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Table 19-17 Race and Ethnicity Characteristics of the State of Mississippi and

Mississippi Counties Where Onshore Support Facilities may be Located

Category Jackson County State of Mississippi

Total Population 139,668 2,967,297

Race and Ethnicity

White 72.1% 59.1%

Black or African

American 21.5% 37.0%

American Indian and

Alaska Native 0.4% 0.5%

Asian 2.2% 0.9%

Native Hawaiian or

Pacific Islander - -

Two or More Races 1.9% 1.1%

Hispanic or Latino (of

any race) 4.6% 2.7%

Source: U.S. Census Bureau 2010

As of the 2010 U.S. Census, the median household income in Mississippi was $36,764,

and 21.8% of families lived below poverty level. Some 26.0% of people are under 18

years and over age 65. Jackson County had a higher median household income

($48,187), a lower than state percentage of families living below poverty level (14.1%).

Economic characteristics data from the 2010 U.S Census for the state of Mississippi and

Jackson County are summarized below in Table 19-18.

Table 19-18 Economic Characteristics of the State of Mississippi and Mississippi

Counties Where Onshore Support Facilities may be Located

Category Jackson County State of Mississippi

Population under 18 years old 25.8% 26.9%

Population Over 65 years old 12.5% 12.8%

Median Household Income in

2009 (Dollars) 48,187 36,764

Total Families 48,332 1,085,836

Families Below Poverty Level

Income 14.1% 21.8%

Source: U.S. Census Bureau 2010

19(b).13 Infrastructure

Marine Support Vessels

As of 2002, there were 376 supply vessels (platform supply vessels) and anchor handling

tugs/supply vessels in the GoM (MMS 2002). Of the 376 supply vessels, 116 were built

since 1996. The numbers of marine support and construction vessels are described in

detail in Section 15.
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Helicopters

Helicopters are one of the primary modes of transporting personnel between service bases

and offshore platforms, drilling rigs, and barges (MMS 2001). They would also be

periodically utilized to transport certain types of equipment and supplies to the FPSO,

drilling rigs, and construction vessels. The number of helicopters to be used is described

in detail in Section 15. Helicopters are regulated by the Federal Aviation Administration

(FAA) and can stop to refuel on several offshore platforms (MMS 2002). The FPSO and

drilling rigs will be setup with fueling stations onboard.

19(b).14 Onshore Infrastructure

Port Fourchon

Port Fourchon is a multiuse port located at the mouth of Bayou Lafourche, approximately

60 miles south of New Orleans. The port has several support bases supporting the

offshore oil and gas industry in the GoM. The port can service deepwater supply vessels

due to the channel depth, allowing these vessels to take on fuel, water, deck cargo, and

other necessities efficiently at the same covered dock (Coastal Marine Institute

[CMI]/MMS 2002). Port Fourchon also houses a large number of docks with crane

service, loading/unloading equipment, warehouses, refrigerated warehouse, and

numerous storage yards. The port is connected to the GoM via the inshore channel of

Belle Pass and Bayou Lafourche, with a depth of 24 feet and a bottom width of 300 feet

(MMS 2004).

Contractors or Vendors

OCS development in the GoM is supported by an extensive onshore infrastructure. In

turn, this industry is supported by thousands of contractors and businesses which can be

found adjacent to port facilities. Offshore support businesses include the fabrication

industry; which in the last 50 years has been termed the cornerstone of the offshore oil

and gas industry, with a corridor extending from the Texas/Mexico border to Alabama

(MMS 2002). Other support services include construction and repair, drilling, chemical,

and transportation companies. Onshore support companies include pipe laying and

burial, shipbuilding, maintenance, and repair. Warehouses are also required onshore for

storage, as well as, quarters for crew. The proposed development would utilize existing

infrastructure at support and service facilities located in Port Fourchon, as well as the

onshore transport, refining, and processing capabilities at the ports and facilities located

along the Gulf coast from Texas to Mississippi.

Land Use

The oil and gas industry in the GoM has resulted in an extensive network of onshore and

offshore support facilities, and onshore refining, separation, and processing facilities for

crude oil and natural gas. No expansion of existing facilities or construction of new

facilities would be necessary as part of the proposed action. No new dredging or land use

changes to coastal areas would occur as a result of the Cascade / Chinook Development.
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Recreational and Commercial Fishing

Marine Fisheries, including recreational and commercial fishing, are previously

addressed in Section 19(b).8 Marine Fisheries. Due to the significant water depth at the

project site, recreational fishing activities are not expected to occur in or around the area.

Some pelagic longline commercial fishing is likely to occur near or within the area of the

Cascade / Chinook fields.

19(b).15 Archeological Resources [PROPRIETARY]

Archeological resources are protected under the Archeological Resources Protection Act

of 1979 (PL 96-95, 16 USC 470aa-mm). Archaeological resources are any material

remains of human life or activities that are at least 50 years of age and are of

archaeological interest. Shipwreck sites on the OCS are protected by MMS through NTL

2005-G07, Archaeological Resource Surveys and Reports. There are more than 2,100

historic shipwrecks in the Federal waters of the GoM (MMS 2005). In addition to

identifying the reported or known locations of these shipwrecks, this study also assigned

a location reliability rating to each of these sites. The report lists blocks currently

requiring an archaeological survey and report; and modifications to the survey lane

spacing for blocks already on the list. The shipwreck database identifies two types of

high-probability areas. The first area is within 10 km from shore and the second is near

to historic ports, barrier islands, and other similar areas (Pearson et al. 2003). Based on

this and other studies, MMS has determined where the highest potential for historic

resources exists in the GoM per NTL 2006-G07, Revisions to the List of OCS Lease

Blocks Requiring Archaeological Resource Surveys and Report. Details about recent

discoveries, and their potential eligibility for listing under the National Register of

Historic Places, can be found in Enright et al. (2006) and MMS (2005).

The Lease OCS-G 16965 block in the Cascade Field (Walker Ridge Area, Block 206) is

not located in an area of high shipwreck potential. To identify shallow hazards and to

ensure any historic sites are identified and avoided, a shallow hazards assessment of the

seafloor was conducted. The location of the shipwreck will not impact the routing of the

pipeline (i.e. there is adequate space in the geophysical survey corridor to avoid the

shipwreck). The finding was reported to BOEM as required.
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19(b).16 Other Uses of the Marine Environment

Nearshore and offshore uses of the marine environment include military use areas and

commercial uses, which are described below.

Military Activities

The military has designated several areas within the GoM for training, operations, and

testing which are known as Military Warning Areas (MWAs). The Central Planning

Area has five designated MWAs used for military operations; four of these are located

within 100 miles of the proposed project locations in Walker Ridge Blocks 425 and 469.

These areas are designated W-92 (approximately 30 miles north of the site), W-59A

(approximately 112 miles), W-59BC (approximately 150 miles), and W-147AB

(approximately 112 miles). PAI would not conduct operations within these areas but the

supply vessels, helicopters, and tankers would likely transit the MWAs on their way to

onshore support facilities.

Ordinance Disposal Areas

There are two inactive disposal areas located in the Mississippi Canyon area but these are

approximately 80 miles (128 km) from the proposed site and PAI is not proposing to

conduct operations that could affect munitions that have been disposed in these areas.

Other Mineral Exploitation

To date, sand and gravel is not being mined offshore Texas in federal waters of the OCS;

however, sources for future mining have been identified. In Louisiana, the Ship Shoal

area has been identified as a potential source of sand for barrier island and inland marsh

restoration projects. Any potential sand and gravel source sites are over 100 miles (161

km) away to not cause any effect to the proposed activities.

Another potential resource for extraction is gas hydrates. There has been exploration into

the location and distribution of gas hydrates along the continental slope of the GoM

which could lead to commercial extraction within the next few years.

Lightering Operations

Lightering operations involve the offloading of crude oil from very large crude carriers

(VLCCs) or ultra large crude carriers (ULCCs) to smaller shuttle tankers at sea. These

small tankers then transport the crude to onshore terminals for offloading. For safety

reasons the USCG has designated lightering areas in the GoM under 33 CFR 156.300

Subpart B; these are located more than 60 miles (96 km) from the baseline of the

territorial sea (Mineral Management Service 2000).

The entire area around the Cascade / Chinook development is within the Gulfmex No. 2

area, which has been designated until 2015 as a lightering zone for single-hulled tankers

as shown in Figure 19-6. Walker Ridge Blocks 469 and 470 are on the zone’s southern

boundary. Only three companies are currently conducting lightering operations in the

Gulfmex No. 2 lightering zone (Clark 2006). These companies, along with the

approximate percentage of lightering operations in the Gulfmex 2 zone, are: Skaugen
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Petrotrans (40-45%), American Eagle Tankers (40-45%) and Heinrich Lightering

Services (15-20%; Clark 2006).

Because most of the lightering vessels are now double hulled and can lighter outside

these areas, the Gulfmex No. 2 lightering zone is not highly utilized by industry and is

only required for non-double hulled tankers; which will be phased out by 2015 (Clark

2006). The area that is used within Gulfmex No. 2 is also located closer to shore in the

very northeast corner of lightering area, which is far from the Cascade / Chinook

Development. Any lightering vessels and crude oil carriers using the Gulfmex No. 2

zone are unlikely to affect PAI’s operations.
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Figure 19-6 - Gulfmex No. 2 Lightering Area
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19(c) Project Impacts

Table 19-19 and subsequent sections describe the potential impacts to marine and coastal

resources that may occur from the impact producing factors that discussed in Section

19(a). If an effect was identified, it has been determined that it would likely result in a

minor, temporary impact. The only impact producing factor which could have significant

effects is a catastrophic oil spill, which would be an extremely unlikely event given the

controls that PAI will have in place. See Section 1(f) to review the controls associated

with well drilling and FPSO offloading, which is the operation which provides the most

credible exposure to oil spills from an FPSO.

Table 19-19 - Potential Impacts to Marine and Coastal Resources

Environmental Resources

Impact Producing Factors (IPFs)

Emissions(air, noise, light,etc.)Effluents (muds,cuttings, otherdischarges to thewater column orseaflo

or) Physical

disturbances to theseaflo

or (rig or

anchore

mplace

m

ents,

etc.)Wastes sent toshore for treatm

ent

or disposalAccidents (e.g. oilspills)N

e

w

or unusual

technology

Site Specific Resources

Chemosynthetic communities      

Water quality      

Fisheries      

Marine mammals      

Sea turtles      

Air quality      

Shipwreck sites (known or

potential)      

Resources in the Vicinity

Essential fish habitat      

Marine and pelagic birds      

Public health and safety      

Coastal and Onshore Resources

Beaches      

Wetlands      

Shorebirds and coastal nesting

birds      

Coastal wildlife refuges      

Wilderness areas      

Key:

 = Denotes that there could be a potential impact. Refer to Section 19(c) for details of the analysis.

 = Denotes that no impact was identified.
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19(c).1 Air Emissions

Emissions of air pollutants during the project would occur from the FPSO, shuttle

vessels, drilling rigs, construction vessels, and marine support vessels and helicopters.

This would primarily occur from the combustion of fuels related to the various engines,

generators, and other pumps or motors. Refer to Section 8 and Appendix 3 for additional

details. The initial evaluation compares the worst-case emissions to the BOEM

exemption criteria. The proposed operations in the Cascade Field do not exceed the

BOEM exemption level criteria and therefore would not be expected to have an impact

on onshore areas.

In some unusual situations during production operations (i.e. process upsets), gas could

be flared for short durations. The FPSO would be equipped with two independent flare

systems, one operating at high pressure and the other at low pressure, to collect and burn

residual gases released from safety valves, pressure control valves, blowdown valves,

pipelines, etc. It is possible that some emergency flaring could occur for short periods

(i.e. several days per well) during well testing. This was addressed in the initial DOCD.

Hydrogen sulfide (H2S) is not present in significant amounts (i.e. the amount present is

less then 20 ppmv) in the Cascade reservoir. Overall, the emissions of pollutants from

this project are not expected to impact offshore air quality.

The project site is approximately 165 miles (265.5 km) from the Louisiana coast. As

indicated in Section 19 (b)1, air quality to onshore is dependent upon meteorological

conditions: wind speed and direction, atmospheric stability, and mixing height which

govern dispersion and transport of potential pollutants; smaller meso-scale wind flow

patterns, such as the land/sea breeze phenomenon, periodic tropical cyclones, and midlatitude frontal systems.

Emissions during well drilling and production would be rapidly dispersed by surface

winds, with an annual average of 13.3 miles per hour (21.3 km per hr)(MMS 2001). The

closest shoreline is to the north of the facility. Therefore, facility emissions traveling

with the prevailing winds have to travel a greater distance before impacting the shoreline,

and have a greater opportunity to be dispersed. In addition, the proposed development is

located more than 200 miles (320 km) from the BNWA, with the prevailing winds

blowing facility emissions away from BNWA.

Near shore air emissions associated with Shuttle Vessels should not provide a significant

impact as there are significantly less emissions from Shuttle Vessel unloading operations

at terminals relative to Shuttle Vessel loading out in the Gulf. Not only will less air

emissions be generated at the terminals due to a decreased need for power utilization (i.e.

holding the Shuttle Vessel on station in offshore environmental conditions), the terminals

will have vapor recovery units to minimize the VOCs that could be released during

unloading operations at terminals.

The project would not result in any changes to onshore infrastructure and the site is

located at least 165 miles (265.5 km) offshore. Therefore, no effects to sensitive

receptors, such as schools, residential areas, and hospitals, would occur. Air quality could
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be affected in the event of an oil spill. The VOCs, which would escape to the atmosphere

from a surface slick, accidental explosion, or clean up response in-situ burning, are

precursors to photochemically produced ozone (MMS 2008). The likelihood of

occurrence is remote and would be relatively short duration.

19(c).2 Noise Emissions

Noise associated with this project will occur from the operation of the FPSO, Shuttle

Vessels, drilling rig, construction vessels, marine support vessels, and helicopters, which

can transmit noise through both air and water. The classification societies will verify that

the major marine vessels (e.g. FPSO, Shuttle Vessels, and drilling rig) have acceptable

noise levels prior to mobilization to the GoM in alignment with the classification society

rules. PAI shall verify that noise limits are managed in accordance with regulatory

requirements during the Phase 1 operations.

Given the amount of vessel traffic from all sources in the GoM, the level of noise from

marine support vessels and Shuttle Vessels transiting to and from shore is expected to

contribute an insignificant amount of the total ambient noise level. According to NOAA

Fisheries in its assessment of oil and gas operations, it is believed that low frequency

noise created by drilling activities may be detected by sperm whales, resulting in some

harassment although no adverse effects would occur (NOAA 2002).

Short-term, minor impacts could occur to marine mammals in the vicinity of the project

area as a result of noise produced during construction, primarily from the use of thrusters

on the DP marine vessels, which would be used to drill the two wells on Cascade Field.

It is possible that underwater noise during FPSO production operations could also have

the potential to affect marine mammals if they are feeding or transiting through the area,

but this is expected to result in less noise than during construction because neither the

FPSO nor the shuttle vessels would use DP thrusters for station keeping, however the

FPSO was addressed in the initial DOCD. The dedicated field tug would assist the

Shuttle Vessels during offloading operations to maintain a safe distance between the

FPSO and the Shuttle Vessel.

If marine mammals are in the vicinity, they are likely to move away from the noise

sources and not be significantly affected. Noise from passing service vessels could also

startle cetaceans and temporarily disrupt their movements. The project would likely have

minimal effects on marine mammals or other sensitive noise receptors in the GoM.

19(c).3 Effluents and Discharges

Operational wastes generated from this development would occur from the FPSO, Shuttle

Vessels, drilling rig, construction vessels, and marine support vessels. These would

include water based drilling fluids, cuttings from water based drilling fluids, cuttings

from synthetic based drilling fluids, mud / cuttings / cement at the seabed, well test

completion fluids, produced water, sanitary wastes, domestic wastes, uncontaminated

seawater, uncontaminated bilge water, uncontaminated ballast water, desalination unit

water, hydrostatic water, and deck drainage. All ocean discharges will be discharged

overboard in compliance with the NPDES GP requirements. All other wastes would be
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transported to shore for disposal in permitted or licensed commercial facilities or for

recycling. Refer to Section 7 and Appendix 7 for details.

Drilling fluids and cuttings would be either water based or synthetic based (SBF); oil

based fluids will not be used. The discharge of SBF is limited to a specific retention on

cuttings (ROC) value required by the NPDES GP. The ROC is a film of SBF that is left

on the cuttings after the cuttings dryer process. Therefore, the majority of the SBF is

separated from the drill cuttings and re-circulated. While the colder temperatures and

greater depths of the fields would likely result in little degradation of the synthetic

components adhering to the discharged drill cuttings, SBFs are not expected to affect

water quality or the benthic community, even in the event of an accidental discharge

(Boland et al. 2004). All drilling muds and cuttings generated would be discharged

according to NPDES GP limitations.

Treatment chemicals could be used, if needed, to stimulate well production, to assist

product flow assurance, or to treat or prevent operational problems that may occur in the

production process.

Minor, localized impacts to marine water quality would occur from the proposed

discharges and effluents during the life of the project. Effects are expected to be minimal

based on compliance with the NPDES General Permit.

19(c).4 Physical Disturbances to the Seafloor

Results of baseline monitoring of the Cascade Field project area show soft bottom

seafloor conditions, in which burrowing infauna are most abundant. There is no known

hard-bottom in project area of the proposed Cascade wells or their associated jumper

connectors. No chemosynthetic communities were observed. Impact producing factors

to the seafloor habitat would involve drilling activities and installing jumper connector

with resuspension of the soft sediments likely. However, impacts from installation of the

well and jumper connection will not likely to have significant impact due to short

duration of construction activities and small aerial footprint. Proposed use of a DP

capable drill ship to install the well further reduces the anticipated impact associated with

the action.

Rapid burial by sediment accumulation of greater than one foot (30 cm) in thickness

would be lethal to those organisms that do inhabit the proposed project area (MMS

2008). Accidental spill from a well blowout could rapidly smother infauna. Recolonization would be expected however. Dispersal from strong ocean currents could

have an effect increasing an impact area should an inadvertent spill occur.

The primary concern is habitat alteration during construction/drilling activities and

inadvertent spills. Site-specific mitigation measures include:

 Conduct pre-drilling surveys;

 Monitor during and post-drilling; and

 No explosives or anchoring are part of this supplemental activity, therefore no

significant impact would occur and no mitigation measure required.
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Petrobras completed seafloor mapping of the project area in advance of project

installation, ensuring appropriate siting to avoid and minimize potential impacts and

hazards associated with the seafloor. As per NTL 2008-G06, PAI will be conducting

Remotely Operated Vehicle surveys to assist with site-specific mitigation, as necessary.

Monitoring results conducted following the successful installation of initial project

activities showed no impacts to the seafloor.

All facilities associated with this development, except for Shuttle Vessel and marine

support vessel transit to and from shore, will be located in water depths beyond 8,000 feet

(2,438 m). Benthic communities such as seagrass beds, corals and live bottom habitat

(typically found in waters less than 100 feet (30.48 m)), pinnacle communities (typically

located in water depths less than 1,300 feet (396 m)), or deepwater corals (typically

located in water depths as deep as 3,280 feet (1,000 m)), would not be affected.

A DP capable drill ship, semi-submersible drill rig would be used to drill and complete

the well which would not cause any effects to the seafloor from mooring.

The jumper connector would also be installed with a DP construction vessel, which

would prevent any impacts to the seafloor. Any pipeline installation activities would

primarily cause suspension of sediments as a pipe is laid across the seabed, which would

cause a slight increase in turbidity of the water column. Suspended sediments would

eventually settle within a relatively short timeframe.

Based on the surveys conducted, geophysical signatures related to chemosynthetic

communities or hard-ground substrates are not present in the project area. There is no

evidence of hydrocarbon seepage to the seafloor in the geophysical data. The occurrence

of periodic strong bottom currents in this area have scoured and eroded the seafloor. The

multibeam data reveal an eroded seafloor exhibiting furrows, anti-dunes, and flukes.

There was also no indication of chemosynthetic communities in the area of the well site

and jumper connector (GEMS 2007; see Appendix 2).

No impacts would occur to either hard bottom substrate or chemosynthetic communities

in the project area. An ROV monitoring survey would be conducted in accordance with

NTL 2008-G06, Remotely Operated Vehicle Surveys in Deepwater, to verify that no

previously unknown, high-value benthic communities exist in the vicinity of proposed

activities. Any potential to impact benthic resources would be further minimized by the

requirement to avoid potential chemosynthetic communities by a minimum of 1,500 feet

per NTL 2000-G20. Slight turbidity and burial from sediment settling would be expected

but these would have short-term, localized and negligible impacts to epifaunal or infaunal

communities.

The proposed Cascade wells and their respective jumper connectors are not located

within a high probability area for archeological resources. Furthermore, the shipwreck

that was identified will not be impacted by the proposed project.

19(c).5 Impacts from Wastes Sent to Shore

The majority of wastes sent to shore would consist of municipal garbage associated with

personnel on the FPSO, Shuttle Vessels, and drilling rig. Other wastes would consist of
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waste oil from machinery. These wastes would be transported to onshore waste disposal

facilities in Louisiana and Texas via supply boats. No expansions of the existing onshore

waste disposal facilities would be required. Refer to Section 7(a) and Appendix 7 for

additional details.

The proposed Cascade wells and their respective jumper connectors would have no

environmental effects on offshore or nearshore coastal resources as a result of the wastes

sent to shore.

19(c).6 Marine and Coastal Resources

Coastal Birds

Proposed activities are located well offshore in the Gulf of Mexico. Other than transient

individuals, the project area is not expected to be in a high use area by birds. Shuttle

vessels from the FPSO to existing ports will use existing shipping lanes. No significant

impacts to coastal birds are likely from well development production.

Fish Resources and Essential Fish Habitat

The proposed project is in over 8,000 feet (2,446.5 meters) of water depth and is no

longer in a blanket designation of EFH. The project area does retain EFH designation for

some specific species: shark, tuna, swordfish, and sailfish. The benthic fish population

that could be in the direct vicinity of the project’s seafloor activities is very low in density

and restricted to species that live below 8,200 feet (2,508 meters): oceanic bathypelagics

while species within the water column above the specific seafloor project site would be

ocean pelagic species above 656 feet (200 meters) and mesopelagics using the water

column between 656 to 3,280.8 feet (200 to 1,000 meters). Shuttle vessels will utilize

existing commercial shipping lanes in shallower water areas. Any impacts would be

temporary, and associated with minimal disturbance during construction /well drilling.

No significant impacts to fish resources and EFH are likely from well development

production.

Sea Turtles

Sea turtles are found through the Gulf of Mexico. Based on the water depth at the

Cascade Field location, only sea turtles in the project area would be considered transient,

either migrating through the area, or foraging. Shuttle Vessels will be using existing

shipping lanes into existing port facilities, which will minimize potential impacts in the

richer shallow water habitats of the Gulf of Mexico. Impacts would be limited to

inadvertent vessel collision with an individual.

Coastal Habitats

The project is located 165 miles (265.5 km) from the nearest coastline, which is

Louisiana. Sensitive coastal habitats include beaches and dunes and barrier islands. A

large scale inadvertent oil release at the well site would take 30 days to travel to beaches

and islands as per oil spill risk analysis undertaken for the FPSO (MMS 2008).

Therefore, lengthy spill travel times and large dilution factors would be involved for
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significant dispersion of an accidental spill prior to reaching a coastline from any of the

Cascade well locations proposed.

No new navigation channels would be required for this project. Primary potential

impacts to coastal habitats would be from shuttle vessel traffic and inadvertent spills

since onshore facilities are existing facilities. No onshore, near shore construction

activities are part of proposed Cascade Field, drilling, completion and production

activities, therefore no impacts are anticipated.

Seagrass beds, another sensitive coastal habitat are located behind barrier islands.

Therefore, likelihood of impact from an inadvertent oil spill is low. Nonetheless, as

demonstrated during the Deepwater Horizon accident, these sensitive resources are

susceptible to impacts from inadvertent spills.

Areas of Special Concern

Areas of Special Concern include marine protected areas. The proposed project is not

located in or near a marine protected area. However, the Gulf of Mexico is considered an

area of special concern. As such, a principal impacting factor would be a significant

inadvertent spill. Fate of hydrocarbons in the Gulf of Mexico is largely uncertain

(Ramseur 2010) following BP’s Deepwater Horizon oil spill of 200 million gallons (4.9

million barrels) of crude oil. According to a Congressional Research study, the fate of

spilled oil was as follows: human intervention (direct recovery 17%; in-situ burning 5%;

skimming 3%; chemical dispersal 16%), natural processes (natural dispersal 13%;

evaporated or dissolved 24%), and other 22% remaining in the water column, settling to

the seafloor, mixing with sediments, ingested by microbes, or collected during shore

clean-up activities. Oiled shorelines (classified as light, moderate, or heavily oiled) were

estimated to extent approximately 700 miles (1,127 km) in Louisiana, Mississippi,

Alabama, and Florida. According to studies following the 1979 Ixtoc oil spill,

approximately 25% of that oil settled on the bottom of the Gulf of Mexico. Monitoring

and other mitigation measures identified in Section 12 would reduce impacts.

Tourism and Recreation

The GOM supports diverse and valuable commercial and recreational fisheries; beaches,

wetlands and barrier island natural resources that support local and state-wide tourism

economics and recreational opportunities for the public. Primary concern to tourism and

recreation is effects from inadvertent spill that could cause 1) change in fish distribution

and abundance; 2) reduced catches of finfish and shellfish; 3) inability to access fishing

areas; 4) loss/damage to fishing equipment; 5) reduced market value of a fishery, i.e.

public perception of contamination.

Shipping and Transportation

No port modifications are required as part of the proposed project. PAI will be using

existing ports that currently accommodate commercial traffic and no additional facilities

or facility expansions are required for this project. Shuttle vessels would use existing

shipping lanes and no modifications to shipping would be required. Therefore, no

impacts to shipping and transportation are likely.
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The Cascade Field wells and their associated jumper connectors would not be expected to

have significant environmental effects on marine and coastal resources.

19(c).7 Accidents and Spills

The FPSO EIS indicates that FPSO-unique spill risks comprise only 5% of the total risk

for this kind of development (MMS 2001). The remaining 95% of spill risks would not

be unique to FPSO operations and would be equally likely to have similar outcomes on a

tension leg platform or other deepwater production facility. Of the total potential FPSOunique spills, it is estimated that approximately 94% of a spill volume would be more

likely to occur during oil transfers from the FPSO to the Shuttle Vessel and from the

Shuttle Vessel’s transit to shore. A well blowout scenario is addressed in Section 2 (j)

and oil spill information is provided in Section 9. An Oil Spill Risk Analysis was

undertaken and is in Appendix 5. The proposed project site for the Cascade wells is more

than 100 miles (161 km) away from established shipping lanes, which occur closer to the

coast.

An attendant vessel with fire fighting capability could also be a significant resource in the

event of a fire on the FPSO or Shuttle Vessel. Lifesaving capabilities on an attendant

vessel would be able to assist in the event of a man overboard or helicopter accident in

the vicinity of the FPSO as previously addressed in the initial DOCD.

The FPSO would also disconnect from the mooring and riser system for hurricanes and

named storms, providing a step change reduction in risks to people, the environment, and

assets regarding hurricane avoidance. Refer to Sections 1(f) and 2(e) for more

information regarding the disconnectable feature of the FPSO and the associated

pollution prevention controls that PAI will utilize.

Small spill less than 1,000 barrels would be expected to have a short term, non-significant

impact to marine water quality. Larger spills, however, could impact marine water

quality more significantly. This is not expected to affect coastal resources due to the

site’s distance from shore and the expected response activities that would occur in event

of a spill (Ji et al., 2007). According to the worst case discharge analysis evaluated

seafloor intervention which anticipated 21 days to kill a well blow out resulting in a

potential discharge of 325,017 barrels and a relief well would take longer, an estimated

110 days resulting in a potential discharge of 1,702,470 barrels. However, the chance of

a large spill is extremely unlikely given the controls that PAI will put in place. The

accidental release of synthetic-based drilling fluids and blowouts could have temporary

localized impacts on marine water quality. Refer to Sections 1(f) to review additional

pollution prevention measures and Section 9 to review oil spill response planning.

Depending on the size of a spill, accidents would have the potential to result in short term

adverse impacts on sperm whales but these impacts would likely be sublethal (NOAA

2002). Sea turtles may be more affected by spills, especially large ones, but this would

not affect the species’ population to survive and recover from any loss (NOAA 2002).

The proposed Cascade wells would not result in different impacts from those assessed in

the FPSO EIS. Potential effects of impacts from other marine vessels would not be
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expected due to the small number of vessels that use the Gulfmex No. 2 lightering zone

far from the project site, the distance of the project to established shipping lanes, and

because a dedicated field tug would maintain a constant watch onsite to prevent such a

situation from occurring.

Military Warning Areas in the Central Gulf of Mexico would be transited by marine

support vessels, Shuttle Vessels, and helicopters. This would be mitigated by following

the Military Areas Stipulation for these lease blocks, which requires that PAI enter into

an agreement with the command headquarters prior to commencing any traffic in one of

the military warning areas. This would prevent any conflicts between PAI and military

operations. Therefore, no impacts to military operations are expected.

19(c).8 Other Impacts Identified

No impacts are expected on socioeconomic and human resources such as coastal

infrastructure, navigation and port usage, or recreational resources. The direct and

indirect expenditures of the project would have a minor and temporary positive impact on

the economic activities around the support facility at Port Fourchon. This project would

have no effects on minority or low income populations. Nor would there be any

secondary impacts to coastal resources or populations as a result of land-based support

activities, use of infrastructure, or traffic.

19(d) Environmental Hazards

A number of environmental hazards exist in this area of the GoM: geological,

meteorological such as named hurricanes; and strong currents that could impact the

project and are described below.

19(d).1 Geological Hazards

The primary geological hazards that could affect a deepwater well development include

variable sediment types, steep slopes, high sedimentation rates, gas hydrates at or near the

seafloor, interstitial gas, faulting, carbonate areas, salt and shale mobilization, and mud

flows (MMS 2001). The GEMS Shallow Hazards Report for Facilities and the Summary

of Environmental Conditions for Cascade / Chinook in Appendix 2 describes the

potential hazards and how they will be mitigated.

19(d).2 Hydrogen Sulfide Determination

The Cascade / Chinook fields were analyzed and addressed in the initial DOCD. H2S is

not present in significant quantities in the project area. The reservoirs will be designated

“H2S Absent” subject to MMS approval.

19(d).3 Loop Current and Deep Ocean Currents

The Loop Current is the dominant circulation feature in the GoM, entering through the

Yucatan Channel and exiting through the Florida Straits. The MMS-funded DeSoto

Canyon Eddy Intrusion Study (Hamilton et al. 2000) was undertaken to take current and
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temperature measurements at British Petroleum’s Atwater Block 618, which is located at

the base of the Sigsbee Escarpment in water depths of approximately 6,561 feet (2,000

m). This is approximately 50 miles (80.5 km) north-northeast of the Cascade / Chinook

Development area. The data showed unusual deep current flows that were typical of

topographic Rossby waves (TRWs); however, the energy levels of TRWs in the study

area were exceptional, while their duration was short compared to other areas of the Gulf

(Hamilton et al. 2003). There are suggestions that deepwater currents are a result of

TRWs that are generated westward by Loop Current fluctuations, Loop Current eddy

shedding events, or the movement of Loop Current eddies (Hamilton et al. 2003). These

waves are most likely to affect the central and eastern portions of the GoM but the

generation mechanisms for them are not well understood (Hamilton et al. 2003).

The Sigsbee Escarpment was the primary focus of the above study, and similar conditions

are expected in the Walker Ridge area. It is known that significant currents (up to 2

knots) occur along the base of the Sigsbee Escarpment (Bryant et al. 2004). The

evidence for this is also found in the form of mega-furrows, which occur throughout the

Cascade / Chinook development area and are the result of high speed currents that have

built up these sediments over thousands of years. Refer to the geophysical report in

Appendix 2 for additional information. In addition to TRWs, density currents associated

with the leaching of exposed salt along the escarpment add to the complex current

conditions in this area (Bryant et al. 2004). Refer also to Section 19(c).4.

The FPSO is designed to remain on station for 1.) a 100-year return winter storm with a

1-year return loop current and 2.) a 100-year return loop current with a 1-year return

winter storm. PAI has access to data collected on the Loop Current and would know

days in advance if a significant Loop Current event, such as a topographic Rossby wave,

is expected to occur near the location of the Cascade Field while the proposed activities

are underway. The associated drill ship could thus respond accordingly by disconnecting

if the thresholds are met. PAI would also measure ocean currents at the site as required

by NTL 2007-G17, Deepwater Ocean Current Monitoring on Floating Facilities.

19(d).4 Hurricanes and Named Storms

Hurricane season in the Atlantic basin officially runs from June 1 through November 30;

however, about 75% of the Category 3 or stronger hurricanes occur in August and

September. Over the last few years, oil and gas activities in the GoM have been

significantly disrupted by several major hurricanes, including Lili (in 2002), Ivan (2004),

Katrina (2005), Rita (2005) and Ike (2008).

Hurricane Ike affected 49 of the 3,800 offshore oil and gas platforms in the Gulf. At one

point just prior to Katrina’s landfall, 79% of Gulf platforms were evacuated and 1.4

million barrels of oil per day (95% of normal Gulf OCS daily production) and 8.8 billion

cubic feet of gas per day (88% of normal Gulf OCS production) were shut in. Katrina

destroyed 44 platforms as it passed over the region, including some deepwater projects

that were under construction. As Rita passed over, 93% of platforms were evacuated

with the shut-in of 100% and 81% of normal daily oil and natural gas production,
19 Environmental Impact Analysis (EIA)

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respectively. Sixty-nine platforms were destroyed by Hurricane Rita (Energy

Information Agency 2006).

In addition to upstream impacts, the hurricanes had significant impacts on midstream and

downstream infrastructure. Four hundred fifty-seven underwater pipelines were

damaged, and the Louisiana Offshore Oil Port temporarily stopped accepting shipments

during the 2005 storms. Some onshore crude oil refineries and natural gas processing

facilities also suffered heavy damage. After Katrina hit Louisiana, nearly 2 million

barrels per day of refinery capacity were shut down either due to direct damage or

interruption of power supplies. More than 4.9 million barrels per day of refinery capacity

were shut down after Hurricane Rita hit the Texas coast (Energy Information Agency

2006; see also MMS 2006b). Hurricanes Rita and Katrina resulted in the destruction of

more than 100 platforms, which were all in shallow water except for a facility located in

Green Canyon block 237 (French et al. 2006).

MMS issued NTL 2009-G13, which provides operators with additional guidance to

ensure that production platforms, drilling and workover rigs, and other equipment and

facilities on the OCS are secured during hurricane seasons in the GoM.

PAI will utilize an FPSO which will have a single point mooring system which will allow

for full passive weathervaning. The single point mooring system will have a

disconnectable feature which will allow the FPSO to disconnect and motor away from

named storms and hurricanes under her own power, returning for re-connection when it is

safe to do so. The disconnectable feature provides a step change reduction in risk

regarding the protection of people, the environment, and assets. After disconnection, the

turret buoy (which is attached to the FPSO mooring lines, FSHRs, and umbilicals) will be

left behind in a submerged condition out of harms way of the environment conditions at

the surface.

Drill ships associated with the proposed operations on the Cascade Field may also

respond by disconnecting if certain thresholds are met.

19(d).5 Operating Environmental Criteria for Product Offloading

PAI has defined more conservative environmental operating criteria for FPSO offloading

relative to the maximum operational conditions for GoM lightering operations as

specified in 33 CFR 156.320. Parameters for shuttle approach and connection as well as

offloading are summarized in Table 2-7 located in Section 2(e).

19(e) Alternatives

PAI evaluated an alternative to installation of the gas export pipeline in Phase 1 during

early conceptual design. Rather than seek BOEM approval for low volume gas flaring

for the early stages of Phase 1, PAI decided to install the gas export pipeline during the

early stages of Phase 1 to eliminate such flaring. The gas export line will be ready for

utilization at first oil production and will minimize impact to the environment. With the

development of previous wells in the Cascade/Chinook Development Area there are no

other least damaging practicable alternatives.
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19(f) Mitigation Measures

Section 1(f) describes the most important safety and pollution prevention controls that

PAI will utilize to mitigate the potential for any adverse effects to GoM resources. Such

controls are generally aimed at minimizing the frequency and magnitude of oil spills.

The effective implementation of such industry proven controls will effectively eliminate

the potential for large oil spills which could have an impact to GoM resources. See also

Section 12 for mitigation measures.

19(g) Consultation and Coordination

Meeting Contacts

Minerals Management Service (MMS), 2006, Meeting between MMS Gulf of Mexico

Region staff (Russell Hoshman; Michael Tolbert, Plans; Manny Gagliano,

Pipelines; Ronald Bowser; Holly Karrigan; Christy Bohannon; Mike Conner,

Field Operations; B.J. Kruse, Field Operations; Mike Saucier; Houma District;

Bryan Domangue, Houma District; Glenn Woltman; Nick Wetzel, Plans; Carole

Current, Leasing and Environment; Stephen Kovacs; Dennis Chew, Leasing and

Environment; and Ed Richardson, NEPA lead) and PAI staff (Luiz Souza, FPU

Production and Operation Manager; Gus Cassity, Phase 1 Coordinator; Mike

Bigler, Corporate HSE Coordinator; Cheryl Saha, Land Manager; Partha

Ganguly, Millennium Technical Consultants; Wanda Richmond, J. Connor

Consulting, Inc.; and Carliane Johnson, Ecology and Environment, Inc.) on

September 6, 2006 in New Orleans, LA to provide an introduction to the

Cascade / Chinook project and discuss the regulatory framework for FPSOs.

State of Louisiana, 2007, Meeting between Louisiana Department of Natural Resources

(DNR) Coastal Management Division (CMD) staff (Brian Marcks; Jeff Harris;

Agaha Brass; and Gregory DuCote) and PAI staff (Mike Bigler, Corporate HSE

Coordinator and Carliane Johnson, Ecology and Environment, Inc.) on February

12, 2007 in Baton Rouge, LA to provide an introduction to the Cascade / Chinook

project and to better understand any concerns by the State of Louisiana.

State of Texas, 2007, Meeting between State of Texas staff (Tammy Brooks, Texas

General Land Office; Jesse Solis, Texas General Land Office; Leslie Savage,

Railroad Commission of Texas; David Nuckels, Texas Department of

Transportation; Jarrett (Woody) Woodrow, Texas Parks and Wildlife Department;

and Cherie O’Brien, Texas Parks and Wildlife Department) and PAI staff (Mike

Bigler, Corporate HSE Coordinator and Carliane Johnson, Ecology and

Environment, Inc.) on March 19, 2007 in Austin, TX to provide an introduction to

the Cascade / Chinook project and to better understand any concerns by the State

of Texas.
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Telephone and E-mail Contacts

Dunlap, K. 2011, Personal communication, Karen Dunlap Plans Section, BOEM, New

Orleans telephone conversation with G Collins regarding greenhouse gas

reporting, frequency of environmental monitoring, extent and duration of oil spill

analysis, and meeting February 28, 2011.

Dunlap, K. 2011, email, Karen Dunlap, Plans Section, BOEM, New Orleans email with

Greg Roland regarding Supplemental DOCD required, requested NTL 2010-N06

information, expanded radius for biological survey, OSRP comparison, CZM

review, and AGOV review.

Anderson, C., 2006, Personal communication, Cheryl Anderson, Operations Research

Analyst, Engineering and Research Branch, Engineering and Operations Division,

Mineral Management Service, Herndon, VA, telephone conversation on June 21,

2006 regarding world wide oil spill records, with Davey Crawley, Ecology &

Environment Inc., Pensacola, FL.

Boland, G., 2006, Personal communication, Greg Boland, Leasing and Environment

Section, Minerals Management Service, New Orleans, LA, telephone

conversations on August 10 and October 20, 2006 regarding the geophysical

mapping surveys and interpretation of 3D seismic to determine the presence of

chemosynthetic communities, with Carliane Johnson, Ecology and Environment,

Inc., Arlington, VA.

Breeding, D., G. Goeke and G. Kozlowski, 2007, Personal communication, Darice

Breeding, Gary Goeke, and Greg Kozlowski, Minerals Management Service, New

Orleans, LA, telephone conference call on May 1, 2007 regarding the quantity to

consider for a worst-case discharge, with Mike Bigler, PAI., Houston, TX and

Carliane Johnson, Ecology and Environment, Inc., Arlington, VA.

Breeding, D., 2006, Personal communication, Darice Breeding, Minerals Management

Service, New Orleans, LA, E-mail correspondence in July 2006 regarding U.S.

and Mexico oil and hazardous spill response agreements, with Carliane Johnson,

Ecology and Environment, Inc., Arlington, VA.

Clark, Tricia, 2006, Personal communication, Co-chair of the Industry Taskforce on

Offshore Lightering (ITOL) Group, Houston, TX, telephone conversation on

August 8, 2006 regarding lightering operations, with Jeff Hammond, Ecology and

Environment, Inc., Buffalo, NY.

Conner, M., 2006, Personal communication, Mike Conner, Technical Assessment and

Operations Support Section, Minerals Management Service, New Orleans, LA,

telephone conversation on August 21, 2006 regarding the scheduling of an

introductory meeting with MMS, PAI officials, and others to discuss the

Cascade / Chinook project, with Carliane Johnson, Ecology and Environment,

Inc., Arlington, VA.
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Current, C., 2007, Personal communication, Dr. Carole Current, Oceanographer,

Minerals Management Service, New Orleans, LA, E-mail correspondence and

phone communication between October 2006 and April, 2007 regarding oil spill

risk analysis (OSRA) modeling runs for hypothetical spill in the Cascade /

Chinook development blocks of Walker Ridge, with Carliane Johnson, Ecology

and Environment, Inc., Arlington, VA.

Cushing, J., 2006, Personal communication, John Cushing, Commander United States

Coast Guard, Washington, DC, telephone conversations on June 14, July 6 and

July 25, 2006 regarding the use of articulated tug barges (ATBs) in the Gulf of

Mexico, U.S. shipbuilding capacity for tanker construction, and regulatory

differences between ATBs and shuttle tankers, with Jeff Hammond, Ecology &

Environment Inc., Buffalo, NY.

Goeke, G., 2006, Personal communication, Gary Goeke, NEPA Specialist, Minerals

Management Service, New Orleans, LA, telephone conversation on June 28, 2006

regarding the sufficiency of data from 3D seismic versus side scan sonar to

determine the presence of chemosynthetic communities, with Carliane Johnson,

Ecology and Environment, Inc., Arlington, VA.

Hefren, F., 2006, Personal communication, Fred Hefren, Minerals Management Service,

New Orleans, LA, E-mail correspondence on June 22, 2006 regarding deepwater

current monitoring requirements, with Carliane Johnson, Ecology and

Environment, Inc., Arlington, VA.

Henry, C., 2006, Personal communication, Charlie Henry, National Oceanic and

Atmospheric Administration, New Orleans, LA, telephone conversation on

August 4, 2006 regarding the oil spill models used by NOAA, with Solange Silva,

Ecology and Environment, Inc., Houston, TX.

Herkhof, D., 2007, Personal communication, Dirk Herkhof, Meteorologist, Minerals

Management Service, New Orleans, LA, telephone conversation on February 26,

2007 regarding the air emissions analysis, with William Vasil, Ecology and

Environment, Inc., New York, NY.

__________, 2006, Personal communication, Dirk Herkhof, Meteorologist, Minerals

Management Service, New Orleans, LA, telephone conversation on December 29,

2006 regarding air emissions modeling that would be required if air emissions

exceed thresholds, with William Vasil, Ecology and Environment, Inc., New

York, NY.

Irion, J., 2006, Personal communication, Dr. Jack Irion, Archeologist, Minerals

Management Service, New Orleans, LA, telephone conversation on July 17, 2006

regarding surveying techniques for identifying archeological sites, with Carliane

Johnson, Ecology and Environment, Inc., Arlington, VA.
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Kozlowski, G, 2007, Personal communication, Gregory Kozlowski, Environmental

Protection Specialist, Minerals Management Service, New Orleans, LA, E-mail

correspondence on May 8 and May 9, 2007 regarding questions on the use of

MMS Form 137 and obtaining a copy of the stipulations from Lease Sale 157,

with Carliane Johnson, Ecology and Environment, Inc., Arlington, VA.

Ramos, J., 2006, Personal communication, Jeff Ramos, Commander United States Coast

Guard, New Orleans, LA, telephone conversations on June 13 and August 2, 2006

regarding articulated tug barge operations in the Gulf of Mexico, whether there

have been any lightering accidents in Gulfmex No. 2 area, and whether

regulations are proposed for the use of FPSOs, with Jeff Hammond, Ecology &

Environment Inc., Buffalo, NY.

Richardson, G.E., 2006, Personal communication, G. Ed Richardson, Mineral

Management Service, New Orleans, LA, telephone conversation on July 13, 2006

regarding NEPA implications of segmenting aspects of the Cascade / Chinook

project, with Carliane D. Johnson, Ecology & Environment Inc., Arlington, VA.

Shedd, W., 2006, Personal communication, Dr. William Shedd, Geophysicist, Minerals

Management Service, New Orleans, LA, telephone conversation on August 10,

2006 regarding the geophysical mapping surveys and interpretation of 3D seismic

to determine the presence of chemosynthetic communities, with Carliane Johnson,

Ecology and Environment, Inc., Arlington, VA.

Violetta, E., 2006, Personal communication, Captain Ernesto Violetta, Oil Spill or

Incident Primary Qualified Individual, American Eagle Tankers, Houston, TX,

telephone conversation on August 8, 2006 regarding lightering operations, with

Jeff Hammond, Ecology & Environment Inc., Buffalo, NY.

Wade, P., 2007, Personal communication, Peggy Wade, U.S. Environmental Protection

Agency Region 6, telephone conversation on February 21, 2007 regarding the

potential impact of a project that could add mobile source emissions to the

Houston/Galveston non-attainment area, telephone conversation with William

Daughdrill, Ecology and Environment, Inc., Pensacola, FL.

Wilson, Scott, 2007, Personal communication, Scott Wilson, Environmental Scientist,

U.S. Environmental Protection Agency, Region 6, Dallas, TX, E-mail

correspondence on January 25, 2007 regarding regulations for cooling water

intake structures on offshore oil and gas facilities, with Carliane Johnson, Ecology

and Environment, Inc., Arlington, VA.

__________, 2006, Personal communication, Scott Wilson, Environmental Scientist,

U.S. Environmental Protection Agency, Region 6, Dallas, TX, telephone

conversation on December 1, 2006 regarding thermal discharges, with Carliane

Johnson, Ecology and Environment, Inc., Arlington, VA.
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__________, 2006, Personal communication, Scott Wilson, Environmental Scientist,

U.S. Environmental Protection Agency, Region 6, Dallas, TX, telephone

conversation on July 12, 2006 regarding the reissuance of the NPDES GP after

the current GP expires in November 2007, with Thierry Garcy, Ecology and

Environment, Inc., New York, NY.

Wright R., 2006, Personal communication, Rusty Wright, Oil Spill Program

Administrator, Minerals Management Service, New Orleans, LA, telephone

conversation on July 6, 2006 regarding the Oil Spill Risk Analysis Model

(OSRAM) and the use of worst case discharge response scenarios for the Oil Spill

Response Plan, with Jeff Hammond, Ecology and Environment, Inc., Buffalo,

NY.

19(h) List of Preparers

The PAI representatives responsible for overall review of this EIA are:

Gregory D.Roland

Regulatory Compliance Area Manager

Petrobras America Inc.

10350 Richmond Ave, Suite 1400

Houston, Texas 77042

Phone: 713-808-2881

Solange Silva, Ph.D.

Walker Ridge Regulatory Advisor

Petrobras America Inc.

10350 Richmond Ave., Suite 1400

Houston, Texas 77042

Phone: 713-808-3004

The contractor responsible for preparing this EIA is:

Georganna Collins

Project Manager

Ecology & Environment, Inc.

2 Riverway, Suite 625

Houston, Texas 77056

Phone: 713-344-3000 Ext. 3505
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Table 19-20 identifies E&E contributors to the preparation of this EIA.

Table 19-20 – E&E Contributors to EIA

Name Role Project Responsibility

Mike Donnelly Project Director Principal Reviewer / Quality Assurance

Georganna Collins Project Manager Project Management and Document Development

Lisa Richard Administrative Specialist Document Production

Bill Vasil Air Specialist Air Emissions Analysis

Paul VanKerkhove Air Specialist Air Emissions Analysis

Jeff Hammond Maritime Support Vessel Requirements and Data Collection

Jennifer Harris Planner Socioeconomic Analysis

Valerie Meyer Biologist Coastal Zone Consistency Assessment

David Trimm Fisheries Biologist Fisheries

David Crawley Environmental Scientist Storm Data/Coastal Resources

Holli Brandt GIS Graphics

Greg Coniglio GIS Graphics

19(i) References

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a series of three maps: U.S. Geological Survey Open-File Report 06-1274.

Baumgartner, M.F., K.D. Mullin, L.N. May, and T.D. Leming, 2001, Cetacean Habitats

in the Northern Gulf of Mexico, Fisheries Bulletin, Vol. 99, pp. 219-239.

Benfield, M.C. and R.F. Shaw, 2005, Potential spatial and temporal vulnerability of

pelagic fish assemblages in the Gulf of Mexico to surface oil spills associated

with deepwater petroleum development, OCS Study MMS 2005-012, U.S. Dept.

of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New

Orleans, LA.

Block, Barbara A., Heidi Dewar, Susanna B. Blackwell, Thomas D. Williams, Eric D.

Prince, Charles J. Farwell, Andre Boustany, Steven L. H. Teo, Andrew Seitz,

Andreas Walli, and Douglas Fudge, 2001, Migratory Movements, Depth

Preferences, and Thermal Biology of Atlantic Bluefin Tuna, Science, 17 August

2001, Vol. 293, Downloaded from www.sciencemag.org on May 8, 2007.
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Boehm, P., D. Turton, A. Raval, D. Caudle, D. French, N. Rabalais, R. Spies, and J.

Johnson, 2001, Deepwater Program: Literature Review, Environmental Risks of

Chemical Products Used in Gulf of Mexico Deepwater Oil and Gas Operations,

Volume I: Technical Report, OCS Study MMS 2001a-011, U.S. Department of

the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New

Orleans, LA.

Boland, G., C. Current, M. Gravois, M. Metcalf, and E. Peuler, 2004, Fate and Effects of

a Spill of Synthetic-Based Drilling Fluid at Mississippi Canyon Block 778, OCS

Report MMS 2004-039, U.S. Department of the Interior, Minerals Management

Service, New Orleans, LA.

Bryant, W., N. Slowey, S. DiMarco, D. Bean, and D. Berti, 2004, Deep-sea furrows:

Physical characteristics, mechanisms of formation and associated environmental

processes, Final Report (August 2003 – September 2004) to Research Partnership

to Secure Energy for America, Subcontract No. R-505, Sugar Land, TX, report

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Offshore Lightering (ITOL) Group, Houston, TX telephone interview with Jeff

Hammond, Ecology and Environment, Inc., Buffalo, NY, August 8, 2006.

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Continental Shelf Associates, Inc., and Texas A&M University, Geochemical and

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Management Service, Gulf of Mexico OCS Region, New Orleans, LA.
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__________, 2000, Deepwater Gulf of Mexico Environmental and Socioeconomic Data

Search and Literature Synthesis, Volume I: Narrative Report, OCS Study MMS

2000-049, U.S. Department of the Interior, Minerals Management Service, Gulf

of Mexico OCS Region, New Orleans, LA.

Cordes, E.E., 2006, Ecology of Gulf of Mexico Deep-Sea Hard-ground Communities,

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nds/hardgrounds.html.

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Service, Southeast Fisheries Science Center, Beaufort, NC.

Couvillion, B.R., Barras, J.A., Steyer, G.D., Sleavin, William, Fischer, Michelle, Beck,

Holly, Trahan, Nadine, Griffin, Brad, and Heckman, David, 2011, Land area

change in coastal Louisiana from 1932 to 2010: U.S. Geological Survey Scientific

Investigations Map 3164, scale 1:265,000, 12 p. pamphlet.

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Development Operations Coordination Document

Cascade / Chinook Development Project

20 Administrative Information

20(a) Exempted Information Description

PAI has determined that the following information in Table 20-1 is considered

proprietary and will therefore not be included in the public version of the SDOCD.

Table 20-1 – Proprietary Information

Description Section

BHL, TVD, and MD information in Plan Information Forms 1(a), 1(b)

Production rates 2(c)

Geological and geophysical information 3 (a), 3(b), 3(c), 3(d), 3(e),

3(f)

Hydrogen Sulfide Classification 4(b)

Reservoir Information and Exploratory Well Results 5(b)

Topographic Features Map 6(b)

Archeological Resources Information and Figure 19(b).15

Geological and geophysical information Appendix 2-B

Worst-Case Discharge Evaluation Appendix 6

20(b) Bibliography

The following citations were used in the DOCD. This list excludes citations that were

used in the EIA contained in Section 19.

Ji, Zhen-Gang, Walter R. Johnson, Charles F. Marshall, and Eileen M. Lear (Editor),

2007, Oil-Spill Risk Analysis: Contingency Planning Statistics for Gulf of

Mexico OCS Activities, U.S. Department of the Interior Minerals Management

Service, Environmental Division, Herndon, VA.
20 Administrative Information

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Petrobras America, Inc. 

Development Operations Coordination Document 

Cascade / Chinook Development Project 

APPENDIX 1

Cascade / Chinook SOP Approvals
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Petrobras America, Inc. 

Development Operations Coordination Document 

Cascade / Chinook Development Project 

APPENDIX 1a 

Approved DWOP - 18 August 2009 
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Petrobras America, Inc. 

Development Operations Coordination Document 

Cascade / Chinook Development Project 

APPENDIX 2a 

GEMS Summary of Environmental Conditions 

for Cascade and Chinook 
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Petrobras America, Inc. 

Development Operations Coordination Document 

Cascade / Chinook Development Project 

APPENDIX 2b 

GEMS Shallow Hazards Report for Facilities - 

    Public Version 
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. 

. 

. 

. 

. 

. 

.

. 

. 

. 

Seafloor and Geologic Assessment 

Cascade and Chinook Development 

Areas 

Blocks 160-162, 203-208, 247-252, 

293-295, 337-338, 381-382, 425-426, 

& 469-470 

Walker Ridge Area 

Gulf of Mexico 

Report submitted to

Petrobras America Inc.

Houston, Texas 

by

Geoscience Earth & Marine Services®, Inc. 

Houston, Texas 

PUBLIC COPY 

Project No. 1106_1257b 

10615 Shadow Wood Dr., Suite 200

Houston, Texas 77043

(713) 468-1410 phone

(713) 468-1438 fax

gems@gemsinc.com
10615 SHADOW WOOD DRIVE 

SUITE 200 

HOUSTON, TEXAS 77043 

 Phone: (713) 468-1410 

Fax: (713) 468-1438 

E-mail: gems@gemsinc.com

June 6, 2007 Project No. 1106_1257b 

Petrobras America Inc. 

Walker Ridge EPS-Subsea Engineering 

2101 City West Blvd. Bldg 3, Suite 300 

Houston, Texas 77042 

Attention: Mr. Kazuhiko Kochi 

SEAFLOOR AND SHALLOW GEOLOGIC ASSESSMENT 

CASCADE AND CHINOOK DEVELOPMENT AREAS 

BLOCKS 160-162, 203-208, 247-252, 293-295, 337-338, 381-382, 425-426, & 469-470 

WALKER RIDGE AREA, GULF OF MEXICO 

 Geoscience Earth & Marine Services®, Inc., (GEMS) is pleased to provide Petrobras America Inc. 

(PAI) with our geophysical and geotechnical evaluation of the Cascade and Chinook development areas in 

the Walker Ridge Area (WR) of the Gulf of Mexico. The purpose of this report is to define seafloor and 

shallow geologic/geotechnical conditions and constraints relevant to future development of the Cascade 

and Chinook areas, as well as along proposed tie-back and export flowlines and umbilicals routes. The 

Cascade development is composed of two drill centers, located in WR Blocks 206 and 249, that tie-back to 

a floating production, storage, and offloading vessel (FPSO) in WR Block 249, having anchors in WR 

Blocks 250, 293, and 294, and pipelines and umbilicals traversing portions of WR Blocks 206, 249, 250 

293, and 294. The Chinook development is composed of a drill center located in WR Block 425. Dual 

flowlines, with associated umbilicals, crossing WR Blocks 293, 337, 371, and 425, will tie-back ~11.5 

miles to the Cascade FPSO. 

The report complies with requirements set forth by the United States Minerals Management Service (MMS) 

in government publications Notice-to-Lessees 2000-G20 (MMS, 2000), Notice-to-Lessees 2002-G01 

(MMS, 2002), and Notice-to-Lessees 2007-G01 (MMS, 2007). This report is in accordance with Purchase 

Order 7000000549 dated 14 November, 2006. We appreciate the opportunity to be of service to PAI on 

this project and look forward to working closely with you as this landmark project progresses. 

 Sincerely, 

 GEOSCIENCE EARTH & MARINE 

 SERVICES®, INC. 

James F. Keenan John R. Brand, Ph. D 

Geoscientist Senior Geologist / Projects Manager 

Michael J. Kaluza 

President 

Distribution: Mr. Kazuhiko Kochi, Petrobras America Inc., Houston, Texas (5) 
Project No. 1106-1257b TABLE OF CONTENTS

TABLE OF CONTENTS 

MAIN TEXT 

 Page

SUMMARY i 

SECTION 1: INTRODUCTION 1 

Purpose ............................................................................................................................................................ 2 

Available Data ................................................................................................................................................ 2

Proprietary Geophysical Data ............................................................................................................... 2 

Proprietary Geotechnical Data .............................................................................................................. 4

Public Data .............................................................................................................................................. 4

Project Responsibilities ................................................................................................................................. 4 

Report Format ................................................................................................................................................ 4 

SECTION 2: REGIONAL GEOLOGIC SETTING 6 

Location .......................................................................................................................................................... 6

Lower Continental Slope ................................................................................................................... 7 

Structure ................................................................................................................................................... 7 

Stratigraphy ............................................................................................................................................. 7 

Sigsbee Escarpment .......................................................................................................................... 9 

Structure ................................................................................................................................................... 9 

Stratigraphy ............................................................................................................................................. 9 

Upper Continental Rise ..................................................................................................................... 10 

Structure ................................................................................................................................................... 10 

Stratigraphy ............................................................................................................................................. 10

Faults ............................................................................................................................................................... 10 

Slope Stability ................................................................................................................................................ 11 

Seafloor Currents ........................................................................................................................................... 11

Hydrocarbon Migration and Related Seafloor Features ........................................................................... 11 

Hydrocarbon Vents ................................................................................................................................ 11

Hydrates ................................................................................................................................................... 12

Authigenic Carbonates ........................................................................................................................... 12 

Chemosynthetic Communities ..................................................................................................................... 12 

Shallow Water Flow ...................................................................................................................................... 13

Exploration Activity and Man-Made Structures ....................................................................................... 13 

SECTION 3: SHALLOW GEOLOGIC CONDITIONS IN THE 

 CASCADE DEVELOPMENT AREA 14 

Bathymetry and Seafloor Gradient .............................................................................................................. 14 

Physiographic Provinces, Seafloor Morphology, and Stratigraphy ....................................................... 14 

 Lower Continental Slope (LCS) ........................................................................................................... 15 

 The Sigsbee Escarpment (SE) ............................................................................................................... 17 

 The Upper Scarp .................................................................................................................................. 19 

 The Bench .............................................................................................................................................. 19 

 The Lower Scarp ................................................................................................................................... 20 

 Upper Continental Rise (UCR) ............................................................................................................. 21 

 Seafloor Furrows .................................................................................................................................. 22 

 Seafloor Flukes ..................................................................................................................................... 23 

 Seafloor Flukes and Furrows ............................................................................................................. 25 
Project No. 1106-1257b TABLE OF CONTENTS

 Topographic Low ................................................................................................................................. 26 

Chemosynthetic Communities ..................................................................................................................... 28 

 LCS Province .......................................................................................................................................... 28 

 SE Province ............................................................................................................................................. 28

 UCR Province ......................................................................................................................................... 28 

SECTION 4: SHALLOW GEOLOGIC CONDITIONS IN THE 

 CHINOOK DEVELOPMENT AREA 30 

Bathymetry and Seafloor Gradient .............................................................................................................. 30 

Physiographic Provinces, Seafloor Morphology, and Stratigraphy ....................................................... 30 

 (UCR) Seafloor Furrows ....................................................................................................................... 31 

 (UCR) Seafloor Anti-Dunes .................................................................................................................. 31

 (UCR) Topographic Low ...................................................................................................................... 32 

Geotechnical Data .......................................................................................................................................... 33 

Chemosynthetic Communities ..................................................................................................................... 34 

SECTION 5: SEAFLOOR AND SHALLOW GEOLOGIC CONDITIONS 

 OF THE CHINOOK TIE-BACK PIPELINE CORRIDOR 35 

Water Depths and Gradient .......................................................................................................................... 35 

Seafloor Currents ........................................................................................................................................... 35 

Seafloor Morphology and Soils ................................................................................................................... 35 

 Seafloor Anti-dunes ................................................................................................................................ 35 

 Seafloor Furrows .................................................................................................................................... 36 

Sediments ........................................................................................................................................................ 36 

Man-made Features and Conditions ............................................................................................................ 36 

GEOLOGIC CONDITIONS ALONG THE PROPOSED WEST FLOWINE ROUTE ..................... 36 

Man-made Features and Conditions ............................................................................................................ 37 

Chemosynthetic Communities ..................................................................................................................... 37 

GEOLOGIC CONDITIONS ALONG THE PROPOSED EAST FLOWINE ROUTE ...................... 37 

Man-made Features and Conditions ............................................................................................................ 38 

Chemosynthetic Communities ..................................................................................................................... 38 

SECTION 6: FINDINGS AND RECOMMENDATIONS 39 

Cascade Development Area ......................................................................................................................... 39 

Chinook Development Area ......................................................................................................................... 40 

Chinook Tie-Back Corridor ......................................................................................................................... 40 

Summary of Geologic and Geotechnical Findings With Respect to Proposed Field Architecture.... 41 

Recommendations.............................................................................................................................. 46 

LIST OF FIGURES 

 Page No.

Figure 1: Location Map ................................................................................................................... 1 

Figure 2: Seafloor rendering showing outline of the data coverage ............................................... 3 

Figure 3: Regional seafloor rendering of the northwestern Walker Ridge area showing the 

 development areas in relation to major seafloor topographic features .......................... 6 

Figure 4: 3-D seismic inline 8100 illustrating the salt related structural setting beneath 

 the Sigsbee Escarpment ................................................................................................. 7 

Figure 5: Regional illustration of the Study Area in relation to the major Pleistocene 

 Mississippi River depositional provinces ...................................................................... 8 
Project No. 1106-1257b TABLE OF CONTENTS

LIST OF FIGURES (Cont.’) 

 Page No.

Figure 6: Isometric view of the Sigsbee Escarpment in the Cascade area showing slump scarps 

 on the Escarpment and associated debris apron on the Upper Continental Rise ........... 9 

Figure 7: Physiographic provinces within the Cascade Development area .................................... 15 

Figure 8: The portion of subbottom profiler line 202 displays typical structure and stratigraphy 

 of the Lower Continental Slope province ...................................................................... 16 

Figure 9: Geotechnical test results for the LCS province ............................................................... 17 

Figure 10: Isometric view of the Sigsbee Escarpment within the Cascade Development area 

showing a bench separating an upper and lower scarp .................................................. 18 

Figure 11: Subbottom Profiler lines perpendicular (left) and parallel (right) to the 

 Sigsbee Escarpment illustrating the varying stratigraphy and highly 

 deformed structure of the Escarpment ........................................................................... 18 

Figure 12: Geotechnical test results for the upper scarp of the SE province ................................... 19 

Figure 13: Geotechnical test results for the bench of the SE province ............................................ 20 

Figure 14: Geotechnical test results for the lower scarp of the SE province ................................... 21 

Figure 15: Subbottom profiler line 138 shows the transition between “fluked” 

 and “Furrowed” seafloor .............................................................................................. 22 

Figure 16: Geotechnical test results for the seafloor furrows of the UCR province ........................ 23 

Figure 17: Geotechnical test results for the seafloor flukes of the UCR province ........................... 24 

Figure 18: Geotechnical test results for the seafloor furrowed furrows of the UCR province ........ 25 

Figure 19: Subbottom profiler line within the topographic low shows folded strata in the 

 shallow subsurface. Darker regions on the side-scan mosaic (Maps 2C and 3C) 

 indicate areas where the “triplet” outcrops .................................................................... 27 

Figure 20: Composite soil information to estimate conditions for the topographic low 

 Region of the UCR province ......................................................................................... 27 

Figure 21: Subbottom profiler line 117 showing mounds in the LCS province .............................. 28 

Figure 22: Physiographic sub-provinces within the Chinook Development Area ........................... 30 

Figure 23: Subbottom profiler line 641 showing furrows in the Chinook Development Area ........ 31 

Figure 24: Subbottom profiler line 641 showing anti-dunes in the 

 Chinook Development Area .......................................................................................... 32 

Figure 25: Subbottom profiler line 725 showing anticlines in WR 469 and 470 ............................ 32 

Figure 26: Subbottom profiler line 720 showing the topographic low 

 in the Chinook Development area ................................................................................. 33 

Figure 27: Geotechnical test results for the Chinook area, UCR province ...................................... 34 
Project No. 1106-1257b TABLE OF CONTENTS

LIST OF TABLES 

Table No.

Table of AUV data coverage ................................................................................................................ 1 

Table of existing and proposed wells ................................................................................................ 2 

List of cores for the LCS province .................................................................................................... 3 

List of cores for the upper scarp of the SE province ......................................................................... 4 

List of cores for the bench of the SE province .................................................................................. 5 

List of cores for the lower scarp of the SE province ......................................................................... 6 

List of cores for the seafloor furrows of the UCR province ............................................................. 7 

List of cores for the seafloor flukes of the UCR province ................................................................ 8 

List of cores for the seafloor furrowed flukes of the UCR province ................................................ 9 

List of cores for the Chinook area, UCR province ........................................................................... 10

Water depth and gradient along the Tie-Back routes ........................................................................ 11 

West Tie-Back block crossings ......................................................................................................... 12 

Water depth and gradient along the west Tie-Back route ................................................................. 13 

East Tie-Back block crossings .......................................................................................................... 14 

Water depth and gradient along the east Tie-Back route .................................................................. 15 

Summary Table ................................................................................................................................. 16 

 LIST OF MAPS 

Map No.

Cascade Development Area 

Base Map, Cascade Development Area ............................................................................................ 1A 

Bathymetry Map, Cascade Development Area ................................................................................. 2A 

Seafloor Gradient Map, Cascade Development Area ....................................................................... 3A 

Seafloor Rendering, Cascade Development Area ............................................................................. 4A 

Isopach Map, Seafloor to “Triplet” ................................................................................................... 5A 

Structure Map, Sea Surface to Top of Salt ........................................................................................ 6A 

Side-Scan Mosaic, Cascade Development Area ............................................................................... 7A 

Features Map, Cascade Development Area ...................................................................................... 8A 

Chinook Development Area 

Base Map, Chinook Development Area ........................................................................................... 1B 

Bathymetry Map, Chinook Development Area ................................................................................ 2B 

Seafloor Gradient Map, Chinook Development Area ....................................................................... 3B 

Seafloor Rendering, Chinook Development Area ............................................................................ 4B 

Isopach Map, Seafloor to “Triplet” ................................................................................................... 5B 

Side-Scan Mosaic, Chinook Development Area ............................................................................... 6B 

Features Map, Chinook Development Area ...................................................................................... 7B 

Chinook Tie-Back Corridor 

Regional Study Map, Chinook Tie-Back .............................................................................................. 1C 

West Flowline Alignment Sheet ......................................................................................2C (Sheet 1 of 2) 

West Flowline Alignment Sheet ......................................................................................2C (Sheet 2 of 2) 

East Flowline Alignment Sheet ........................................................................................3C (Sheet 1 of 2) 

East Flowline Alignment Sheet ........................................................................................3C (Sheet 2 of 2) 

Note: Maps are in pockets at rear of report. 
Project No. 1106-1257b TABLE OF CONTENTS

LIST OF APPENDICES 

Appendix A: Side-Scan Sonar Targets 

Appendix B: Geotechnical Core Logs 

Appendix C: References 

Appendix D: Interpretive Procedures 

Appendix E: R/V Northern Resolution and AUV Descriptions
Project No. 1106-1257b SUMMARY

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SUMMARY 

 Petrobras America Inc. (PAI) contracted Geoscience Earth & Marine Services®, Inc., (GEMS) to 

evaluate the geologic and stratigraphic conditions in the Cascade and Chinook development areas in 

Walker Ridge (WR), Blocks 160-162, 203-208, 247-252, 293-295, 37-338, 381-382, 425-426, and 469-

470. The purpose of this study was to assess the seafloor and shallow geologic conditions at the planned 

floating production, storage, and offloading (FPSO) facility in WR 249, at the Cascade and Chinook drill 

centers in WR 206, 249, and 425, along infield pipelines and umbilicals in portions of WR Blocks 206, 

249, 250 293, and 294, and along the proposed flowline and umbilical routes between the Chinook drill 

center in WR 425 and the FPSO in WR 249. The study was conducted using AUV, 3-D seismic, and 

shallow geotechnical soil samples to assess the upper 150 ft BML of sediment in the Cascade and Chinook 

development areas. 

General Conditions in the Cascade Development Area 

• The geologic and geotechnical conditions observed at Chinook appear favorable for field 

development. 

• Water depths in the Cascade Development area range from 5,637 ft in the northeastern corner of 

WR 247 to 8,510 ft in the north-central part of WR 338. 

• The area consists of three geomorphologic provinces, the Lower Continental Slope, the Sigsbee 

Escarpment, and the Upper Continental Rise, with the Escarpment crossing the northeastern portion 

of the area. 

• The proposed Cascade facilities will be placed below the Escarpment on the Upper Continental 

Rise. 

• The seafloor above the Escarpment, on the Lower Continental Slope, is generally smooth and 

featureless. The Escarpment seafloor is rugged. The seafloor below the Escarpment is irregular due 

to seabed furrows and flukes. 

• Seafloor gradients range from near 0o above the Sigsbee Escarpment on the Lower Continental 

Slope to approximately 70° along the steeper portions of the Escarpment. The Upper Continental 

Rise has a low general gradient, however, furrows and flukes can cause locally high gradients. 

• The shallow stratigraphy over the area consists generally of parallel bedded hemipelagic clays. 

Local slump deposits exist at the base of the Escarpment and sands are present along the floors of 

the furrows. 

• Periodic strong seabed currents are responsible for the formation of the furrows and flukes on the 

Upper Continental Rise. Evidence of significant erosion is also evident on both the Escarpment 

and Lower Continental Rise. PAI is aware of these conditions and is addressing the placement of 

seafloor architecture in these areas from a siting and design standpoint. 

• Past slope instability along the Escarpment has resulted in deposition of debris aprons which 

extend up to one mile downslope of the base of the Escarpment. The nearest proposed facility to 

the Escarpment is the Cascade East drill center located approximately one mile downslope of the 

Escarpment. PAI intends to conduct a future, detailed slope stability of the Escarpment with 

respect to locations of the Cascade facilities. 

• Several gas expulsion mounds are identified on the Lower Continental Slope in northeastern WR 

160, more than four miles away from the proposed facilities. 

• In the area of the Upper Continental Rise, where the Cascade facilities are planned, there are no 

geologic constraints such as active faulting, gas venting, or hard bottom conditions that would 

impact field development. 
Project No. 1106-1257b SUMMARY

- ii -

• There is no potential for encountering chemosynthetic communities near the planned infrastructure. 

General Conditions in the Chinook Development Area 

• The geologic and geotechnical conditions observed at Chinook appear favorable for field 

development. 

• Water depths in the Chinook Development area range from 8,607 ft in the northwestern corner of 

WR 425 to 9,260 ft in the southeastern corner of WR 470. 

• Seafloor gradients range from close to 0o over much of the southwestern two-thirds of the area with 

locally high gradients, approaching 50°, along the sides of furrows in the northeastern third of the 

area. 

• The shallow stratigraphy over the area consists generally of parallel bedded, differentially eroded, 

hemipelagic clays. Sands are present along the floors of the furrows. 

• Seafloor furrows are present in the north, and seafloor anti-dunes are present in the south and 

southeastern portion of the area. Periodic strong seabed currents are responsible for the formation 

of the furrows and anti-dunes. 

• There are no geologic constraints such as active faulting, gas venting, or hard bottom conditions 

that would impact field development. 

• There is no potential for encountering chemosynthetic communities in this area. 

General Conditions in the Chinook Pipelines Tie-Back Corridor 

• The geologic and geotechnical conditions appear favorable for flowline installation and 

performance, with appropriate engineering design. 

• There are two proposed tie-back pipelines and one production umbilical in a corridor between the 

Chinook development area in WR 425 and the planned Cascade FPSO in WR 249. 

• Water depths in the corridor range from -8,820 ft at the planned Chinook wellsite to -8,170 ft at the 

end of the pipeline route near the Cascade FPSO facility. 

• The shallow stratigraphy over the area generally consists of differentially eroded, parallel-bedded, 

hemipelagic clays. Sands are present along the floors of the furrows. 

• Seabed gradients in the corridor range from nearly 0o to locally approaching 32° along the sides of 

furrows. The average gradient along the west and east tie-back routes is 9° and 10°, respectively. 

• Irregular seafloor consisting of anti-dunes, furrows, and flukes are present at various locations 

along the entire length of the corridor. 

• A sidescan sonar target (Sonar Contact No. 24) lies about 7 ft from the proposed East Gas Pipeline 

Route at about Sta. 385+37.94. This target, which has no measurable height, is 4-ft wide, and 10-ft 

long, and may be modern debris. No other sonar contacts lie directly along the proposed pipeline 

or umbilical routes. 

• An ROV pre-lay survey will confirm the presence of the identified potential man-made debris with 

respect to Sonar Contact No. 24. The debris can be removed if necessary. 

• There are no geologic constraints such as active faulting, gas venting, or hard bottom conditions 

that would impact pipeline lay operations. The potential for encountering chemosynthetic 

communities is remote. 
Project No. 1106-1257b SECTION 1

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SECTION 1: INTRODUCTION 

 Petrobras America Inc. (PAI) is evaluating development of the Cascade and Chinook fields in the 

Walker Ridge protraction area (WR) in the Gulf of Mexico (Figures 1 and 2). PAI has proposed placing a 

floating production, storage, and offloading facility (FPSO) in Block 249 that will service production from 

the Cascade and Chinook drill centers. The Chinook drill center will be a sub-sea tie-back to the Cascade 

FPSO. The FPSO will also export produced gas along a future gas export pipeline route. Included in this 

report is an assessment of the general shallow geologic and geotechnical conditions and engineering 

constraints in the Cascade and Chinook development areas, and along the proposed Chinook tie-back and 

Cascade FPSO gas export pipeline routes. 

Figure 1. Location Map. 

The Cascade and Chinook development areas, and the tie-back corridor, encompass the following Federal lease 

blocks in the north-eastern portion of the Walker Ridge area: 

Block 117 (OCS-G-21846) Block 247 (OCS-G-20305) Block 295 (Open) 

Block 160 (OCS-G-21854) Block 248 (OCS-G-18669) Block 337 (Open) 

Block 161 (OCS-G-18651) Block 249 (OCS-G-16969) Block 338 (Open) 

Block 162 (Relinquished) Block 250 (OCS-G-16970) Block 381 (Relinquished) 

Block 203 (OCS-G-23038) Block 251 (OCS-G-18670) Block 382 (Relinquished) 

Block 204 (OCS-G-18658) Block 252 (Open) Block 425 (OCS-G-16987) 

Block 205 (OCS-G-16964) Block 292 (OCS-G-20309) Block 426 (OCS-G-16988) 

Block 206 (OCS-G-16965) Block 293 (OCS-G-18681) Block 469 (OCS-G-16997) 

Block 207 (OCS-G-20297) Block 294 (OCS-G-18682) Block 470 (OCS-G-16998) 

Block 208 (Open) 

~132 MILES
Project No. 1106-1257b SECTION 1

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Purpose 

 This study identifies the seafloor and shallow subsurface geologic and geotechnical conditions and 

evaluates engineering constraints within the Cascade and Chinook development areas. This report also 

provides identification of conditions and evaluations of constraints specific to the Cascade drill centers, 

FPSO riser bases and anchors, and infield flowlines and umbilicals, as well as at the Chinook drill center, 

the proposed tie-back pipeline corridor between the two development areas, and along two possible 

Cascade FPSO gas export pipeline options. 

The results of this study will assist PAI in the planning of all seafloor and shallow-founded architecture 

within, and between, the Cascade and Chinook development areas. This report can also be used for 

permitting of the tie-back flowline and umbilical route. 

The report complies with requirements set forth by the United States Minerals Management Service (MMS) 

in the following government publications: 

• Notice-to-Lessees 2000-G20 (MMS, 2000) 

• Notice-to-Lessees 2007-G01 (MMS, 2007a) 

The planned facilities are not located within a historically significant area, where archaeological surveys 

and assessments are required per NTL 2005-G07 (MMS, 2005). 

Available Data 

 This assessment results from the analysis of both proprietary data specific to the development areas 

and publicly available data. 

Proprietary Geophysical Data. An autonomous underwater vehicle (AUV) survey was conducted to 

assess the seabed and shallow geologic conditions in this area. GEMS worked with PAI to design the 

survey layout over the respective areas. The survey was designed to acquire data for identifying geologic 

constraints to facilities engineering. The survey meets or exceeds the requirements set forth in Notice-toLessees 2007-G01 ), MMS, 2007a. PAI contracted C&C Technologies, Inc., (C&C) of Lafayette, 

Louisiana, to conduct the data acquisition for the planned geophysical survey. The AUV survey was 

conducted from December 12, 2006 to January 26, 2007 and collected 1,770 miles of multi-beam echo 

sounder bathymetry, side-scan sonar, and chirp subbottom profiler data over the following areas: 

Area Total Line Miles # Inlines Spacing (m) # Tie-Lines Spacing (m)

Cascade Development 1124.60 74 200 31 600

Chinook Development 472.00 67 200 33 400

Chinook Tie-Back Corridor 278.00 13 centers, 50m offset, 100 2 6,800

Table 1. Table of AUV data coverage. 

The multibeam swathe bathymetry was binned at 3m. The sidescan sonar was reviewed and mosaicked at 

1.0m resolution. The chirp subbottom profiler provides an assessment of the shallow stratigraphy do a 

depth of ~ 125 ft below the seafloor (bsl). 

In addition to the AUV data PAI provided a 3-D exploration seismic depth volume in a SEG-Y format to 

assist in the study. These data cover approximately 163 square miles in the Walker Ridge area including all 

or portions of Blocks 160-163, 204-207, 248-251, 293-295, 338, 339, 382, 383, 426, 427, 470, and 471 

(Figure 2, page 3, and Figure 3, page 5). The 3-D volume has an inline spacing of 65.62 ft, a crossline 

spacing of 81.18 ft, was sampled at 16 ft increments, and has a record length of 48,000 ft (0 to 48,000 ft). 
Project No. 1106-1257b SECTION 1

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AUV SURVEY

3-D DEPTH VOLUME

X/Y: (ft)

 Figure 2. Seafloor rendering showing outlines of the data coverage. 
Project No. 1106-1257b SECTION 1

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The 3-D data was used to push the geologic interpretations from the AUV survey deeper and ensure 

complete review of the potential shallow foundation zone. The data confirmed the observations of the 

AUV and provided information on deeper stratigraphy as well as geologic structure of the Escarpment, the 

latter of which is essential for planning geotechnical programs for future slope stability studies. 

Proprietary Geotechnical Data. GEMS planned a geotechnical program that would define the 

geotechnical properties throughout the Cascade-Chinook Development areas to support facilities layout and 

engineering. The primary objective of this study was to process and interpret the appropriate geotechnical 

data as required to: 1) define the spatial soil conditions along the various pipeline segments and mudmat 

locations; 2) interpret soil parameters needed for pipeline, SCR, and mudmat foundation analyses; 3) make 

recommendations relative to spatial soil variability and relevant soil properties that should be considered in 

the foundation analyses to be performed for the planned production infrastructure; and 4) integrate with 

existing geophysical data to assess overall feasibility of the proposed field layout. 

The scope of the project was to acquire seafloor soil samples with the piston corer and 0.5 m box corer 

around the proposed Cascade-Chinook Development and perform geotechnical laboratory testing. TDIBrooks collected 58 piston cores and 57 box cores for the Cascade-Chinook Development in Walker Ridge 

and Green Canyon Areas for PAI in November and December of 2006. The piston core samples were 

obtained using a maximum 20-ft long core barrel with an outside diameter of approximately 3.0 in. A 

0.3x0.3x0.5 m box corer was used to collect mudline samples. Core locations and water depths are 

included on the individual cores logs that follow this report in Appendix B. 

The field investigation was conducted in two legs: the first leg occurred from 25 October to 10 November 

2006, using the R/V Justo Sierra, and the second leg occurred from 10 to 18 December, 2006, using the 

R/V Ferrel. Water depths at the core locations ranged from 4,187 to 8,794 ft. Navigation of the vessel was 

provided with dual differential GPS signals: Thales Geosolutions (Racal) Skyfix and US Coast Guard 

DGPS. 

Public Data. The regional framework for this study was established by referencing public sources such as 

the MMS and various published technical papers. References are included in Appendix C. GEMS has 

compiled a database of information including Federal lease blocks of reported chemosynthetic 

communities, shallow water flow, shipwrecks, obstructions, and infrastructure. Regional bathymetry data 

is from the National Oceanic and Atmospheric Administration (NOAA) swath bathymetry with additional 

data from the Texas A&M Sea Grant program. 

Project Responsibilities 

 The field operations and office reporting were conducted under the management of GEMS. Dr. 

John Brand was the overall GEMS project manager for this project. C&C conducted the AUV geophysical 

data acquisition from the M/V Northern Resolution. The C&C Technologies field party manager was Mr. 

Chas Honea. PAI contracted GEMS to provide QA/QC for the field operations and to interpret all 

collected data. Mr. James Keenan was the GEMS QA/QC personnel on the vessel. Mr. Keenan was also 

the lead geologist performing the interpretations and report of the geophysical data. Dr. Brand, Mr. Sanjay 

Shinde, and Ms. Jill Rivette reviewed the geotechnical data and contributed to the integrated reporting. 

Report Format 

 The remainder of this report is divided into the following sections: 

Section 2: Regional Geologic Setting Page 6 

 Section 3: Shallow Geologic Conditions in the 

 Cascade Development Area Page 14 

 Section 4: Shallow Geologic Conditions in the 

 Chinook Development Area Page 30 
Project No. 1106-1257b SECTION 1

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 Section 5: Seafloor and Shallow Geologic Conditions of the 

 Chinook Tie Back Pipeline Corridor Page 35 

 Section 6: Findings and Recommendations Page 39 

Appendices follow the main text of this report. Appendix A contains tables and images of the side-scan 

sonar targets. Appendix B contains the geotechnical core logs. Appendix C is a list of the references cited. 

Appendix D describes the mapping and interpretive procedures performed for this assessment. Appendix E 

contains the R/V Northern Resolution and AUV geophysical survey information. Full-size maps are folded 

and placed in pockets at the end of each section of the report. 
Project No. 1106-1257b SECTION 2

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SECTION 2: REGIONAL GEOLOGIC SETTING 

 The Cascade and Chinook development areas are on the Upper Continental Rise, just west of the 

continental slope edge, in the northeastern portion of the Walker Ridge protraction area (Figures 1 and 2). 

The Sigsbee Escarpment delineates the boundary between the continental rise and the continental slope and 

occupies the northwestern portion of the Cascade area (Figures 1 and 2). The escarpment is the expression 

of the lobate frontal edge of allochthonous salt masses which form a complex system of salt ridges, 

overthrust tongues, and steep-sided massifs (Martin and Bouma, 1978). Upslope of the Escarpment the 

Lower Continental Slope displays a hill and basin seafloor morphology. Below the Escarpment the 

continental rise is relatively flat but does display a scalloped and furrowed seafloor due to erosion from 

bottom currents. The following section defines the study area within the context of the regional 

morphological and geologic conditions. Man-made features, including exploration and production activity 

in the general area, are also discussed. 

Location

 The Cascade and Chinook development areas are approximately 132 and 150 nautical miles southsouthwest of New Orleans, Louisiana respectively, (Figure 1). The survey areas include three distinct 

geomorphologic regions: (1) The Lower Continental Slope, (2) The Sigsbee Escarpment and, (3) The 

Upper Continental Rise (Figures 3 and 4). 

Figure 3. Regional seafloor rendering of the northwestern Walker Ridge area showing the development areas in relation to 

major seafloor topographic features. 
Project No. 1106-1257b SECTION 2

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Horizontal Distance (ft)

Depth Below Sea Level (ft)

SALT

LOWER CONTINENTAL SLOPE SIGSBEE ESCARPMENT UPPER CONTINENTAL RISE

THRUST FAULTS AT

TOE OF ESCARPMENT

UPPER

SCARP

BENCH

LOWER

SCARP

NORMAL FAULTS BENEATH

THE ESCARPMENT FACE

Horizontal Distance (ft)

Depth Below Sea Level (ft)

SALT

LOWER CONTINENTAL SLOPE SIGSBEE ESCARPMENT UPPER CONTINENTAL RISE

THRUST FAULTS AT

TOE OF ESCARPMENT

UPPER

SCARP

BENCH

LOWER

SCARP

NORMAL FAULTS BENEATH

THE ESCARPMENT FACE

General Location

of proposed Cascade

Facilities

Figure 4. 3-D seismic inline 8100 illustrating the salt related structural setting beneath the Sigsbee Escarpment. 

Figure 4 illustrates the basic stratigraphy and structure of the different provinces. These provinces are 

discussed in the following sections. 

Lower Continental Slope 

 Much of the Lower Continental Slope along the northern Gulf of Mexico margin lies within the 

Tabular Salt-Minibasin Province as defined by Diegel et al., (1995). This province is described as a region 

containing extensive salt sheets with intervening deepwater, sediment-filled basins. This morphology is 

consistent to the southern edge of the province, which is the Sigsbee Escarpment.

Structure. Salt tectonics is the dominant process controlling the geologic structure of the Lower 

Continental Slope. A thick accumulation of the Jurassic aged (160 to 140 million years, B.P.) Louann Salt 

layer underlies much of the Texas-Louisiana continental slope (Lehner, 1969). Initial deformation of the 

salt layer occurred in the Eocene to early Oligocene (55 to 37 million years, B.P.). Additional loading of 

the salt during the lower Miocene to middle Pliocene (14 to 2.3 million years, B.P.) caused a remobilization 

of the salt and created spreading across the slope in the form of large amalgamated salt canopies seaward to 

the Sigsbee Escarpment. The salt masses attempt to achieve isostatic equilibrium with the surrounding 

sediments, forcing both horizontal and vertical responses. Updip extensional regions are characterized by 

growth (extensional) faulting. Downdip contractional regions exhibit folding and thrusting at the base of 

the slope. 

The mobilization of the salt affected the surrounding sediments by causing deformation (e.g., faults and/or 

folds) and by placing a structural control on subsequent sediment depositional patterns. Topographic highs 

can block the downslope transport of sediments. Structural lows around diapirs or salt ridges can act as 

conduits for the transport of sediment downslope and out onto the continental rise. Salt withdrawal basins 

(Intraslope Basins) can act as traps for the ponding and accumulation of large volumes of sediment (Apps 

et al., 1994). 

Stratigraphy. Most of the shallow stratigraphy on the Lower Continental Slope is correlated to the 

Pleistocene (1.8 million years to 11,550 years B.P.) Mississippi River. The Pleistocene Mississippi River 

depositional province spans a large portion of the central Gulf of Mexico and has been classified into two 

major depositional systems: the Western Deposystem and the Eastern Deposystem (Winker and Booth, 

PROPRIETARY 
Project No. 1106-1257b SECTION 2

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2000), Figure 5. Shifts in the depositional focus of the Mississippi River have been attributed to sea level 

fluctuations and river meander, which has had a direct impact on the facies assemblages observed across 

the continental slope (Prather et al., 1998; Winker and Booth, 2000; Damuth et al., 2003). 

Figure 5. Regional illustration of the Study Area in relation to the major Pleistocene Mississippi River depositional 

provinces. 

Both the Western and Eastern Deposystems exhibit intraslope fans and shelf margin deltas, as well as 

subsequent incised valleys and canyons (Winker and Booth, 2000). The sediments were delivered 

downslope through a fill and spill process of linked intraslope basins (Steffens, 1993; Prather et al., 1998; 

Winker and Booth, 2000; Damuth et al., 2003). 

Prather et al., (1998) and Winker and Booth (2000) classify the sedimentary sections within intraslope 

basins as bypass and ponded facies. Many basins show a cyclic succession of bypass and ponded facies 

with the more chaotic bypass facies overlying the layered ponded facies. Bypass facies are generally 

dominated by mass-transport complexes, channel fill, and overbank deposits. These units are, in large part, 

sand poor and are thickest in a proximal setting to the major Pleistocene depocenters. Ponded facies 

generally consist of slope fan deposits and sand-enriched turbidites. The ponded facies dominate down 

slope in a distal setting from the Pleistocene depocenters. The Cascade and Chinook development areas are 

located downslope and approximately mid-way between the two major late Pleistocene slope fan units (i.e., 

the GB Orange and GC Red units of Winker and Booth, 2000). Therefore, the layered or ponded units in 

the shallow section are likely to be predominantly clay-rich and generally sand poor. This is supported by 

the overall continuity and amplitude character of the stratigraphic section for the Lower Continental Slope 

in Figure 4. 

Cascade and 

Chinook

Modified from Winker and Booth, 2000.
Project No. 1106-1257b SECTION 2

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Sigsbee Escarpment 

 The Sigsbee Escarpment is a continuous scarp marking the boundary between the Lower 

Continental Slope and the Upper Continental Rise along the northern margin of the Gulf of Mexico 

(Figures 3 through 5). It extends continuously over 300 miles from the Perdido Foldbelt in the southwest 

to the Mississippi Fan in the northeast. 

Structure. The Sigsbee Escarpment is a complex topographic and morphologic feature which represents 

the seaward limit of mobile allochthonous salt (Jackson and Hudec, 2004). Formation of the Escarpment 

results from sediment loading on the upper slope causing mobilization of the viscous salt. Through this 

process, the salt attempts to achieve isostatic equilibrium with the surrounding sediments, forcing both 

horizontal and vertical responses. Beneath the Escarpment face the vertical movement of salt results in 

growth (extensional) faulting. Downdip, contractional forces resulting from the horizontal movement of 

salt result in folding, and more commonly, thrust faulting at the toe of the Escarpment (Figure 4). 

The Escarpment is underlain by a series of coalescing salt tongues and sheets known as the Sigsbee Nappe. 

The Escarpment face is characterized by steep slopes and contains numerous faults, slumps, and gullies. 

Many of the slumps have created mounded debris aprons that extend out onto the adjacent Upper 

Continental Rise as shown in Figure 6. Several canyons are identified along the Sigsbee Escarpment within 

the Walker Ridge area. Two such canyons are, Farnella Canyon located approximately 18 miles to the 

southwest, and Green Canyon located approximately 15 miles to the north of the development areas. The 

Farnella Canyon and Green Canyon salt re-entrants are relict sediment pathways for Mississippi Riverderived sediments. The canyons were abandoned during episodes of sea level rise and/or geographic shifts 

in the Pleistocene Mississippi River depocenter. 

SLUMP SCARPS

DEBRIS APRONS

U P P E R C O N T I N E N T A L R I S E

S I G S B E E E S C A R P M E N T

SLUMP SCARPS

DEBRIS APRONS

U P P E R C O N T I N E N T A L R I S E

S I G S B E E E S C A R P M E N T

Figure 6. Isomet view of the Sigsbee Escarpment in the Cascade area showing slump scarps on the Escarpment and 

associated debris aprons on the Upper Continental Rise. View is looking northwest. The proposed Cascade facilities are 

located southeast out of the frame. 

Stratigraphy. The stratigraphy along the Escarpment is highly variable, consisting of recently deposited 

draped and ponded sediments, fault- or failure-exposed older strata, and slump and landslide deposits. The 

ponded drape deposits will likely be soft to very soft Holocene clays overlying stiffer Pleistocene/Pliocene 
Project No. 1106-1257b SECTION 2

- 10 -

clays. Stiff to very stiff clays are most likely exposed along fault scarps. Multiple episodes of slumps or 

debris slides have deposited debris aprons at the base of the Escarpment (Figure 6). These sediments will 

generally exhibit high variability both laterally between adjacent deposits and vertically within individual 

deposits. 

Upper Continental Rise 

 The Upper Continental Rise extends from the base of the Sigsbee Escarpment out to the abyssal 

plane. Regionally extensive seafloor bed forms consisting of furrows, anti-dunes, and other erosion related 

features on the seafloor have recently been identified along the base of the Sigsbee Escarpment in the 

Green Canyon area (Bryant et al., 2001). These seafloor features are typically longitudinal bed forms that 

occur in fine-grained sediment caused by erosion from bottom currents (Scott et al., 2001). The erosional 

nature of the furrows indicates the presence of potentially strong bottom currents along the Sigsbee 

Escarpment. Bottom currents of two knots have been reported to the east in AT 618 and experimental work 

near the Bryant Fan to the west indicates the occurrence of at least two-knot bottom currents (Scott et al., 

2001). 

Structure. The only dominant structural process affecting the Upper Continental Rise in the development 

areas is thrust faulting at the base of the Sigsbee Escarpment (see Figure 4). The thrusts are usually 

duplexes and are typically characterized by reverse displacements that eventually die out up-section of the 

basement decollement. 

Stratigraphy. The deep water stratigraphy on the Upper Continental Rise generally consists of alternating 

units of thick, chaotic reflection sequences with well-stratified, parallel reflection sequences as evident in 

Figure 4. The chaotic sequences are “expanded” sections of rapidly deposited slumps and landslides 

sourced from both the Sigsbee Escarpment and distal Lower Continental Slope mass-transport systems 

during times of lowered sea level. The parallel (bedded) sequences are "condensed sections" composed of 

hemipelagic and pelagic sediments deposited during times of stable or rising sea level.

The near-surface sediments, or Late Pleistocene-Holocene drape, along the rise is likely very similar to the 

drape deposits found on the slope above the Escarpment. These sediments consist of very soft, high water 

content, silty clays, and normally consolidated to slightly under-consolidated (Booth and Dunlap, 1977). 

This drape was deposited during the Late-Pleistocene-Holocene epochs. A generic slope soil profile shows 

a gradual, linear increase in strength with depth along with a corresponding decrease in water content. 

Actual geotechnical properties, however, can differ greatly from the generic profile, due to the presence of 

buried landslides, turbidity flow deposits, faulting, possible presence of gas hydrates, and erosion of the 

seabed. 

Faults 

 Extensional faults dominate the northern Gulf of Mexico basin. These faults are primarily listric 

growth faults that sole into a salt layer and show an increase in displacement with increasing depth. Rowan 

et al., (1999) describe many salt-related, extensional fault families, including several salt-rooted growth 

fault families and faults over crests of fold structures, i.e., anticlines. In many instances, growth faults root 

into the crests of salt diapirs, forming fault-bounded graben and half-graben structures. Many of these 

graben families can form complex interconnected patterns on the seafloor. 

Faults at the edge of the salt structures are contractional, i.e., thrust faults near the downdip limit of 

allochthonous salt bodies. These “toe-thrust” faults counterbalance the updip extension created by the 

basinward-dipping normal faults (Rowan et al., 1999). Thrust faults are typically characterized by reverse 

displacement that eventually dies out up-section. 

Although not as common as extensional faults, strike-slip faults are also observed in the Walker Ridge area 

of the Gulf of Mexico. These faults are salt-rooted and oriented roughly parallel to the regional seafloor 

dip. The position and geometry of the strike-slip faults suggest that the deformation may connect the 

extensional normal faults further landward to the contractional structures basinward (Rowen et al., 1999). 
Project No. 1106-1257b SECTION 2

- 11 -

Slope Stability 

 Uplifting of underlying salt can put stress on low-shear strength surface sediments. With continual 

uplifting and rotation, the surface materials may eventually fail downslope from the uplift. Increases in 

pore-pressure due to loading and salt motions also contribute instability. These failures are characterized by 

their arcuate shapes with irregular seafloor downslope of the feature. Many of these failures throughout the 

continental slope region are covered with a drape of Holocene-aged pelagic sediments (Doyle et al., 1992). 

The presence of a drape over a slump scar and debris field would indicate that the slump event is an ancient 

feature. A lack of drape would indicate that the landslide is a relatively recent feature and slope stability 

could be of a concern for the area. The exception to this is where strong currents may erode, or prevent, the 

deposition of overlying drape, resulting in “fresh-looking” slide deposits that may in fact be quite old in the 

geologic record. Detailed studies of the Escarpment suggest an increase in failures during periods of lowsea level and reduced events during periods of high sea-level. 

Seafloor Currents 

 The Loop Current is the dominant water circulation in the Gulf of Mexico. The current formed in 

the middle Miocene when circum-equatorial currents were blocked by the formation of the Isthmus of 

Panama, thus redirecting the flow of the Caribbean current into the Gulf of Mexico. Modern-day sea 

surface currents associated with the Loop Current are well documented and are monitored by satellite 

observations of seafloor altimetry due to their significant impact on deep-water drilling operations. 

However, the nature of the deep-water currents is more difficult to observe and are not fully understood. 

Regional mapping of the seafloor in portions of the Green Canyon and Walker Ridge areas has uncovered 

regionally extensive bed forms consisting of furrows, anti-dunes, and other related features on the seafloor 

along the Sigsbee Escarpment (Bryant et al., 2001). These seafloor features are typically longitudinal bed 

forms that occur in fine-grained sediment caused by erosion from bottom currents (Scott et al., 2001). The 

furrows extend for miles along the base of the Escarpment and, in some places, are present on and above 

the Escarpment. The erosional nature of the furrows demonstrates the presence of potentially strong 

bottom currents along the Sigsbee Escarpment in the Walker Ridge area. These currents may, at least in 

part, originate from strong eddies that spin off the Loop Current and “feel” bottom along the Escarpment. 

Another hypothesis is that the currents are a result of deep-ocean Rossby waves propagating along the 

Escarpment. 

Hydrocarbon Migration and Related Seafloor Features 

 Hydrocarbon seepage on the northern Gulf of Mexico slope is widespread (Anderson et al., 1983; 

Brooks et al., 1985). Thermogenic hydrocarbons are generally believed to form at depths greater than 5 km 

(>16,400 ft) in the Gulf of Mexico (Kornacki et al., 1994). Biogenic gas can be generated at shallower 

depths from the decomposition of organic matter or the degradation of migrating hydrocarbons. 

Hydrocarbons can migrate vertically along diapiric salt bodies and faults and accumulate at a shallower 

level if a stratigraphic or structural “trap” is encountered. If nothing traps migration, the hydrocarbons will 

reach the seafloor and be expelled into the water column, in some cases resulting in significant topographic 

features. 

Hydrocarbon Vents. The greater the depth of the gas accumulation beneath the mudline, the more likely 

pressures greater than hydrostatic may occur (Dutta, 2002). In general, shallow zones (less than a few 

hundred feet below the mudline) are not expected to have a significant pressure gradient because the low 

shear strength of the soils at these shallow depths generally prevents any appreciable buildup of pressure. 

In some instances, pressure in shallow soils may reach a point where they exceed the seal capacity of the 

soil; thus, releasing gas from the formation that vents upwards and bleeds off pressure. 

The venting process can be slow and imperceptible at the seabed, or it can be dynamic, forming large 

topographic features. On the continental slope of the Gulf of Mexico, large blowout craters, mud 

volcanoes, and mud diapirs have been attributed to the venting of gas and other fluids (Prior et al., 1989; 
Project No. 1106-1257b SECTION 2

- 12 -

Neurauter and Bryant, 1989; Neurauter and Roberts, 1992). These features are relatively common around 

salt bodies and major fault scarps. 

Active hydrocarbon seepage at the seafloor is a possible indication of overpressured sediments in the 

subsurface. Penetrating shallow gas in the near-surface may create difficult well control conditions, such 

as, gas kicks, loss of circulation, or well blowouts. It is important to identify shallow trapped gas 

accumulations so that these areas can be either avoided or mitigated through an appropriate casing and/or 

mud program. 

Hydrates. Hydrates are a solid form of light gases that have been compressed into an ice matrix of water 

molecules (Kvenvolden and Barnard, 1983). Hydrates may form near gas vents under proper temperature 

and pressure conditions. Gas hydrates have been found in water depths exceeding 1,500 ft in the northern 

Gulf of Mexico (Brooks et al., 1989). Gas hydrates can sometimes be detected on seismic data by the 

presence of bottom simulating reflectors (BSRs). BSRs mimic the seafloor, cross-cut stratigraphy, and are 

caused by the impedance contrast at the hydrate-gas phase boundary (Holbrook et al., 2002). It is 

important to note, however, that hydrates can also exist where BSRs are not observed. 

The presence of gas hydrates in shallow sediments can affect the geological and physical properties of the 

seafloor including shear strength, porosity, permeability, fluid composition, and fluid flow (Dillon et al., 

1989). Changes to pressure or temperature can allow the gas hydrates to dissociate, which could become a 

triggering mechanism for slope failures (Max and Chandra, 1998; Moridis and Kowalsky, 2006). The 

slumps and slides could pose a threat to pipelines and other bottom founded structures on the seafloor. 

Drilling into hydrates could alter the temperature regime in the shallow sediments, allowing the hydrates to 

disassociate and create uncontrolled gas releases, cement failure, collapsed casing, and well control 

problems (Szczepanski et al., 1998; Collett and Dallimore, 2000; Moridis and Kowalsky, 2006). 

Various reports indicate the presence of hydrates along the continental slope in the Gulf of Mexico. 

Milkov and Sassen (2001) estimate an area of potential gas hydrate resources that covers portions of the 

East Breaks, Garden Banks, Green Canyon, Atwater Valley, Mississippi Canyon, and Walker Ridge 

protraction areas. Water depths in these portions of the Gulf of Mexico are suitable for hydrate formation. 

Authigenic Carbonates. Venting gases may react with the interstitial, near-surface pore water in shallow 

sediments to produce carbon dioxide and bicarbonates (Roberts et al., 1990). Under proper conditions, this 

reaction catalyzes the production of calcium and magnesium carbonates. The result is an accumulation of 

authigenic carbonates creating large caps, or seals, over gaseous sediments and the formation of boulderlike cemented, hard rock outcrops. These lithified surfaces could pose problems for casing penetration or 

anchor holding. 

Authigenic rock outcrops have been recognized in many areas along the continental slope in association 

with diapiric uplifts and seafloor fault scarps. At the seafloor, such hard rock outcrops are commonly 

associated with textural changes and seafloor amplitude variations on seismic sections. 

Chemosynthetic Communities 

 No blocks in the Walker Ridge area have been designated by the MMS as having significant 

chemosynthetic communities (MMS, 2007b). However, there are published accounts of seepage locations 

within the Walker Ridge area (McConnell and Kendall, 2002; Sassen, 2000). In water depths greater than 

400 meters (1,312 ft) in the Gulf of Mexico, there have been an increasing number of chemosynthetic 

communities found associated with gas seeps and rock outcrop zones (MMS, 2000). Chemosynthetic 

communities are organisms that have a food source, at least in part, from chemosynthesis rather than 

organic carbon derived from plankton or marine photosynthetic algae. These organisms can form colonies 

consisting of dense assemblages of tubeworms, clams, and mussels, while others consist of mats or traces 

of the bacteria Beggiatoa (Brooks et al., 1987; Brooks et al., 1989; Kornacki et al., 1994). The biologic 

variety and density of chemosynthetic communities has been associated with the flux rate at which 

hydrocarbons are expelled at the seafloor (Roberts et al., 2001). The MMS has outlined measures that 
Project No. 1106-1257b SECTION 2

- 13 -

require the operator to protect high-density chemosynthetic communities from potentially harmful 

anthropogenic activities (MMS, 2000). 

Shallow Water Flow 

 Shallow water flow phenomenon has more frequently been observed while drilling through shallow 

overpressured formations at deepwater sites in the Gulf of Mexico (Ostermeier et al., 2000). Encountering 

overpressured sands in the shallow section has been a problem because of the low formation strengths and 

fracture gradients. It is difficult for drillers to control formation pressures with mud weights when the 

surrounding formation has a fracture gradient at or less than the mud weight. Water flow originating from 

these overpressured zones can cause large and long lasting uncontrolled flows, well damage, foundation 

failure, formation compaction, damaged casing, and re-entry and control problems (Ostermeier et al., 

2000). 

No shallow water flow events have been reported in the Walker Ridge area (MMS, 2007b). As previously 

stated, the Walker Ridge area lies downslope and between the GB Orange and GC Red units (Figure 5, 

page 7), two late Pleistocene slope fan systems that have been the source of shallow water flow in wells 

along the upper continental slope (Ostermeier et al., 2000). Because of the distance from the fan systems, 

this area probably has a low potential for water flow in the shallow stratigraphic section. 

Exploration Activity and Man-Made Structures 

 There are no pipelines or platforms in the study area (MMS, 2007b). The following table lists the 

wells and proposed locations within and near the study area. 

AREA/BLOCK OPERATOR WELL No. STATUS* API #

WR 206 PETROBRAS 2 TA 608124001601

WR 206 PETROBRAS 1 PA 608124000801

WR 425 PETROBRAS 1 PA 608124000200

WR 425 PETROBRAS 2 PA 608124000500

WR 469 PETROBRAS 1 TA 608124001000

WR 165 MARATHON 1 PA 608124000100

WR 29 CHEVRON 3 DSI 608124002300

WR 29 CHEVRON 1 PA 608124001900

WR 29 CHEVRON 2 TA 608124002004

WR 30 MARATHON 1 TA 608124000602

WR 70 CHEVRON 1 PA 608124000000

GC 1001 MARATHON 1 PA 608114029502

Borehole Status as of 04/10/07: DSI = Drilling Suspended; PA = Permanently Abandoned; 

 TA = Temporarily Abandoned 

Table 2. Table of existing and proposed wells. 

The proposed Cascade and Chinook facilities have been planned to either fully avoid or utilize the existing 

wells within the development areas. 
Project No. 1106-1257b SECTION 3

- 14 -

SECTION 3: SHALLOW GEOLOGIC CONDITIONS IN THE 

CASCADE DEVELOPMENT AREA 

 Petrobras America Inc. (PAI) is evaluating development of the Cascade area in Walker Ridge Area 

(WR) in the Gulf of Mexico. PAI has proposed placing a floating production, storage, and offloading 

facility (FPSO) in Block 249 that will service the Cascade and Chinook drill centers. The FPSO will be the 

first of its kind in the Gulf of Mexico. The FPSO will also serve as a host for gas export pipelines, the 

routing of which is still to be determined. The area surveyed for the Cascade Development area includes 

all or portions of WR 117, 160-162, 203-207, 247-251, 292-295, and 338 (Map 1A). All of the Cascade 

facilities are planned to be placed on the Upper Continental Rise, south of the Sigsbee Escarpment. 

Bathymetry and Seafloor Gradient 

 Water depths in the Cascade Development area range from 5,637 ft in the northeastern corner of 

WR 247 to 8,510 ft in the north-central part of WR 338 (Map 2A). Above the Escarpment water depths 

vary from 5,637 ft to about 5,960 ft and are generally shallowest near the Escarpment and deepen to the 

west and northwest. This occurs along the uplifted of stratigraphic section at the Escarpment that had been 

caused by the local, shallow emplacement by salt. Water depths deepen rapidly across the Escarpment, 

averaging a change in elevation of between 2,000 ft and 2,500 ft. Below the Escarpment the water depth 

generally deepens to the southeast reaching a maximum of 8,510 ft in WR 247. 

Seafloor gradients range from nearly 0o on the Lower Continental Slope up to approximately 70° along the 

steeper, more rugged portions of the Sigsbee Escarpment (Map 3A). Seabed gradients on the Upper 

Continental Rise, where the facilities are intended, are generally low the central portion of the area. 

Seafloor gradients above 20° are common in the southeastern third of the area associated with the sidewalls of seafloor furrows. 

Physiographic Provinces, Seafloor Morphology, and Stratigraphy 

 The Cascade area displays a variety of seafloor and geologic features resulting from past salt 

related structural deformation, as well as past and present seafloor erosion. The most prominent feature is 

the Sigsbee Escarpment, which runs roughly north to south through the western part of the area (Map 4A). 

The Escarpment divides the relatively smooth and gently dipping Lower Continental Slope from the Upper 

Continental Rise. Seafloor currents have significantly eroded the Upper Continental Rise in the Cascade 

area, resulting in furrows and flukes on the seafloor. The Escarpment itself has variable gradients and 

thickness of sedimentary cover overlying older, very stiff to hard soils. Faulting, in many places along the 

Escarpment, results in a rough topography, has uplifted and exposed older strata, and contributed to 

numerous past failures. 

Three physiographic provinces have been identified in the Cascade area as illustrated in Figure 7 (next 

page). 

• Lower Continental Slope (LCS) – Shallow seabed dip over most of the area. Soils are 

normally to slightly over-consolidated clays exhibiting high plasticity and low sensitivity. 

Occasional faulting and erosion by currents have scoured the very soft, surficial 

sediments near the top of the Escarpment. 

• The Sigsbee Escarpment (SE) – Characterized by high slope angles and rugged 

topography. Ponded hemipelagic and debris flow sediments occur in benched portions of 

the Escarpment, while stronger sediments are exposed along steep slopes. 

• The Upper Continental Rise (UCR) – Generally parallel and continuous undisturbed clayrich stratigraphic section. Seabed topography is variable as a result of erosion by seafloor 

currents. Seafloor furrows exist to the east and give way to flukes toward the 

Escarpment, suggesting a change in current velocity regime. Soils in this province are 

differentially eroded, very-soft to soft, highly plastic clays with low to medium 
Project No. 1106-1257b SECTION 3

- 15 -

sensitivity. A thin drape of foraminiferal sand may be present at the seabed. The 

Cascade facilities will be placed in this province. 

WR

250

WR

251

WR

293

WR

294

WR

295

WR

207

WR

206

WR

161

WR

162

WR

162

WR

249

WR

250

WR

251

WR

293

WR

294

WR

295

WR

207

WR

206

WR

205

WR

204

WR

248

WR

161

WR

162

WR

162

UPPER CONTINENTAL RIS

SI

E

GSBEE ESCARPMENT

LOWER CONTINENTAL SLOPE

WR

250

WR

251

WR

293

WR

294

WR

295

WR

207

WR

206

WR

161

WR

162

WR

162

WR

249

WR

250

WR

251

WR

293

WR

294

WR

295

WR

207

WR

206

WR

205

WR

204

WR

248

WR

161

WR

162

WR

162

UPPER CONTINENTAL RIS

SI

E

GSBEE ESCARPMENT

LOWER CONTINENTAL SLOPE

Gas Export 

Option 1

Gas Export 

Option 2

Chinook

Tie-Back

Routes

FPSO

DC

DC

Figure 7. Physiographic provinces within the Cascade Development area. FPSO located in WR 249. DC denotes Drill 

Center. Gas Export Route will be determined in the future. 

Each of the three above provinces displays seafloor morphology and shallow structure and stratigraphy 

quite different from the other provinces. Shallow stratigraphic units are primarily defined from the 

subbottom profiler data collected by PAI, while deeper stratigraphy and structure were defined utilizing the 

3-D depth volume also provided by PAI. 

Lower Continental Slope (LCS). The LCS province is a benign setting relative to the other two 

provinces. Seafloor gradients are generally below 6° over most of the province. The shallow stratigraphy, 

to approximately 260 ft below the mudline (bml) consists of well-layered to amorphous reflectors (Map 5 

and Figure 8, next page). The base of the surficial unit is identified as the “Triplet” as defined by Brand et 

al., 2003. Carbon-14 dating of the three distinct silt-rich layers indicate that the layers were deposited 

between ~18.9 – 20.2 ka (1ka=1,000 yrs) slightly before the end of the last lowstand, i.e., 

Pleistocene/Holocene boundary (Brand et al., 2003). The Triplet is an important marker horizon in the area 

because it both marks the base of the transitional late Pleistocene (low-stand) and current Holocene (high-
Project No. 1106-1257b SECTION 3

- 16 -

stand) sediments and can be mapped both above and below the Sigsbee Escarpment. Although the stratum 

is parallel and continuous, the thickness of sediments above the triplet is variable across the LCS province. 

Faults are present, caused by the underlying salt movement, and have resulted in the uplift and offset of the 

sediments above the Triplet, primarily in the northern and southern portions of the province (See Map 5A). 

The soils are also differentially eroded due to the presence of seabed currents. Below the Triplet the 

stratigraphy is characterized by intact, parallel continuous reflectors. 

TRIPLET

10 ms

~25 ft

1,000 ft

TRIPLET

10 ms

~25 ft

1,000 ft

Figure 8. The portion of subbottom profiler line 202 displays typical structure and stratigraphy for the Lower Continental 

Slope province (near top of Escarpment). 

A number of box cores and short piston core samples were recovered from this physiographic province 

(Appendix B). Typically the piston core samples were less than 20 ft in length. Table 3 lists the cores in 

the LCS province. Results of the standard geotechnical testing are presented in Figure 9. 

Piston Core Box Core 

C-ESC-PC-5 CEXP2-BOX5 

C-ESC-PC-6 CEXP2-BOX6 

CEXP2-PC-3 CEXP2-BOX7 

CEXP2-PC-4 CEXP2-BOX8 

CEXP2-PC-5 CEXP2-BOX9 

CEXP2-PC-9 CEXP2-BOX10 

CEXP2-PC-11 CEXP2-BOX13 

CEXP2-PC-13 CEXP2-BOX14 

CEXP2-PC-14 CEXP2-BOX15 

CEXP2-BOX18 

CEXP2-BOX20 

CEXP2-BOX21 

CEXP2-BOX22 

CEXP2-BOX23 

Table 3. List of cores for the LCS province. 

PROPRIETARY 
Project No. 1106-1257b SECTION 3

- 17 -

0 6 12345

Sensitivity

0 500 100 200 300 400

MV Shear Strength (psf)

0 2.5 0.5 1 1.5 2

Liquidity Index (LI)

0 200 40 80 120 160

Moisture Content (%)

20

0

18

16

14

12

10

8

6

4

2

Penetration below Seafloor (ft)

Figure 9. Geotechnical test results for the LCS province. 

Soils in the area are generally very soft, highly plastic, normally to slightly overconsolidated clay. The 

soils are fairly uniform over the province as is expected from soils that have been differentially eroded and 

slightly scoured in locations due to currents. There is excellent correlation between the geologic 

observations and the ground-truth soils data. 

As can be seen in Figure 9, the moisture content data follows a decreasing trend from generally over 120% 

at the seafloor to about 70% at 18 ft. Liquidity index (LI) also decreases with depth. Shear strength was 

measured with miniature vane testing. The results fall within a narrow range and are linearly increasing 

with depth. The strength of the surficial sediments varies between 40 and 70 psf and increases to about 

155 psf at 18-ft depth. The soil sensitivity generally ranges between 2 and 5 which is typical of very soft, 

normally consolidated GOM clay. Soil sensitivity is the ratio of undisturbed to remolded strength and is 

typically used to indicate sample disturbance. Values below 2 can indicate sample disturbance. Figure 9 

does show occasional sensitivity results below 2, but in general the sample quality is good with little 

disturbance. 

The only potential future facility planned for the LCS is the Export Option 2 Route (see Figure 7). The 

route has yet to be selected and may never occur. The conditions on the LCS are favorable for pipeline 

installation and performance. 

The Sigsbee Escarpment (SE). The Sigsbee Escarpment crosses the entire Cascade area and separates the 

LCS province from the UCR province (Figure 7). The Escarpment represents the distal limit of the salt 

province in the Cascade area with salt located to the west and absent to the east (Map 6A). The topography 

of the Escarpment is highly variable (Figure 10, next page). Vertical and horizontal movement of the 

underlying salt has deformed the shallow stratigraphy and initiated slope failures. The result of the uplift 

and deformation is the formation of an escarpment consisting of a relatively flat bench separating an upper 

and lower scarp. 

The upper and lower scarps are rugged, faulted, and steeply dipping. Faults are salt-rooted, trend parallel 

to the Escarpment face, and are typically downthrown to the southwest (Map 8A). Throw across the faults 

is highly variable, but is as much as 20 ft. Numerous slump scarps and gullies incise the lower scarp with 

debris aprons extending up to about 1 mile out onto the Upper Continental Rise. 

PROPRIETARY 
Project No. 1106-1257b SECTION 3

- 18 -

L O W E R S C A R P L O W E R S C A R P

U P P E R S C A R P U P P E R S C A R P

B E N C H B E N C H

WR

205

WR

WR 206

208

L O W E R S C A R P L O W E R S C A R P

U P P E R S C A R P U P P E R S C A R P

B E N C H B E N C H

WR

205

WR

WR 206

208

Figure 10. Isometric view of the Sigsbee Escarpment within the Cascade Development area showing a bench separating an 

upper and lower scarp. View is looking northwest. The proposed Cascade facilities are southeast of the frame. 

Deposition of hemipelagic and mass-transport sediments has covered the Escarpment with a surficial layer 

of varying thickness. The geophysical data show parallel layered reflectors and amorphous intervals within 

ponded sediments underlying the bench (Figure 11). Thin to absent drape, or outcropping strata, 

characterize upper and lower scarps. The multibeam data show furrows present on the Escarpment, 

indicating seabed currents are actively eroding and re-depositing the surficial sediments. 

10 ms

~25 ft

1,000 ft

PONDED

MASS -TRANSPORT

SEDIMENTS

BENCH

10 ms

~25 ft

1,000 ft

PONDED

MASS -TRANSPORT

SEDIMENTS

BENCH

UPPER

SCARP

10 ms

~25 ft

LOWER

SCARP

BENCH

1,000 ft

PONDED

MASS-TRANSPORT

SEDIMENTS

UPPER

SCARP

10 ms

~25 ft

LOWER

SCARP

BENCH

1,000 ft

PONDED

MASS-TRANSPORT

SEDIMENTS

10 ms

~25 ft

1,000 ft

PONDED

MASS -TRANSPORT

SEDIMENTS

BENCH

10 ms

~25 ft

1,000 ft

PONDED

MASS -TRANSPORT

SEDIMENTS

BENCH

10 ms

~25 ft

1,000 ft

PONDED

MASS -TRANSPORT

SEDIMENTS

BENCH

10 ms

~25 ft

1,000 ft

PONDED

MASS -TRANSPORT

SEDIMENTS

BENCH

UPPER

SCARP

10 ms

~25 ft

LOWER

SCARP

BENCH

1,000 ft

PONDED

MASS-TRANSPORT

SEDIMENTS

UPPER

SCARP

10 ms

~25 ft

LOWER

SCARP

BENCH

1,000 ft

PONDED

MASS-TRANSPORT

SEDIMENTS

UPPER

SCARP

10 ms

~25 ft

LOWER

SCARP

BENCH

1,000 ft

PONDED

MASS-TRANSPORT

SEDIMENTS

UPPER

SCARP

10 ms

~25 ft

LOWER

SCARP

BENCH

1,000 ft

PONDED

MASS-TRANSPORT

SEDIMENTS

Figure 11. Subbottom profiler lines perpendicular (left) and parallel (right) to the Sigsbee Escarpment illustrating the 

varying stratigraphy and highly deformed structure of the Escarpment. 

Based on the geology, the soil properties of the SE province should cumulatively be either normally 

consolidated, very soft to soft drape soils, or, overconsolidated stiff to hard older strata. We present the 

discussion of the soil properties based on the following mapped Escarpment sub-provinces: the Upper 

Scarp, the Bench, and the Lower Scarp. 

PROPRIETARY 
Project No. 1106-1257b SECTION 3

- 19 -

The Upper Scarp. Two shallow piston cores were recovered from this portion of the SE province. Sample 

recovery was 5 to 12.5 ft in length. Table (next page) lists the cores in the Upper Scarp for the SE 

province. Results of the standard geotechnical testing are presented in Figure 12. 

Piston Core Box Core 

C-ESC-PC-4 

C-ESC-PC-7 

Table 4. List of cores for the upper scarp of the SE province. 

0 12 2 4 6 8 10

Sensitivity

0 1500 300 600 900 1200

MV Shear Strength (psf)

0 2.5 0.5 1 1.5 2

Liquidity Index (LI)

0 200 40 80 120 160

Moisture Content (%)

20

0

18

16

14

12

10

8

6

4

2

Penetration below Seafloor (ft)

Figure 12. Geotechnical test results for the upper scarp of the SE province. 

Figure 12 shows that Core C-ESC-PC-4 exhibits soil characteristics consistent with a soft drape, and Core 

C-ESC-PC-7 has soil characteristics consistent with exposed, overconsolidated strata (Appendix B). As 

mentioned earlier a normally consolidated, soft, ponded soil drape of variable thickness occurs over higher 

strength overconsolidated soils. Erosion from currents is also likely to redistribute the soft soil drape. The 

geotechnical data correlates with the geologic conditions observed from both the shallow high-resolution 

AUV data and the 3D-seismic data. 

The moisture content data in Figure 12 follows a slightly decreasing trend. The soft drape soils of the 

Upper Scarp will have a higher moisture content with surficial results in excess of 100%, but the moisture 

content will drop rapidly as the old overconsolidated strata are encountered. The LI also show decreasing 

trends with depth. The lower LI values correspond to the higher strength soil. Shear strength was 

measured with miniature vane testing. The results show two types of soil conditions: soft drape soils and 

exposed, overconsolidated soils. Soil sensitivity ranges from 2 to 7 indicating good sample quality with 

minimal sample disturbance. 

The Bench. The formation of a relatively flat bench separates the Upper Scarp from the Lower Scarp. The 

Bench has occurred from extension, via normal faulting, of the supra-salt section behind the underlying 

advancing salt front (see Figure 4). Some of the material eroded by seafloor currents is likely deposited on 

the bench due to drop in the current velocity as it traverses over the bench. The overall low gradient of the 

Bench also allows the preservation of the softer soils. 

Two piston core samples were recovered from the Bench (see Table , next page). Sample recovery was 11 

to 12 ft in length. Results of the standard geotechnical testing are presented in Figure 13. 

PROPRIETARY 
Project No. 1106-1257b SECTION 3

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Piston Core Box Core 

C-ESC-PC-3 

C-ESC-PC-8 

Table 5. List of cores for the bench of the SE province. 

0 12 2 4 6 8 10

Sensitivity

0 1500 300 600 900 1200

MV Shear Strength (psf)

0 2.5 0.5 1 1.5 2

Liquidity Index (LI)

0 200 40 80 120 160

Moisture Content (%)

20

0

18

16

14

12

10

8

6

4

2

Penetration below Seafloor (ft)

Figure 13. Geotechnical test results for the bench of the SE province. 

As expected, the drape sediments of the Bench are normally to slightly overconsolidated, the same as 

observed on the Upper Scarp. This material is underlain by the stronger, overconsolidated layer, which is 

the continuation of the stratigraphic sequence observed in the Upper Scarp. 

The moisture content and LI results tend to decrease with depth corresponding to the increasing shear 

strength. Very soft to soft normally consolidated clay was present at both core locations with Core 

C-ESC-PC-8 encountering the underlying stiffer, overconsolidated soils at ~11 ft (Appendix B). The 3Dseismic data from the Escarpment (shown in Figure 4) suggests as one moves down the Escarpment, and 

thus deeper in the exposed stratigraphic section, soil strengths should increase. Soils underlying the drape 

on the Bench are similar to those of the Upper Scarp, with strengths slightly stronger at ~1,000 psf. Soil 

sensitivity ranged between 2 and 4 with good sample quality. The geotechnical data correlates well with 

the geologic conditions observed from both the shallow high-resolution AUV and the 3D-seismic data. 

The trend should continue into the Lower Scarp area. 

The Lower Scarp. The Lower Scarp sits over the snout of the underlying salt front, as shown in Figure 4. 

The shallow soil characteristics of the material encountered on the Lower Scarp are expected to be similar 

to those observed for the Upper Scarp and Bench. 

Two shallow piston core samples were recovered from the Lower Scarp (see Table , next page). Sample 

recovery was about 2 and 15 ft in length. Results of the standard geotechnical testing are shown in 

Figure 14 as well as a more detailed presentation in Appendix B. 

PROPRIETARY 
Project No. 1106-1257b SECTION 3

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Piston Core Box Core 

C-ESC-PC-2 

C-ESC-PC-9 

Table 6. List of cores for the lower scarp of the SE province. 

0 12 2 4 6 8 10

Sensitivity

0 2500 500 1000 1500 2000

MV Shear Strength (psf)

0 2.5 0.5 1 1.5 2

Liquidity Index (LI)

0 200 40 80 120 160

Moisture Content (%)

20

0

18

16

14

12

10

8

6

4

2

Penetration below Seafloor (ft)

Figure 14. Geotechnical test results for the lower scarp of the SE province. 

The moisture content and LI data decrease with depth in each individual core corresponding to an 

increasing shear strength. The measured soil strengths are similar to those observed for the drape and 

underlying stiffer soils in both the Upper Scarp and Bench area. Core C-ESC-PC-9 illustrates a normally 

consolidated strength profile expected of the overlying soft drape to about 15 ft. In addition, this core 

penetrates the underlying stiffer overconsolidated material at depth. Core C-ESC-PC-2 also sampled the 

stiffer, overconsolidated soils of the outcropping strata which appear to be stronger for the Lower Scarp 

than in the previous two area of the SE province. Soil sensitivity ranged between 2 and 4 with good sample 

quality. The geotechnical data correlates well with the observed geometry of the stratigraphy and expected 

relative increase in soil strength within strata exposed near the base of the Escarpment. 

The only potential future facility that may be placed on the Escarpment is the Gas Export Option 2 

pipeline. The final selection of the route is yet to be determined. Engineering of a pipeline route on the 

Escarpment is feasible. If Option 2 is selected, more detailed studies of the crossing with respect to 

topography, soils, slope stability, and chemosynthetic communities should be undertaken. 

Upper Continental Rise. The Upper Continental Rise in the Cascade area is defined as an erosional 

environment. Seafloor currents have scoured and removed a significant amount of surficial sediments from 

the area resulting in a seafloor comprised of furrows and flukes. This province is subdivided into four subprovinces (Map 7A) based on the following types of observed seafloor morphology: Seafloor Furrows, 

Seafloor Flukes, a combination of Seafloor Flukes and Furrows, and a Topographic Low. 

PROPRIETARY