in the southern Beaufort Sea in Alaska have
been the leaders in supporting the various ISB technologies developed over the years.

There are many advantages of the ISB technique. The buming of thick, fresh slicks can be initiated
very quickly by igniting the oil with devices as simple as an oil-soaked sorbent pad. Jn situ burning
can remove oil from the water surface very efficiently and at very high rates. Removal efficiencies
for thick slicks can easily exceed 90%. Removal rates of 1600 m’/hr (10,000 bbl/hr) can be achieved
with a fire diameter of only about 100 m (300 ft). The use of towed fire containment boom to
capture, thicken and isolate a portion of a spill, followed by ignition, is far less complex than the

operations involved in mechanical recovery, transfer, storage, treatment and disposal. If the small

quantities of. residue from an efficient burn require collection, the viscous, taffy-like material can be
collected and stored for further treatment and disposal.

There are two major concerns over the technique. First, there is the fear of causing secondary fires

that threaten human life, property and natural resources, and, second, there are concerns over the
potential environmental and human-health effects of the by-products of burning, primarily the
smoke. Both concerns can be dealt with by good planning and operations.

154


', TABLE 5-2

wabtbebih min taene

"

Summary of Logistics Inventory and Applicability

Category - . ‘Equipment Number and Capacity Applicability:
1 . Break-up, Freeze-up
or Both
Fixed Wing: light (1) ARCO Twin Otter ; Both
Fixed Wing: heavy “| (6+) Anchorage to Prudhoe or Both
. : _, | Seattle to Prudhoe - various operators, e g ,
"| 24,400 Ib (DC-6) or 46,000 Ib (Herc)
Helicopter: light (1-2) 4-6 persons or Both
‘ 800 - 2,200 Ib (e g , Bell 206/B0105)
Additional machines available out of. Anchorage
on short notice in October
Helicopter: medium | (None Local) 12 persons or 3,000 Ib Freeze-up
- (e.g, Bell 212) available out of Anchorage on '
short notice in October
Helicopter: heavy (2) 9 persons Both
‘ 7,900 Ib sling (e.g , Bell 214ST out of Barrow)
Marine Tugs Crowley Marine Services © : :
(2) Ice capable offshore (Point Class) . * Both .
it : . - Both
(3) shallow draft inshore (River Class)
Note. one Point tug taken south for dry-docking ‘
' summer 97 due to ice damage - due back 98
, Break-up

| Beaufort Marine (Lynden)
(1) shallow draft inshore (Arctic Tem) .



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After the initial massive breakup, the ice cover typically requires two weeks or less to pass through
the 75% to 90% ice coverage stages. During this period many of the ice floes are still relatively large
and the floes and ice cakes are generally touching. , . : ©

The next phase of breakup (from an operational standpoint) involves i ice coverages between 75% and
25%. Depending again upon the weather, this phase lasts for one to two weeks in many of the areas
that are the subject of drilling activities. Floe sizes continue to decrease during this period, while the
distances between floes increase. Rarely do floes exceed 1600 feet once the ice concentrations reach
about 40% or less in early August. ;

The 75% to 25% ice coverage portion of breakup is frequently characterized by extensive regions
of heavier ice concentrations seaward of the barrier islands. At the same time, there are often areas ~
of open water nearshore and in the lee of the barrier island chains. Depending on the weather, the
water depths, and the proximity to natural or man-made islands, the actual ice cover frequently drops
Considerably below the 75% to 25% coverage in many of the operational areas.

Once the average ice concentrations reach about 25% orless, open water conditions begin to prevail.
Such conditions normally exist for approximately two months prior to the onset of freeze-up in
October. During this summer period, usually the months of August and September, the waters of the
Beaufort Sea remain relatively free of ice except for short periods of ice incursions due to northerly
winds.

The rapid drop both in daylight hours and average air temperatures in October is generally
accompanied by the formation of frazil ice and grease ice nearshore and in inshore and backwater
areas, Depending on the wind and sea conditions, young ice forms offshore and develops into thin
areas and/or pancake ice. Eventually, the creation of solid ice cover begins and builds toa 10- or 12-
inch layer, normally in November. Beyond this time only a major storm will cause significant
disruption of the ice growth process. Currents beneath the ice decrease to 0.1 knots or less and
remain at that level i in most regions until H spring breakup.


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of portable rope mop skimming systems within the North Slope response equipment inventories that ~
could be placed into service as required. In areas of heavy oil concentration near the coastline orin
available open water leads other portable skimming systems could be utilized. These would include
vacuum, drum and disc type skimmers It is possible to utilize weir type skimmers under building
.ice conditions as long as the skimmers are equipped with mechanical systems to handle debris and *
ice. Any conventional skimming operations would hkely be curtailed by thicker, more concentrated
ice within one to two weeks of initial freeze-up. - .

In the beginning of the ice growing season many of the spill response vessels would remain
operational. The jet powered vessels would become ‘inoperative as the brash ice and slush thickens ,
and begins to interfere with the exposed mechanical parts of the jet systems. Outboard powered
vessels would also be taken out of service when the thickness of the forming ice begins to clog the
water intake ports on the lower units. Screw driven vessels along with the tug and barge systems
would have the longest sustainable operational period

One possible strategy during freeze-up conditions might be to use in situ burning, with the ice
providing natural containment and Heli-torches providing a remote ignition source. A number of
tests have shown the feasibility of burning oil trapped in leads with and without the presence of brash
ice and slush (Brown and Goodman 1987; SL Ross and D. F. Dickins 1987). Depending ¢ on |

. conditions, high removal efficiencies could be achievable.

Inevitably, asthe ice continues to thicken, the oil would gradually become incorporated into the new

*, ice formation. No cleanup measures could be effective at this point, so tracking the oiled ice would

become a priority. This would be done with the use of satellite tracking beacons deployed at the spill -

_ Source. The oiled ice may move only short distances (thousands of feet) in October before becoming

landfast. At this point the coastline is protected fiom oiling by the fringe of new landfast ice that
* develops at the shoreline. For this oiled i ice, conventional winter response procedures could be
followed by transporting personnel and equipment to the site. Due to the low temperatures, remote
locations and darkness involved in these type of operations, personnel safety considerations would
require additional attention. Resources such as personnel shelters, portable lighting, portable heaters
and restroom facilities would be required along with the initial response resources. ,

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; TABLE 5-1
: Summary of Key Skimmers
Skimmers held by ACS Number ; Derated recovery rate,
. available ** bbi/hr
Weir-type skimmers| : , ‘
TRANSREC 250 1 314
DESMI 250 Ocean’ * ‘14 126
DESMI Harbor 3 88
Walosep W1 1 50
_[ Walosep W4 1, 113
DESTROIL 2 31
Oleophilic skimmers :
LORI side collector ‘1 217 *
Foxtail 4 66
*| T-54 disc 3 60

5.3 Operational and Safety Considerations

In general, containment and recovery operations are most effective when carried out as close as
possible to the source of the spill. There are two main reasons for this: 1) as the slick moves away
from the source it will tend to spread laterally, perhaps to widths that cannot be contained with
manageable lengths of boom; and 2) over time the oil may emulsify, making it more difficult to skim
oil from the water and pump oil once recovered. With blowout spills this must be balanced with the
safety considerations of operating within an area affected by the plume of oil droplets from the
blowout. The criteria for a safety zone boundary, thati is, the area in which continuous operations can
be conducted, is an oil particulate concentration of 5 milligrams/m’ which is the OSHA standard for
an 8-hour exposure for response workers. This corresponds to a downstream distance of 4600 feet
- for the Point Mcintyre scenario, and 5600 feet for Northstar.

~45-


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‘The slick conditions of interest are those estimated for 3 hours down drift of the blowout. This” :

“corresponds to a distance of about 7000 feet, which is judged to be a safe operating distance based

on hydrocarbon-in-air concentrations. At this point the thick slick is 240 feet wide and has an
average thickness of 0.7 mm. For a containment system positioned downstream of a blowout, the
encounter rate is calculated by multiplying the encounter width of the system by the slick thickness
and the slick drift rate of 0.4 knots. In addition to this, one must account for the fact that, on average,
30% of the slick width would be covered by ice. Thus the encounter rate for oil on water and
available for recovery would be reduced by 30%. So, for each containment system employing 360 "
feet of boom, the encounter rate is: : : ‘
encounter rate = (360 feet x 033 gap ratio) x 0.7 mm x04 knots x(1 =30% ice)
= 83 bbi/hour .
an “8 , ”

As noted above, this is within the derated Tecovery rate of several of the offshore skimmers that
could be used; therefore, the encounter rate will be the limiting factor and will be used in subsequent
calculations. Using this as the recovery rate, and using the guidelines of 20% oil recovery efficiency
and 40% water-in-oil emulsion in storage, the total fluid recovery rate can be estimated as shown in

the following table. ‘
“TABLE 6-5
Fluid Recovery Rates for Scenario 1
Fluid Calculation . Recovery rate
oil lesser of system encounter rate and derated recovery rate 83 bbi/br |
total water oil content in recovered fluid (recovery efficiency) = 20% 332 bbl/hr
emulsified water | emulsified water content in recovered fluid = 40% 55 bbl/hr |
free water - | total water less emulsified water ° 277 bbi/hr |
total fluids oil + emulsified water + free water : 415 bbi/hr
“214. .


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containment area. It may be possible to use skimmers, without containment boom, to recover ,

isolated pockets of oil; however, this approach would also severely limit the encounter rates

owing to the relatively thin initial slick conditions resulting from blowout spills.

+ In the freeze-up scenarios, the limited number of daylight hours restricts the possible
effectiveness, It is assumed that operations will only be conducted during daylight hours due to
the difficulties in positioning the containment and recovery equipment relative to the thick
portions of the slick.

:Employing additional containment and recovery equipment is unlikely to improve significantly on -
the above estimates of effectiveness. In each of the scenarios, the entire swath of thick oil can be
encountered by one or two containment and recovery systems using modest lengths of boom. Any
additional equipment would be limited to chasing relatively thin slicks of oil and would contribute

little to the overall effectiveness.

Dispersants should be useful for responding to blowout spills in light ice conditions. Dispersant-use
is likely to be more effective than mechanical systems in removing oil from the surface because the
method, involving application of dispersant from helicopters, avoids the usual inefficiencies of
vessels and spill equipment operating in an ice-infested environment. The major problem with
dispersants, however, is that wave energy is required to mix the treated oil into the water. Because
of this, it was assumed in the 50% and 70% ice scenarios that dispersant-use would be ineffective _
due to the dampening effect on wave energy in these higher ice concentrations. Another factor that
strongly influences dispersant effectiveness is the viscosity of the oil being treated. In the break-up _
scenarios, the viscosity of the Pt. McIntyre crude oil was judged to be too high to allow for the -
effective use of dispersants. Oils less viscous than Pt. McIntyre crude oil will be more amenable to
chemical dispersion. so ‘ ‘
In-situ burning could add to the overall effectiveness, particulary in the break-up scenarios. In those
scenarios, ‘with above-freezing temperatures, oil that lands on ice floes will tend to be herded into
pools on the ice that may be subsequently burned. This burning of oil on ice would be an oil removal
_‘ capability that would supplement an on-water buming operation or containment and recovery effort.

360°. .


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Effects of Ice. The ice concentrations in the six scenarios varied from 30% to 70% coverage. For
spills in ice resulting from a blowout, the presence of ice floes has two negative implications. The
first is simply that a certain percentage of the blowout lands on ice and is thus unavailable for
containment and recovery based countermeasures. The second is that as the ice coverage increases,
it will become more and more difficult to operate containment boom to concentrate oil for recovery.
While broken ice is sometimes said to have a positive effect on spill behavior by reducing the normal
effects of spreading, this is of little benefit for blowout spills where the initial slick thicknesses, even

» “in the thick portion of the slick, are often less than 1 mm.

Particularly for the spills in 70% ice coverage, ‘the effect of ice is to make a containment and
recovery response essentially pointless. ‘The combination of only 30% of the blowout flow actually
landing on water and thus being available for recovery and the low efficiency of containment
operations means that less than one percent, at best, of the total blowout flow could be recovered.

The situation for the 30% ice scenarios is somewhat better, with more of the oil landing on the water
_ between floes, and more efficient containment operations. - ,

Initial Slick Conditions. As described in each of the scenarios, the blowout plume comprises a

range of sizes of oil droplets that rain down on the ice/water surface at some distance from the spill

source. The result is a thick, relatively narrow band of oil directly down drift of the blowout source,

with a much wider, relatively thin area on each side of the thick slick. It is estimated that about 60%

of the oil that eventually reaches the surface will land in the thick portion of the slick.

It was also assumed that 20% of the total blowout flow would evaporate from the droplets in the air,
and it was estimated that 10% of the droplets would be so small that they would remain suspended
in the atmosphere. In total, an estimated 70% of the blowout flow will eventually reach the ice/water

surface.

Combining the above numbers means that only about 40% of the total blowout flow (0.6 x 0.7) will

> reach the surface and form a thick slick. About 30% of the total blowout flow (0.4 x 0.7) will reach

“129.


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The above parameters are used exactly as indicated throughout the study. The only exception is that
the oil type considered is not ANS crude, which is a blend of North Slope crude oils. Rather two

_ other, more relevant crude oils have been selected for study: Pt. McIntyre crude oil itself and Milne

Point crude oil, an oil known to have properties close to that of crude oil from the Northstar field

1.6 Structure of Report

This introductory chapter is followed by four chapters, Chapters 2 through 5, that set the scene for
the main job in Chapter 6 of developing and evaluating the six blowout scenarios.

Chapter 2 presents a detailed description of actual broken ice conditions in the study area, then
presents simplified broken ice models that can be used in the scenario evaluation work. Chapter 3
provides a general description of blowouts and marine spills, with a particular emphasis on the ‘
problem of oil spilled in broken ice. ,
Chapter 4 presents an overview of response options for dealing with marine oil spills, especially
oil spills in ice, and Chapter 5 discusses in greater detail the three main methods of mechanical
Tecovery, dispersant use and in situ buming that exist in Alaska for responding to spills in the North. _

Chapter 6 describes in much detail the behavior and fate of the six blowout scenarios and the likely
effectiveness of countermeasures in recovering their spills. First, the effectiveness of the mechanical
recovery systems that exist on the North Slope is assessed. Then the possible benefits are evaluated _
of adding more mechanical systems to the response, and of adding the countermeasures of dispersant
use and in situ burning to the mix of response options available. Also discussed, but not on a
scenario-by-scenario basis, i is the possibility and benefits of igniting and burning the blowout at ;
source and thus preventing amajormarine spill from occurring in the first instance. The long chapter
ends with a tabular summary of the evaluation and a mass balance of the spill in terms ofevaporation <
losses, losses due to tiny-particle anit and amounts of oil that can be Physically recovered, bumed

and dispersed.

Chapter 7 ends the report with conclusions and recommendations.

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Equipment and Logistical Limitations. As discussed above, the relatively narrow thick slick does
allow for reasonable encounter rates using a limited number of containment and recovery systems
and relatively short lengths of boom. In fact, in each of the six scenarios, the entire width of the thick
slick could be encountered using one or two systems with a total boom length of no greater than 720

' feet. Similarly, there are a number of skimmers with (derated) recovery rates that exceed the rate at
-which oil would be encountered in the thick slick, so the capability of recovery equipment should

not limit the operation. Finally, there are adequate logistical systems to support the containment and
recovery operation, including the storage and transfer of recovered fluids.

In each of the scenarios, consideration was given to the possible effectiveness of additional
containment and recovery systems. In each case it was found that any such equipment would be
limited to chasing relatively thin slicks of oil - either that which originally landed outside the thick
portion of the slick or that which was lost past containment due to ice problems - and would
' contribute litle to the overall effectiveness. ,

6.10.2 Alternative Countermeasures . -

‘For each of the six blowout scenarios the potential effectiveness of alternative countermeasures was
also examined. This includes the use of dispersants, in-situ burning, and igniting the well to burn off
the oil as it is emitted from the well. The results are summarized in the table below. In each case,
effectiveness is defined as the percentage of the blowout flow over the 15-day period that could be

dealt with by the particular technique. =< .

“BI


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used in the subsequent scenarios. Attachments contain contact lists, specification sheets and resource
material prepared by ACS for logistics planning ‘

The focus here is on equipment currently in operation on the North Slope, together with additional
equipment that could be made available within a few days of travel time (helicopters and air cushion
vehicles). Other than small boats which can be brought in by road, there is no means of adding to”
the existing tug and barge fleet i in the months of. July or October due to heavy ice on the approaches .
to Prudhoe Bay. '

The final analysis of each scenario considers the anticipated improvements which could result from -
using other forms of specialized logistics equipment not presently available or accessible at Prudhoe

‘Bay. Possible examples would be additional air cushion vehicles, more capable ice strengthened tugs -

with icebreaking barges and larger IFR helicopters. Suggestions for either increasing or adding to
the logistics resources available to support abroken ice response operation are provided in Appendix ,

” 49.


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evaluation, it is assumed that dispersants would be only 25% effective in 30% ice. For the 50% and °
70% ice scenarios dispersant-use is assumed to be ineffective due to the limited wave energy,
although treatment might be attempted.” * .

Another problem, not related to the ice coverage, is the properties of the oil chosen for the break-up
scenarios. Although the 24-hours of daylight would have otherwise made these scenarios attractive
to a serious dispersant effort, the oil is of a viscosity that is resistant to dispersant effectiveness. It

~ should be noted that the Pt. McIntyre oil used in the break-up scenarios has a viscosity that is

atypical of North Slope crudes, and that most other oils could be much more amenable to dispersion

For the freeze-up scenarios at low and medium ice concentration, in-situ burning offers little
advantage over containment and recovery techniques. Because the slicks emanating from the ‘
blowout are below burnable concentrations, containment is required to concentrate and thicken the
oil before it is burned As in the evaluations of booming and skimming, in-situ burning is limited in -
these scenarios by both the inability to effectively contain oil among broken ice and the fact that
there is only 10-1/2 to 12 hours of daylight ,

For the freeze-up scenario in 7/10ths ice, there is a potential to contain and burn oil using the area
of open water ~ or wake ~ that is likely to be present down drift of the production island. In this
situation, a batch-type contain-and-burn operation is estimated to burn off up to 6.4% of the total
blowout flow, well in excess of the predicted effectiveness ofa containment and recovery operation.
For the break-up scenarios, buming on water using fire containment boom provides an effectiveness
that is approximately equal to that afforded by containment and recovery. Because of the above-
freezing temperatures, oil that lands on ice will tend to be herded into concentrations that may allow
burning using only the natural containment provided by the ice. In this situation, burning the oil that
lands on floes and concentrates in melt pools offers an oil removal capability that would supplement
either the on-water burning operation or containment and recovery.

The possibility and potential effectiveness of intentionally igniting the blowing well was briefly
examined. Based on previous studies on this subject, it is estimated that up to 74% for the Pt.
Mcintyre scenarios (break-up) and up to 99% of the Northstar scenarios (freeze-up) would be
consumed in such a fire.

“hot _ oO Executive Summary - Page $


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“Suggested Guide to Barge Operating Limits in Solia Ice

possibility that any oil water left in the tanks for an extended period in October could start to freeze
solid, at which point pumping out may be impossible until the following summer. This problem can
be prevented by careful decanting of recovered fluids before filling barge tanks in a freeze-up
situation.

The shortage of tugs may become a limiting factor, particulary i in the higher ice concentrations

when anchoring in moving ice may not be possible. In 3/10 and 5/10 ice, the shallow draft River
class tugs may be able to manage at one or possibly two additional barges on site, while the more

_ capable Point tugs are dedicated to the Endeavor to fully utilize her icebreaking capability. In 7/10

of ice it may not be feasible to lighter with the Endeavor while leaving other barges and systems
offshore at the same time (assuming that any marine equipment could be broken out from West Dock
and moved offshore through over a foot of fast ice).

' From discussions with the operators, the following ice limits are suggested for barge operations after

freeze-up. Note: these limits should be treated as a rough guide; there are no hard and fast rules
which will apply in every ice situation Depending on unpredictable factors such as air temperature,

_ snow on the ice, and winds compacting and deforming the new ice, a tug and barge which may be

making steady progress one day can be stopped twenty four hours later in conditions which appear
visually to be the same.

Endeavor ‘ ‘ 14 to 15 inches of solid unbroken (fast) ice with two
(icebreaking bow) _ + Point Class tugs, up to 12 inches with one Point Class tug,
; * and up to 24 inches partially consolidated ice in a previously

broken channel. The Endeavor can operate in thicker ridged

or rafted ice (over two feet in places) by taking advantage of

* cracks and leads to maintain forward progress, not necessarily

in the direction desired (Sawin, pers. comm.)

Crowley 200 series _ 4to 6 inches of solid unbroken i ice or up to 9 inches .

“(non ice strengthened) * of broken ice in a fresh channel through fast ice Ge., ina
- : convoy situation behind the Endeavor)
Lynden 20 and 23 Ato 6 inches of solid unbroken ice or uptoabout12 |
(ice class barges) inches of broken ice in a fresh channel (estimated as possible
_ with sufficient tug power)

Note: The above guidelines refer to very close pack ice or compact ice (9 to 10/10). Itis
assumed that all of the barges presently on the slope could operate in closely packed broken
ice offshore at slow speed during October and November up to about 7/10 concentration.

The estimated minimum time to mobilize tugs and barges from a cold start in October is two days
(Roth, pers. comm ), following which some additional time may be needed to install response
equipment, accommodation modules etc. Hopefully, much of this could be ongoing while the
equipment itself is being mobilized. Mobilization in July becomes a matter of: hours as the Point
tugs are usually operating by July 4-5 out of W. Dock.


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the wind speed). Small waves (only a few inches in height, because of the reduced fetches in the ice)
are Present on the open water between the floes on Days 7 through 15.

“As the oil ‘and gas exit the 6.3-inch inside diameter tubing at the wellhead the high velocity of the
gas atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces
and the droplets agglomerate. After this the volume median diameter' of the oil spray droplets is

~ assumed to be 0.75 mm. The kinetic energy of the gas jet from the wellhead carries the droplets to

a height of 120 feet above the release point. From this point the oil droplets begin to fall as they are
__ cartied downwind by the wind. The speed at which the droplets fall is governed primarily by their
diameter: larger oil drops fall much faster than smaller droplets. For ‘example, i in still air, a 0.75 mm
droplet falls at a speed of 7.5 ft/sec. If there were no turbulence in the wind, in the 16 seconds
required for a 0.75 mm diameter droplet to fall 120 feet, it would be carried more than 360 feet
downwind. In real wind conditions considerable amounts of turbulence exist and must be accounted
for in determining the trajectory of the oil spray. If the oil spray generated by the blowout were
imagined to be all one drop size (i.c., 0.75 mm diameter), the drops would still fall at different
. distances from the blowout because of the turbulence in the wind. As the spray of oil drops falls, it
is being spread horizontally and vertically by air turbulence, or meandering of the wind. In the time
required for 99.7% of the 0.75 mm droplets to fall to the surface the wind has carried the final few
0.75 mm droplets 920 feet from the blowout. The air turbulence also spreads out the droplets
' Jaterally as they fall, with the width of the “footprint” of the oil on the surface i increasing with
distance from the source in a parabola-like shape. -

_ In reality, the spray of oil droplets i is made up of many different droplet sizes. In in determining the
” footprint of the oil spray on the surface, this must also be taken into account. This is accomplished
by dividing the full range of oil drop sizes produced by the blowout into nine smaller ranges, each
representing 10% of the total volume of all the oil droplets. Only nine drop-size ranges are used
because 10% of the volume of oil released is assumed to be in droplets so small (much less than 50
jum) that they remain suspended in the atmosphere and never settle out. Each range is characterized

« by adroplet diameter that is representative of the droplets in the same range. For example the largest
10% of the volume of oil spray droplets is represented by a 1.55 mm diameter oil droplet; the

~ smallest 10% that will settle is represented by a 0.05 mm diameter droplet. The dimensions of the
oil spray footprint on the surface of fast ice adjacent to the island were calculated by determining the
' deposition tate as a function of distance downwind (from the product of the mean concentration of
a given droplet size in the air and that droplets terminal settling velocity) and the width of the oiled
area for 99.7% of the representative droplets i in each range to settle to the surface.

As the warm oil droplets fall in the air they evaporate. It is assumed that, regardless of fall time or
‘droplet diameter, the slick formed by the droplets has lost 20% of i its volume to evaporation

3.1 Day1 -

° As the oil rains down on the surface of the fast ice it begins to accumulate in depressions and pools
_ on the surface of the adjacent ice. Close to the source, starting about 50 m downwind of the

<1 50% of the volume of oil is contamed in droplets leiger than the volume median diameter and 50% is contained
. in droplets smaller than the volume median diameter .

“4.


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- Protection Agency, Office of Air Programs Publication No. AP-26, 1970.

The following example is provided to illustrate how to use these figures. A

.well is assumed to be discharging oil and gas at a rate of 12000 BOPD with a GOR

of 750 scf/barrel through a 6.3 inch diameter (7 inch outer diameter) pipe. To
determine the amount of oil that falls within 200 meters from the source one would
complete the following steps. From Figure 2 determine the gas flow to be about

8.75 mmscf/d. On Figure 4 interpolate between the 5 and 10 mmscf/d curves to
approximate the required 8.75 mmscf/d curve. From this interpolated curve get the
percent of oil falling within 200 meters of the source (about 72%). The total volume’
of oil falling within 200 meters of the source will be the total oil flow of 12000
BOPD times 0.72 times the duration of the blowout period. To determine the width
of the fallout at 200 meters, use Figure 6 in the same way, and determine the fallout
width at 72% of oil on "ground" (about 35 meters). This is the width that would be
oiled if the wind came from the same direction during the entire release. If the wind
is shifting the plume will deposit oil over a much wider area. If the wind's . oO
directional persistence throughout the release period is known these values can be .
applied to determine the percentage of oil falling and the resulting oil thicknesses in
the various sectors around the spill source.

References

Audunson, T., The Fate and Weathering of Surface Ou | from the Bravo Blowout,
Marine Environmental Research 3, 35-61, 1980.

Beychok, M.R., Fundamentals of Stack Gas Dispersion, Published by Milton R.
Beychok, Consulting Engineers, 63 Oak Tree Lane, Irvine, CA. 92715, 1979.

Buist, 1.A., D.F. Dickins, Oil and Gas Under Sea Ice Volume 1, Dome Petroleum
Ltd., 1980. ‘ ‘ ‘

Martec Limited, Report on the Environmental Program associated with the blowout
at Shell et al Uniacke G-72, report for Shell Canada Resources Limited, 1984.

Tumer, B.D., Workbook of Atmospheric Dispersion Estimates, U.S. Environmental

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6.2 Scenario 1: Northstar in 3/10ths Ice Cover During Freeze-up

6.2.1 Blowout and Spill Behavior (Scenario 1. Northstar, 3/10ths Ice, Freeze-up)

An uncontrolled blowout occurs in early October at the Northstar artificial island releasing 15,000

_ barrels of oil per day (BOPD) and 33 x 10° standard cubic feet (scf) of natural gas per day (a Gas-to-

Oil Ratio [GOR] of 2200 scf/bbl). Over the first 72 hours of the incident, the air temperature ranges

. .from a nighttime low of 13 °F to a daytime high of 23 °F. The wind speed averages 13.5 knots from
, the east. The surrounding water is covered by 3/10ths new ice floes. The ice is 0.4 to 0.6 feet thick

and covered by 1 to 2 inches of snow. The floes are hundreds to thousands of feet in size. The ice

“is drifting at the same speed as the water (both wind-driven at 3% of the wind speed) at 0.4 knots

to the west. Small waves (only a few inches in height, because of the reduced fetches in the ice) are
present on the open water between the floes. These conditions do not change over the time period
of the scenario; as well, ; the ice concentrations do not change asit drifts away from the spill site (i.e.,

_ no convergence or divergence of the ice). eo, , ’

"As the oil and gas exit the 6.3-inch inside diameter tubing at the wellhead the high velocity of the

gas atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces
and the droplets agglomerate. After this the volume median diameter” of the oil spray droplets is
assumed to be 0.75 mm. The kinetic energy of the gas jet from the wellhead carries the droplets to
a height of 120 feet above the release point. From this point the warm oil droplets begin to fall as
they are carried downwind by the wind. Evaporation occurs during the droplets’ descent, and it is
assumed that, regardless of fall time or droplet diameter, the slick formed by the droplets has lost
20% of its volume to evaporation. > -

n

The speed at which the droplets fall is governed primarily by their diameter: larger oil drops fall

much faster than smaller droplets. For example, instill air, a 0.75 mm droplet falls at a speed of 7.5

aa

2 50% ofthe volume ofol ts contaned in droplets larger than the volume median dameter and $0961 contained
in droplets smaller than the volume median diameter. ,


| com ES wane SE onan SE enon |

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¢ Broken-ice scenarios will be developed in which ice floes cover 30%, 50% and 70% of the
water surface. . ot

» © The scenarios will be used in modeling and delineating the distribution of spilled oil onto

the surrounding water and ice. '

© The ice and oil spill scenarios will be used to analyze countermeasures capability in 30%,
50% and 70% ice concentrations, on a daily basis and over the 15-day blowout period.

_Simplified Broken Ice Scenarios. Based on ice studies, climatic data, and personal observations,

typical environmental parameters are developed for spill response scenarios at the Northstar ,
” production island during freeze-up and at the Pt. McIntyre location at West Dock during break-up.
The parameters are presented in Tables 1 and 2 (at the end of this section) for the specified ice
concentrations of 30%, 50% and 70%. Appendix B provides supplemental data on ice and climate

_ Parameters which can be used to determine the percentage time that a particular condition may

exceed the values used in the scenarios.

The following briefly outlines the sources used to generate the climate and ice parameters that are
in the tables. Reference numbers in the text identify sources in the attached list.

2
1

Ice Conditions (Concentration variability, ice thickness, floe size, and snow on the ice, melt pool ©
coverage): As discussed earlier, there is considerable variability in establishing the range in ice

* concentrations which could actually be encountered in each scenario. Although the regional
* concentration averaged over a few square miles may be 30, 50 or 70% the actual concentrations on

distance scales of hundreds of feet may range from open water to solid ice (a large floe being |

“ equivalent to 100% ice coverage within its perimeter). Average or median values for the ice

parameters shown in Tables 1 and 2 were extracted from a'combination of References 2, 4, and 9

4


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the range of possible conditions. The full approach for analyzing the scenarios for the purpose of

determining spill response capability in broken ice conditions was explained in Chapter 2 (in Section
2.5.3) and is summarized below. :

Furst, detailed broken-ice scenarios will be developed in which ice floes cover 30%,
50% and 70% of the water surface uniformly. This, in fact, has already been done in
Chapter 2 where each of the scenarios is described in detail, in terms of ice properties
and environmental conditions, on the basis of certain simplifying assumptions, and
these descriptions are summarized in Tables 2-1 and 2-2 at the end of that chapter.

‘Next, the ice/environment scenarios will be used in modeling and delineating the
distribution and movement of spilled oil onto the surrounding water and i ice.

Then, the ice and oil spill scenarios will be used to analyze countermeasures
capability in fixed 30%, 50% and 70% ice concentrations, on a daily basis and over
* the 15-day blowout period. ©

1

The broken ice capabilities will be quickly compared with the known
_ countermeasures capabilities for spills that take place in open water and in a complete

ice cover environment.

The major emphasis of the analysis is on the effectiveness of the mechanical recovery systems that
now exist on the North Slope. However, because the spill scenarios are presented in detail in this

chapter, it is also convenient in each scenario to discuss the use of additional mechanical equipment :

and other cleanup techniques (particularly in situ buming and dispersant vse) and determine the

extent to which these might improve cleanup effectiveness.

Before proceeding directly tothe ‘scenarios, please note the following. The first part of each scenario

isa two-page description of the blowout behavior and the fate of the spill in ice. The behavior of the

: discharging oil from the blowouts is a very complicated affair involving drops of different size


oS

[care 2 rH Come TERE corre EE ots EK crone HEL Gove, 2 ane) SEE cue SE une SE nan SE Oot TE ove EE wen 2 woe BE woes BE ese |

ho MED ERICTENERNeREETNE ae ~~ on Soe

Mackay, D. 1984. The fate and behaviour of oil in cold climates. Department of Chemical
> Engineering and Applied Chemistry. Report to Environment Canada, Ottawa.

Mackay, D. and w. Zagorski. 1982. Water in oil emulsions: a stability hypothesis. Proceedings of
the Sth Annual Arctic and Marine Oilspill Program Technical Seminar. Environment Canada,
Ottawa. . 5

» Mackay, D., W. Stiver and P.A. Tebeau. 1983. Testing of crude oils and petroleum products for

- environmental purposes. Proceedings of the 1983 Oil Spill Conference. American Petroleum
Institute, Washington, D.' c.

McMinn, LTSG T.J. 1972. Crude oil behavior on Arctic winter ice: Final report. Office of Research
and Development, United States Coast Guard, Project 734108, Washington, D.C., NTIS
Publication No. AP-754, 261p. .

Nadeau, J.S., and D. Mackay. 1978 Evaporation rates of complex hydrocarbon mixtures under
“environmental conditions. Spill Technology Newsletter, vol 3(2) Environmental Protection
Service. Environment Canada. Ottawa.

NORCOR Engineering and Research Ltd. 1975. The interaction of crude oil with Arctic sea ice.
Prepared for the Beaufort Sea Project, Department of the Environment, Victoria, Beaufort Sea
Technical Report No. 27. . .

_ Ross, S.L, C.W. Ross, F. Lepine, and K-E. Langtry. 1979. Ixtoc I blowout. Spill Technology

Newsletter, July-August. Environmental Protection Service. Environment Canada. Ottawa.

S.L. Ross Environmental Research Ltd. 1998, The efficacy of in situ buming for Alaskan risk oils.
Report to the Alaska Department of Environmental Conservation and Alaska Clean Seas. Juneau
and Prudhoe Bay, AK.

S.L. Ross Environmental Research n Lid, 1997. review of dispersant use on spills of North Slope
crude oil in Prince William Sound and the Gulf of Alaska. Report to the Prince William Sound
Regional Citizen’s Advisory Council. Anchorage, AK. , .

S.L. Ross Environmental Research Ltd. 1995. Demulsifiers and modified heli-torch fuels to enhance
in situ burning of emulsions, Report to Alaska Clean Seas. Prudhoe Bay, AK,

S.L. Ross Environmental Research Limited and DF. Dickins Associates Ltd. 1987. Field research

spills to investigate the physical and chemical fate of oil in pack ice. Environmental Studies
Revolving Funds, Report No. 062, Ottawa. .

SL Ross Environmental Research Ltd. 1996. Laboratory studies of the properties of in situ bum
. residues. Marine Spill Response Corp. Technical Report Series 95-010. Herndon, VA

. 7140-.


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Wind and current can herd a slick against a barrier, such as a towed boom, thus thickening the oil

. for continued burning. As little as a 2 m/s wind is capable of herding oil to thicknesses that will

sustain combustion. Indeed, the phenomenon of “uncontained” in situ burning is based on the
requirement ofa self induced wind (drawn in by the combustion process and the rising column of
hot gases), to "herd" and keep an uncontained shck at burnable thicknesses. Current can also
‘dramatically i increase burning efficiency (ie., reduce the amount of burn residue) by herding burning
oil against a barrier. The detrimental effects of current can include entrainment of residue beneath
a floating barrier as the residue density and viscosity increase during the burn process, and
overwashing of the burning slick, causing extinction of the flames Excessive waves can also have
a negative effect on the burning process. , .

The residue from a typical, efficient (85%) n im situ burn of crude oil 10 to 20 mm thick i is asemi-
solid, tar-like layer that has an appearance similar to the skin on an old, poorly sealed can of latex
paint that has gelled. For thicker slicks, typical of what might be expected i in a towed fire boom

~ (about 150 to 300 mm), the residue can be a solid. The cooled residue from thick (>100 mm),

efficient in situ burns of heavier crude oils can sink in fresh and salt water (SL Ross 1996).

A two-step process is likely involved in emulsion burning: "breaking" of the emulsion, or possibly
boiling off the water, to form a layer of unemulsified oil floating on top of the emulsion slick; and

* subsequent combustion of this oil layer. High temperatures are known to break emulsions. Chemicals

called “emulsion breakers”, common in the oil industry, may also be used.

For stable emulsions the bum rate declines significantly with increasing water content. The decrease ~
in burning rate with increasing water content is decreased further by evaporation of the oil. The —
effect of water content on the removal efficiency of stable weathered crude emulsions can be
summarized by the following rules-of-thumb:

* little effect on oil removal efficiency (ie, residue thickness) for low water contents up to
about 12.5% by volume; os


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3.4 SL Ross Oil Spill Model ~~. _
The computerized oil spill behavior model that is used in this study — the SL Ross Oil Spill Model
—has been used extensively in various studies of offshore oil spill behavior. The model incorporates
and integrates all the processes noted above to arrive at an estimate of an oil's likely behavior. SL
Ross has drawn upon the work of a number of researchers in developing its models for these
processes and has added enhancements to deal with pour point, viscosity changes and waxy oil
behavior. The model only applies to the behavior of oil spills on open water; it does not handle the ’
effects of ice. . : os

The model is able to provide the following spill data as a function of time: slick areas, thicknesses
and volumes, for both the thin and thick slick portions; viscosity, density, pour point and water
content of any emulsions that may form; the volumes and percentages of the thick and thin slick
portions that evaporate and disperse; and the maximum possible in-water oil concentration asa result

3.5 Modeling of Pt. McIntyre and Northstar Crude Oils

Because the behavior of a spill is significantly affected by the oil’s initial properties, a spill model’s
particular utility lies in its ability to predict the spill behavior of specific oils. This cannot be done
without testing the oil in the laboratory. At SL Ross a number of laboratory analyses are performed
on crude oil and oil products to generate the parameters necessary for the modeling exercise. A ;
distillation i is completed on the fresh oil, and an oil sample is weathered for a prolonged period in

“awind tunnel. The distillation and wind tunnel data provide the information necessary to predict the

fraction of oil that will evaporate in a given time under a specific wind history or evaporative

. exposure. The wind tunnel weathering procedure also provides aged oil samples for property

analysis. Oil density, viscosity, pour point, interfacial tension, flash point, and emulsification factors.

are determined at two temperatures for both the fresh and weathered oil samples. These analyses
provide the coefficients needed to estimate oil properties and behavior at different temperatures and
weathered states. The expressions used to estimate property changes with time and temperature are
those given by Mackay etal. 1983. . . -

-31-


S GS a es ae as ae hh) See ee ee _ oo

Oil Deposition Modeling For °
Surface Oil Well Blowouts

Randy Belore
S.L.Ross Environmental Research Limited
Ottawa, Ontario, Canada
(613) 232-1564, randy@slross.com

Jim McHale
Alaska Clean Seas
‘Anchorage, Alaska, U.S.A. .
(907) 659-3220 -

Tom Chapple -
Alaska Department of Environmental Conservation
Anchorage, Alaska, U.S.A.

Abstract : hoe Lo :

A surface oil and gas well blowout can send a plume of oil droplets into the
atmosphere near the discharge site. The location that the oil falls to the surrounding
ground or water and the rate of deposition at this point depends upon the height to
which the oil is propelled, the size of the oil drops and the prevailing wind speed. A -
simple method is presented for estimating the fallout width and rate as a function of
distance from the source, for the range of oil and gas flows likely to occur in the
Alaska North Slope operations. This paper summarizes the results of a project
completed for Alaska Clean Seas.

” Project Objective
The objective of the project was to estimate the likely ‘fallout zone from a

> surface well blowout, under specific environmental conditions and blowout

characteristics, for spill response planning purposes. The work was not intended to

* be a detailed scientific evaluation of the best modeling approach to the problem,

but rather to use an existing method to meet the Project's Practical objective.

Model Description

’ A computer model was developed based on the workbook method for
atmospheric dispersion estimation by Turner (1970). The blowout and oil deposition
model functions as follows. Input parameters of oil flow, gas flow, discharge pipe
diameter, oil density, average wind speed, oil drop diameter, release height, and
“atmospheric Stability class are read into the model. The gas exit velocity is
estimated using a simple “ ‘gas flow divided by discharge area” relationship. The jet

» rise is calculated using a cold jet rise equation (Beychok, 1979). The oil drop

settling velocity is calculated using an iterative terminal velocity equation. The
distance that the drop will travel prior to hitting the 'ground’ is determined using the

"rise height, settling velocity and wind speed. The plume spread in both the vertical

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TABLE 5-2 (cont.)

ES Ey ner See See ee mat) Sa

: _Summary of Logistics Inventory and Applicability

Category

Equipment Number and Capacity

Applicability:
Break-up, Freeze-up
or Both ©

‘Manne: Barges ,

wi larine Service:
(2-3) deck barges non-ice strengthened

(2+ 3) combination deck/tank barges with liquids
capacity up to 5,500 bbl each

(1) icebreaking barge capable of storing 21,700 bbl
at 12.5 ft draft or 16,000 bbl for hghtering to West
Dock.

Notes. Barge #213 does not have a current
certification to carry oil cargoes. Crowley normally
maintains 5 barges on the slope with one taken out
each summer for dry-docking and inspection.

eau: Et

Beaufort Marine (Lynden)
(1) ice strengthened deck barge (#23)

(1) ice strengthened combination déck/tank barge
(#20) with 12,200 bbl capacity

(2) non ice strengthened deck barges (ex ARCO)

Ice Services- T) Borden ~ . .
(2) 40 x 140 flexa float shallow draft 250 ton cap. *

Both

Both .
Break-up

Break-up

Support Boats

(3) 30-40 ft inboard screw driven offshore workboats
(5) 38-55 ft jet drive oo
(about 45) 14-28 ft. assorted work boats

MISC, (Oceanic & BP)
(2) survey vessels 43-70 ft.

- Both -
Break-up
_ Break-up

Break-up -

Air Cushion
Vehicles

» Alaska Hovercraft .
(1) LACV-30 (30 ton payload or 5,000 gallons)

Note: additional craft available out of. ‘Anchorage :

Both

51-


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2.5 Persistence of Broken Ice

The detailed descriptions i in the | previous sections of freeze-up at Northstar and break-up at Pt.
Mclntyre suggest that ice at either location will rarely be in the form of ice floes that cover the water
surface uniformly at fixed concentrations of 30%, 50% or 70% The reality of the situation i is that
broken ice in any selected area will be in the form of closely packed i ice in one part of the area and
open water in the other. The average ice concentration for the area at any given time might be some
value in the range of 30 to 70%, but generally the area is not uniformly distributed with ice floes.
There can be a transition period following a storm or other disruption where the ice is redistributing,
and where there is indeed ice concentration of ice floes of 30 percent or whatever, but this transition
period is very short- lived i in the onder oft hours. This is explained in the following discussions.

+

 Freeze-Up at Northstar. The most likely scenario for freeze-up at Northstar is that a young solid

(10 tenths) ice sheet will grow until a storm wind of sufficient strength and duration occurs. The
sufficiency requirement will depend primarily on ice thickness and confinement of the ice sheet
(which in tum depends on the previous storm sequence). For example, an easterly storm creates an
open water lead offshore of the Northstar production island and makes the ice sheet surrounding the
island susceptible to movement from a westerly storm. When the young (thin) solid ice sheet at
Northstar moves as aresult of a storm wind, typically large (1000s of feet across) ice floes will break
free of the coastline or landfast ice edge and move quickly away from the area. This will create an

open water condition, not a broken ice condition, around the island. Depending on how cold it is ,

the open water will start to re-freeze, usually within a few hours to one day. This scenario may be
repeated several times during freeze-up (October through mid-November), depending on the ice

* thickness, storm intensity, and wind direction. The broken ice condition that occurred when the ice

_ cracked and movement started i is relatively short-lived and within a afew hours an open water lead

(one to several miles across) is formed.

Break-up at Pt. Mclntyre. The most likely scenario for break-up at Pt. McIntyre is that the
deteriorated, melting sheet ice (solid 10 tenths ice concentration) on the east side of West Dock
becomes susceptible to movement during a moderate storm wind from the west (e.g., 15-20kts). Any
such wind during late June or early July ikl o cause break-up ofthe sheet ie When break-up

a


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8. References . Soe

ADNR. 1998, Oil and Gas Lease Sale 87, North Slope Areawide, Final Finding of the Director,
Volume 1, Tuesday, March 17, 1998. Alaska Department of Natural Resources, Division of Oil
and Gas, Anchorage, Alaska.

Allen, A.A. 1987. Test and evaluation of the Helitorch for the ignition of oil slicks. In proceedings
of the Tenth Arctic and Marine Oilspill Program Technical Seminar, Edmonton.

Audunson, T. 1980. The fate and weathering of oil from the Bravo blowout. Marine Environment
Research no.3. .

Bech, C., P. Sveum, and I. Buist. 1993. The effect of wind, ice and waves on the in-situ burning of
emulsions and aged oils. Proceedings of the 16th AMOP Technical Seminar, June 7-9, Calgary,
Alta. Environment Canada, Ottawa, Ontario, pp 735-748. .

- Belore, R.C. and I.A. Buist. 1988. Modeling of oil spills in snow. Proceedings of the Eleventh Arctic

and Marine Oilspill Program Technical Seminar, pp 9-29.

Belore, Randy, Jim McHale, and Tom Chapple. 1998. Oil deposition modeling for surface oil well
blowouts. Paper submitted to the 21st Annual Arctic and Marine Oilspill Program Technical °
Seminar. Environment Canada, Ottawa. ,

Brown, H.M. and R.H. Goodman. 1987. Jn situ buming of oil in experimental ice leads. Esso
Resources Canada Ltd., Calgary. Environmental Studies Revolving Funds, Report No. 64,
* Ottawa.

Buist, 1, J. McCourt and J. Morrison. 1997. Enhancing the in situ burning of five Alaskan oils and

emulsions. Proceedings of the 1997 Oil Spill Conference, American Petroleum Institute,
“Washington, D.C. pp 121-136. 1

Buist, .A., N. Glover, B. McKenzie and R. Ranger. 1995. Jn situ burning of Alaska North Slope

emulsions. Proceedings of the 1995 Oil Spill Conference, February 27 - March 2, Long Beach,
‘CA. American Petroleum Institute, Washington, DC, pp 139-146.

DF. Dickins Associates Ltd., and Fleet Technology Limited.1992. Behavior of spilled oil at sea ~

(BOSS): Oil-in-ice fate and behaviour; Draft report submitted to Environment Canada, U.S.
Minerals Management Service and American Petroleum Institute.

Dickins, D. and N. Glover. October 1996. oil and ice: Beaufort Sea nearshore oil spill response
options. Presented at the Symposium on Oil Spill Prevention and Readiness, Valdez, Alaska.

-138-


a a es S05) Gees 4 satin ts

,

the oiled strip to 0.004 mm at the edges. This oil will evaporate at a rate negligibly different from
the oil that falls on the water, reaching a total evaporative loss of 34% after 72 hours.

Table 6-7 summarizes the predicted characteristics of the thick slick over a time period of 72 hours.

” ‘The oil that forms the thick slick on the water has a viscosity of 120 cP and a Pour Point of 10 °F
at the point where the on-water modeling is started. For the first 12 hours after its creation, the thick

portion of the slick on water continues to spread laterally as it drifts with the ice, reaching a width
of 250 feet and a thickness of 0.4 mm. After 12 hours, the oil has evaporated to a point (28%) where
it’s Pour Point (30 °F) exceeds the ambient water temperature and the thick portions of the slick

cease to spread on water. For the duration of the scenario (72 hours) the slick moves with the oiled

_ice floes and does not spread further, although the thick slick may meander somewhat in the pack

ice field due to oceanic eddies or large-scale turbulence. a

The presence of ice inhibits the wave action that would normally exist with a 19 knot wind and
suppresses natural dispersion of the oil slick. The ice also suppresses the formation of awater-in-oil

emulsion.

The thick oil slick continues to evaporate slowly throughout the 72 hour scenario. It loses 31% of
its volume to evaporation after 24 hours; 33% after 48 hours; and, 34% after 72 hours. The viscosity

’ of the unemulsified oil increases to 210 cP after 24 hours; 240 cP after 48 hours; and, 250 cP at 72

hours. The Pour Point of the oil after 72 hours has increased to 47°F.

At the end of the 72 hour scenario period, 17% of the oil released at the beginning of the scenario

,- Still remains in thick slicks on the water surface between floes and 30% remains on the surface of

ice floes. The oiled water area is a long (41 nautical miles), narrow (250 feet) strip that contains 0.4
mm thick unemulsified oil slicks between floes. The ice floes that were sprayed with oil as they
passed under the blowout plume are coated with 0.004 mm to 0.9 mm of oil covering the snow on

: their surface. The thicker coatings are on the floes near the center-line of the oiled strip. ~


[my |

‘and provisions for overnight tie downs.

oan ae ae pe we :0b) iene _ 1}. Sis

‘

‘Two to three light helicopters (BO105 or Bell 206L) are normally available in the Prudhoe area
within 2 to 3 hours These will likely be used in the first stages of the response for low level visual

reconnaissance, helitorch operations, and deployment of oil spill tracking beacons.

A major consideration with helicopter support of an offshore blowout will be securing a safe landing
site offshore during break-up or freeze-up, when the sea ice itself cannot provide a safe bearing
surface. Helicopters on young or rotting ice are limited to temporary set downs on the larger ice
floes (e.g., to collect samples and check oil film thickness), usually with the rotors turning (at the
pilot's discretion). There are no hard and fast rules for these types of operations; any decision will
depend on a safety evaluation by the pilot considering the local conditions (e.g., evidence of local
cracking and proximity to any substantial areas of open water). “Longer set downs and short term
parking with light helicopters may be possible in late October once the ice thickness exceeds one
foot. One barge on location needs to be established as a helicopter landing base with emergency fuel

Although there are no legal requirements preventing single engine VFR FR helicopters from operating
offshore with Popout floats, the safety of an extended operation would be greatly enhanced by

insisting on twin engine IFR capability and full pontoon floats. There is no guarantee that such ‘

equipment would be available on short notice.

The availability of medium to heavy lift helicopters is limited, particularly i in July when most, ifnot
all, of the equipment in Alaska is on full-time contract (ERA - pers. comm.) ERA estimates that
a minimum of three days would be required to bring in additional machines from their Louisiana
base. In October, an Astar (2,200 Ib sling) and a Bell 212 (3,000 Ib) are often available for spot
charter in Anchorage and could be on-site at Deadhorse within 6 hours, weather permitting. The
closest source for a medium to heavy lift machine at any time of year is the North Slope Borough
Search and Rescue (SAR) unit at Barrow with two Bell 214ST's (7,900 Ib sling load or 9 people).
Response time from Barrow would likely be less than three hours; a memorandum of understanding
exists between ACS and the Borough to ensure that the equipment will be available in an emergency.
Neither helicopter would be available in the case of any pre-existing or new life threatening situation
which developed during the spill.

There are no heavy lift helicopters permanently based in Alaska outside of the military. Columbia

Helicopters may be able to release a Boeing-Vertol 107 (10,000 1b) from ongoing logging operations ‘
‘in southeast Alaska, but this would need to be negotiated at the time. Travel estimates from
. Ketchikan to Deadhorse are ~15 hours in July and 2 days in October. The same company has a

number of Chinooks with up to 14 tons extemal sling capacity, but the only two machines in North
America are on long-term contracts and neither can be considered available. The 107 or Chinook
are essentially flying shells with a hook and are not certified for Passengers or internal loads
(Patterson, pers. comm )

Fixed wing aircraft are primarily useful as an airbome command post and for regular mapping of
contaminated area and oil movement; the ARCO Twin Otter based at Kuparuk is well equipped in
this regard, with FLIR (Infrared) and high resolution (low light) video linked to onboard GPS and

compatible with Geographic Information System (GIS) mapping systems like MapInfo. The system ~

can be installed and ready to go in 25 minutes and with an endurance of 4 -5 hours, the Twin Otter
could serve as an airborne command post to coordinate offshore activities. A typical altitude for the

2-

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4.2.1 Mid-winter Response (January to April)

Current technology is considered capable of successfully cleaning up oil spilled on solidice. By late -
December, the landfast ice is normally stable and, from this time until late May, cleanup operators
can utilize the ice cover as a secure platform for support equipment, including trucks, bladders and

“portable trenching equipment. For oil trapped on or within the ice sheet i in mid-winter, direct

pumping would result in almost complete removal of the spilled oil. Ice roads and pads could be
built to allow heavy equipment and vacuum trucks direct access to the oil pools These trucks would

‘recover oil directly into attached insulated tankers for transportation to waste disposal facilities. :

During extremely cold Periods it might be necessary to use steam wands on the oil pools to facilitate
recovery. + . . os

Cleanup could be accelerated by the use of in situ burning. Final cleanup in June, in particular, would
benefit by the use of selective buming of oil on melt pools followed by manual recovery of any
residue. The choice of burning on site or removal to shore would depend on both time of year and
water depth. Once an encapsulated oil layer is delineated, drilling or trenching would be conducted
to expose the oil layer for recovery. Snow melters could be placed on site or at shoreside positions
tomelt contaminated snow and ice. Recovered oil could then be trucked to designated disposal wells
for re-injection orto.adesignated production facility for reprocessing. Burning on-site would become
the preferred « option late in winter when there might be insufficient time to transport the ‘recovered
oil to shore prior to break-up. ‘

4.2.2 Spring Response (May to June)

The period between the first onset of surface snow melt and final deterioration of the landfast ice
provides the best opportunity for in situ burning of oil freshly deposited on the surface, or oil
remaining on the surface following a winter cleanup operation. However, this period also marks the
beginning of the end of easy site access 3 with any heavy equipment.

Insitu burning is an efficient and effective wind of removing oil from a solid ice cover in late May
and June, after ice roads have been closed to traffic. Tests have demonstrated that the oil on the

-38-


me et me mmeenanes a —— oP i

treatment. In that case, only one pass might be required. However, tobe conservative we will assume
that a DOR of 1:20 will be used.

The oil available cach day for dispersing (about 2500 barrels after evaporation) would therefore
require about 5300 gallons of dispersant per day (2500x42/20). The two helicopter/oucket systems

_ would therefore need to carry out about 10 sorties each per day (that is, during the 12 hours of

daylight). Logistically, this would be accomplished as follows
The dispersant bucket system requires a helicopter with a sling capacity of at least 2,700 Ib allowing
for the payload and bucket weight. Bell 212s are readily available for charter out of Anchorage and

“could arrive at Deadhorse within 12 hours from a call-out (6 hours flight time plus mobilization and

crewing). At the same time dispersant and the helibuckets would be loaded on Northen Air Cargo
DC-6 aircraft for delivery to the Slope. The existing agreement with Alaska Clean Seas is to have
the aircraft available for loading within two hours. It is assumed that all systems could be in place
and ready to start operation within 12 hours of the accident. This is sooner than the mechanical
recovery systems can be in place picking up oil (60 hours after the accident), Therefore,
theoretically, the dispersant response could deal with all the oil discharged and on the surface in the
first 12 hours of the spill and also the oil discharged over the next 48 hours before the mechanical
systems arrive. ° ’

Thereafter it would only have to deal with the oil that was not recovered by the mechanical systems.

Based on the twelve hours of daylight available, the following conservative logistics plan is
proposed for using two machines to treat the offshore slicks falling within one to two miles of the
Northstar production facility. .

‘ Assumptions: (Bell 212 ~ operating limits supplied by ERA)

e endurance with 2,700 Ib on the hook - 80 minutes
~,¢ "transit and search speed with sling load - 65 knots . .
© refueling time - 10 minutes (5 min min. hot refuel) ‘
° average pump rate - 100 gallons/min ‘ ‘

-79-


_ aoe aes on eon ommmemmeie ; tt) See ae on pet nasmemee

Crowley Marine Services. .
_Endeavor (ABS Class Al) 16,000 bbl at 9 ft draft (W. Dock limit)

90X205R  ‘s 21,700 bbl at 12.5 ft draft (offshore storage)
Icebreaking barge liquids + dry deck cargo

Typical Ice Limit: 1.2 ft continuous in October, 2 ft rafted in
spots with 2 Point Class tugs (up to to one foot solid ice with a

single Point Class tug)
BG 210/211/213 5,500 bbl liquids, stern ramp + dry deck cargo
60 X 200 ft . 1g mo Co.
, Non - ice strengthened Notes: 211 & 213 in Seattle at time of writing (due back at

. Prudhoe, summer 1998); 211 has a 16 person camp; 213
roy lacks current inspection certificate as a tank barge (assume
waiver for temporary storage inan emergency)

"+ Typical Ice Limit: 4 to 6 inches at freeze-up or thicker floes

at break-up
BG 215/216/218 Deck barges, non ice strengthened
60 X 200 ft ‘ _ Typical Ice Limit: 4 to 6 inches at freeze-up

Point Barrow/Point Thompson . Twin screw nozzles, ~ 47,000 Ib
2,110 bp bollard thrust, 8 - 9 ft draft :
- Most useful offshore for Northstar scenarios at freeze-uy

Sag River/Toolik River/Kavik R. Triple screw, open props ~

* 1,100 hp ~ 22,000 Ib bollard (est.), 3.5 ft draft
Most useful inshore for Pt. McIntyre scenarios at break-up
{still able to operate in broken ice for part of October - move
offshore i inconvoy) ~ .

. ‘ :

Endeavor is scheduled to leave the Beaufort for USCG inspection late 1998 or 1999 No decision has been
made on whether this barge will be positioned back into the Beaufort (Tomga, pers. comm) The Endeavor
is the most ice capable vessel in the US Beaufort and the only barge able to operate offshore in most years up
to the end of October. Crowley maintains a much larger and heavier icebreaking barge in storage in Seattle,
the Arctic Challenger This vessel has dimensions of 90 X 205 ft with capacities up to 22,000 bbl at a9 ft
draft or 50,000 bbl at 16 7 ft draft. Challenger 1s designed to be pushed through thicker ice with over three
times the horsepower of the Endeavor. With two 6,000 hp tugs, this barge could operate routinely in level ice
up to about 18 inches (early to mid-November) No decision has been made to keep the Arctic Challenger in
the long-term Refer to discussion on future possibilities at the end of this section

Note at the end of September, Crowley winterizes all of its vessels, leaving the 200 series barges pushed bow
on into the beach near West Dock, with the Point Class tugs moored in deeper water at the stern of the barges
and the shallow draft tugs lifted out of the water onto the barge decks. Endeavor is moored bow im to the
causeway alongside West Dock.


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ISB unit daily removal rate from the water surface =(71 bbl/hr x 24 hr) x 0.5 = 852 bbl -

If two units were deployed to encounter the entire thick slick ‘available the total daily ISB removal
rate from water would be 1704 bbl.” ‘

As in the Day 3 scenario, the oil that falls on the ice floes could also be dealt with by in situ burning.
After allowing the surface oil to concentrate in melt pools, about 75% of the surface area of the pools
would be covered with 10 mm-thick oil. Taking into account an average oil-removal-by-burning
efficiency of 80% and conservatively estimating that only oil in melt pools greater than 50 ft? (90%
of the total) would be ignited by Heli-torch operations results i in an overall oil removal by burning
of:
daily oil removed from floes by burning = 15,000 bbl x x 35% on ice x 80% x 90%

, : . ' “= 3780 bbl og
The ISB operations targeting the oil on ice floes would continue until all the available oil had been
ignited. Delays in operations due to response time and environmental factors would not affect the
overall removal effectiveness. The estimate of ISB effectiveness expressed as a percentage of the
total blowout flow and including operations on both water and ice for each of Days 4, 5, and 6 of the
scenario, is: : : : :
Oil volume removed byISB ‘= (1704 +3780 bhttday) = ~ 15,000 bovday .
‘ : = 37%

4.6 Days 7 through 11

. In ice conditions of 3 to 5/10ths, either containment and recovery or in situ buming could be

considered. As described in the main report, these two options would be similarly effective at dealing
with oil on the water among ice floes. Jn situ burning does provide a major advantage in the break-up
situation in that oil that is deposited onto the ice will form melt pools on the ice that can be
subsequently burned. For this reason, it is assumed for the following that the response tactic would

- be in situ burning, using fire-resistant boom to concentrate oil from amongst i ice floes, and using the

Helitorch to ignite oil contained in melt pools on the ice.

’.. The cleanup tactics would be the same as those employed for Days 4 through 6, but the effectiveness .

estimates will vary slightly as the ice concentration decreases to 3 to 5/10ths. At a distance
corresponding to 12 hours downwind of the spill source, the thick slick width is 540 feet and the
thickness is 0.8 mm. Again, the ice and the slick are drifting at a rate of only 0.15 knots which, if

_used as an encounter speed would result in a very slow operation. Rather, the calculation procedure
_ here assumes that the operation would proceeds at a speed of 0.4 knots, in a downwind direction to

maximize the encounter rate of oil. (Selecting 0.4 knots as the encounter speed allows two units,
each with an encounter width of 100 feet, to effectively encounter the entire width of the thick slick:
2 units x 100 feet x 0 4 knots is approximately equal to 540 feet x 0.15 knots.) Using two in situ bum
units, each comprising 300 feet of fire-resistant boom and two tugboats and supported by one

-18-


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os Aste

oO co

aon ome od oot oe oO On Oo

Figure H-5

’ n

Distance from Source vs Avg. Thickness
, 12-hour release ;
_ 40 4--— —- +-
“30 J; | “
Eyl] ouoe.
in|] |
. : yo,
246 \ .
9 -b-L + 2 bee 7
0 4000 ,2000 ' 3000 «4000 5000 _ 6000
Distance from Source (ft) 2
* - Figure H-6
Width of oiled area downwind
‘ After 24 hours deposition
2000 ;—---2--- == -—-— = -
e ot
© 1500
oo
3.
2 1000 -
_)
Oo.
= 500
2.
s
0+ + tt '
0 1000 2000 3000 ‘4000 5000 6000 -
Distance downwind (ft) -
Lge


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-Emulsification of an oil spill negatively affects slick ignition ‘This is because of the water in the

emulsion, which can have a concentration of up to 90% for highly stable emulsions. The oil in the
emulsion cannot reach a temperature higher than 100 °C until the water is either boiled off or

- removed. With emulsions, the heat from the i igniter or from the adjacent burning oil must first boil
~ the water before it heats the oil to its fire point. ’

The rate at t which in situ burning consumes oil is generally reported in units of thickness per unit
time (mm/min is the most commonly used unit) The removal rate for i situ oil fires is a function
of fire size (or diameter), slick thickness, oil type and ambient environmental conditions. For most
large (> 3 m diameter) fires of unemulsified crude oil on water, the “rule-of-thumb” is that the
burning rate is 3.5 mm/min. Automotive diesel and jet fuel fires on water burn at a slightly higher
rate of about 4 mm/min. a me
Oil removal efficiency is a function of three main factors: the initial thickness of the slick; the
thickness of the residue remaining after extinction; and, the coverage of the flame. The general rules-
of-thumb for residue remaining after a successful bum are described below. Other, secondary factors
include environmental effects such as wind and current herding of slicks against barriers and oil
weathering. . ,

"The following rules-of-thumb apply for the residue thickness at burn extinction:

+ — for pools of unemulsified crude oil up to 10 to 20 mm in thickness the residue thickness is
~ 1mm; : * . ‘

+ for thicker crude slicks the residue is thicker; for example, 3 to 5 mm for 50 mm thick oil,
+ for emulsified slicks the: residue ‘thickness can be much greater; and,
* — for light and middle-distillate fuels the residue thickness is 1 mm, regardless of slick


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aot oo

Results:

average speed while pumping - -40 knots (68 ft/sec)

average open water (assume, Slick) area between typical floes of 400 ft. dai in 3/10
ice = 288,900 ft2 corresponding to an an average lateral slick dimension of about 600
ft (for illustrative purposes only) - '

loading and refueling at WDSP staging area at foot of West Dock causeway (8
nautical miles from Seal Island) ; Loe ‘

(one machine - multiply by number available) -

~ transit time to and from the site - 15 minutes 1

time to traverse typical slick - 8.8 seconds (600168)
repositioning time to empty bucket

‘= (((240/100] x 60)/8. 8)3 x 2.25 = 36.8 minutes

total time on site = = repositioning time + bucket dump time = 36.8 min + 2.4 min = :
39.2 min

: r

total sortie time = time on site + transit = 39. 2 +15 =54 min. Need to refuel after

each sortie - add 10 min making total net sortie time = 64 min.
total number sorties per day = (12 x 60)/64 = 11.25

*_ allowing for crew change and reorientation half way through the day, a realistic

scenario can call for 10 sorties/day .

The above value of 10 sorties per 12-hr day is conservative in the sense that the helicopter

repositioning time (360°) is taken to be 2.25 minutes. This could be cut in half easily by using 180°
turns. In any case, it appears feasible to plan on twenty sorties with two machines flying 12 hours

per day. The most sensitive parameter controlling the productivity of the operation is the average

slick dimension, which is controlled in part by the floe size and other factors such as wind speed,

distance downwind etc. Many more small slicks will greatly increase the repositioning time. On the

other hand, larger floes may lead to fewer large slicks, with a corresponding reduction in the number

. of repositionings between individual applications.


i sae

L poe |

sp a a ee 0h) S| ees

6.6.4 Dispersant-Use and Burning (Scenario 5. Pt. McIntyre, 5/10ths Ice, Break-up)

Dispersant Use. As mentioned in Scenario 4 this spill becomes too viscous too soon to consider

‘ using chemical dispersants.

‘In situ Burning. As discussed in the mechanical recovery analysis above, most of the thick slick
. emanating from the blowout can be dealt with by the containment and recovery operation. However,

a description and assessment of an on-water in situ burning operation is given below for illustrative
Purposes. Burning of the oil that lands on ice floes i is also discussed. ‘

The requirements for zn situ burning in this scenario would be 300 feet of fire boom and two tugs.
A helicopter carrying a Heli-torch would support the bum operation. The encounter rate of each bum

unit for this scenario is the same as for the recovery unit at: ,

"ISB encounter rate (max) = (300 feet x 0.33 gap) x 2.1 mm x 0.3 knots x rel - 50% ice)
<= 112bbyhr Lo!

- Again, the ISB system would be used in a "batch" mode. Oil is collected in the back of the boom for

acertain period of time, then the system is moved away from the heavy concentrations of oil and the
accumulated oil is burned off. It is assumed that the thick slick is encountered and collected for 50%
of the time, and the remainder of the time is spent burning off the accumulated oil and maneuvering
the unit back into the thick oil slick. This equates, over a 24-hour day, to collecting oil for 12 hours
and buming and maneuvering for 12 hours. Each individual burn would take about 1.2 hours from
ignition to extinction. Twice each day, the section of fire boom would have to be replaced. It is
potentially twice as efficient to collect and bum simultaneously; however, because the average oil
slick thickness emanating from the source equals the minimum ignitable for weathered crude (ca.
2 mm) there would be a danger of the fire buming back to the spill source. |

The estimated daily removal rate for one ISB unit is thus:
ISB unit daily removal rate from the water surface = (112 bbvhr x24 hy); x 0.5 = 1344 boi °

-115-


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Appendix H

a

. Addendum to Report: +
. Realistic Scenario for the Spring Break-up Period

1. Introduction : oon : .

Following a review of the initial draft report, a subsequent analysis was undertaken to address one

of the key limitations of the study. In the initial work, as reported in the main text of this report, the
weather and ice conditions were assumed to be unvarying throughout each of the six scenarios. This
is not a realistic situation. As described in detail in Chapter 2, the break-up and freeze-up periods
are likely to include a range of ice concentrations, This addendum to the original work considers the
response capability under a more realistic set of conditions for the break-up period only. The freeze-
up situation has been analyzed separately and is reported elsewhere. To avoid unnecessary repetition,
it is assumed that the reader is familiar with the approach and methodology of the analysis used in
the main text of the report, and where possible, reference is made to those analyses.

2. Description of Environmental Conditions

2.1 Assumptions and Background ~

_The patterns and behavior of ice in the study area during the June and July ice melt and break-up

period were studied in detail for a five-year period (Vaudrey 1981 to 1985). This experience was
incorporated in the design basis ice criteria for the Northstar Development (Vaudrey 1996). Results
indicated that break-up typically commenced in the vicinity of Seal Island around July 4 with year-to-
year variations from an early break-up in the last week of June to a late break-up in the second week
of July. The decrease in ice concentrations from 10/10 fast ice immediately prior to break-up is
usually rapid with close to open water conditions (less than 1/10 ice) being achieved by July 26 on
average (std. deviation of 11 days). . .

A typical progression of ice concentrations in the vicinity of Seal Island would follow the pattern
below: ~~

Onset of break-up: Day1 . —_ 9/10 ice with leads and fractures

“Days2-3 7 to 8/10
Days4-5 510 6/10
Days 6 - 15 3 to 5N0
. Days15-220 - |, "1 to 3/10,
Day22-summet - |: Oto 1/10
ae


| eae

:6.7.1 Blowout/Spill Behavior (Scenario 6. Pt. McIntyre, 7/LOths Ice, Break-up)

__ divergence of the pack).

ooo ae ~~ ee serene sn . San ae

6.7 Scenario 6. Pt. McIntyre in 7/10ths Ice Cover During Break-up

An uncontrolled blowout occurs in early July at the Pt. Mcintyre drill site releasing 12,000 barrels
of oil per day (BOPD) and 9x 10° standard cubic feet (scf) of natural gas per day (a Gas-to-Oil Ratio
[GOR] of 750 scf/obl). Over the first 72 hours of the incident, the air temperature ranges from a
nighttime low of 34 °F toa daytime high of 44 °F, The wind speed averages 17.5 knots from the SW.
The water to the east of the causeway is covered by 7/10ths melting ice floes. The i ice is 3 to 4 feet
thick and its surface is 40% to 50 % covered by melt ponds. The floes are fifty to five hundred feet
in size. Thei ice is drifting at the same speed as the water (both ‘wind-driven at 3% of the wind speed)

at 0.5 knots to the NE. These conditions do not change over the time period of the scenario; as well,

the ice concentrations do not change as it drifts away from the spill site (i.e., no convergence or

As the oil and gas exits the 4-inch inside diameter tubing at the wellhead the high velocity of the gas
atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces and
agglomerate. The kinetic energy of the gas jet from the wellhead carries the droplets to a height of
40 feet above the release point. From this point the oil droplets begin to fall as they are carried
downwind by the wind.

~ In this scenario, the thick slick is 100 feet wide and 1.1 mm thick at the starting point of the surface

slick modeling. This is at a distance of some 500 feet downwind of the blowout. At this point, the
oil slick is assumed to be evaporated to 20% loss. : 7

For the purposes of this scenario, it is estimated that 30% of the oil spray lands on water and 70%
lands on the ice surface. The spray that lands on ice floes coats the surface and is slowly flushed by

. melt water into the melt pools on the floes. The range of oil thicknesses initially deposited on the
floe surfaces ranges from 1.9 mm near the center-line of the oiled strip to 0.006 mm at the edges. The

-118- .


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ae S| eee eae

4 -TABLE2.
Typical Environmental Parameters for Pt. McIntyre during Break-up

helo ops)

NA.

Ice Concentration (tenths) ’'
Local variability * 0,2 to 0.3 0.4 to 05 0.6 to 0.8
in concentration : ” :

*| Date (from-to) 7/10 through 7/12 7/7 through 7/9 7/4 through 7/6
Daylight hours 24 _ 24 24
(incl. twilight) . : .

Floe ice thickness 3to4 3to4 3to4

(ft) :

Floe size (ft) 50 to 500 50 to 500 50 to 500

Melt ponds (% of 40 to 50% 40 to 50% 40 to 50% |
surface area of ice) ve ‘Jo

Ice drift speed (kt) 0.3 to 0.4, up to 0.8 0.2 to 0.3, up to 0.7, 0.3 to 0.5, up to 1.0
Ice direction (to) E SE - NE ”

Wind speed (kts) 10 to 12 8 to 10 15 to 20 |

.| Wind direction Ww NW sw |
(from) ‘ a : :

Air temp. (day) - 45 45 44 .
°F . ’ ~

‘Air temp. (night) - 35 ye 33
°F

_ Precipitation 0 0 O°
(snow) (inches) :
Sea state : 95% of time < 3 ft N/A _ N/A ~
height (ft)/period | and periods of 6 to 10s
()_*

_ | Visibility (NM) 22% of time < %2NM 22% of time<%%NM | 22%oftime<%NM
(helo ops) (~15 to 16 hrin 3 days) | (~15 to 16 hr in 3 days) | (~15 to 16 hr in 3 days)
Ceiling height (ft) ‘11% of time 11% of time. - 11% of time ~ |
(fixed wing ops) _] ceiling ht.< 1500 ft with J ceiling ht. < 1500 ft ceiling ht. < 1500 ft

visibility < 1 NM with visibility <1.NM_| with visibility <1NM |
Atmospheric icing > :


Appendix C

. Paper on the subject of

Oil Deposition Modeling for Surface oi Well Blowouts

. "delivered at the 21 Arctic and Marine Oil spi Program
. ‘Technical Seminar in Edmonton, June 1998


Catamaran . Seismic vessel, sleeps 12, good working deck area
oof + Unknown ice capability - possible use in July only

‘

_QOut-of-Regi ine

There is no practical means of gaining access out of region marine equipment beyond those

resources which are on hand at Prudhoe Bay in July or October. Exceptions would be small

work boats which could be brought up the haul road or shipped by air.

The inventory « of available marine equipment in the Beaufort Sea region has become much
more limited since offshore exploration and development ended in Canada in the late 1980's.

All of the ice capable barges, supply ships, and icebreakers once operated by Amoco and
Gulf have now left the Beaufort Sea. Northern Transportation Company (NTCL) operates

, an extensive fleet of powerful tugs and barges (non ice strengthened) along the Beaufort Sea

coast between late July and September 30. They recently acquired two ex-Canmar ice class
barges (thought to be US bottoms - Jones Act exempt), but the company has no plans in the
future to winter-over these or any other ice capable equipment within reach of Prudhoe after
the end of September (Briggs, pers. comm.). Similarly, the Canadian Coast Guard is no
longer committed to maintaining icebreakers in the Western Arctic.

. At present the most capable icebreaker operating along the Alaskan coast in any given year

is likely to be the 22,000 shp Kapitan Khlebnikov on tourist cruises. This class of vessel
could operate in the vicinity of Northstar for much of the winter, but would be restricted by
draft from approaching any closer to shore. At 9.4 m draft, the USCG icebreakers which
occasionally appear in the Beaufort Sea area on research voyages have the same problem.

Marine Attachments: refer to selected spec sheets, ACS Marine Vessel Support Guide,
company/agency contact lists, Photographs « of barge operations in broken ice from the Tier
II demonstrations. ; ‘

Air Cushion Vehicles

Hovercraft (often referred to as ACV’), offer a number of unique advantages over other

forms of transportation, especially in shallow water areas with a mix of ice and water.

To make up for the relative lack of direct experience (compared with conventional marine -
” equipment), this section provides background on hovercraft capabilities, with an outline of

their history and operating record in different ice environments in Canada and Europe.

ACV's are completely amphibious and can travel just as well over a mix of broken floes as
they can over solid ice or open water. At the same time they can come up on the beach to

be loaded or unloaded on dry land before returning to the spill location. Major limitations .

CG


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I _ mararete- oc cematintenee dnseemnanneeeaeneeneenntse ae bi Pen

1. Introduction . _

1.1 Industrial Setting
This study focuses on the problem of major oil spills that might occur during oil development
activities that are now taking place in the offshore waters of the Alaskan North Slope, in the southern
Beaufort Sea. Readers not familiar with the industrial setting can refer to Appendix A which presents
‘a brief history of oil development on the Slope. This will help in understanding the following
discussions of oil fields in the area that have been selected for special analysis.

1.2 NSSRPT Goals SY

This study was performed for Alaska Clean Seas and the U.S Minerals Management Service on
behalf of the North Slope Spill Response Project Team w SSRPT), atask group formed i in 1997 by
the Alaska oil industry and federal and state regulators'. The team’s objective was to develop a
comprehensive oil spill response plan that could be used for all exploration and production
operations on the Alaska North Slope. Such a plan was needed to: -

assure adequate spill response capability in meeting federal and state laws;
“  @ minimize duplication of effort through effective planning including shared use of: spill response

equipment and expertise; and
: @ foster timely and efficient review of contingency plans for new wand existing operations. ‘

?

The following goals were set by NSSRPT to reach their objective:

' The NSSRPT members include: Alaska Clean Seas, Alaska Department of Environmental
Conservation, Alaska Department of Natural Resources, Alyeska Pipeline Service Company,
* Bntish Petroleum Exploration (Alaska) Inc., North Slope Borough, US Environmental Protection

. Agency, ‘and US Minerals Management Service. :
ele

’


Thick oil | Emulsification | . Slick «
remaining on (% water vol.) viscosity
water(%oftotal |. =. | (CP @ 30°F)

3.5 Days 7 through 11

On Days7 through 8 | the wind is 5 knots fiom the North aid the current is 0. 15 knots to the North-
west. As such, the thick slick is 180 feet wide and 2. 5 mm thick at the starting point of the surface

"slick modeling

Table H-4 summarizes the predicted characteristics of the thick slick on Days 7 through 11 over a
time period of 24 hours. The oil that forms the thick slick on the water has a viscosity of 120 cP and
a Pour Point of 10 °F at the point where the on-water modeling is started. For the first 24 hours after
its creation, the thick portion of the slick on water continues to spread laterally as it drifts with the
ice, reaching a width of 720 feet and a thickness of 0.6 mm.

" ‘The presence of ice dampens the wave action that would normally exist with a 5 knot wind and

reduces natural dispersion of the oil slick compared to open water conditions. The slick is predicted
to begin to form a water-in-oil emulsion 42 hours after the oil had been deposited on the water
surface. If emulsification rates are the same in loose pack ice as in open water under identical winds,
the slick would be fully emulsified (75% water content by volume) after more than72 hours on the
water. ‘

The thick oil slick continues to evaporate slowly throughout the 24 hour modeling period. It loses
a total of 27% of its volume to evaporation after 24 hours. The viscosity of the unemulsified oil
increases to 150 cP after 12 hours and reaches 170 cP at 24. The Pour Point of the thick oil after 24
hours has increased to 26 °F.

-12-)


ee ee a ee ennai me tt) Se ee anne 1,

"available" for dispersing into the water. This latter point applies equally to containment and

recovery.

An additional negative, not related to the ice coverage, is the properties of the oil chosen for the
break-up scenarios. Although the 24-hours of daylight would have otherwise made these scenarios
attractive to a serious dispersant effort, the oil is of a viscosity that is currently thought to be resistant

to dispersant effectiveness. It should be noted that the Pt. McIntyre oil used in the ‘break-up scenarios

has a viscosity that is atypical of North Slope crudes, and that most other oils could be much more

amenable to dispersion.

"On the positive side, a dispersant operation as descnbed here could be mounted relatively quickly,

within 12 hours as opposed to the 60 hours estimated for containment and recovery in the freeze-up :
scenarios. - yo .

In-situ Burning. For the freeze-up scenarios at low and medium ice concentration, in-situ buming
offers little advantage overcontainmentand recovery techniques. Because the slicks emanating from .
the blowout are below bumable concentrations, containment is required to concentrate and thicken
the oil before it is bumed. As in the evaluations of booming and skimming, in-situ burning is limited
in these scenarios by both the inability to effectively contain oil among broken ice and the fact that
there is only 10-1/2 to 12 hours of daylight. It should be noted that in these scenarios, although
burning offers little theoretical improvement in effectiveness compared with containment and
recovery, the lesser logistical requirements may lead to greater effectiveness in an actual spill

incident.

For the freeze-up scenario in 7/10ths ice, there is a potential to contain and bum oil using the area

of open water -- or wake -- that is likely to be present down drift of the production island. In this

situation, a batch-type contain-and-burn operation is estimated to bum off up to 6.4% of the total
blowout flow, well in excess of the predicted effectiveness ofa containment and recovery operation.


‘ . 1

SL Ross Environmental Research and Energetex Engineering. 1986. Decision-making aids for
igniting or extinguishing well blowouts to minimize environmental impacts. Environmental
Studies Revolving Funds, Report No. 051, Ottawa.

: SLRoss Environmental Research Ltd. 1994. Spill-related properties of fresh and weathered Alaskan

ctude oils. Report to Alaska Clean Seas. Prudhoe Bay, AK.

SL Ross Environmental Research Ltd. 1996. Laboratory testing t to determine weathering and
operational parameters for i situ burning and chemical dispersion of Northstar crude oil spills.
Draft report to BP Exploration. Anchorage, AK.

SL Ross Environmental Research Lid 1998. Blowout and sd spill probability assessment for the
Northstar and Liberty oil development projects in the Alaskan North Slope. Draft report to BP
* Exploration (Alaska), Inc., Anchorage, April 1998. : .

Stiver, W. andD. Mackay. 1983. Evaporation rate of spills of hydrocarbons and petroleum mixtures.
Environmental Protection Service, Environment Canada, Ottawa

Trudel, B.K., B.J. Jessiman and S.L. Ross. 1988. Guide to dispersant-use decision making for oil
spills in the Canadian Southern Beaufort Sea. Environmental Studies Research Funds Report
No. 092. National Energy Board. Calgary. AB.

-Tumer, DB. 1970. Workbook of atmospheric dispersion estimates. Environmental Protection

Agency. Research Triangle Park, North Carolina.

' Wotherspoon & Associates. 1992. Detection of oil in ice & burning of oil spills in winter conditions:

‘ State of the art review. Prepared for PROSCARAC Inc., Calgary, Alberta.

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As the ice begins to break up in mid-June nearshore, and in early July near the barrier islands, the
response options would depend on the ice concentrations. There will bea period of several weeks
when response operations would need | to apply a mix of strategies over short periods as conditions
allow: booms and skimmers operated from shallow draft barges i in light to moderate ice, in situ
burning of thick oil trapped between the floes i in heavier i ice, and manual cleanup and pumping from
any ice rubble remaining attached to the island, as well as cleanup of any shoreline or gravel pad
surfaces that may have been affected . oo
As ice concentrations diminish to less than 3/10 by mid-July offshore and by mid-June in the
nearshore areas, response operations would become increasingly less restricted by ice and more able

. to rely on traditional open water mechanical containment and recovery techniques.

423 Summer Response (Angus and September) . «

Spills during the summer period, in open water or in water with some ice (say, concentrations up to

_ 20 to 30%) would behave no differently than open-water spills elsewhere in the world. Response

methods could include the usual combination of physical recovery, in situ burning and dispersant
use. For platform blowouts as envisioned in this study the discharging oil could be contained and
concentrated as it falls on the water downwind, and either physically recovered or bumed as
appropriate. Oil escaping this operation could be dispersed chemically, if this were deemed to be
appropriate environmentally. All in all, the total operation could be highly efficient, mostly because
of the reasons given earlier: the oil discharge rate would be relatively low, the spill location would
be fixed, the oil discharged would always t be fresh and unemulsified and the ‘slick swath or area
would be relatively small .

.4.2.4 Fall and Early Winter Response (October to December)
This is the most difficult situation. There are limited mechanical options for recovering large
volumes of oil spilled under or among new and young ice in the fall months of October and
November. Rope-mop style: skimmers could be deployed by crane over the side of a response barge
or vessel to recover localized oil patches trapped i in water and slush between floes. There are dozens

3 “

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Table H-5: Summary of Day 12 slick characteristics
_ Thick oil + | Emulsification Slick Thick slick | Thick slick
remaining on (% water vol.).|_.' viscosity thickness width
water (% of total | - _ | ©P @ 30°F) (mm) (ft)

* takes emulsification mto account =~ '

3.7 Days13,14and15 is a mae

On Days 13, 14 and 15 the wind increases further to 20 knots from the East and the current is 0.6
knots to the West. As such, the thick slick is 180 feet wide and 0.6 mm thick at the starting point of
the surface slick modeling. .

Table H-6 summarizes the predicted characteristics of the thick slick on Days 13, 14 and 15 overa
time period of 24 hours. The oil that forms the thick slick on the water has a viscosity of 120 cP and
a Pour Point of 10 °F at the point where the on-water modeling is started. After 9 hours, the oil has
evaporated to a point (28%) where it’s Pour Point (30°F) exceeds the ambient water temperature and
the thick Portions of the slick cease to spread c on water. At this point it is 240 feet wide.

The presence of ice dampens the wave action that would normally exist with a 15 knot wind and
reduces natural dispersion of the oil slick compared to open water conditions. The slick is predicted

~ to begin to form a water-in-oil emulsion 12 hours after the oil had been deposited on the water

surface. If emulsification rates are the same in loose pack ice as in open water under identical winds,
the slick would be fully emulsified (75% water content by volume) after 18 hours on the water.

The thick oil slick continues to evaporate slowly throughout the 24 hour modeling period. It loses
a total of 31% of its volume to evaporation after 24 hours. The viscosity of the unemulsified oil

increases to 2900 cP after 12 hours and reaches 8500 cP at 24 (due to emulsification). The Pour Point
, of the thick oil after 24 hours has increased to 39 °F,


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’ Table of Contents (cont) : ce : LO

~ 6. Detailed Scenarios

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6.1 Introduction .
6.2 Scenario 1. N iz
62.1 Blowout and Spill Behavior (Scenario 1. Northstar, ‘othe Ice, Freeze-up) ... $s
6.2.3 Additional Recovery Systems (Scenario 1. Northstar, 3/10ths Ice, Freezeup)
* 6.2 4 Dispersant-Use (Scenario 1. Northstar, 3/1 0ths Ice, Freeze-up) .
6.2.5 In situ Burning (Scenario 1. Northstar, 3/10ths Ice, Freeze-up) .
6.3 Scenario 2. Northstar in 5/10ths Ice Cover During Freeze-up .......... .
6.3.1 Blowout and Spill Behavior (Scenario 2. Northstar, 5/10ths Ice, Freeze-up) ... 83
6.3.2 Existing Mechanical Methods (Scenario 2. Northstar, 5/10ths Ice, Freeze-up) .. 85
6.3.3 Additional Recovery Systems (Scenario 2. Northstar, 5/10ths Ice, Freeze-up) .. 89
6.3.4 Dispersant-Use (Scenario 2. Northstar, 5/10ths Ice, Freeze-up) ..........- .. 89
6.3.5 In situ Burning (Scenario 2. Northstar, 5/10ths Ice, Freeze-up) . .
6.4 Scenario 3. Northstar in 7/10ths Ice Cover During Freeze-up ...
6 4.1 Blowout and Spill Behavior (Scenario 3. Northstar, 7/10ths Ice, Freeze-up) °. .
6.4.2 Existing Mechanical Methods (Scenario 3. Northstar, 7/10ths Ice, Freeze-up) . . 95
6.5 Scenario 4. Pt. McIntyre in 3/10ths Ice Cover During Break-up ..............4.+- 98
6.5.1 Blowout/Spill Behavior (Scenario 4. Pt. Mcintyre, 3/10ths Ice, Break-up) ...'.. 98
6.5.2 Existing Methods (Scenario 4. Pt. McIntyre, 3/10ths Ice, Break-up)......... 100
6.5.3 Additional Systems (Scenario 4. Pt. McIntyre, 3/10ths Ice, Break-up) - 106
662 Existing Methods (Scenario 5. Pt. McIntyre, 5/10ths Ice, Break-up) . eee lll

6.6 3 Additional Systems (Scenario 5. Pt. McIntyre, 5/10ths Ice, Break-up)....... 114

6.7 Scenario 6. Pt. McIntyre in 7/10ths Ice Cover During Break-up ...........2.000 118
6.7.1 Blowout/Spill Behavior (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up) .... 118

6.7.2 Existing Methods (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up) ....’.... 120

6.7.3 Additional Systems (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up) ....... 123

6.7.4 Dispersants and Burning (Scenario 6. Pt. McIntyre, 7/10ths Ice, Break-up) ... 123

6.8 Potential Benefits of Well Ignition ..... pace wceancescatecsncscones seceeveee 126

6 9 Potential Benefits of Deflecting the Blowout Plume ...........e.ccceeseeeeees 126

‘ ~ 6,10 Summary of Countermeasures Effectiveness ......0cssssceesseseeeeeeeesees 128
6.10.1 Existing Countermeasures ........ccceeeecccscccecececeecesecenes - 128

-6 10.2 Alternative Countermeasures ........ceceecnccecrecscececsceceseees 131
7. ConClUSIONS 1.2... ccecececece cece rereee sees cence seee eee see eeseeseeseeens 135
8. References .......+.+e008 se eeceeceececceceerececcecesesctececesecesecscess 138
Appendix A. Background on Petroleum Activities in the Alaskan North Slope
Appendix B. Supplemental Data on Ice and Climate .
Appendix C. Oil Deposition Model for Surface Oil Well Blowouts
Appendix D. Properties of Point McIntyre and Milne Point Crude Oils it
Appendix E. Estimate of Containment Efficiency in Broken Ice :
Appendix F. Background Information and Details on Logistics
Appendix G. Probability of Very Large Blowouts During Broken Ice Periods

Appendix H. Addendum to Report: Realistic Scenario for the Spring Break-up Period

“ii.


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For the case of oil trapped within or under newly forming pancakes or sheet ice in the fall, the likely

; _fate will be rapid entrapment, with new ice quickly growing beneath the oil. The fate of oil trapped
~ between floes will depend largely on the ice concentration and time of, year. *

During freeze-up, the oil will most likely be entrained i in the solidifying grease ice and slush present
on the water surface prior to forming sheet ice. 'Storm winds at this time often break up and disperse ‘
the newly forming ice, leaving the oil to spread temporarily in an open water condition until
incorporated in the next freezing cycle (within hours or days depending on the air and water
temperatures at the time). Ice drift rates at this time of year are highly variable, but a daily average
of five nautical miles per day can be expected i in October, decreasing | as the ice thickens and
stabilizes through November.

At spring break-up, ice concentrations are highly variable from hour to hour and over short distances.
In high ice concentrations (greater than 5/10), the oil is effectively prevented from spreading and is
contained by the ice. As the ice cover loosens, more oil is able to escape into larger openings as the
floes move apart. Eventually, as the ice concentration decreases to less than 3/10, the oil on the water
surface behaves essentially as an open water spill, with localized oil patches being temporarily
trapped by wind against individual floes. Any oil present on the surface of individual floes will move
with the ice as it responds to winds and nearshore currents. ,

3.6.3 Oil Spilled on ‘Top of the Ice

The resulting area of contamination from arelease of oil on top of ice will be influenced by anumber
of site-specific factors. such as wind speed, surface Toughness and the amount of snow cover in the
area of the release. A number of process equations are available to predict the spreading and
evaporation behavior of oil in snow (Belore and Buist 1988). Key behavioral factors associated with —
oil spilled on snow can be summarized as follows (after Wotherspoon 1992):

© Evaporation rates in snow are substantially less than oil slicks on open water;

” @ Oil mixed with snow does not form emulsions; and '

© Once ignited, there are no appreciable differences between buming oil in snow or

oil in water. . :

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‘Predicted Effectiveness of Existing Mechanical Systems in Recovering 15-Day Discharge

The final step in this section is to use the above calculations to assess the effectiveness of existing
systems to deal with the total volume of oil discharged over the 15-day blowout period. The
assessment includes the effects of response-time delays, and the environmental derating factors of
visibility, VFR flying conditions, and wave heights. As for all the break-up scenarios, the response
time is estimated to be 12 hours, so for the 15-day period the effect is to reduce effectiveness by 3%
(15 - ¥) + 15 = 0.97). Also for all break-up scenarios, the combination of the three environmental
factors are such that, on average, mechanical containment and Tecovery will be effective 66% of the
time. The following is the estimate of effectiveness for the 15-day period, expressed as a percentage
of the total blowout flow: :

Recovered oil volume= 2332 bbl/day x 0.97 x 0.66 + 12,000 bbV/day
= 12% .

6.6.3 Additional Systems (Scenario 5. Pt. McIntyre, 5/10ths Ice, Break-up)

The above analysis described the potential effectiveness for four containment and recovery systems.

_ Although one system can encounter the entire width of the thick slick, itis assumed that a substantial

amount of oil is lost due to having to maneuver around ice floes and clear smaller ice from the
containment configuration. Three additional systems were then analyzed for their ability to
sequentially recover oil missed due to these inefficiencies. Any additional systems would be limited
to chasing thin sheens outside the area of thick oil, or attempting to recover oil missed by the first
four systems. In either case, the daily recovery volume would be less than 1% or less of the daily

 plowout volume.

»

“114.


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Using the same assumptions used previously regarding a batch-bum process effectively using 50%
of a 24-hour day, the estimated daily removal rate for one ISB unit is:

ISB unit daily removal rate from the water surface = (45 bbl/hr x 24 hr) x 0.5 = 540 bbl ‘

-If three units were deployed to encounter the entire thick slick available the total daily ISB removal

rate from water would be 1620 bbl.

The calculation of oil removal by burning from ice floes is similar to the previous s Days 3 through ,
11, except that the percentage of oil in pools greater than 50 ft” diameter is reduced to 85% to
account for the lighter coating of oil:

15,000 bbl x 21% on ice x 80% x 85%

daily oil removed from floes by burning
: 2142 bbl

The ISB operations targeting the oil on ice floes would continue until all the available oil had been
ignited Delays in operations due to response time and environmental factors would not affect the
overall removal effectiveness. The estimate of ISB effectiveness expressed as a percentage of the

* total blowout flow and including operations on both water and ice for each of Day12 of the scenario,

is: ‘ - . ‘

Oil volume removed fromice byISB = (1620+ 2142 sD + 15,000 bbl/day
= 25%

48 Days 13, 14, and 15

In ice conditions of | to 3/10ths, containment and recovery operations would be the preferred option
applicable and could be fairly effective. Compared with the scenarios in higher ice concentrations,
a greater percentage of the oil falls on water (rather than ice) and is thus available for recovery. Also,
the lesser ice concentrations mean that containment operations can be carried out with little down-
time due to ice incursions

As in the scenarios previously described in the main report, the relatively narrow slick of thick oil
means it can be encountered in its entirety by one or two containment and recovery systems. For the
moment the evaluation will consider one system operating at a fixed location down drift of the
blowout site, with the potential effectiveness of additional systems analyzed later.

The slick conditions of interest are those at a point 3 hours down drift of the blowout: the thick slick
is 200 feet wide and averages 0.5 mm thick. Combining this with the drift rate of 0.6 knots, and
accounting for the ice concentration of 10%, the encounter rate for oil on water and available for
recovery is estimated as: .

encounter rate (300 feet x 033 gap ratio) x 0.5 mm x 0. 6 knots x (1 - 10% ics)

96 beV/hour

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2.3 Descriptions of Freeze-up at Northstar. ‘

October. Freeze-up occurs first in the calm, shallow water of the protected bays and lagoons, such
as Prudhoe Bay and Simpson Lagoon south of Long and Stump Islands (see Figure 1). The average

date of freeze-up for the Northstar location is October 6, with a range from the third week in

September to the fourth week in October. The young ice cover spreads rapidly offshore into deeper
water. Most of the lagoons become entirely ice covered within one week after freeze-up begins.

This young, first-year ice is only 6 to 8 inches thick and very susceptible to movement and
deformation by storm winds in October. On October 19-20, 1982, ‘for instance, the 8-inch thick ice
that was present moved more than 10 nautical miles past Seal Island, driven by a 30 to 40 knot
westerly storm However, at the same time the ice in Simpson Lagoon and around West Dock moved
very little (on the order of 50 to 75 feet). Such storms may produce ice ride-up and pile-up along the
gently sloping beaches of the barrier islands and Create ice rubble around man-made gravel islands
and offshore structures, such as the Northstar production island.
November. Ice movement will be very small (1 to 2 feet) to nonexistent in Simpson Lagoon, after
the ice becomes 1 s feet thick, typically in mid-November. However, there is a small, but finite, risk
of large ice movernents (100 feet or more) in the corridor between the Northstar production island
and Stump Island or West Dock during the late freeze-up season (from mid-November to late
November) when the ice thickness is 1.5 to 2.0 feet. Based on six freeze-up studies from 1980 to ,
1985, five years of satellite imagery collected during freeze-up (1987 to 1991), and personal
observations by K. Vaudrey in 1995, there was only one year (out of 12 years) in which there was
an ice movement greater than 100 feet during mid-to-late November. This occurred in 1983 when
20-inch thick ice moved 100 to 200 feet, creating a 10 to 12 foot high pile-up on Stump Island.
Itis clear that any storm wind that might create a broken ice condition in November would have to «
be very strong indeed. In addition, such @ storm would have to be a southwesterly wind in order to -
produce alarge-scale ice movement at the production island. This combination must be considered
an unlikely possibility. - . ,

“13. ||


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1.7 Limitations of Study ,

The study has certain limitations as noted below:

4

1. In the terms of reference for the study the following subjects were explicitly excluded:

* — sourcing of manpower requirements

¢ — disposal (water, recovered oil, debris)

* command infrastructure’ ~ ;

¢ wildlife response _ Co ‘
* — source control _

N

The subject of spill prevention is not addressed. This issue requires separate analysis.

3. The study focus is on the cleanup of spills very close to source. Less attention is paid to the
response phase of “chasing slicks” that have escaped near-source countermeasures. Predicted
recovery efficiencies in this report refer only to the recovery of oil on the water and not to the”

“ subsequent collection of oil that has somehow reached and stranded on shorelines.

>

The study is not a contingency plan for responding to large spills in the area, nor is it a
countermeasures manual. The oil spill cleanup measures described are not necessarily the ones
that will be adopted by industry i in fighting spills i in the area. The study simply attempts to
evaluate spill cleanup capabilities i in broken ice in the area. ,

5. The hypothetical oil spill scenarios developed in the study were designed for illustrative and

- evaluation purposes only. They should not be considered to be probable events. The

‘hypothetical spills should also not be used to predict the general behavior of spills in the area.
There are infinite possibilities; the selected scenarios are but six. a

6. There are a number of assumptions made in the scenarios to simplify the analysis. Examples
include: having all spills evaporate the same amount regardless of spill circumstance; keeping”


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5. Report Addendum Lo.
Subsequent to the preparation of the draft teport of this ‘study’ it was decided to re-analyze the
situation using more realistic conditions instead of the unvarying winds and ice concentrations that
were used originally. The spring break-up and fall freeze-up situations were examined separately by
two different study teams. The spring break-up situation at Pt. McIntyre was reanalyzed by the
orignal study team and is reported here as an addendum Coon

The first step in the re-analysis was to prepare a sequence of ‘weather and ice events that would typify
a 15-day blowout spill during the break-up period. This included two days of relatively stationary
ice, followed by increasing ice movements and decreasing ice concentrations, and finally an increase

~in winds leading to a near-open water situation. Next, the blowout deposition modeling was redone
* to account for the varying ice movements and concentrations. Finally, the countermeasures options

were re-examined for their potential effectiveness. w . -

For the first two days of the scenario, the ice is relatively stationary, leading to pooling of oil close
downwind of the blowout. In this situation, in situ burning of oil on the ice would be the preferred
countermeasure and would likely be very effective. For the next 10 days of the scenario, in situ

burning could be accomplished, using fire-resistant boom to concentrate oil amongst oil and also by

igniting oil that accumulates in melt pools. On the last two days of the scenario, the response tactics
would include a combination of containment and recovery from amongst the Hightie ice concentrations,
and in situ burning to deal with oil that lands on the ice.

The table below summarizes the estimated effectiveness for each of the 15 days of the scenario. The

_ highest effectiveness values are for Days 1 and 2 when the oil pools in a thick layer on the relatively

stationary ice and can be removed through in situ burning. The lowest value is for Day 12 where the
moving broken ice reduces the effectiveness of cleanup operations. The average effectiveness over

» the 15-day period is 38% of the total 15,000 barrel/day blowout flow, and 52% of the oil that lands

on the ice and/or water surface.

Executive Summary - Page6


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6.8 Potential Benefits of Well Ignition

One option available to reduce or prevent oil entenng the water is to intentionally ignite the well and
consume as much as possible of the oil spray in the ensuing gas fire. The decision to ignite a well
blowout is not one that should be taken lightly or made quickly. Checklists of questions and
guidelines to assist with the decision are available (SL Ross and Energetex 1986). Based on
equations in that report used to estimate the oil droplet combustion efficiency in such situations, 99%
of the volume of oil droplets from the hypothetical blowout at Northstar would be consumed and
75% of the volume of oil droplets from the Pt. McIntyre blowout would be bummed The main -
difference between the two efficiencies is the greater flow-rate of gas with the Northstar well, 33x
10° standard cubic feet (scf) of natural gas per day as opposed to 9 x 10° scf/day.

Based on measurements of the “ot produced by burning oil and gas blowouts during the Gulf War,
about 2 to 3% of the mass of oil burned in the blowout fire would by emitted as particulate matter
(Laursen et al. 1992). This is much less than the expected soot yield of large in situ oil fires, which
is on the order of 15% by mass (Fraser et al. 1997).

6.9 Potential Benefits of Deflecting the Blowout Plume

It has been suggested that perhaps the plume of gas and oil droplets emanating from the wellhead
could be mechanically deflected horizontally to reduce the initial rise height of the oil spray. This

, could cause the droplets to fall to the surface sooner and allow removal operations to take place

closer to the source. Considering the momentum of the gas jets (for the Northstar blowout the gas

- is exiting at sonic velocity - 1160 mph and for the Pt. McIntyre scenario the gas is exiting at 810

mph) the positioning of a deflector in the jet would be a considerable engineering challenge. As well,
the deflection of the gas jet towards horizontal would change the dispersion of the gas and quite -
likely considerably extend the ground-level hazard zone associated with explosive concentrations
of gas. The assessment of the feasibility of this concept is beyond the scope of this study.

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concentration; that i is, due to interruptions related to the broken ice the containment operation is
effective for 10% of the time. ,

The total oil, emulsion, and free water that could be recovered per unit time period are then estimated
based on the above figures. The table below shows the estimated fluid volumes per day, which are

» calculated by combining the hourly rates, the 70% encounter efficiency, and the 24 hours of daylight

available at this time of year.

TABLE 6-14
Estimate of Recovered Fluids per 24-hr Time Period for Scenario 4 :

_Item - Calculation Volume
total fluids per 24 hours 780 bbl x 24 hours x 70% = "| 13,104 bbl
total free water 624 bbl/hr x 24 hours x 70% ' | 10,483 bbl
volume that can be decanted © | total free water x 80% 8387 bbl

| total fluids stored per 24 hours _| total fluids less decant . : 4717 bbl
oil "1-70 bbl/hr x 24 hours x 70% 1176 bbl
emulsified water 86 bbi/hr x 24 hours x 70% 1442 bbl
free water ‘| total free water x 20% 2096 bbl

. The above calculations were for one system. As there is adequate equipment and marine support to

provide for two systems, the above estimates per system can be multiplied by two, resulting in the
following estimates of oil and fluid recovery per 24-hours period.

Estimate of Fluids Recovered by Two Systems per 24-hr Period

total oil recovered , ; 2352 bbl
| total fluid recovered 9434 bbl
-104- - .


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6. Detailed Scenarios

6.1 Introduction

This chapter uses the knowledge and information presented in the previous chapters to describe in
succinct terms the likely behavior and cleanup potential of the six selected blowout scenarios. s. The
general parameters for the scenarios are shown in Table 6-1.

TABLE 6-1
General Parameters for Blowout Scenarios at Northstar ‘and Pt. Meintyre Sites
Scenano Description Blowout Rate ' | Gas-to-Oil Ratio, | Wind Speed, Wind
Number . — and Duration SCF/barrel knots Direction
. (from)
1 North Star, 30% | 15,000 BOPD 2200 13.5 ‘'E
. Ice, Freeze-Up for 15 days an ‘ *
. minus 20% +]. ws
evaporation ’ ‘ |
2 North Star, 50% | same as above 2200 19 WSW
Ice, Freeze-Up - 5
3 North Star, 70% | same as above ~ 2200 225 sw
Ice, Freeze-Up ae .
4 Pt. McIntyre, 30% | 12,000BOPD } 750 u w.
‘. . Ice, Breakup for 15 days . ]
| minus 20% for .
evaporation
5 Pt. McIntyre, 50% | sameasabove | © 750 9 SE j
Ice, Breakup : '
6 Pt. Mclatyre, 70% | same as above 750 - 175 > E
| Ice, Breakup . |

As explained in detail in Chapter 2 it is inconceivable that any of the above scenarios will truly
involve a uniform distribution of ice floes at an unvarying concentration (either 30, 50 or 70%).
Nonetheless, this simplifying assumption will be used to illustrate the Potential effectiveness over ,


a ooo

'

_ Thick oll Emulsific cation | . "Slick - : Thick slick

remaining on (% water vol.) viscosity thickness
water (% of total aan (cP @ 30 °F) (mm)
_|___released) ‘ ,

3.6 Day 12

On Day 12 the wind increases to 15 knots from the east and the current is 0.45 knots to the west. As
such, the thick slick is 180 feet wide and 08 mm thick at the starting point of the surface slick
modeling.

Table H-5 summarizes the predicted characteristics of the thick slick on Day 12 over a time period
of 24 hours. The oil that forms the thick slick on the water has a viscosity of 120 cP and a Pour Point
of 10 °F at the point where the on-water modeling is started. After 12 hours, the oil has evaporated
to a point (28%) where it’s Pour Point (30°F) exceeds the ambient water temperature and the thick
portions of the slick cease to spread on water. At this point it is 290 feet wide.

The presence of ice dampens ‘the wave action that would normally exist with a 15 knot wind and

. reduces natural dispersion of the oil slick compared to open water conditions. The slick is predicted

to begin to form a water-in-oil emulsion 15 hours after the oil had been deposited on the water
surface. If emulsification rates are the same in loose pack ice as in open water under identical winds,
the slick would be fully emulsified (5% water content by volume) after 24 hours on the water.

The thick oil slick continues to evaporate slowly throughout the 24 hour modeling period. It loses
a total of 30% of its volume to evaporation after 24 hours. The viscosity of the unemulsified oil
increases to 180 cP after 12 hours and reaches 7900 cP at 24 (due to emulsification). The Pour Point
of the thick oil after 24 hours has increased to 36 °F.

-13-


occurs, the 8-9 tenths ice concentration immediately begins to pull away from West Dock and moves
quickly to the southeast, east, or northeast, leaving an open water lead along the east side of the
Dock. The open water condition typically will extend offshore of the Dock for several miles, where

the ice concentration abruptly changes from no-ice to 5 tenths or greater i ice as the broken ice floes ‘

(50 to 100s of feet across) start stacking up on each other as they pack up against the eastern side of
Prudhoe Bay or against the barrier islands (e.g., Reindeer or Cross).

For either location, a broken ice condition, meaning a situation in which floes of ice are distributed ~

over the surface in concentrations ranging from 30 % to 70%, is more likely to occur during mid-to-
late summer (August or September) when an ice invasion may occur. One or more such invasions
of 3 tenths ors tenths ice concentration have a 56% or 35% chance of occurrence, respectively, at
Northstar. Summer ice invasions are less likely, but certainly do occur, in and around West Dock.

2.6 Other Ice Features Affecting Broken Ice Spill Response and Logistics

Boundary Conditions. During a storm or strong wind condition one can imagine that “broken ice”

in concentrations of 30 to 70% can flow past either site for as long as the wind condition lasts.
Typically, however, ice movement that occurs at Northstar during freeze-up or at Pt. McIntyre during
break-up cannot go on indefinitely due to constraining boundary conditions. Any i ice motion to the

. east, south, or west from the Northstar area is significantly restricted by the barrier island chain or

West Dock. Larger movements to the east-southeast can occur, but are eventually constrained by the
shallow water of Prudhoe Bay. Similarly, ice motion to the north and northeast is constrained by
shoals, However, ice motion to the northwest (from a southeasterly or easterly wind) may continue
almost indefinitely (as long as the duration of the storm wind) due to the absence of natural

: obstructions for a distance of some 30-40 miles.

1

Given that the westside of West Dock at break-up i likely to bein open wate, the only ice ,

movement at break-up will occur ‘on the east side of the Dock. Any ice motion occurring at West

Dock during break-up will be constrained by the barrier islands to the northeast and the shallows of .-

Prudhoe Bay to the southeast. Even ice movement to the east in Stefansson Sound may be impeded
by the Endicott Development and the shallows offshore of the Sag. River delta. Again, the only

-18-


Consideration could be given to intentionally igniting the well such that the oil is consumed in the ~

burning plume of gas (The feasibility or advisability of this option was not examined, only the
possible effectiveness.) Well ignition would have the potential to significantly reduce the volume

of oil entering the marine environment, consuming between 74% and 99% of the assumed oil -

volumes.

* 2137+


ae Oy apenas nee eens ee saat halls nde eetanmene Ceara stdbelenpentnioates

© the lessee complies with all laws and regulations, ;
* the lessee participates in a five year R&D program, and
¢ - drilling personnel are trained in well control techniques.

“In addition, it was decided, if well control were not possible, that the oil well could be ignited.

However, lessees were not allowed to drill exploration wells outside the barrier islands prior to and

during the fall bowhead-whale migration, but were allowed to drill on and inside the barrier islands

if there were a whale monitoring program in place.

_ The agencies issuing the Tier 2 decision said that the decision was based on the following factors:

+ — Lowprobability of a large spill ,
*  Industry’s extensive contingency planning efforts
“e — Availability of spill cleanup equipment (barges, tugs, helicopters, storage tanks, front-end
loaders, camp facilities, and smal boats) ;
¢ — Short periods of broken ice
+ Effectiveness of recovery and burning at the wellhead and of in situ buming

1.4 Current Regulatory Situation and Related Questions : 4

In 1990, the State of Alaska reiterated the Tier 2 decision and issued a seasonal drilling policy for
exploration drilling in the Beaufort Sea. That policy is still in effect, but does not address production ~
Subsequent to the Tier 2 work, the state of Alaska implemented detailed spill response regulations.
These regulations require that operators plan to beableto mechanically contain and recovery, within ~
72 hours, a “response planning standard” (RPS) volume of oil. For an exploration or production
facility, the RPS from an uncontrolled blowout is a minimum of 5,500 barrels of oil per day (if well
data indicates a higher production rate, the RPS is adjusted accordingly). Burning, which was
recognized as an effective tool in the Tier 2 work, cannot presently be considered in addressing the

” state RPS.


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4

7. Conclusions os

Six hypothetical oil well blowout scenarios were examined to determine the potential effectiveness
of spill countermeasures in broken ice situations The evaluation first analyzed the existing

“countermeasures capability, and then looked at the potential for improvements to effectiveness using

alternative techniques such as dispersant use and zn situ burning.

The spills that result from the blowouts will result ina relatively narrow slick of thick oil surrounded
by a much wider, relatively thin slick. Near the spill source, the thick portion of the slick will have
a width of 100 to 240 feet, a thickness of 0.5 to 2.1 mm, and will contain approximately 40% of the
total blowout flow. The thin portion of the slick will have a slick thickness of only 0.035 mm, and
will contain an estimated 30% of the total blowout volume. (The remaining 30% is predicted to
either evaporate from airborne droplets or remain suspended in the air due to their very small size.)

. The analysis of existing countermeasures predicts a range of spill recovery effectiveness values

depending on the amount of ice coverage and season (break-up vs. freeze-up). Expressed as a
percentage of the total blowout volume, estimated effectiveness varies from about 1% for the 7/10ths
ice cover at freeze-up to as high as 18% for the 3/1 0ths ice cover during break-up.

+ As discussed in detail at the conclusion of the previous chapter these seemingly low percentages are

caused by a combination of factors inherent to the scenarios:

* Only about 40% of the total blowout volume lands on the ice/water surface in a slick that is
thick enough to allow effective use of containment and recovery equipment.

+ Of the oil that lands on the ice/water surface, a fixed percentage (ie., the assumed ice
concentration) lands on ice floes and cannot be efficiently recovered mechanically. :

¢ In the 50% and 70% ice scenarios, a containment and recovery operation would be severely
limited by the need to regularly reposition containment booms and/or clear ice from the

BB


csnaamslamiees

oe coher beoermants

1

Category Transport On-site Support Mobilization Time
: _ (hours)
Air Cushion ‘ _
Vehicles - + personnel rotation - skimmer platform with | July or Oct
= recovered oil lighter deck tanks (transfer to
“A166 @0pass) |“ SIO manveres) 2nd LACVS0 or ne
- LACV-30 (30 tons) ‘
_ | Note est. hghter * AP.1-88 from
capacity between . Anchorage in 5 days
"| Northstar and West ‘ .
Dock - 1,800 to 2,600
bbV/day with (2) .
machines

Options to Improve Logistics Capabilities

Future logistics options involve asking a number of what if questions. For example, what
_if there were dedicated heavy-lift helicopters on the Slope? what if there were more capable
icebreaking barges and tugs etc.?

In reducing what could be anendless list of, possibilities, it helps initially to identify possible
solutions to deal with the particular deficiencies in the existing logistics resources currently
available in the Prudhoe Bay area. The significance of these deficiencies must be weighted
against the needs of specific scenarios. For example, the lack of heavy lift helicopters may
not be significant if it turns out that there is no great need to sling heavy loads offshore.

Based on the equipment overview presented above, a number of potential logistics
shortcomings stand out during periods of broken ice in July, October and early November.

@ Shortage of helicopters with any significant load carrying capacity or IFR
capability (particularly in July when almost all commercial machines are fully
committed). Offshore scenarios in October or November may need twin engine
IFR to establish an acceptable level of safety and reliability. The only short-
notice source of medium/heavy lift equipment is the SAR unit at Point Barrow.

" Given the difficulty in operating small support boats under freezing conditions
in October, there are only two possible avenues to move and support large
number of personnel offshore: air cushion vehicles and helicopters.

Possible solution: (1) rely on military support for a long term response beyond
72 hours; (2) contract for a medium/heavy lift helicopter(s) (e.g., Puma, Bell 212
or 214) to be available within a specified number of hours out of Anchorage; (3)
plan on using air cushion vehicles as fast offshore work "boats" at freeze-up.


+

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70% ice concentration scenario (amounting to between 7 and 22 hours out of 72-hour Tesponse
period). . ; ;

« Wind directions at freeze-up were chosen as the most likely direction, based on wind direction

occurrence presented in Table B-2. Directions at break-up are dictated by the somewhat artificial
situation created by the West Dock causeway. For example, winds from the ENE in July would lead
to the oil plume falling in open water on the west side of the causeway. Consequently, the wind
directions used in Table 2 were deliberately chosen as westerlies to carry the oil into the broken ice -

remaining on the east side of the causeway. Such winds are common in July; strong winds needed - —

to initiate break-up in Prudhoe Bay are most often from the west.

. . . }


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fj 10 TYPE Crude - ‘
. WEATHERING (Volume %)
if : Q 345 416
20 DENSITY (g/mL) >
vc 0844 0 894 0898
18°C * ‘ , 0834 ' 0883 0888
fi ‘ 30°C ‘ 0823 ‘0871 - 0879
30 VISCOSITY 4
‘ 31 DYNAMIC VISCOSITY (mPa s) >
fj 15°C 80 77.41 .946
30°C , , §2 , 168 307
32 KINEMATIC VISCOSITY (mm/sec) _
[i ' 18°C . - 96 _ 873 1065
30°C _ 63 193 349
40 INTERFACIAL TENSIONS @ 20°C (mN/m)
41 AIR-OIL: 252 293 32.9
{i 42 OIL-SEAWATER “171 ee 23.4 249
50 POUR POINT (°C) <-9 () 12
6 0 FLASH POINT (°C) <4 85 92
[i 7.0 EMULSION FORMATION TENDENCY AND STABILITY a
7.1 TENDENCY ;
15°C 012 > ‘090. , 091
[i . 72 STABILITY. * . so , .
. 15°C 000 030 030
80 DISTILLATION DATA (°C) :
VOLUME LIQUID « VAPOR
[i % EVAPORATED TEMPERATURE _ TEMPERATURE
IBP .« 87.1°C 43.3°C
5 - 1216 728 0. -
10 - . 1405 822
16 . 1957 103 2
20 213 1 109 8
30 : } _ | 287.9 “1302
40 - 3046 144.2
50 3509 2015
90 WEATHERING
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‘ . (6534/Tk)
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in is natural log
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large volumes of recovered liquids to a shore tank farm. The only practical
alternative to this approach i is to rely on hovercraft as lighters. .

Lack of any means of accessing an offshore ‘spill location with conventional
marine equipment (existing) from early to mid-November. As discussed above,
even icebreaking barges reach their realistic operating limit in about 1.2 ft of

~ level ice in late October or early November. By the third week in November

there is a very low probability of experiencing broken ice in the vicinity of Seal

Island (Northstar). In early December, ice road construction can usually begin” ~

and offshore response can start to use the ice surface as a reliable working”
platform. This leaves ten to 20 days in late October and November when the
available marine equipment may no longer able to access the offshore area from
West Dock. Air cushion vehicles could provide the only possible form of surface

. access to the spill site at this time.

Possible solution(s): (1) contract for a LACV-30 hovercraft through the critical

‘. period from early October to early December; (2) utilize a more capable ice

Contacts

breaking barge such as the Arctic Challenger to expand the marine operating
season (this would require substantially more powerful tugs than those currently
available at Prudhoe Bay)

Names with telephone numbers indicate individuals contacted during the course of this

project.

Aircraft and Helicopters

ERA Helicopters, Anchorage

* Lynden Inc.
Northern Air Cargo

Air Logistics, Fairbanks

Evergreen Helicopters, Anchorage ~

Bob Law |

* (907) 248-4422
Dave Haugen —— (907) 245-1544
see ACS agreements

owner Alyeska BO-105 (helitorch)
mise. light machines

“ North Slope Borough SAR Unit, -emergency call out with Bell 214ST
Barrow an
| Columbia Helicopters, Oregon. DonPatterson : (503) 678-1222
ARCO Flight Operations (Kuparuk) Denis Parrish _ (907) 659-7626
- Marine Equipment _ ; a . '
“16, :


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6.4 Scenario 3. Northstar in 7/10ths Ice Cover During Freeze-up

6.4.1 Blowout and Spill Behavior (Scenario 3. Northstar, 7/10ths Ice, Freeze-up)

An uncontrolled blowout occurs in late October at the Northstar artificial island releasing 15,000
barrels of oil per day (BOPD) and 33 x 10° standard cubic feet (scf) of natural gas per day (a Gas-to-
Oil Ratio [GOR] of 2200 scffobl). Over the first 72 hours of the incident, the air temperature ranges

« from a nighttime low of 3 °F to a daytime high of 13 °F. The wind speed averages 22.5 knots from

the SW. The surrounding water is covered by 7/10ths new ice floes. The ice is 1 to 1.2 feet thick and
covered by 5 to 6 inches of snow. The floes are hundreds to thousands of feet in size. The ice is
drifting at the same speed as the water (both wind-driven at 3% of the wind speed) at 0.7 knots to

_the NE. These conditions do not ‘change over the time period of the scenario; as well; the ice

concentrations do not change as it drifts away from the ‘spill site (L.e., no convergence or divergence
of the pack), except for the presence of an ice-free wake in the lee of the island. Small waves (only

* afew inches in height due to the restricted fetch) will exist in this wake area. The water in the wake

area will be covered with newly growing ice crystals and slush. The pack ice drifts back in to fill the
wake area within 1000 feet downwind of the island. , ot

As the oil and gas exits the 6.3-inch inside diameter tubing at the wellhead the high velocity of the ~
gas atomizes the liquid oil. The gas and oil droplets pass through the derrick or machinery spaces
and the droplets agglomerate. The kinetic energy of the gas jet from the wellhead carries the droplets
to a height of 75 feet above the release point. From this point the oil droplets begin to fall as they

are carried downwind by the wind.

In this scenario, the slick is 180 feet wide and 0.6 mm thick at the starting point of the surface slick
modeling. This is at a distance of some 920 feet downwind of the blowout. At this point, the oil slick

is assumed to be evaporated to 20% loss. . ‘ '


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i

For the break-up scenarios, burning on water using fire containment boom provides an effectiveness
that is approximately equal to that afforded by containment and recovery. Because of the above-
freezing temperatures, oil that lands on ice will tend to be herded into concentrations that may allow
burning using only the natural containment provided by the ice. In this situation, burning the oil that
lands on floes and concentrates in melt pools offers an oi! removal capability that would supplement

either the on-water burning operation or containment and recovery.

Well Ignition. The possibility and potential effectiveness of intentionally igniting the blowing well
was briefly examined. Based on previous studies on this subject, it is estimated that up to 74% for
the Pt. Mcintyre scenarios (break-up) and up to 99% of the Northstar scenarios (freeze-up) would
be consumed in such a fire. The main differences between the two wells is the much higher gas flow
rate at Northstar. . .


Over time, the oil remaining on water will be incorporated into the surface layer of the growing ice
and the oil remaining on floes will be covered by snow. A portion of the oiled ice will likely be
formed into ridges and rubble fields during November and December as the thin ice deforms under
pressures from wind and heavier pack ice to the north. Any oiled ice which escapes being
incorporated into the fast ice will gradually drift west, and in many years could end up in the

Chukchi Sea by spring. During the spring (late May to early June) any oil still remaining near the

surface of level ice will rise to lie in melt pools; the oil incorporated into ridges and rubble fields will
be released more slowly. Ultimately, rotting ice will release any oil still remaining at breakup in the
form of thin sheens trailing the drifting floes. ,

“TABLE 6-7 __
Summary of Slick Characteristics from a Blowout During Freeze-up
at Northstar in 5/10ths Ice Cover over 72 Hours

Thick oil left on | Emulsification Thick slick | Thick slick
(h) water (% of total | (% water vol.) thickness width
: teleased) (mm) : (ft)
Initial 21% 0 120 0.7 180
3 20 . 0: 155 05 230
| 6 20 az) 170 05 249
| 12 “1g 0 190 04 250
24 - 18 0 210 0.4 250
48 18 0 240 04 250
72 17 250 0.4

i—)
gR
iJ

6.3.2 Existing Mechanical Methods (Scenario 2. Northstar, 5/10ths Ice, Freeze-up)

As in the first scenario, the ice conditions at West Dock as well as those at the spill site will limit
the marine equipment that can be used for the response. In this scenario, midway through the freeze- -
_up period with 5/10ths ice concentration, up to four tugs and two ice-strengthened barges could be *

1 \85=


moon

_ Appendix H

ot Addendum to Report:
Realistic Scenario for the Spring Break-up Period


anmnonnnoon.

ac

. Tier 2?

deal with spills in such ice.

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~ This then begs the question as to what the current capability might be in broken ice with mechanical

systems only. In the Tier 2 exercise it was made clear that there were severe technological and
logistical limitations to mechanically recover oil spilled in broken ice. Has the situation changed
substantially over the past 15 years? - :

An equally important question is: What is the current cleanup capability with respect to other
countermeasures in broken ice , such as in situ burning, and have these improved substantially since .

The final question worth asking is: Do we have a better understanding today of the meaning ‘and
actuality of “broken ice”in the Alaskan Southern Beaufort Sea, and, if so, should not regulations and
contingency plans both be modified to take this into account?

The expression “broken ice” that is used in regulations and in industry plans really has no
scientifically-acceptable, quantitative definition. The Tier 2 exercise was concerned with ice break-
up during springtime only, so the broken-ice definition used at that time was expressed in spring
break-up terms as any ice condition from decaying ice at 8 okta (100 percent) ice coverage at the
beginning of spring breakup to widely scattered ice at 1 okta (12.5 percent) coverage at the end of

+ breakup (SL Ross 1983). For the Tier 2 exercise it was assumed that this broken ice period lasted

about 12 weeks. As mentioned above, for the Tier 2 regulators, the condition of concern in this
“broken ice” period was the 3 to 5 okta (37.5 to 62.5 percent) ice coverage period, which is known

to last for a much shorter period, perhaps a few days only. It is clear that this study needs to address

the realities of “broken ice” in the Beaufort Sea, in both physical and temporal terms, and in both
spring break-up and fall freeze-up periods. This must be done before attempting to analyze how to

1.5 Terms of Reference of Study

* The terms of reference for the study were developed ty NSSRPT, The objective of the project ‘was

to consider six well-defined oil well blowout scenarios and determine i in quantitative terms:


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source could be close (0.5 mm at 3 hours is the average thickness across the width of the thick slick)

‘to the minimum ignitable for weathered crude (ca. 2mm) there would be a danger of the fire burning

back to the spill source. st
The estimated daily removal rate for one ISB unit is s thus: .
ISB unit estimated daily removal rate= (61 bbI/hr x 10.5 ht) x05

= 320 bbl

_If all the vessels capable of operating in this scenario were used for ISB operations, a total of two
ISB units could be deployed, removing an estimated 640 bb! of oil from the water surface per day.

If more vessels were available, four ISB units could be operated to remove 1280 bbl per 10.5-hour
day. This is slightly higher than the case of containment and recovery because it is envisioned that
burning, then maneuvering the ISB unit back into the thick oil will take less time than for the
conventional boom and skimmer system.

A similar overall reduction in in situ buming effectiveness to that determined above for mechanical
containment and recovery, can be estimated using the same response time and environmental factors
as for mechanical containment and recovery. For ISB operations the additional factor of the
percentage of time that winds are less than 20 knots (80%) i is also taken into account. The estimate

"of ISB effectiveness for the 15-day period, expressed as a percentage of the total blowout flow is:

‘

640 bbl/day x 0.83 x 0.77 x 0.80 + 15,000 bbl/day
“+ 2.2% .

Oil volume removed by ISB


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co

mIonmoarnmonmMmtOeOe oO Doo oO oOo

Crowley, Anchorage Craig Tomga’ —-(907) 257-2822
Crowley, Seattle . Richard Roth? (206) 340-2904
, Chris Sawin? + (206) 340-2904
; 2 | General Manager - + Alaskan Operations
3 Manager Pacific Operations
Arctic Operations Manager
Lynden Inc. (Beaufort Marine J.V.) David Haugen vee (907) 245-1744
Northern Transportation Company Derek Briggs — : (403) 874-5100
Hay River, NWT Canada . .
Air Cushion Vehicles ,
Alaska Hovercraft, Anchorage David Haugen (907) 245-1931 * |
~ References for Appendix F

Dickins, DF. 1989. Arctic Transportation. in . i
Applications Ed. J.R. Amyot, Elsevier Science Publishing, Amsterdam.

Dickins, D.F. 1984. The Jeff (A) Arctic Test Program. In: Proceedings, 1984
International Conference on Air Cushion Technology, Vancouver (includes results
from a spring demonstration over broken ice in the Prudhoe Bay area).

Dickins, D.F. 1979. ‘Review of State of the Art Air Cushion Vehicle Capabilities in
Support of Oil Spill Clean-up Operations in the Alaskan Beaufort Sea Nearshore.
report by DF Dickins Engineering for the Lease Sale Planning and Research
Committee, Alaska Oil and Gas Association. roe

Hatfield, P.H. and D. F. Dickins. 1981. Preliminary Concept Feasibility Study- Barge/Tug -
Operations in Broken Ice Behind an Air Cushion Vehicle. for SOHIO
Construction Co., San Francisco.

; Industry Task Group (Amoco, Exxon, Shell, Sohio). August 1 1983. Oil Spill Response In
the Arctic - Field Demonstrations in Broken Ice. prepared by A. Allen and J.
Lukin, Anchorage.

SL Ross Environmental Research. 1983. Evaluation of Industry's Oil Spill

Countermeasures Capability in Broken Ice Conditions in the Alaskan Beaufort
Sea. for Alaska Department of Environmental Conservation.


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Predicted Effectiveness of Existing Mechanical Systems in Recovering 15-Day Discharge «

This final step in this section is to use the above calculations to assess the effectiveness of existing
systems to deal with the total volume of oil discharged over the 15-day blowout period. The
assessment includes the effects of response-time delays, and the environmental derating factors of
-visibility, VFR flying conditions, and wave heights. As for all the freeze-up scenarios, the response :
time is estmated to be 60 hours, so for the 15-day period the effect is to reduce effectiveness by 17%
((15 - 2.5) + 15 = 0.83). Also for all freeze-up scenarios, the combination of the three environmental
factors are such that, on average, mechanical containment and recovery will be effective 77% of the
~time. The following i is the estimate of effectiveness for the 15-day Period, expressed as a percentage
of the total blowout flow: ~ > cyt

Recovered oil volume = 138 bbl/day x 0.83 x 0. 77+ 15,000 beeay
° = | 06%

6.4.3 Additional Recovery Systems (Scenario 3. Northstar, 7/10ths Ice, Freeze-up)

As in the previous two freeze-up scenarios, the entire width of the thick slick can be encountered by |
~ two containment and recovery systems. Any additional systems would be limited to chasing thin
sheens, or oil lost from the first two systems due to ice-related inefficiencies, and would add little
to the overall effectiveness of ‘the response.

6.4.4 Dispersants and Burning (Scenario 3. Northstar, 7/10ths Ice, Freeze-up)

: Dispersant use does not make sense in this scenario, mostly because there is not enough mixing
energy available to promote dispersion of the treated oil into the water. _ .

Considering in situ burning, this scenario differs from the previous two in that a wake exists in the
lee of the island, into which much of the oil spray is falling. At the end of the wake, just before the
ice floes move back together, the thick slick is predicted to be 180 feet wide, 0.6 mm thick and |

96-

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Figure H-3

Schematic view of the oiled i ice on Day | 1 after 24 hrs deposition.

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» 0 .1000 . 2000 3000 4000 5000

: se r Distance downwind (ft)
-T-

Cumulative percentage of total

Figure H-4

Cumulative Percentage on Ice Downwind
-Percent of total deposited on ice .

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encounter rate = (300 feet x 0.33 gap ratio) x 2.1 mm x 0.3 knots x(1-50% ice)
= 112 bbl/four

This encounter rate is less than the derated recovery rate of several of the offshore skimmers that
‘could be used, so the encounter rate is the limiting factor and is used in the calculations of recovery
effectiveness. Following the same calculation procedure and guidelines for oil recovery efficiency,
the total fluid recovery rate can be estimated as shown below:

.  TABLEGIS
‘ Fluid Recovery Rates for Scenario 5
Fluid ~ Calculation —- Recovery rate

oil lesser of system encounter rate and derated recovery rate 112 bb/hr

:' total water oil content in recovered fluid (recovery efficiency) = 20% . 448 bbyhr |
. J emulsified water | emulsified water content in recovered fluid = 40% ‘ 75S bbl/hr
*| free water total water less emulsified water ‘ . 373 bbl/hr
| total fluids *| oil + emulsified water + free water . 560 bbl/nr

Compared with the previous break-up scenario, the main difference here is the greater ice
~ concentration and its effect on containment efficiency. For the 50% ice condition, the containment
efficiency is assumed to be 40%; that is, the containment operation is effective for 40% of the time
accounting for interruptions related to Clearing i ice from the containment and repositioning the
system when avoiding large floes. Given the 24-hours of daylight at this time of year, the total fluid
volumes per day are calculated in the following table, combining the hourly rates and the 40%

~ encounter efficiency. vos '-

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has been that spills more viscous than 2000 ep to 10,000 ep are not dispersible. Recent research,
using a relatively new dispersant product, Corexit 9500, indicates that the value could be up to ‘
20,000 cp (see Lewis et al. 19982 or Lewis et al. 1998b). More research i is needed in this area.
Dispersant will work only if the dispersant chemical, sprayed by aircraft or vessel, is thoroughly
mixed into the oil. This is not a problem for thick slicks of oil, but is for very thin slicks. This is
because the dispersant droplets in the spray, having to be fairly large to avoid being carried away by
the wind (the recommended size is in the 0.5 mm range), cannot make good contact with slicks much
thinner than the droplet diameter. The usual problem is that the dispersant droplets crash through the
thin slicks and are quickly lost to the water before having a chance to blend with the oil.

The most controversial problem with dispersant use, aside from any issue related to effectiveness,
is that dispersed oil can be toxic to animals in the water under the spill. When the small oil droplets
enter the water they dilute quickly to concentrations in the range of 1 to 10 parts-per-million

- immediately under the treated slick. After spraying stops, concentrations decline rapidly towards

background levels The areas of elevated oil concentration in the water are temporary and restricted

“to the near surface waters. This oil will not be lethal to animals (except perhaps to extremely

sensitive species directly under the treated slicks), but concentrations are theoretically high enough «
to cause tainting. Research has shown that if such contamination or tainting were to occur, the fish

- would purge the contamination within days or weeks. In the recent spill from the tanker, Sea
‘Empress, off the coast of Wales, where large amounts of dispersant were used to treat the spill, no
tainting was observed i in fish caught in the vicinity of dispersant operations.

With specific regard to the use of dispersants on the blowout spills described in this study, the
prospects are not promising (except for one scenario, Scenario 1) for reasons summarized below:

¢ Generally speaking, because the presence of ice tends to dampen surface mixing caused by
wind, there is less opportunity for treated slicks to disperse easily. This is not to say that
effective dispersion is not possible, but that it more difficult all things being equal.

-59-


Ne ee ee ee as meth) Sle denen +3) ee he

falling at different rates and at different locations. This is explained in detail in Scenario 1, but isnot .
repeated in the following scenarios. This extra technical discussion is presented in Italc type to
allow uninterested readers to easily pass over it if desired. Similarly, inthe countermeasures analysis, ~
the first scenario in each of the broken ice regimes (freeze-up and break-up) is discussed in more ° ;

detail than the ones that follow. This is done simply to avoid repetition.

“+ '65-


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Lose |

” . , . 4

> Figure H-1

Distance from Source vs Avg. Thickness.
- , 24-hour release:
40 4 + - _ -- -
-20-
E
3
2 20 \
. \
g \
\
“10 \
0 we ee | ee ee lee LTO EES ep ee pre nw
te) 1000, (2000 + 3000 4000 5000 6000
fa . Distance from Source (ft) .
Figure H-2
Width of olled area downwind
After 12 hours deposition
1200 | we eee ee
e
‘g 1000 3
.@ 800
B 600;
2
So 400
s
= 200
=
0 Wo pnt ee pe epee

0

,1000 2000 3000 4000 ‘5000 6000
Distance downwind (ft)

‘ob

tg.

rr


¢

mm i ees ig neem TR ore DR ores meme a once ne TR wore mee i cere sD ene Sone woe Town es oe wo

2.1 Introduction . ,

« which in turn refreezes in a matter of hours.

HE —_ ES Ge Oe eee SS Lee S sath me stnoees Te aigeaees

, : *

2. Ice and Other Environmental Conditions

'

The ice conditions and other key environmental parameters associated with the six spill scenarios
are documented in this chapter. The scenarios include spills in 30%, 50%, and 70% ice: concentration
ineach of the following broken-ice situations: (1) freeze-up atthe Northstar Development production
island and (2) ice break-up at the Pt. McIntyre Development on the West Dock Causeway.

: . . a
The behavior of ice during the break-up and freeze-up prods needs to be characterized and
delineated for the purposes of: (1) estimating quantitatively the distribution and fate of oil from each
blowout scenario and (2) evaluating the applicability and effectiveness of spill countermeasures.

“Unfortunately, the behavior of ice during these transition periods is a complex phenomenon which

varies greatly from year to year. Ice is constantly converging and diverging in response to wind

’ shifts, and running up against physical boundaries such as shorelines, islands, and the offshore pack. |
Belts and patches of varying concentrations are common during break-up, while during freeze-up

the young ice often breaks into large floes which quickly drift out of the area, leaving open water

To deal with this natural variability in assessing cleanup capability it becomes necessary to make
simplifying assumptions in characterizing ice conditions for each scenario. One helpful assumption
is to keep the ice concentration fixed for a given length of time. It is important to emphasize that
such assumptions are not meant to be realistic; rather they are simply meant to serve our purpose of
“testing” and evaluating the effectiveness of spill countermeasures techniques and systems i in
specific ice concentrations.

The following steps were taken for describing ice and environmental conditions in the study area,

* starting with the situation in real terms and ending with a simplified model of the situation that can

be used for assessing spill countermeasures quantitatively and objectively.


Free a eee re ~ i ae

The model was run for the drop diameters that correspond to the 10, 20, 30...
90 % cumulative volume cutoffs in Figure 1. Early modeling results identified that
the wind speed has no effect on the deposition pattern due to two counteracting
effects: the wind speed affects the rise height of the plume as well as the distance a
drop will travel downwind prior to falling to the ground. A high wind reduces the
rise height by bending the rising plume. Drops will fall to the ground sooner due to
the reduced height but will travel just as far from the source due to the increased
wind speed. The wind speed variable was therefore dropped from the test matrix.
The results presented apply for most wind speeds but not for extreme cases (i.e.,
zero winds or very high winds will result in plume behavior different than that
presented in this report).

_ It should also be noted that the horizontal dispersion relationship adapted from
Turner (1970) is strictly valid only for distances greater than 100 meters from the
source. We have applied Turner's relationships to points closer to the source and
these results should be used with caution.

The gas flow exiting from the rupture controls the plume height and
subsequent fallout characteristics. The plume fallout dimensions are therefore
reported as a function of gas flow rather than oil flow and GOR. Figure 2 has been
provided to permit a quick estimate of the gas flow from an oil flow (in barrels of

. oil per day) and a GOR (in scf/barrel). This figure also shows the maximum gas

flow possible through the two pipe diameters considered (4 and 6.3 inch inner
diameter pipes). Gas flows at the limits shown represent sonic exit velocities.

Gas Flow-OilFlow-GOR_ ~

Ges Flow (mmscfd)

Figure 2 : Gas Flow - Oil Flow- GOR Relationship | -

, Figures 3 and 4 can be used to determine the percentage of the total oil flow
that will fall to the ground or water within a given distance downwind of the source
for the 4 and 6.3 inch pipe diameters, respectively. The oil flow rate and the
duration of the release can be applied to this number to determine the oil deposition
Tate and “average” oil thickness that would exist at the location.


sae SN cose I ose JN ware (IE poses FANE owes (IE noes (EE ovan DEEN cance [EEE ave BE wor |

=1

[enn FE se TR vee BE vere BE ommn  oomwe En

It has been noted that, in the lee of the artificial island, an open water area, or wake, will exist,

stretching up to 1000 feet downwind. It is in this area that 60% of the oil will fall to the surface of

the water. For the purposes of this scenario, it is estimated that 72% of the oil spray lands on water
(60% falls out in the wake and 30% of the other 40% that settles out past the wake lands on water
between floes and forms a very thin - 35 m - slick) and 28% lands on the surface of ice floes past
the wake zone. The spray that lands on ice floes coats the surface and is absorbed by the snow. The
range of oil thicknesses on the floe surface ranges from 0.2 mm near the center-line of the oiled strip
to 0.003 at the edges. This oil will evaporate at a rate negligibly different from the oil that falls on .

” the water, reaching a total evaporative loss of 35% after 72 hours. *

Table 6-10 summarizes the predicted: characteristics of the thick slick over a time period of 72 hours.
The oil that forms the thick slick on the water has a viscosity of 120 cP and a Pour Point of 10 °F
at the point where the on-water modeling is started. For the first 9 hours after its creation, the thick
portion of the slick on water continues to spread laterally as it drifts with the ice, reaching a width
of 240 feet and a thickness of 0.4 mm. After 9 hours, the oil has evaporated to a point (28%) where
it’s Pour Point (30 °F) exceeds the ‘ambient water temperature and the thick portions of the slick

_ cease to spread on water. For the duration of the scenario (72 hours) the slick moves with the oiled

ice floes and does not spread further, although the thick slick may meander somewhat in the pack
ice field due to oceanic eddies or large-scale turbulence. °

The presence of ice inhibits the wave action that would normally exist with a 22.5 knot wind and .
suppresses natural dispersion of the oil slick. The ice also suppresses the formation of a water-in-oil

emulsion.

The thick oil slick continues to evaporate slowly throughout the 72 hour scenario. It loses 32% of
its volume to evaporation after 24 hours; 34% after 48 hours; and, 35% after 72 hours. The viscosity
of the unemulsified ‘oil increases to 220 cP after 24 hours; 250 cP after 48 hours; and, 260 cP at 72
hours. The Pour Point ‘of the oil after 72 hours has increased to 48 °F.


December. Typically by mid-to-late December (when the first-year ice sheet becomes about 2.5 to
3 feet thick), the ice in the vicinity of the Northstar production island becomes relatively stable, and
the region becomes part of the stable landfast ice zone. During this period only small ice movements
are likely to occur. For example, ice motion measured during 1995-96 at a wireline station located
5 miles east of the Northstar pipeline route in 21 feet of water, produced i ice movements on the order
of 10 to 15 feet. Exceptions to httle ice movement do occur, however. For example, a 90 to 100 knot
i southwesterly storm in late February, 1989, removed most of the “landfast” ice north of the barrier
island chain and drove it 20 to 30 nautical miles offshore. ‘ : :

_ January. After January 1 the tisk of ice movement and the magnitude of ice movement is reduced
significantly as the ice sheet becomes thicker and more stable. It should be remembered, however,
that there still is a small chance of a major ice movement event occurring during the winter, as
documented during the late February storm in 1989. The wind speeds measured during the storm
were the largest ever measured (94 kts) and close to the 100-year maximum wind speed for Barter
Island (98 kts), according to the Climatic Atlas (1988).

4

Itshould be noted that multi- -year ice invasions (of 1 tenth concentration or greater) can occur during
freeze-up at a rate of once every 3 to 4 years, but multi-year ice is not part of this study.

nN

2.4 Descriptions of Break-Up at Pt. McIntyre

Break-up usually occurs inside the barrier islands and sround the West Dock Causeway (WDC)
between the last week of June and the second week of July, with an average date of July 4. Break-up
is defined as the time when the ice concentration goes from 10 tenths to 9 tenths or less. The break-
up season usually lasts for approximately three weeks, from the time of initial break-up until first
open water occurs. oo : .

In the period before break-up, in mid-May, the ice starts to deteriorate to a point where ice roads can
no longer support over-ice operations. Water in the Kuparuk River typically reaches the coast in late
May or early June and begins to overflood the sea ice in Simpson Lagoon. Within a few days after ,
the flooding beains | the water flows out of | Simpson Lagoon (to the north between Egg Island and

-15-. . , To :

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he = " a ne ee ee a | nas bl) oe a

purposes of this evaluation, the swath width will be assumed to be one-third the boom length. The
slick thickness will vary with the distance from the spill source, and i is provided by the scenario
descriptions. The encounter speed may be as high as 0.7 knots, which is assumed to be the upper
limit for containment effectiveness; at higher speeds oil will be lost past the boom: due to entrainment
failure. However, i in responding to a blowout spill, the containment and recovery operation will
generally be stationed ‘at a fixed point at some safe distance from the source. In this case the
encounter speed will simply be the speed at which the Slick drifts i into the containment configuration, :
estimated to be 0.3 to 0.7 knots in these scenarios. .

In moderate to heavy ice conditions, it may not be practical to operate a barge/booming combination, °
in which case an oleophilic skimmer such as the Foxtail could be used to recover pockets of oil.
Such an operation will be much less effective than one using containment booms due to the relatively

‘thin slicks emanating from the blowout site. For evaluation purposes in these scenarios, a contain

and recover approach i is used throughout

5.2 Booms and ‘Skimmers and their Capacities

Containment Boom. Containment of ‘il in ice infested waters will tequire the use of rugged, high-
strength boom to withstand contact with ice. An ideal candidate for this task would be the Ro-Boom
ocean model (36x43), of which ACS has astockpile of 8000 ft, as well as an additional 2500 ft of

. other Ro-boom of similar size. This amount will be more than adequate for the blowout spills under

consideration, i in which the width of the thick portion of the slick is less than 300 feet, and the total
slick widths are less than 2000 ft at a (safe operating) distance of 1 to 2 miles downstream of the
source. . , ‘

Skimmers. There are a number of different skimmers that could be employed in these scenarios, the
selection of which will depend on the estimated encounter rate and the slick thickness. The following
is alist of the key skimmers in the ACS inventory. The list includes each unit’s derated recovery rate,
which is meant to reflect a realistic estimate of the skimmer’ 's recovery capacity. Note that in each -
of the subsequent scenarios, the calculated encounter rates will be compared to the derated Tecovery

rates, and the lesser of the two will be used in determining recovery efficiencies. °

alle


TO MO OO OM oO oO

2 ee eyo ee i - os. Senn
- 4

visibility, VFR flying conditions, and wave heights. For all the freeze-up scenarios, the response :
time is estimated to be 60 hours, so for the 15-day period the effect is to reduce effectiveness by 17%
((15-2.5) + 15 = 0.83). Also for all freeze-up scenarios, the combination of the three environmental -
factors are such that, on average, mechanical containment and recovery will be effective 77% of the
time. The following is the estimate of effectiveness for the 15-day period, expressed as a percentage

of the total blowout flow:

Recovered oil volume= = 512 bbl/day x 0.83 x 0.77 + 15,000 bbi/day
22%

_ 6.3.3 Additional Recovery Systems (Scenario 2. Northstar, 5/10ths Ice, Freeze-up)

As in the previous scenario (section 6.2.3), the entire width of the thick slick can be encountered by
two containment and recovery systems. Any additional systems would be limited to chasing thin
sheens and would add little to the overall effectiveness of the response. Additional systems could
be considered to attempt to deal with oil outside the thick slick, as well as portions of the thick slick
missed by the first two systems due to ice-related inefficiencies; however, any additional systems

' a

would be even less effective than is described above. so _

63.4 Dispersant-Use (Scenario 2. Northstar, 5/10ths Ice, Freeze-up)

In this scenario the amount of oil that falls on water to form relatively thick slicks (> 0.4 mm) - after
unavoidable losses due to evaporation, tiny-particle drift, and oil falling on ice ~ is 3150 barrels per
day (15,000 BOPD x 0.21 - see Table 6-7). According to the above analysis of mechanical recovery
capability the amount that can be physically recovered is 512 barrels of oil per day. This leaves 2638 «
barrels of oil per day as a target for a dispersant program. .

‘

” The oil available each day for dispersing would therefore require about 5500 gallons of dispersant

per day (2638x42/20). The two helicopter/oucket systems would therefore need to carry out about
10 sorties each per day (during the 12 hours of daylight), that is, about the same as the first scenario

-89-


ar — NTE Oe Ey Otis arene wine putin drtenaore

" 3, General Behavior of Offshore Blowouts and Oil Spills in Ice

3.1 Introduction

In subsequent sections of this report six hypothetical oil-well blowouts are selected for study and
described tersely in terms of blowout behavior and oil spill behavior. The purpose of this chapter is
to provide background information that will assist the reader i in understanding the specifics of later
discussions of these subjects. The next chapter has a similar purpose with respect to spill

countermeasures.

‘There are two basic kinds of offshore oil-well blowouts. The first isa subse a blowout in which the
‘ drilling platform moves off site or is destroyed during the blowout. In this case the discharging oil

emanates from a point on the sea bed and rises through the water column to! the water surface. An
example of this kind of oil-well blowout was the 1979 Ixtoc J blowout in the Bay of Campeche,
Mexico (Ross et al. 1979). The other possibility i is a platform blowout or above-surface blowout in
which the platform maintains its Position during the accident (because it is undamaged or
bottom-founded) and the oil discharges into the atmosphere from some point on the platform above
the water surface, and subsequently falls on the water surface some distance downwind. Examples ©
of this kind of blowout include the 160,000-barrel Ekofisk blowout in the North Sea in 1977
(Audunson 1980) and the 1500-barrel Uniacke blowout of condensate off Nova Scotia in 1984 (Gill
et al. 1985). Oil-well blowouts that might occur at either the Northstar or Pt. McIntyre locations
could only be of the above-surface kind, and further discussion is restricted to this kind.

32 Behavior of Above-Surface Blowouts

As demonstrated in the Ekofisk and Uniacke blowouts noted above, the gas and oil released from an -

above-surface blowout will exit at a high velocity from the well-head and the oil will be fragmented
into a cloud of fine droplets. The height that this cloud rises above the release point will vary
depending on the gas velocity and the he prevailing wind velocity. The fate of the oil and Bas at this

1

"27+


ae 6 eee eee eae he) bans e+) Ses

a . _ ‘Appendix E -
Estimate of Containment Efficiency in Broken Ice

When operating containment and recovery systems among broken ice there will be inefficiencies
related to the avoidance of large ice floes and the accumulation of floes within the containment

boom. There has been little experience or field studies to quantify this, although it is believed that
conventional boom and skimmer operations would be effective at least in light ice concentrations

‘, (say, up to 3/10ths coverage), somewhat applicable in 5/10ths coverage with effectiveness declining

rapidly as concentrations approach 7/10ths or greater. For the purposes of this evaluation it is
necessary to quantify this in some manner. The following is a Proposed approach for this.

Carrying out containment operations in a broken ice field could involve maneuvering around large
. floes, periodically reorienting the boom, and perhaps emptying the contained area of brash ice, slush,
and smaller ice pieces. For the purposes of this evaluation scheme, the ice field can be idealized as
being of equally spaced floes of equal sizes This can be then used to calculate the average distance
between floes for a given ice concentration and floe size. This average distance would be the amount
of open water between floes, within which one could operate containment equipment without
obstruction. For a given average speed of advance, one could then calculate the amount of time that
a containment system could advance through open water. Finally, this could then be combined with
, agiven amount of time to reposition the system to calculate an estimated percentage of time that the
containment system is able to advance and effectively contain and concentrate oil for recovery.

It is acknowledged that an ice field is not made up of equally spaced floes of equal size, and that a
containment and recovery system operating in a broken ice field would likely encounter “longer-
than-average” periods of open water, just as it would also encounter “longer-than-average” periods
of ice in concentrations greater than the 30, 50, or 70% assumed. Since the objective of this exercise
is to produce an overall efficiency number that would apply over a period of time, it should be
reasonable to assume that these effects average out over time. _

For example, floes of ‘an average diameter of 1000 feet would have an average separation of 740 feet

given a 30 % average ice concentration, calculated as follows:

R = floe radius , ;
X = floe separation, center to center NS

an eee ae


J 5 SS ee ee ann een we 0h) Ee ee Sa = Sean

Ithas also been suggested that a device could be inserted into the gas jet to agglomerate the oil spray
droplets, increase their size and cause them to fall to the surface in shorter distances. Many such
devices exist in the realm of air pollution control technology. The simplest, and perhaps most
applicable to the envisioned use, are called demisters. These devices involve passing a gas stream
laden with small droplets through a section of duct loosely packed with fine mesh. The droplets
collide with and collect on the strands of mesh. As the strands become saturated with liquid, larger
droplets are torn off by the passing gas. This process causes the droplet size distribution to be shifted
upwards significantly. For a given liquid, there is a droplet diameter below which demisters are not
effective, because these small droplets do not have sufficient mass to cross gas flow streamlines and
collide with the strands, but are carried around the strands by the gas. As with the placement ofa
deflector in a blowout plume, the positioning of a demister in the jet would be a considerable
engineering challenge. The assessment of the feasibility of this concept is beyond the scope of this
study.

-127-


+ -Anoverview of year-round ice dynamics in the southem Beaufort Sea is Presented;
. istorically-accurate, detailed descriptions of freeze-up a at Northstar and break-up and Pt.
McIntyre are presented; and then :

‘

° simplified ice scenarios are presented, including mean values of ice conditions and other
_ pertinent environmental parameters; these are summarized in tabular form for use in
subsequent oil fate-and-behavior and countermeasures analyses.

2.2 Overview of Ice Conditions in the Alaskan Beaufort Sea -

Petroleum activities in the southern portions of the Alaskan Beaufort Sea are occurring on gravel
islands and structures, which in winter are surrounded by solid, immobile, landfast ice. By late April
or early May the ice will have grown to a maximum thickness of about 5 to 6 feet. The i ice during

‘this period is subject to various types of. stress cracks resulting from rapid temperature changes, tidal

action, and storm surges. These cracks quickly re-freeze to form a continuous layer of ice.
During the months of May and June the ice is warmed by increasing sir temperatures and
lengthening periods of sunlight. Surface melting and river outflows adds to the deterioration of the
ice rendering it increasingly susceptible to deformation, cracking and movement. The increased
absorption of solar radiation in water as compared to snow and ice, causes accelerated melting in
puddled areas. The ice thickness beneath these melt pools decreases more rapidly than the
surrounding ice, in some cases resulting in holes through the ice. .

During-this period of decay, typically about six weeks, 100% ice coverage persists until the ice
deteriorates to the point of breaking up under the influence of winds and currents. Following the
onset of breakup, the ice cover begins to shift, crack, and deteriorate further into a field of ice cakes

and brash ice (<65 feet across) combined with small to medium floes (65-1600 feet) and large floes

(>1600 feet). Giant floes exceeding 5 nautical miles normally break up rapidly depending on the
wind and the sea. « - ‘

* ell-


COGS Sees Cane semen me 0h) ee —_— 54) nen

ao

eee J es I ws BE one BR cee DE cas BE ae cece cons J wee DE ems IE coe Es BE oe xe BE =n

te

Extensive experimentation on crude and fuel oils with a variety of igniters‘in a range of

environmental conditions has confirmed the following rules-of-thumb for non-emulsified oil in

relatively calm, quiescent conditions:

_ * +the minimum ignitable thickness for fresh, volatile crude oil on water is about 1 mm;
¢ the minmum ignitable th thickness for aged, unemulsified crude oil and diesel fuels is about
3to5 mm; .

. ‘ther minimum mignitable thickness for residual fuel oils, such as Bunker “C” or No. 6 fuel oil,
: is about 10 mm; and, :

v8 once | m? of burning slick has been established, ignition can be considered accomplished. ~
Aside from oil type, other factors that can affect the ignitability of oil slicks on water include: wind
speed, emulsification of the oil andi igniter strength. Secondary f factors include ambient temperature

“and waves. ‘

¢ * The maximum wind speed for successful i ignition of. Target burns has been determined to be
10 to 12 m/s. °
© For weathered crude that has formed a stable water-in-oil emulsion, the upper limit for *
successful i ignition is about 25% water. Some crude oils form meso-stable emulsions that
” can be easily ignited at much higher water contents, Paraffinic crude oils ‘appear to fall into
this category (Fingas et tal. 1997).

* — If the ambient temperature is above the oil's flash point, the slick will ignite rapidly and
easily and the flames will spread quickly over the slick surface; flames spread more slowly
over oil slicks at sub-flash temperatures. se :

-55-


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Table H-9: Summary of Response Tactics and Estimated Effectiveness

Day Main Response Tactics - Estimated Effectiveness
‘ | oftotal blowout | of oil that lands
flow on ice/water
surface’
1 in situ burning of oil on ice (|. 6% > 87%
2 in situ buming of oilonice «+ 63% 87%
3 “| in situ burning of oil amongst and on ice 41% 57%
4-6 in situ burning of oil amongst and on ice 37% ~ 51%
7-11 in situ buming of oil amongst andonice ~ + 31% 43%
12 in situ burning of oil amongst and on ice ® 25% 35%
13-15 | containment and recovery and in situ burning |)  - 35% 49%
Average : 38% 52%
‘Note the estimated volume of oil that lands on the ice/water surface takes into account the assumed 20%
“evaporative loss and the further 10% of oil drops that are so small when discharged from the well that they
remain in the air and never land

5. References “| 7 Sy

McMinn, LTJG T.J. 1972. Crude oil behavior on Arctic winter ice: final report. Office of Research
and Development, United States Coast Guard, Project 734108, Washington, DC., NTIS
publication no. AP-754. toe

_Vaudrey, K. 1984, 1983 Breakup study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA

Project 224, , Vaudrey & Associates, Inc., San Luis Obispo, CA.

Vaudrey, K. 1985, 1984 Breakup study of the Alaskan Beaufort and Upper Chukchi Seas, AOGA
Project 274, Vaudrey & Associates, Inc., San Luis Obispo, CA. °

Vaudrey, K. 1996. Design basisi ice criteria for the Northstar development, draft report prepared for
BP Exploration (Alaska), Inc., by Vaudrey & Associates, Inc., San Luis Obispo, CA.

23-0 ° ey


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a oc oo

Tome BE oom I cons SA come I vaee coon J come BE tose BI wre J oe

aan

emanating from the source is only one-half the minimum ignitable for weathered crude (ca. 2 mm)
there would be a danger of the fire burning back to the spill source.
The estimated daily removal rate for one ISB unit is thus: , .
ISB unit est. daily removal rate from the water surface © = 59 bbl/hrx 24 hrx0.5
= 708 bbl

If two units were deployed to encounter the entire thick slick available the total daily ISB removal

rate from water would be 1416 bbl. This is slightly higher than the case of containment and recovery
because it is envisioned that burning, then maneuvering the ISB unit back into the thick oil will take
less time than for the conventional boom and skimmer system. .

The oil that falls on the ice floes in this scenario is ideal for in situ burning operations. After
allowing the surface oil to concentrate in melt pools, about 40% of the surface area of the pools
would be covered with 10 mm-thick oil. Taking into account an average oil-removal-by-burning _
efficiency of 80% and conservatively estimating that only oil in melt pools greater than 50 ft? (85%
of the total) would be ignited by Heli-torch operations results in an overall oil removal by buming
of : ‘ ‘ , . .
12,000 bbl x 49% on ice x 80% x 85%
4000 bb

daily oil removed from floes by burning

ty

» Asimilar overall reduction in on-water in sit burning effectiveness to that determined above for *

mechanical containment and recovery, can be estimated using the same response time and
environmental factors as for mechanical containment and recovery. For ISB operations the additional
factor of the percentage of time that winds are less than 20 knots (95%) is also taken into account.
The estimate of ISB effectiveness for the 15-day period, expressed as a percentage of the total
blowout flow:

Oil removed from water by ISB = 1416) bbi/day x 0.97 x 0.66 x 0.95 + 2 000 bbi/day -
+= 711% o

124-0 7 oF


RD th) Hie ee eee a 1) Seen Oe

A similar overall reduction in on-water in situ buming effectiveness to that determined above for
mechanical containment and recovery, can be ‘estimated using the same response time and
environmental factors as for mechanical containment and recovery. For ISB operations the additional
factor of the percentage of time that winds are less than 20 knots (95%) is also taken into account.
The estimate of ISB effectiveness for the 15-day period, expressed as a percentage of the total

blowout flow:

Oil removed from water by ISB = = 0 bbl/day x 0.97 x 0.66 x 0. 95 + 12,000 bbl/day
=0%

. The ISB operations targeting the oil on ice floes would continue until all the available oil had been
ignited. Delays in operations due to response time and environmental factors would not affect the

overall removal effectiveness. The estimate of on-ice ISB effectiveness for the 15-day period,
expressed as a percentage of the total blowout flow reduced to account for evaporative losses is:

* Oil volume removed from ice by ISB= 1815 bbl/day + 12,000 bbl/day
' = 15%

The total oil removed by ISB operations both on water and ice is:

0% +15 %
15%

"

Total oil removed by ISB operations :


OSS SGy Seer aes Seen es snk ne ll-someanats v8 il) Seana

flushing process results in wind-herded oil thicknesses on the melt pools of 10 mm. The oil covers
up to 75% of the surface area of the melt pools; the largest slicks are on floes near the centerline of
the oiled strip. This oil will evaporate at a rate negligibly different from the oil that falls on the
water, reaching a total evaporative loss of 22% after 72 hours. _,

ge
i
+

Table 6-14 summarizes the predicted characteristics of the thick slick over a time period of 72 hours.
The oil that forms the thick slick on the water has a viscosity of 25,000 cP and a Pour Point of 68

- °F at the point where the on-water modeling is started. As such, the oil slick does not spread on

~ water. For the duration of the scenario (72 hours) the slick moves with the oiled ice floes and does .
not spread further, although the thick slick may meander somewhat in the pack ice field due to . -

oceanic eddies or large-scale turbulence.
The presence of ice inhibits the wave action that would normally exist with a 9 knot wind and
suppresses natural dispersion of the oil slick. The ice also suppresses the formation of a water-in-oil

emulsion.

ey '

The thick oil slick continues to evaporate slowly throughout the 72 hour scenario. It loses 20% of : ,

its volume to evaporation after 24 hours; 21% after 48 hours; and, 21% after 72 hours. The viscosity
of the unemulsified oil increases to 27,000 cP after 24 hours; 28,000 cP after 48 hours; and, 30,000

’ oP at 72 hours The Pour Point of the oil after 72 hours has increased to 70 °F.

At the end of the 72 hour scenario period 22% of the oil released at the beginning of the scenario still
remains in thick slicks on the water surface between floes and 35% on the surface of ice floes. The
oiled area is a long (19 nautical miles), narrow (100 feet) strip that contains 2.1 mm thick

- unemulsified oil slicks on the water between floes. The ice floes that were sprayed with oil as they

passed under the blowout plume contain melt pools with 10 mm thick slicks of oil covering up to
75% of the pool’s surface. The larger pools of oil are on the floes near the center-line of the oiled

strip.

“110.


1 _ _ SE Se es Ses LOSS nee ae bi ee ee ae an mi SRaeen

Summary of Response Tactics and Estimated Effectiveness

Day ‘Main Response Tactics Estimated Effectiveness
° of total blowout | of oil that lands
flow on ice/water
surface
1 in situ burning of oil on ice 63% 87%
2 in situ burning of oil on ice ‘ 63% | 87%
3 in situ burning of oil amongst andonice 41% 57%
4-6 in situ burning of oil amongst and on ice 37% | 51%
7-11 in situ burning of oil amongst and on ice “31% °— B%
12 in situ buming of oil amongst and on ice » 25% * 35% .
13-15 | containment and recovery and in situ burning 35% , 49%"
Average . ‘ 38% 52%
‘Note. the estimated volume of o1l that lands on the ice/water surface takes into account the assumed 20% 1
evaporative loss and the further 10% of oil drops that are so small when discharged from the well that they
remain mm the air and never land

rons "a 5, ' Executive Summary - Page7


_ - Peete achat: mehr nth meee

‘

: TABLE 6-8
Fluid Recovery Rates for Scenario 2

Fluid Calculation Recovery rate
oil lesser of system encounter rate and derated recovery rate 61 bbl/hr
total water | oil content in recovered fluid (recovery efficiency) = 20% 244 bbV/hr |
emulsified water | emulsified water content in recovered fluid = 40% 41 bb\/hr
free water total water less emulsified water 203 bbyhr |

-| total fluids oil + emulsified water + free water 305 bbl/hr

aa MO OO OPM OO oO ee Om Oo eo ol) lhl

avoiding large floes. *

3°87-

Compared with the first scenario, the main difference here is the greater ice concentration and its
effect on containment efficiency. For the 50% ice condition, the containment efficiency is assumed
to be 40%, that is, the containment operation is effective for 40% of the time accounting for
interruptions related to clearing ice from the containment and repositioning the system when

Assuming that operations are restricted to daylight hours, the total fluid volumes per day are
; calculated by combining the hourly rates, the 40% encounter efficiency, and the 10-% hours of
daylight available at this time of year. me


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‘Both oils considered in the modeling of the six scenarios were tested and modeled as described

above and are now part of the SL Ross library of crude oils, available for use in the model. The two
oils are (1) Pt. Mcintyre Crude oil, for the Pt. McIntyre site, obviously, and Q) Milne Point crude
oil for the Northstar site. Reports on these tests are available in SL Ross 1994 and SL Ross 1996, -

‘respectively, and tabular summaries of these are available in Appendix D. Milne Pt. crude oil was

used to represent Northstar oil because at the time of testing not enough Northstar crude was
available for a full program of testing, so Milne Pt. crude, which comes from a nearby oil field, was
studied instead. A small sample (100mL) of Northstar crude was analyzed in order to compare

, Selected properties with those of the Milne Pt crude. “The Northstar oil was found to be less dense,

less viscous, and more volatile. This means that the oil spill scenarios at the Northstar site, described

in Chapter 7, present a conservative picture of the persistence of spills that might oceur at that

location. _ . -

‘The following are brief summaries of the properties of each of the selected oils. Milne Point crude

oil is a hght oil (density of 0.849 g/mL @ 1°C, viscosity of 8.0 cP @ 15°C) with a high

concentration of volatile Components. It will not form emulsions until the oil is highly weathered

(evaporated more than 20 %) and the emulsions that do form are likely unstable; that is, they break

naturally when mixing energy is removed and also respond well to emulsion breaking chemicals. Pt.

McIntyre crude oil is a medium crude oil (density of 0 911 g/mL @ 1°C and viscosity of 756 cP P@
1°C). It has a very high tendency to form stable emulsions, even when fresh.

3.6 Behavior of Oil Spilled on Ice and in Broken Ice ©

Many studies on the behavior of oil spilled in ice infested waters have been performed over the past
20 years. Dickins and Fleet 1992 contains a comprehensive summary of all known references on the
subject of oil-in-ice fate and behavior, including analytical studies, tank and basin tests, spills of
opportunity, and experimental spills at sea. Another review of the subject that is more focused on
the Alaskan situation is found in Dickins and Glover 1996, and it is this reference that we draw on
now to summarize our current knowledge on | the subject. Please note that a large portion of the
Dickins and Glover review deals with the problem of oil spilled under ice, a case that could occur, ‘
for example, if an oil well blowout were to occur on the sea bed during winter and rose to the

32-


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=e

and horizontal is assumed to follow a Gaussian form as described by Turner (1970).
A factor of 2.67 is applied to the final travel distance to account for vertical spread
(this adds three standard deviations to the mean distance travelled). This results in

: 99% of the droplets, of the diameter being considered, falling by the distance

calculated. The width that the plume will spread to, at the point of ground contact, is
determined using Turner’s (1970) atmospheric dispersion relationships. The 2.67
factor also is applied to the plume width to account for 99% of the droplets.

Oil Drop Size Distribution

The oil drop size distribution from a surface oil and gas blowout is the one
parameter about which little is known. Measured oil drop-size distributions for such
events could not be found in a search of the libraries of $ L.Ross, Environment
Canada and Canadian Institute of Scientific and Technical Information. The __
following steps were taken to provide an estimate of the size distribution of these
drops. : : '
Observational data from the Uniacke (Martec, 1984) and Ekofisk (Audunson,
1979) blowouts were used to approximate the volume median drop diameter from
surface blowouts. The spill model was run using the blowout conditions reported in

‘ the literature for these two incidents and various volume median oil drop diameters.

The reported slick conditions for these spills were adequately predicted when a 500
ym volume median diameter was used in the Uniacke discharge and a 750 um
volume median diameter (VMD) was used for the Ekofisk spill. The comparisons
between reported and modeled values can be seen in Table 1. This provides an
average drop size but does not teveal the drop-size distribution.

Table 1 : Comparison of Reported and Modeled Slick Characteristics _

Percent Evaporated Slick Width(m) .] Thickness (mm)

Ol Reported | Modeled | Reported | Modeled | Reported | Modeled

Ekofisk' | 35-40 | 39.5 | 100-200 | 200 1 1.14

Uniacke” 70 - 67.5 200 * 700 __|__0.003 0.0046

18.5 m/s wind, 0.5 m/s water current, 5°C air and water temp, 750 um drop
diameter
2 123 m/s wind, 0.26 m/s water current, 1°C air and water temp, 500 zm drop

. diameter”

' The only oil drop-size distribution data that could be found from an oil and

‘gas discharge were from measurements taken during an experimental subsea release

under an ice cover (Buist and Dickins, 1980) In this study oil drop-size

distributions were measured from ice core samples taken at various distances from ,
_ the release point. These distributions have been combined in an area- weighted

scheme to identify the likely drop-size distribution of the oil as it was discharged.

- The result of this analysis can be seen in Figure 1. The resulting distribution is

linear rather than the log-linear relationship exhibited by most gas-atomization


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flushing process results in wind-herded oil thicknesses on the melt pools of 10 mm. The oil covers
up to 40% of the surface area of the melt pools; the largest slicks are on floes near the center-line of
the oiled strip. This oil will evaporate at a rate negligibly different from the oil that falls on the
water, reaching a total evaporative loss of 22% after 72 hours. ,

Table 6-17 summarizes the predicted characteristics of the thick slick over a time period of 72 hours.

"© ‘The oil that forms the thick slick on the water has a viscosity of 25,000 cP and a Pour Point of 68

°F at the point where the on-water modeling is started. As such, the oil slick does not spread on
water. For the duration of the scenario (72 hours) the slick moves with the oiled ice floes and does

_Rot spread further, although the thick slick may meander somewhat in the pack ice field due to
_ oceanic eddies or large-scale turbulence.

The Presence of ice inhibits the wave action n that would normally exist with a 17.5 knot wind and
suppresses natural dispersion of the oil slick. The ice also suppresses the formation of a water-in-oil

emulsion. - : *

The thick oil slick continues to evaporate slowly throughout the 72 hour scenario. It loses 21% of
its volume to evaporation after 24 hours; 22% after 48 hours; and, 22% after 72 hours. The viscosity
of the unemulsified oil increases to 29,000 cP after 24 hours; 33,000 cP after 48 hours; and, 36,000

_¢P at 72 hours. The Pour Point of the oil after 72 hours has increased to 73 °F. .

At the end of the 72 hour scenario period, 12% of the oil released at the beginning of the scenario
still remains in thick slicks on the water surface between floes and 49% remains on the surface of
ice floes. The oiled area is a long G8 nautical miles), narrow (100 feet) strip that contains1 mm thick
 unemulsified oil slicks on the water between floes. The ice floes that were sprayed with oil as they
passed under the blowout plume contain melt pools with 10 mm thick slicks of oil covering up to
40% of the pool’s surface. The larger pools of oil are on the floes near the center-line of the oiled
strip.


° form of thin sheens trailing the drifting floes.

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At the end of the 72 hour scenario period, 33% of the oil released at the beginning of the scenario_
still remains in thick slicks on the water surface between floes and 23% remains on the surface of
ice floes. The oiled area is a long (68 nautical miles), narrow (240 feet) strip that contains 0.4 mm
thick unemulsified oil slicks on the water between floes. The ice floes that were sprayed with oil as
they passed under the blowout plume are coated with 0.003 mm to 0.2 mm of oil covering the snow

on their surface. The thicker coatings are on the floes near the center-line of the oiled strip. ,

Over time, the oil remaining on water will be incorporated into the surface layer of the growing ice

and the oil remaining on floes will be covered by snow. A portion of the oiled ice will likely be
formed into ridges and rubble fields during November and December as the thin ice deforms under
pressures from wind and heavier pack ice to the north. Any oiled ice which escapes being
incorporated into the fast i ice will gradually drift west, and in many years could end up in the
Chukchi Sea by spring. During the spring (late May to early June) any oil still remaining near the
surface of level ice will rise to lie in melt pools; the oil incorporated into ridges and rubble fields will
be released more slowly. Ultimately, rotting ice will release any oil still remaining at breakup in the

TABLE 6-10
Summary of Slick Characteristics from a Blowout During Freeze-up
' _at Northstar in 7/10ths Ice Cover over 72 Hours

i Thick oil lefton | Emulsification’ Slick’, _} Thick slick | Thick slick
water (% of total | (% water vol.) viscosity thickness width
released) -| (@@30°F | (mm) (ft) |
Initial - al 0 120 0.6 ° 180
3 38 oO 160.” 05 230 :
6 1 37. o <<} ° 180 - 0.4 |
12 36°. 0. 200 | 04 | 240 |
24 35 o-: 220 - 04 =: 240
48 34 0 250 04 ‘|. 240,
2 33 0 260 0.4 240 -


. rt ‘ .
4 4 4

4, Overview of Spill Countermeasures

As with the previous chapter the purpose of this chapter is to provide background information onoil
spill countermeasures that should help readers better understand the terse, scenario-based
descriptions of countermeasures that are presented in Chapter 7.

Before starting the detailed review, some discussion of the differences between spills from blowouts
and spills from tankers is warranted Alaskans are painfully aware of the difficulties of f cleaning up
large tanker spills, so it is natural for them to believe that similar difficulties would exist in dealing
with large spills from blowouts. This may not always be the case, ‘as discussed below. _

. 41 Differences between Fighting Blowout Spills ia Tanker Spills

-Tanker Spills. Although hundreds of millions of dollars have been spent developing containment

and recovery equipment (i.e., booms and skimmers) for dealing with tanker spills, the problem
remains extremely difficult. The cleanup equipment i itself is not the issue because offshore boom-
and-skimmer systems are generally effective in containing and removing large amounts of oil on
open water if the sea states and currents are not too high, and if the spill is small in area and large

* in thickness. Rather, the usual problem in recovering major oil spills in the open ocean is that spills

tend to spread to large and unmanageable areas before cleanup systems can arrive on site. A 100,000
barrel spill, for example, can spread to a total, patchy area of about 8 square miles or 5000 acres -
within just 12 hours. Another problem is that recovery systems must move through slicks slowly
(less than one knot) to avoid major surface oil losses due to entrainment, so recovery itself is a
relatively slow process. Because response and eleanup times can be long, another problem arises:

water-in-oil emulsification. Most crude oils will begin to emulsify within a short time — within
minutes or hours for some — and this process can increase the amount of oily substance on the
surface by a factor of four or so. This makes the spill recovery process that much slower because up
to four times the amount of product must be picked up and disposal of. :

“352°