I bureau of mines

report of investigations 5706

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*

WELL PRODUCTIVITY RELATED

TO DRILLING MUDS: UMIAT FIELD,

NAVAL PETROLEUM RESERVE NO. 4,

ALASKA

By George L. Gates and W. Hodge Caraway

1910

THE BUREAU OF ANNIVERSARY

UNITED STATES DEPARTMENT OF THE INTERIOR

I - -
S

WELL PRODUCTIVITY RELATED

TO DRILLING MUDS: UMIAT FIELD,

NAVAL PETROLEUM RESERVE NO. 4,

ALASKA

By George L. Gates and W. Hodge Caraway

* * * * 4 * . .* . report of investigations 5706

UNITED STATES DEPARTMENT OF THE INTERIOR

Fred A. Seaton, Secretary

BUREAU OF MINES

Marling J. Ankeny, Director
Gates, George L

Well productivity related to drilling muds: Umiat Field,

Naval Petroleum Reserve No. 4, Alaska, by George L. Gates

and W. Hodge Caraway. [Washington] U.S. Dept. of the Interior,

Bureau of Mines [1960]

ii, 21 p. illus., tables. 27 cm. (U. S. Bureau of Mines. Report

of investigations. 5706)

Bibliographical footnotes.

1. Petroleum engineering. 2. Drilling mud. 3. Umiat Field,Naval

Petroleum Reserve, No. 4, Alaska. (Series)

[TN23.U7 no. 57061 622.06173

U. S. Dept. of the Int. Library

This publication has been cataloged as follows:

J.
CONTENTS

Page

Introduction and summary .................................. 1

Acknowledgments ........... .............. .................. 1

General description of the area........ ..................... 2

Climate ........................ ........................ 3

Length of day ................................ ....... 3

Vegetation ............. ....................... 3

Permafrost ..... ............................. ......... 4

Geothermal gradients ................................ 4

Transportation ....................................... 7

Drilling and completion data on test wells................ 7

Water-base mud completions--wells 1, 2, and 3 ........ 7

Description of reservoir rocks...... ............ 9

Drilling mud................................ 9

Cable-tool completions--wells 4, 6, 8, and 10 ........ 9

Drilling mud ..................................... 9

Well 7 ... ........................................ 9

Emulsion-mud completion--well 11 ................... 10

Drilling mud .... ........................... 10

Cable-tool completion followed by wall scraping using

crude oil--well 5 .................................. 10

Oil-base mud completion--well 9 ...................... 11

Drilling mud.. ................. ..... *... 11

Swabbing and pumping tests...................... 11

Effect of water on permeability of core samples

from well 9............... . ........ ...... 13

Volume of drilling mud filtrate in cores from

well 9......................... .. ........... 16

Discussion of results .................................... 16

Comparison of wells 2 and 5........................ 17

Unusual features of well 9........................... 18

Effect of water on relative permeability to oil...... 18

Formation pressure ................................... 19

Low formation temperatures ........................... 19

Properties of the crude oil ................... .......20

Basic well data...... .......................... 20
ii

ILLUSTRATIONS

Fig. Page

1. Umiat field and Naval Petroleum Reserve No. 4 in

northern Alaska..................... ................ 2

2. Permafrost zones in Alaska, showing location of Naval

Petroleum Reserve No. 4 and Umiat field.... ......... 5

3. Temperature-depth relation in permafrost zone of

well 6 ................. . .................. 6

4. Well location map, Umiat field, Alaska.. .............. 8

5. Permeability of core samples to oil and water ......... 14

6. Production capacity of Umiat wells related to drilling

mud ....... . ....... .... ............ ....... 18

7. Effect of water content of sands on permeability to

oil ................................................. .19

TABLES

1. Properties of oil-base drilling mud used in Umiat

well 9............... .. . .. .. . ......... . 12

2. Permeability of well 9 core samples to oil and water.. 15

3. Permeability of selected Umiat 9 cores to air, salt

water, and fresh water ..... ..... .............. 16

4. Drilling and production data, Umiat field, Alaska,

1944-53.. ..... ...................................... 17

,.

-
WELL PRODUCTIVITY RELATED TO DRILLING MUDS:

UMIAT FIELD, NAVAL PETROLEUM

RESERVE NO. 4, ALASKA-/

by

George L. Gates 2/ and W. Hodge Caraway-/

INTRODUCTION AND SUMMARY

This report presents an evaluation by the Federal Bureau of Mines of the

effect of clay-water, brine, and oil-base drilling fluids on the productivity

of test wells drilled on the Umiat anticline in U.S. Naval Petroleum Reserve

No. 4 in northern Alaska. Eleven wells were drilled on the Umiat structure

as part of the U.S. Navy's extensive exploration of the Reserve during 1944-53

to determine the possibilities for oil production. The Federal Geological

Survey cooperated in the exploration program and has published a comprehensive

report3/ on the geology of the area and case histories of the wells. The report also includes the results of special studies by the Bureau in connection

with the drilling and coring of well 9 with oil-base mud in the hole and was

the source of much of the information used in preparing this publication.

Of the eleven wells, four were drilled with rotary tools and water-base

mud (one of the water-base muds was an oil-in-water emulsion mud), five were

drilled with cable tools with brine in the hole, one was drilled with cable

tools with brine in the hole and later reamed with rotary tools and crude oil,

and one was drilled with rotary tools and oil-base mud. Although all of the

wells penetrated sandstones that contained oil and gas, some were productive

and others were not. The latter two wells, one completed with crude oil in

the hole (with some added brine) and the other with oil-base mud, had the

greatest productive capacities. The wells drilled with cable tools and brine

in the hole had lower productive capacities. In contrast, two of three wells

completed with rotary methods and fresh-water drilling mud and the well completed with rotary and emulsion mud were unproductive.

ACKNOWLEDGMENTS

Grateful acknowledgment is made to members of the Alaska Branch of the

Federal Geological Survey, headed by George 0. Gates, who supplied helpful

information used in preparing this report.

1/ Work on manuscript completed November 1959.

2/ Petroleum engineer, Bureau of Mines, San Francisco, Calif.

3/ Collins, Florence Rucker, Bergquist, Harlan R., Brewer, Max C., and Gates,

George L., Test Wells, Umiat Area, Alaska: Geol. Survey Prof. Paper

305-B, 1958, pp. 71-206.
r

2

GENERAL DESCRIPTION OF THE AREA

The Umiat area (fig. 1) is in the southeastern part of the Reserve on the

Arctic slope. The arctic slope is bounded on the south by the crest of the

Brooks Range and on the north by the Arctic Ocean. The Brooks Range, the

Alaskan counterpart of the Rocky Mountains, comprises several groups of rugged,

glaciated mountains having a relief of 3,000 to 6,000 feet and maximum altitudes of 3,600 to 9,200 feet. Anaktuvuk Pass (2,200 feet) is the highest

elevation on the land route between Fairbanks and the Arctic plain.

The Arctic coastal plain is characterized by abundant lakes, swampy areas,

wet tundra, meandering streams and--during the summer--hordes of hungry mosquitoes. Local relief rarely exceeds 100 feet; however, the surface of the

Umiat anticline is marked by a maximum relief of about 500 feet.

- - ,,, go - -

50 0 50 100 150

Scale, miles Scale, miles

1320

FIGURE 1. - Umiat Field and Naval Petroleum Reserve No. 4 in Northern Alaska.

(Adapted From Federal Geological Survey Outline Map.)
1

3

The Umiat anticline is about 150 miles southeast of Point Barrow (fig. 1).

The anticline is about 10 miles long, 3 miles wide; the axis trends east and

west and the structure has more than 800 feet of closure. It is the highest

part in a structural trend extending many miles beyond the limits of the

closed anticline and its limits were defined by field and photogeologic mapping. Seismic data on the region are also available.

The oil-productive sand in this area is the Grandstand formation of

Cretaceous age. Most of this formation is within the designated zone of continuous permafrost. It is not known that all of the producing formation is

colder than the freezing temperature of the interstitial brine. Nearly waterfree oil, produced from this sandstone, indicates that the interstitial water

is virtually immobile.

Climate

The climate on the Arctic slope is cloudy, cold, and sometimes windy.

The annual mean temperature is 10.8° F. at Umiat. The maximum recorded temperature at Umiat is 79° F. and the minimum is -57° F. At Barrow the warmest

month, July, has an average of 13 days with freezing temperatures. Mean annual precipitation is 5.4 inches at Umiat. Half of the precipitation is derived from rainfall during July, August, and September. Annual snowfall is

about 33 inches at Umiat. Low temperatures, high humidities, and cloudy

skies minimize the rate of evaporation and tend to conserve the small total

precipitation for surface and ground-water supplies. In contrast to northern

Alaska precipitation, the average annual precipitation in southeastern Alaska

is about 100 inches.

Length of Day

At the Arctic Circle on the shortest day of the year the sun touches the

southern horizon at noon, then drops from sight. Below the Arctic Circle the

sun rises a correspondingly longer time, but farther north it stays below the

rim of the horizon on this day. For instance, on December 21 at Fairbanks,

about 2.5 degrees south of the circle the sun rises at 9:58 a.m. and sets at

1:40 p.m. At Barrow, about 4 degrees north of the circle, the sun is not seen

from late November until late January. In summer the length of the days is

the reverse of the winter.

Vegetation

The Arctic slope lies beyond the northern limit of the spruce. Small

willows and scattered alders grow along the channels of some of the streams

in the southern part of the region. Tundra consisting primarily of dwarf

shrubs, grasses, sedges, lichens, and herbaceous plants cover a large part

of the other areas.
__ .___

4

Permafrost

One of the important characteristics of the region to be considered in

drilling and producing operations is the permafrost. This area of subgroundlevel ice is discussed in detail by Hopkins, Karlstrom, and others.4 /

Permafrost has been defined by MullerS/ as "a thickness of soil or other

surficial deposit or even of bedrock, at a variable depth beneath the surface

of the earth in which a temperature below freezing has existed continuously

for a long time (from two to tens of thousands of years)."

The four permafrost zones in Alaska (fig. 2) are not rigidly defined and

their boundaries are arbitrarily drawn. The ground is perennially frozen

nearly everywhere in the continuous-permafrost zone; unfrozen ground is found

only at a few widely scattered sites. As shown in figure 2, the Umiat area is

entirely within the continuous-permafrost zone. Perennially frozen ground is

less widely distributed in the discontinuous-permafrost zone, and areas of unfrozen ground predominate in the southern part. In the sporadic-permafrost

zone perennially frozen ground is confined to isolated sites where vegetation,

topography, soil, and drainage permit its continued existence or its formation. Permafrost also is encountered locally in the no-permafrost zone, but

it is so rare that it has little influence on the landscape. or human

activities.

Permafrost is affected locally by subsurface drainage and surface insulation. In the rigorous climate of northern Alaska local differences in these

conditions generally result only in differences in the depth to permafrost.

Permafrost is affected by lakes, ponds, and streams which have appreciable

heat capacity.

Permafrost is present nearly everywhere beneath the Arctic slope of

Alaska. Frozen ground generally extends to a depth of about 1,000 feet in

this area. The permafrost lies at considerable depth or may be absent under

major rivers, such as the Colville, which flows throughout the winter and has

flood plains several thousand feet wide. Permafrost also lies at considerable

depth or is absent beneath most lakes deeper than 8 feet and wider than 2,000

feet.

Geothermal Gradients

The geothermal profile or depth-temperature relation in well 6 is shown

in figure 3. This survey was made by the Federal Geological Survey by placing

thermistor cables in the bore for a period of about one year (10 months) after

completion and abandonment of the hole.

4/ Hopkins, David M., Karlstrom, N. V., and others, Permafrost and Ground

Water in Alaska: Geol. Survey Prof. Paper 264-F, 1955, pp. 113-146.

5/ Muller, S. W., Permafrost or Permanently Frozen Ground and Related

Engineering Problems: J. W. Edwards, Inc., 1947, 231 pp.
r I

FIGURE 2. - Permafrost Zones in Alaska, Showing Location of Naval Petroleum

Reserve No. 4 and Umiat Field.

(Adapted From Federal Geological Survey Prof. Paper 264-F.) m
100

200

- 300

IaLL.

a 400

500

600

Ann

6

TEMPERATURE, °F The geothermal gradient

o!4 ,14 16 16 18 18 20 20 22 22 24 24 26 26 28 28 30 30 32 32 in well 9 shows an increase of

I I I | I i I I- 1" C. per 135 feet (1.33" F.

per 100 feet) of depth from

approximately 100 to 870 feet.

This is the largest gradient

found in the Umiat area. The

geothermal gradient at wells 4

and 6 is approximately 115

feet per degree Centigrade

(1.56° F. per 100 feet) for

similar depths.

A short extrapolation of

the thermal profile in well 9

on Oct. 13, 1953 indicated a

depth of permafrost of 1,055

feet. This thickness of permafrost is approximately 150 feet

greater than that found at any

of the other Umiat wells where

temperature measurements have

been made.

A Schlumberger temperature

survey was run in well 2 when

the final electrical log was

run. The lowest recorded temperature was 40.5° F. at 260

feet. Above that depth the

temperature was about 42° F.

It fluctuated slightly around

43° F. between 310 and 525

feet and increased gradually

with depth to 104° F. at 6,198

feet. These well temperatures

L~ vu -- are htiher than the undisturbed

temperatures found in a temperFIGURE 3. - Temperature-Depth Relation in Permafrost ature study in a well drilled

Zone of Well 6 (data from Geol. Survey). near Barrow, Alaska.6/ The

warming of the formations is

the result of friction developed in the drilling operation and the circulation

of relatively warm mud during drilling.

The method used to obtain the temperatures has been described by Brewer.-/

6/ Lachenbruch, Arthur H., Brewer, Max C., Dissipation of the Temperature

Effect of Drilling as Well in Arctic Alaska: Federal Geological Survey

Bull. 1083-C, 1959, 109 pp.

7/ Brewer, Max C., Some Results of Geothermal Investigations of Permafrost in

Northern Alaska: Trans. American Geophysical Union, vol. 39, No. 1,

Feb. 1958, pp. 19-26.
The first U.S.S.R. oil deposits in permafrost were found in Nordvik,

Siberia, where the permafrost was 540 meters (1,770 feet) deep and the rock

temperature was -12.7° C. (+9.2° F.) at a depth of 56-60 meters (184-197

feet).8/

Transportation

Development of this area is greatly dependent on air travel. Point Barrow

has a hard-surfaced airstrip and Umiat has a gravel airstrip. Lakes suitable

for float planes are not abundant, however, a few such lakes are in the area.

Ships can reach Point Barrow about three months of the year.

Tracked vehicles such as weasels are suitable for use in this region. In

the winter sleds pulled by tractors on tracks are well suited for hauling

equipment in the Arctic Coastal plain and the Arctic foothills when the ground

is covered with snow.

DRILLING AND COMPLETION DATA ON TEST WELLS

The eleven wells drilled are considered in groups to point out important

differences in drilling and completion practices that could have affected the

productivity of the wells. A map of the well locations is shown in figure 4.

Water-Base Mud Completions--Wells 1, 2 and 3

The first and least productive group, comprising wells 1, 2, and 3, were

drilled with rotary tools using water-base drilling mud. Well 1 was drilled

about 5 miles west of 2 and 3, and oil-bearing formations were logged in each

well. Formation tests were made either by bailing or running a packer on

2-1/2-inch tubing and swabbing. Wells 1 and 2 were dry and well 3 produced

oil at a rate of about 24 barrels per day.

Evidence of the presence of petroleum in formations penetrated by these

three holes was observed during drilling. Additional evidence of oil and gas

in well 2 was obtained when the hole was being prepared for a temperature survey after it had been drilled to 6,212 feet. The Grandstand formation was

found between 365 and 1,060 feet in this hole. Preparatory to the temperature

survey, well 2 was bailed to 950 feet. When the blowout preventers were removed a small gas flow was noted. In preparation for a gas-flow test the hole

was found to contain liquid at 730 feet. The hole was bailed to 1,075 feet

and the gas flow, as measured by means of a Pitot tube and a water manometer,

was estimated at 15,000 cubic feet per day. The gas contained 82 percent

methane, 16 percent heavier hydrocarbons, and 1.7 percent carbon dioxide.

Natural gas containing such a large quantity (16 percent) of hydrocarbons

heavier than methane generally is associated with crude oil in the formation.

7

8/ Lappo, V. I. (Petroleum Occurrence in Nordvik (IfURUNG-TUMUS): Neftfanoe

mestorozhdenie Nordvik (lUrung-Tumus): Nedra Arktiki, vol. 1, 1946,

pp. 74-129.
0c

FIGURE 4. - Well Location Map, Umiat Field, Alaska.

(Adapted From Geol. Survey Prof. Paper

305-B, Test Wells, Umiat Area, Alaska.)
Well 2 is of particular interest because of its proximity to well 5 which

had good productivity. This relationship is discussed in detail later in this

report.

Description of Reservoir Rocks

A study2/ of thin sections from cores from these wells showed that the

fine Graywacke sandstone was not well sorted and that it was composed primarily of angular quartz grains. Authigenic illite was present, surrounding

and partly replacing some quartz grains as coatings or elongate masses. An

X-ray diffraction pattern of the material through 325-mesh sieve showed that

it was composed of quartz and illite with small amounts of montmorillonite,

albite, kaolinite, and chlorite. The pore space was lined with a thin coating

of clay minerals, mostly illites.

Drilling Mud

The drilling mud used in wells 1, 2, and 3 was a water-base mud containing Wyoming bentonite, to which only a little lost circulation material and

chemicals were added to control cement contamination. The density of the mud

ranged from about 72 to 85 pounds per cubic foot. The API funnel viscosity

ranged from about 33 to 40 seconds. The API filtrate volume ranged from about

17 to 7.0 milliliters.

Cable-Tool Completions--Wells 4, 6, 8, and 10

Several wells were drilled with cable tools after the first three holes

drilled with rotary tools and water-base mud were unproductive (although oil

and gas shows were observed). A sodium chloride brine was used to minimize

the invasion of water into the formation and possible swelling of the clay

minerals observed in the oil-bearing sandstones. Sloughing was common in

drilling these holes and it retarded drilling. Good showings of oil and gas

were observed in this group of wells and the average oil productivity was

about 78 barrels per well per day. Most of the production testing was done

by bailing which would result in lower than normal productivity when compared

with testing by pumping.

Drilling Mud

The brine drilling muds were prepared by adding about 35 pounds of sodium

chloride to each barrel of water. This lowered the freezing temperature of

the solution below that of the minimum permafrost. The objective was to prevent freezing of the brine filtrate in the cold petroleum reservoir rocks and

to minimize the swelling of clay minerals.

Well 7

Well 7 was drilled with cable tools and brine drilling mud. Sandstones

containing oil and gas were penetrated and considerable water was produced in

9/ Work cited in footnote 3, p. 1.

9
10

the bailing tests. Small quantities of oil and gas were recovered by bailing.

Based on the meager information available, some investigators believed this

well to be below the edgewater in this reservoir.

Emulsion Mud Completion--Well 11

Well 11 was drilled to test the production possibilities of the sandstones of the Grandstand formation on the northern downthrow side of a fault

that parallels the axis of the structure. The hole was drilled with rotary

tools using an oil-in-water emulsion mud which had a water filtrate. Oil and

gas shows were noted in the permeable sandstones penetrated, but no commercial

production was indicated in eleven formation tests.

Drilling Mud

The drilling mud had an API filgrate volume of about 2.0 milliliter (ml),

an API funnel viscosity of about 100 seconds, a weight density of about 85

pounds per cubic foot, and about 30 percent (by volume) of Umiat crude oil

which had the fractions boiling below 325° F. removed.

Cable-Tool Completion Followed by Wall Scraping

Using Crude Oil--Well 5

Well 5, 175 feet east and 97 feet north of well 2, was drilled with cable

tools using 5-7/8-inch bits and brine drilling water. Bailing tests showed

the presence of oil and gas. When the depth reached 615 feet a pump was installed to test the productive capacity of the well. In a test that lasted

15 days production averaged about 70 barrels of clean oil per day. Drilling

with cable tools was continued to 1,075 feet, using a brine containing 40 to

50 pounds of sodium chloride per barrel of water.

Tubing was run for a swabbing test. A packer set at 630 feet was used to

shut off liquids from sands that had been tested at a depth of 615 feet. After

the drilling water was swabbed from the hole, oil flowed at the rate of 10 to

16 barrels per hour for short periods. Flow stopped several times; apparently

resulting from restricted flow into the well bore or from the formation of ice

in the tubing at shallow depths. The tubing was pulled, the rig removed in

September 1950, and the well was shut in for the winter.

In April 1951 a rotary rig was moved in place. The hole was cleaned out

and reamed in an effort to stimulate production. Circulation was lost and

some brine was added to the crude-oil drilling fluid to restore circulation.

The hole was reamed to 9-1/2 and 10-1/4 inches in the sandstone sections

penetrated by the bit.

During alternate reaming and swabbing tests from May 21 to June 17 the

first liquids recovered were brine and crude oil used for circulation while

reaming. In the last part of the reaming operation, fresh crude oil was

swabbed from the hole at an estimated rate of 400 barrels per day. One of

the first samples of oil recovered contained 4.7 percent water and 0.1 percent

sediment.
A pump with an electrical heater attached to the bottom of the tubing was

set at 1,055 feet. In a 93-day pumping test the maximum production rate was

about 400 barrels per day. However, the pump was too small to test the full

productive capacity of the well. The water content of the 35.5° API gravity

oil decreased from 1.35 to 0.4 percent. The temperature of the oil in the

flow line ranged from 27° to 28° F.

Oil-Base Mud Completion--Well 9

Well 9, about two miles west of well 2, was drilled with a rotary rig.

Core analyses indicated that this well penetrated a sandstone with appreciable

porosity, permeability, and oil content.

Drilling Mud

Water-base mud was used to 209 feet. Below 209 feet to 1,257 feet, an

oil-base mud was used to prevent the infiltration of water from a water-base

mud into the formations penetrated and to provide cores uncontaminated by water

from the mud. The mud contained a chemical tracer that was soluble in oil, insoluble in water, and unaffected by bacteria, to determine the volume of oil

filtrate that entered the cores. The tracer was an organic chloride compound

containing about 54 percent chlorine by weight. The method for following the

volume of tracer-bearing filtrate has been described in detail. 0/

The oil-base mud was composed of diesel oil, a low-gravity crude oil from

Fish Creek test well 1, Ken-Oil concentrate, and some unslaked lime. Addition

of the concentrate and/or the heavy crude oil increased the viscosity of the

mud, whereas, addition of diesel oil decreased viscosity. Gel strength was

increased by adding the concentrate and lime, which also decreased the filter

rate. The mud weight was kept low to minimize the flow of drilling mud filtrate into the formations. To keep the weight low, it was necessary to reduce

the viscosity to less than 50 seconds API funnel viscosity at about 45° F.

Cuttings would not drop from suspension otherwise, as no vibrating screen was

available during drilling.

The properties of the drilling mud are listed in table 1.

Swabbing and Pumping Tests

Three formation tests in both the upper and lower sandstone sections in

the Grandstand formation were made by swabbing through 2-1/2-inch tubing for

about 4 hours. A cone packer set above different sections of the formation was

used but no oil was produced. The Grandstand formation was found in this hole

between 425 and 1,090 feet. The first swabbing test was made with the hole

open from 476 to 533 feet. The second swabbing test was made with the hole

open from 866 to 901 feet. The third test was made with the hole open from

959 to 1,017 feet.

11

10/ Gates, George L., Morris, Frank C., and Caraway, W. Hodge, Effect of OilBase Drilling Fluid Filtrate on Analysis of Cores From South Coles

Levee, Calif., and Rangely, Colo., Fields: Bureau of Mines Rept. of

Investigations 4716, 1950, 25 pp.
PTABLE 1. - Properties of oil-base drilling mud used in Umiat well 9

Drilling fluid Drilling fluid

API funnel filtrate

Core Core Filtrate viscosity, Water Tracer

No. interval, volume, Water content (1 quart out) content, concenfeet mg./30 min. Weight density Weight- Volume- Time, Temperature, weight- tration,

45° F. 75° F. lb./gal. lb./ft.3 percent percent seconds °F. percent mg./ml.

374-384 0 - 8.6 64.5 10.95 11.34 95 61 - -

4 413-423 0 9 8.8 66.0 8.85 9.38 79 50 - 14.2

9 464-474 1.3 12 9.0 67.0 9.08 9.77 83 48 1.05 14.7

10 474-484 1.1 10 9.1 68.0 9.07 9.90 85 45 1.07 14.3

11 484-494 1.1 10 9.2 69.0 8.76 9.70 95 46 0.33 14.3

15 502-512 1.1 12 9.4 70.0 8.59 9.65 90 44 0.82 14.1

23 573-583 5.2 16 9.8 73.0 6.92 8.11 72 45 0.16 10.4

38 858-868 20.0 29 10.2 76.0 3.65 4.45 76 48 0 4.5

39 868-878 20.0 30 10.3 77.0 3.57 4.41 69 47 l/ 18.5

40 878-888 20.0 27 10.3 77.0 3.64 4.50 69 47 do. 17.7

41 888-898 20.0 34 10.4 78.0 3.71 4.64 69 46 do. 21.7

42 898-901 20.0 33 10.4 78.0 3.72 4.65 69 46 do. 17.5

43 901-911 21.0 36 10.3 77.0 4.03 4.98 59 45 do. 15.6

48 949-959 21.0 38 10.4 77.5 4.02 5.00 60 46 do. 15.3

49 959-969 21.0 42 10.4 77.5 4.29 5.37 60 46 do. 14.6

50 969-979 6.4 12 10.4 78.0 4.33 5.42 59.5 46 do. 13.8

52 989.5-1,000 7.9 14 10.5 78.5 4.54 5.72 57.0 46 do. 13.4

53 1,000-1,010 7.9 10 10.5 78.5 4.67 5.88 57.0 46 do. 12.8

54 1,010-1,017 - 13 10.4 78.0 4.41 5.52 57.0 46 0 13.2

57 1,037-1,047 3.4 7 10.2 76.5 5.01 6.15 53.0 41 - 10.6

58 1,047-1,057 2.2 - - 72.0 - - 52.0 42 -

59 1,057-1,067 3.0 - - 72.0 - - 46.0 42 - -

61 1,077-1,086 1.9 - - 59.5 - - 42.0 45 - -

62 1,086-1,096 4.1 - - 59.5 - - 44.0 42 - -

67 1,137-1,147 2.0 - - 60.5 - - 48.0 40 - -

I/ The drilling-tluid filtrates trom drilling fluid samples

water content of the combined samples was negligible.

39, 4U, 42, 43, 48, and 49 were combined, and the
U

After the third formation test, the hole was reamed with 7-7/8-inch bits

to total depth of 1,257 feet. Two-inch tubing was run to 1,247 feet and the

oil-base mud was swabbed from the hole and pumped into storage tanks. Shortly

before all of the mud was swabbed from the hole, crude oil flowed into the

hole. After twelve hours of swabbing no trace of oil-base mud was detected

in the produced oil. Two hundred barrels of crude oil were swabbed in 15

hours. When swabbing was stopped, for lack of storage space, the liquid level

rose to 50 feet from the surface. A subsequent pumping test of 6-1/2 weeks

indicated a maximum productivity of approximately 300 barrels per day of clean

oil.

Following the pumping test the well was plugged back, in stages, to 400

feet from the surface in an effort to determine the source of the oil. This

procedure was partly successful in disclosing the productive sands. The

cement plug was then drilled out to 1,077 feet using reverse circulation

with oil as the drilling liquid. From that depth to bottom, 1,257 feet,

brine containing 40 pounds of salt per barrel of water was used in drilling

out the cement. Circulation was lost several times and cleaning the hole

was difficult.

A string of 5-1/2-inch casing was cemented at 1,257 feet, total depth.

The pipe was perforated repeatedly opposite the permeable sandstones but no

oil entered the hole, even after swabbing, for periods longer than a week.

The pore space around the well bore was blocked to the flow of crude oil and

apparently the blocked area could not be penetrated by gun perforating.

Effect of Water on Permeability of Core Samples

From Well 9

A series of tests was made to study the effect of water on the permeability of cores from the Grandstand formation. The effect of invasion of the

sandstone by water from a fresh-water drilling mud was simulated. In this

series of tests at room temperature one sample from each of four cores was

selected. The cores had been sealed in cans at the well. The four selected

samples containing the interstitial water and oil, present in the cores when

they came from the core barrel, were mounted in low-temperature-setting

plastic inert to both water and kerosine. The permeability of these four

samples to kerosine was measured without cleaning the samples. The initial

water and oil contents were not changed except that the crude oil was displaced by kerosine. The same unextracted core samples were then used in

determining the permeability to fresh water. Note in table 2 that only one of

the samples had measurable permeability to water. However, a small volume of

water entered the three samples that were impermeable to the water. The samples were left in water overnight. Entrance of water into the core samples

is analogous to exposure of the wall of the bore hole to fresh water from

drilling mud during completion of the well. Following the contact of the

cores with water, the permeability to kerosine was determined again and oil

was flowed through the samples for several hours, apparently flushing part

of the invasion water from the core sample. The results are shown graphically

in figure 5 and are listed in table 2.

13
14

2

I

.-

-J

0

20

a

ca_

QI

I00

150

100

50

0

871.5 --

0

0

.-

a, a,

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3

0

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-

E

a.

DoL

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D Permeability to water

D Permeability to oil

o 0 .0-

4-

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876.5 - 977 --- 995

CORE DEPTH, feet

FIGURE 5. - Permeability of Core Samples to Oil and Water.

The observed reduction in permeability to oil after water invaded the

core sample is believed to be, primarily, the result of the relative permeability changes.

When water entered the pore space the permeability to oil was reduced.

Apparently when oil was flowed through the core some of the invasion water

remained in the pore space. The core samples were left in water overnight

so that the clays in the sandstone would have ample time to become fully hydrated. Overnight may not have been long enough for complete hydration because some clays required several days to reach equilibrium. In evaluation

of drilling-mud clays the American Petroleum Institute Recommended Practice

29, May 1957, the minimum time for hydration of bentonite is 72 hours.

f
TABLE 2. - Permeability of well 9 core samples to oil and water

Sample from--feet

871.5 | 876.5 977 I 995

Permeability before soaking, md.

Oil (water phase remained immobile)............ 206.0 56.5 24.0 2.1

Water (oil phase remained immobile)........... 78.1 .0 .0 .0

Oil permeability after soaking overnight in water, md.

Immediately after removal ...................... 31.4 - -

30 minutes after beginning test ................ 37.9 - 10.8

1 hour after beginning test.................... - 8.9 - -

2 hours after beginning test..................... - - - 0.3

2-1/4 hours after beginning test............... - 13.4 - -

3 hours after beginning test ................... - - 13.4

4-1/2 hours after beginning test............... 56.6 - -

6 hours after beginning test........ .......... - - - .6

Six samples having a range of permeabilities were selected to determine

the relative effects of air, oil, salt water, and fresh water on the permeability of extracted cores. The samples were cleaned by extraction with toluene to remove the water and oil simultaneously. The permeability to dry air

was measured, cores were saturated with oil, and the oil permeability was determined. As shown in table 3 the two values were nearly the same. The core

samples were cleaned of oil by toluene extraction again and then saturated

with 0.5 N sodium chloride solution. The permeability to this solution was

found to be less than the previously determined values. Finally the permeability to distilled water was measured and found to be less than any of the

previous permeabilities. This change in permeability indicates that the fresh

water entered the cores to lower the permeability as shown in figure 5. Similar reduction in permeability of Umiat cores was found by Yusterll/ and

Baptist.l2/ This permeability reduction is independent of reduction that

may have been caused by freezing of fresh-water filtrate in the pore channels.

When the formation tests in well 9 indicated no producible crude oil although the cores contained crude oil and gas, a study was made to determine

the effect of the low formation temperature on the filtrate from the oil-base

mud. A sample of filtrate from the mud was blended with crude oil and placed

in the camp refrigerator for several days. The refrigerator was maintained

at 8° F., which is 10° F. below the lowest permafrost temperature measured in

this hole. Neither the filtrate nor the blends of filtrate with crude oil

gelled at this temperature, indicating that filtrate from the oil-base mud

was not blocking the pore channels of the formation by the formation of a gel.

15

11/ Yuster, S. T., Oil and Gas Investigations Map OM 126 (in 3 sheets)

sheet 2: Geol. Survey, 1951.

12/ Baptist, 0. C., Oil Production From Frozen Reservoir Rocks, Umiat, Alaska:

Jour. Petrol. Technol., vol. 11, No. 11, Nov. 1959, pp. 85-88.
16

TABLE 3. - Permeability of selected Umiat 9 cores to air,

salt water. and fresh water

Permeability in millidarcys to--

0.5 normal

Depth (feet) Dry air Oil sodium chloride Distilled

____________________solution./ water

866-867 ................................ 22 18 15 13

867-868......................... 31 34 32 30

873-874......................... 270 260 250 200

875-876......................... 150 160 140 120

880-881......................... 140 150 130 100

907-908 ......................... 54 54 35 26

1/ Samples were extracted and dried before permeability to salt water was

determined.

Volume of Drilling Mud Filtrate in Cores From Well 9

A tracer was added to the drilling mud to obtain a quantitative measure

of the volume of filtrate from the oil-base drilling mud that entered the pore

space of the cores. This tracer was soluble in oil, insoluble in water, and

not affected by bacteria. Analysis of the oil extracted from the cores was

made by a chemical method that has been described previously. 13 / The results

indicated that about 3 percent of the pore space in the permeable sections

contained filtrate from the oil-base mud.

DISCUSSION OF RESULTS

Drilling and production data for the eleven test wells in the Umiat field

are summarized in table 4 and shown in figure 6. The results indicate that

the use of clay-water and clay-brine completion fluids damaged the productivity of some of the wells. This damage was a result of reduction in permeability of the sand at the well bore by the invasion of filtrates from the

drilling fluids.

The two best wells in the field were completed with oil-base mud. These

wells were approximately two miles apart. Four wells completed with brine mud

(using cable tools) had a productivity of about 78 barrels of oil per day. In

contrast, three wells drilled with water-base mud also penetrated oil-bearing

(not necessarily oil-productive) sandstones, but none was completed as

producers.

Information on the wells drilled indicates that all of the wells penetrated oil-bearing sandstones and the correlation between the type of drilling

fluid used and the well productivity has been shown. However, any study of

well completion practices is difficult because generally a well can be completed only once and the productivity attainable by any other method is a

13/ Gates, George L., Morris, Frank C., and Caraway, W. Hodge, Effect of OilBase Drilling Fluid Filtrate on Analysis of Cores From South Coles

Levee, Calif., and Rangely, Colo., Fields: Bureau of Mines Rept. of

Investigations 4716, 1950, 25 pp.
conjecture. It should be noted that wells 1 and 11 are located an appreciable

distance from the producing wells. The lack of production from these holes

may be due to lack of sufficient permeability of the reservoir rock. Also,

lack of production from the other holes may be complicated by the lack of

permeability. However, observed damage to wells 5 and 9 could not be the

result of these factors.

TABLE 4. - Drilling and production data, Umiat field, Alaska, 1944-53

Total

Well Drilling Production rate, Production Length of depth,

No. method Drilling mud barrels per day test method test, days feet

1 Rotary.. Clay-water.. 0 Formation.. <1 6,005

2 ..do.... ....do.... Trace ....do..... <1 6,212

3 ..do........do...... 24 Pumping .... 14 approx. 572

4 Cable... Brine....... 100 ....do..... 18 840

6 .. do........ do...... 80 (wet) ....do..... 1 approx. 825

7 ..do.... . . <1 Bailing .... 1 approx. 1,384

8 ..do.... ....do..... 60 Pumping.... 14 1,327

10 ..do........ do ..... 70 Bailing .... 1 1,573

5 ..do ... Brine ... 400+. Pumping.... 93 1,077 'Reamed, oil.

9 Rotary.. Oil-base.... 300+ ....do..... 45 1,257

11 ..do.... Oil-in-water 0 Formation.. 1 3,303

_____ emulsion _____

Comparison of Wells 2 and 5

Comparison of the productivity of wells 2 and 5 indicates that damage results from completion practice in which water from the drilling fluid invades

the reservoir formation. Well 2, completed with clay-water mud, was a dry

hole and well 5, which was about 200 feet from well 2, was completed first

with brine. Both holes penetrated oil-bearing sandstone with appreciable

permeability. Well 5 then was reamed with oil as the drilling mud and a

sustained production test indicated productivity to 400 barrels per day.

The brine drilling mud used in these holes had a freezing point below

the formation temperature, therefore, the filtrate from these drilling muds

reasonably would not be expected to be in the state of ice.

Study of the electrical logl 4 / of well 2 indicated that the Grandstand

formation might have been expected to be productive. The spontaneous potential and resistivity curves indicated that this formation might be expected

to contain oil. However, very little oil was produced from this hole which

was completed with water-base mud. Well 5, about 200 feet from well 2, was

completed in this formation with oil-base mud and the productive rate was

about 400 barrels per day.

14/ Collins, Florence Rucker, With Bergquist, Harlan R., Brewer, Max C., and

Gates, George L., Test Wells Umiat Area, Alaska: Geol. Survey Prof.

Paper 305-B, 1958, P1. 11.

17
400

.0

x 300

soo

|200

o

3

a00

n- 100

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1-

- 1 Salt-water

l Clay-water

18

II II II

II

a Oil-base drilling mud completion

II II

I

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3

4 c

a

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0

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1 2 3 1 1 4 6

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7 8 10 9 nv

WELL NUMBER

FIGURE 6. - Production Capacity of Umiat Wells Related to Drilling Mud.

Unusual Features of Well 9

Because of the time required to pump the oil-base mud from the mud pit

into tanks the formation was exposed to a low pressure from the liquid column

for about 6 hours. Why the crude oil came into the hole after this time interval and did not flow into the hole during the 4-hour formation tests is

not understood. There is nothing in Darcy's law to indicate that time (several hours) is required for crude oil to flow from the formation into the

bore hole.

Effect of Water on Relative Permeability to Oil

f

Where water from the drilling mud or any other source enters the pore

space (especially if the water freezes) the channels available to the flow

of oil are greatly reduced. A large decrease in permeability to oil with a

small increase in water content has been established from relative permeability studies. Dunlap.5/ showed this relation in a laboratory study of the oil

15/ Dunlap, Eldon N., Influence of Connate Water on Permeability of Sands for

Oil: AIME Petrol. Trans., vol. 127, 1938, pp. 215-225.
U

100

C

0

to

C,

a

QW

0

AL

>-

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19

...

80

60

40

20

0

permeaoDilty ot sanas containing increasing volumes of

water (fig. 7). The tests

showed that a 5 percent increase in the water content

of the sand resulted in a 40

percent decrease in permeability to oil. The permeabilities of the sands used

in the laboratory tests were

much higher than normal oilreservoir sands. However,

data are considered indicative of relative permeability

trends.

Formation Pressure

Although few data are

available regarding the formation pressure in the Grandstand sandstone in the Umiat

field, some indication of the

pressure may be obtained indirectly. Shut-in gas pressure at the surface of well 8

reached a maximum observed

0 20 40

PORE SPACE SATURATED WITH WATER, perc

60 value of 270 pounds per

square inch. The depth from e nt which the gas was flowing and

the liquid level in the well

were unknown. FIGURE 7. - Effect of Water Content of Sands on

Permeability to Oil. (Adapted From

Junlap, ANIME I'etrol. I rans. 1J3). Wells 5 and 9 had liquid

levels that reached nearly to

the surface. Based on a crude oil specific gravity of 0.84 the pressure in

well 9 at a depth of 900 feet was 900 x 0.84 x 0.43 lb./ft. of water = 325

pounds per square inch. The calculated pressure in the upper Grandstand sandstone at a depth of 470 feet was 170 pounds per square inch.

These pressures available to push water (brine) or ice from the pore

channels are not large. The affinity of the clays in the reservoir rock also

tends to hold water solutions in the pore channels thereby restricting the

rate of flow of crude oil through the rock into the well bore.

Low Formation Temperatures

Wells in this field penetrated rocks at temperatures below the freezing

temperature of water and some of the oil produced from these holes was shown

to be flowing through rocks below 32° F. The measured oil flow temperature

was about 26° F. indicating approximately the temperature of the oil-reservoir
20

- -- --- ·

rock. Although this temperature is below the freezing temperature of fresh

water in large containers, tests have shown that water solutions in small

pores may have a freezing point at temperatures below 32° F.l6/ The relative

amounts of water in the liquid and solid states in ground at temperature below

32° F. depend on the physiochemical composition of the ground, on the presence

of water-soluble particles, and on the temperature and pressure.

PROPERTIES OF THE CRUDE OIL

The produced crude oil has the following characteristics: API gravity,

about 36°; pour point, -5° F.; sulfur, 0.1 percent, no hydrogen sulfide;

Saybolt Universal viscosity at 100° F., 37 seconds; color, National Petroleum

Association No. 4; and carbon residue, Conradson, weight percent, 0.1 to 0.2.

The crude oil was relatively high in naphthene hydrocarbons. Analyses of some

crude oils from Alaska have recently been published by the Bureau of Mines.17/

BASIC WELL DATA

Well 1 had a ground elevation of 801 feet and the elevation of the kelly

bushing was 810 feet. The total depth from the surface was 6,005 feet. Sixteen feet of 24-inch conductor pipe was set 19 feet below the kelly bushing

in a 30-inch hole. Sixteen-inch casing was cemented at 97 feet. A string of

11-3/4-inch casing was cemented at 685 feet.

Well 2 had a ground elevation of 333 feet and the kelly bushing was located at an elevation of 342 feet. Sixteen-inch conductor pipe was cemented

at 103 feet. A string of 11-3/4-inch casing was cemented at a depth of 1,005

feet. The well was drilled to a total depth of 6,212 feet.

Ground elevation at well 3 was 351 feet and elevation of the kelly bushing was 360 feet. Seven-inch casing was cemented at a depth 72 feet below the

kelly bushing. The well was drilled to a total depth of 572 feet.

The ground elevation of well 4 was 482 feet. Surface pipe was set at a

depth of 33 feet. This hole was drilled to a total depth of 840 feet.

The ground level of well 5 was 334 feet and the rig floor was 335 feet

above sea level. At a depth of 23.5 feet, 8-5/8-inch casing was cemented.

The well was drilled to a total depth of 1,077 feet. After the 93-day pumping

test, 5-1/2-inch casing was cemented at a depth of 1,068 feet with the top of

the plug at 1,065 feet. The pipe was filled with Umiat crude oil and shut in.

16/ Nersesova, Z. A., (The Relative Amounts of Water the Solid and Liquid

States Present in the Ground During Freezing or Thawing.) Fazovyy

sostav vody v gruntakh pri zamerzanii i ottaivanii, Materialy po

Laboratornym Issledovaniiam Merzlykh Gruntov, vol. 1, 1953, pp. 37-51.

17/ McKinney, C. M., Garton, E. L., and Schwartz, F. G., Analyses of Some

Crude Oils From Alaska: Bureau of Mines Rept. of Investigations

5447, 1959, 29 pp.
Well 6nwas at a ground level of 334 feet and the rig floor was at 337

feet. Surface casing was driven to a depth of 35 feet. The hole was drilled

to a total depth of 825 feet.

Well 7 was spudded from a ground level of 326 feet and a derrick floor

level of 330 feet. Surface pipe was driven to 52 feet. The hole was drilled

to a total depth of 1,384 feet.

Well 8 was at a ground level of 735 feet and the derrick floor was 5 feet

higher. Two joints of 11-3/4-inch casing were set at 50 feet. After testing

promising sandstones, excessive caving of the walls of the hole resulted in

setting 8-5/8-inch casing at a depth of 1,231 feet. The hole was drilled to

a total depth of 1,327 feet.

Well 9 was at a ground level of 418 feet and the kelly bushing was 6 feet

higher. A string of 8-5/8-inch surface pipe was cemented at a depth of 61

feet. After a sustained pumping test, 5-1/2-inch casing was run to bottom,

cemented, and gun perforated. The total depth of this hole was 1,257 feet.

Well 10 was at a ground level of 741 feet and the derrick floor was 5

feet higher. A string of 11-3/4-inch casing was cemented at a depth of 70

feet. After caving and several fishing jobs, casing was cemented at a depth

of 1,339 feet. The hole was drilled to a total depth of 1,573 feet.

Well 11 was at a ground level of 464 feet and the kelly bushing was 7

feet higher. The 13-3/8-inch casing was cemented at a depth of 89 feet, with

57.7 feet jacketed with 16-5/8-inch casing. The hole was drilled to a total

depth of 3,303 feet.

I

21

INT. - BU OF MINES.PGH. PA. 2027