U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3036

May 2008

National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Biogenic Gas Resources,

North-Central Montana Province

Printed on recycled paper

Application of 

a geology-based 

assessment 

methodology by 

the U.S. Geological Survey 

resulted in an 

estimated mean 

of 6,192 billion 

cubic feet of 

shallow biogenic 

(continuous) 

undiscovered gas 

in the NorthCentral Montana 

Province. Oil, 

gas, and natural 

gas liquids in 

conventional 

accumulations 

were not 

assessed.

Introduction

In 2000 the U.S. Geological Survey (USGS) 

assessed the undiscovered biogenic (also known as 

microbial) continuous gas resource potential of the 

North-Central Montana Province in eastern Montana 

(fig. 1) as part of a national oil and gas assessment 

project. The assessment was based on the general geologic elements used to define a total petroleum system 

(TPS), including hydrocarbon source rocks (hydrocarbon 

generation and migration), reservoir rocks (sequence 

stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this 

geologic framework, the USGS defined the Cretaceous 

Judith River through Belle Fourche Biogenic Gas TPS 

and seven assessment units (AUs) within it, and quantitatively estimated the undiscovered continuous gas 

resources within each AU.

Resource Summary

Assessment of the undiscovered continuous gas resources 

for the seven AUs— Judith River Formation AU, Eagle Sandstone and Claggett Shale East AU, Eagle Sandstone and Claggett 

Shale West AU, Niobrara–Carlile AU, Greenhorn–Lower Belle 

Fourche AU, Greenhorn–Upper Belle Fourche AU, and Bowdoin 

Dome AU—resulted in an estimated total mean of 6,192 billion 

cubic feet (BCFG) of continuous biogenic gas in fields within 

the Cretaceous Judith River through Belle Fourche Biogenic Gas 

TPS (table 1). The Eagle Sandstone and Claggett Shale West and 

East AUs contain a combined estimated mean of 2,334 BCFG, 

representing 37.6 percent of the total undiscovered microbial gas 

resources. The Judith River Formation AU contains an estimated 

mean of 1,855 BCFG, representing an additional 30 percent of 

the total resource. Undiscovered petroleum (oil, gas, and natural 

gas liquids) in conventional accumulations in the province was 

not assessed at this time.

Figure 1. Map showing the North-Central Montana Province (enclosed by red line) in eastern Montana. 

Small closed polygons within the province are areas where source or reservoirs rocks are not present.

§ ̈¦15

§ ̈¦90

§ ̈¦94

§ ̈¦15

§ ̈¦90

§ ̈¦90

§ ̈¦90

WYOMING

IDAHO

NORTH DAKOTA SOUTH DAKOTA

MONTANA

Butte

Havre

Helena

Broadus

Billings

Glendive

Cut Bank

Lewistown

Miles City

Wolf Point

Bowdoin Dome

Great 

Falls

CANADA

UNITED STATES

Fort 

Peck Lake

X

114° 113° 112° 111° 110° 109° 108° 107° 106° 105° 104°

49°

48°

47°

46°

45°

0 50 100 MILES

ID WY

MT ND

SD
Total Petroleum System 

and Assessment Unit

Field 

Type

Total Undiscovered Resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Cretaceous Judith River through 

Belle Fourche Biogenic Gas TPS

Judith River Formation AU Gas 550 1,529 4,250 1,855 0 0 0 0

Eagle Sandstone and

Claggett Shale East AU Gas 501 1,070 2,283 1,189 0 0 0 0

Eagle Sandstone and 

Claggett Shale West AU Gas 473 1,025 2,221 1,145 0 0 0 0

Niobrara-Carlile AU Gas 42 114 305 136 0 0 0 0

Greenhorn-Lower

Belle Fourche AU Gas 166 412 1,025 481 0 0 0 0

Greenhorn-Upper

Belle Fourche AU Gas 211 544 1,400 641 0 0 0 0

Bowdoin Dome AU Gas 484 723 1,079 745 0 0 0 0

Total Undiscovered

Continuous Gas Resources 6,192 0

Table 1. North-Central Montana Province basin assessment results.

[MMBO, million barrels of oil. BCFG, billion cubic feet of gas. MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. 

F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. TPS, total petroleum system; AU, assessment unit. 

Gray shading indicates not applicable.]

For Further Information

Geologic studies of total petroleum systems and assessment units, as well as reports on the methodology used in 

assessing undiscovered gas resources for the North-Central 

Montana Province and other provinces, are available at the 

USGS Central Energy Team Web site: http://energy.cr.usgs.

gov/oilgas/noga/. Published geologic studies resulting from this 

assessment project include the following:

Condon, S.M., 2000, Stratigraphic framework of Lower and Upper 

Cretaceous rocks in central and eastern Montana: U.S. Geological Survey Digital Data Series DDS–57, one CD–ROM.

Fishman, N.S., Ridgley, J.L., and Hall, D.L., 2001, Timing of gas 

generation in the Cretaceous Milk River Formation, southeastern Alberta and southwestern Saskatchewan—Evidence from 

authigenic carbonates, in Christopher, J.E., Gilboy, C.F., Haidl, 

F.M., and Kreis, L.K., eds., Summary of Investigations 2001, 

Volume 1: Saskatchewan Geological Survey, Saskatchewan 

Energy and Mines Miscellaneous Report 2001–4.1 p. 125–136.

Hester, T.C., 1999, Prediction of gas production using well logs, 

Cretaceous of north-central Montana: The Mountain Geologist, v. 36, no. 2, p. 85–97.

Lillis, P.G., 2007, Upper Cretaceous microbial petroleum

systems in north-central Montana: The Mountain Geologist,

v. 44, no. 1, p. 11–35.

Ridgley, J.L., 2000, Lithofacies architecture of the Milk River 

Formation (Alderson Member of the Lea Park Formation), 

southwestern Saskatchewan and southeastern Alberta—Its 

relation to gas accumulation, in Christopher, J.E., Gilboy, 

C.F., Haidl, F.M., Harper, C.T., and Brown, C.L., eds., 

Summary of investigations 2000, Volume 1: Saskatchewan 

Geological Survey, Saskatchewan Energy and Mines Miscellaneous Report 2000–4.1, p. 106–120.

Ridgley, J.L., Hester, T.C., Condon, S.M., Anna, L.O., Rowan, 

E.L., Cook, T.A., and Lillis, P.G., 1999, Re-evaluation of the 

shallow biogenic gas accumulation, Northern Great Plains, 

USA—Is the similar gas accumulation in southeastern 

Alberta and southwestern Saskatchewan a good analog?, in 

Christopher, J.E., Delaney, G.D., Gilboy, C.F., Haidl, F.M., 

Harper, C.T., and Paterson, D.F., eds., Summary of Investigations 1999, Volume 1: Saskatchewan Geological Survey, 

Saskatchewan Energy and Mines Miscellaneous Report 

99–4.1, p. 64–78.

Ridgley, J.L., McNeil, D.H., Gilboy, C.F., Condon, S.M., 

and Obradovich, J.D., 2001, Structural and stratigraphic 

controls on sites of shallow biogenic gas accumulations 

in the Upper Cretaceous Belle Fourche and Second White 

Specks–Greenhorn Formations of southern Alberta, Saskatchewan, and northern Alberta, in Anderson, D.S., Robinson, J.W., Estes-Jackson, J.E., and Coalson, E.B., eds., Gas 

in the Rockies: Rocky Mountain Association of Geologists, 

Denver, Colo., p. 241–270.

North-Central Montana Province 

Assessment Team

Jennie L. Ridgley (Task Leader), Lawrence O. Anna, 

Steven M. Condon, Neil S. Fishman, Timothy C. Hester,

Paul G. Lillis, Elizabeth L. Rowan, Ronald R. Charpentier, 

Troy A. Cook, Robert A. Crovelli, Timothy R. Klett, and 

Christopher J. Schenk.