CHUKCHI

SEA

ARCTIC OCEAN

Prudhoe

Bay

Point

Barrow

Cape

Lisburne

Icy

Cape

BEAUFORT SEA

UNITED STATES

CANADA

Brooks Range

Sagavanirktok Formation AU

Coalbed gas: Assessed areas in the

Prince Creek and Tuluvak Formations AU

Nanushuk Formation AU

170° 162° 154° 146° 138°

66°

68°

70°

72°

0 50 100 MILES

Trans-Alaska

Pipeline System

National Petroleum

Reserve—Alaska

(boundary)

Arctic National

Wildlife Refuge

(boundary)

Area of

map

ALASKA

The U.S. Geological Survey (USGS) recently 

completed an assessment of undiscovered coalbed 

gas resources on the North Slope of Alaska. A mean 

estimate of undiscovered, technically recoverable 

resources indicates a potential for about 18 trillion 

cubic feet (TCF) of coalbed gas.

Assessment of Coalbed Gas Resources in Cretaceous

and Tertiary Rocks on the North Slope, Alaska, 2006

Introduction

The North Slope of Alaska is a vast area of land north of 

the Brooks Range, extending from the Chukchi Sea eastward to 

the Canadian border (fig. 1). This Arctic region is known to

contain extensive coal deposits; hypothetical coal resource 

estimates indicate that nearly 4 trillion short tons of coal are in 

Cretaceous and Tertiary rocks (Flores and others, 2004). Because 

of the large volume of coal, other studies have indicated that 

this region might also have potential for significant coalbed gas 

resources (for example, Smith, 1995; Tyler and others, 1998).

The present study represents the first detailed assessment 

of undiscovered coalbed gas resources beneath the North Slope 

by the USGS. The assessment is based on the total petroleum 

system (TPS) concept. Geologic elements within a TPS relate 

to hydrocarbon source rocks (maturity, hydrocarbon generation, 

migration), the characteristics of reservoir rocks, and trap and 

seal formation. In the case of coalbed gas, the coal beds serve as 

both source rock and reservoir. The Brookian Coalbed Gas Composite TPS (fig. 1) includes coal-bearing rocks in Cretaceous and 

Tertiary strata underlying the North Slope and adjacent Alaska 

State waters. Assessment units (AUs) within the TPS (from 

oldest to youngest) include the Nanushuk Formation Coalbed 

Gas AU, the Prince Creek and Tuluvak Formations Coalbed Gas 

AU, and the Sagavanirktok Formation Coalbed Gas AU.

Resource Summary

USGS assessments provide estimates of the volumes of undiscovered petroleum resources (oil, gas, and natural gas liquids) 

that are technically recoverable and have the potential to be 

Figure 1.  Boundaries of the USGS Northern Alaska Petroleum Province (red outline) and the Brookian Coalbed Gas Composite Total Petroleum

system (blue outline).

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3105

September 2006 Printed on recycled paper
Table 1.  Alaska North Slope: Coalbed gas resource assessment results.

[BCFG, billion cubic feet of gas. MMBL, million barrels of natural gas liquids. Results shown are fully risked estimates. F95 denotes a 95 

percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive under the assumption of perfect 

positive correlation. Accum., accumulation; CBG, coalbed gas]

added to known reserves. Because there is currently no production 

of coalbed gas on the North Slope, all assessment units within the 

Brookian Coalbed Gas Composite TPS are considered hypothetical. 

Geologic factors that influenced the resource estimates include (1) 

the distribution and cumulative thickness of coal beds in each AU, 

(2) depth of permafrost relative to coal-bearing strata, (3) thermal 

maturity of the coal, and (4) key structural elements (folds, faults) 

that might affect gas migration and entrapment. This assessment 

also utilized production data from wells in coalbed gas fields in the 

Wasatch Plateau (Utah) and the Powder River Basin (Wyoming) to 

gain insight into production potential that might be applied to North 

Slope coalbed gas wells. The Utah and Wyoming fields are considered viable analogs for assessing North Slope resources based on 

similarities in such criteria as coal thickness, thermal maturity, and 

overall geologic setting. In addition, this assessment only considered coals within 6,000 ft of the ground surface because of the 

potential decrease in coal permeability with increasing depth.

Coal beds in the Nanushuk Formation Coalbed Gas AU are 

distributed over the largest area; cumulative total coal thicknesses 

exceed 200 ft and individual coal bed thicknesses are as much as 30 

ft. The Sagavanirktok Formation Coalbed Gas AU has cumulative 

coal thicknesses of more than 180 ft with individual bed thicknesses 

as much as 35 ft. Coal in the Prince Creek and Tuluvak Formations 

Coalbed Gas AU is more limited in areal extent. Cumulative coal 

thickness can exceed 70 ft, and individual beds are as thick as 15 ft.

Of the mean total estimated undiscovered coalbed gas resources of 18 TCF in the Brookian Coalbed Gas Composite TPS, 

about 84 percent or 15 TCF is estimated to be in the Nanushuk 

Formation. About 12 percent (2.2 TCF) is in the Sagavanirktok 

Formation and about 4 percent (0.8 TCF) is in the Prince Creek 

and Tuluvak Formations.

North Slope Coalbed Gas Assessment Team

Steve Roberts, Charles E. Barker (scientist emeritus), Kenneth 

J. Bird, Ronald R. Charpentier, Troy Cook, David W. Houseknecht, 

Timothy R. Klett, Richard M. Pollastro, and Christopher J. Schenk

References Cited

Flores, R.M., Stricker, G.D., and Kinney, S.A., 2004, Alaska coal 

geology, resources and coalbed methane potential: U.S. Geological Survey Digital Data Series 77, version 1, CD-ROM.

Smith, T.N., 1995, Coalbed methane potential for Alaska and 

drilling results for the upper Cook Inlet: Intergas, May 15−19, 

1995, Tuscaloosa, Ala., University of Alabama, p. 1−21.

Tyler, Roger, Scott, A.R., and Clough, J.G., 1998, Coalbed 

methane potential and exploration targets for rural Alaskan 

communities: Texas Bureau of Economic Geology and Alaska 

Division of Geological and Geophysical Surveys Final Report 

(Agreement No. UTA97-0042), 169 p.

For Further Information

Geologic studies supporting the North Slope coalbed gas 

assessment are in progress. Assessment results are available at: 

http://energy.cr.usgs.gov/oilgas/noga/ or contact Steve Roberts: 

sroberts@usgs.gov (303) 236-7788.

Coal bed in the Sagavanirktok Formation in the eastern part of the North Slope.

Coal bed is 8 ft thick. View is to the north.

Total undiscovered resources Total Petroleum System 

(TPS) and Coalbed Gas

Assessment Units (AU)

Accum.

type Gas (BCFG) Liquids (MMBL)

CBG

CBG

CBG

5,834 13,279 30,225 15,047 10 28 83 35

350 709 1,436 778 0 0 0 0

889 1,981 4,416 2,231 1 4 12 5

7,073 15,969 36,077 18,056 11 32 95 40

Brookian Coalbed Gas

Composite TPS

Nanushuk Formation AU

Prince Creek and Tuluvak Formations AU

Sagavanirktok Formation AU

Total Undiscovered

Oil and Gas Resources