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National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Oil and Gas Resources of the Powder River Basin Province of Wyoming and Montana, 2002

Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 16.5 trillion cubic feet of undiscovered natural gas, a mean of 1.5 billion barrels of undiscovered oil, and a mean of 86.5 million barrels of natural gas liquids in the Powder River Basin Province.
Introduction
The U.S. Geological Survey (USGS) recently completed an assessment of the potential for undiscovered resources in continuous oil and gas accumulations of the Powder River Basin Province of northeastern Wyoming and southeastern Montana (fig. 1). The assessment of continuous oil and gas resources is based on geologic elements such as hydrocarbon source rocks (source-rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing) in four Total Petroleum Systems (TPS) identified in the province by the USGS. Six continuous assessment units and one conventional assessment unit were defi ned within the TPSs. Estimates of the undiscovered oil and gas resources in these seven assessment units, along with previous estimates of undiscovered oil and gas resources in 11 conventional plays within the province (Dolton and Fox, 1996), are presented in table 1.
Resource Summary
The USGS estimated a mean of 16.5 trillion cubic feet of undiscovered gas, a mean of 1.5 billion barrels of oil, and a mean of 86.5 million barrels of total natural gas liquids. Most of the undiscovered gas resource (94 percent, or 15.5 trillion cubic feet) is continuous (table 1). Of the 15.5 trillion cubic feet of continuous gas at the mean, about 14.3 trillion cubic feet is estimated to be coal-bed gas in three AUs of the Tertiary≠Upper Cretaceous Coal-Bed Methane TPS. The Cretaceous Biogenic Gas TPS is estimated to contain a mean of 0.78 trillion cubic feet of gas (table 1). The Mowry TPS is estimated to contain a mean of 198 million barrels of undiscovered continuous oil, and the Niobrara TPS is estimated to contain a mean of about 227 million barrels of undiscovered continuous oil, together representing about 27 percent (424 million barrels) of the total mean undiscovered oil in the province. One-third of the mean undiscovered oil (33 percent, or 522 million barrels) is estimated to be in conventional accumulations of the Upper Minnelusa Sandstone Play (table 1).
For Further Information
Supporting geologic studies and reports on the assessment methodology used in the Powder River Basin Province assessments of continuous resources are in progress.
Assessment results from 1995 and 2002 are available at the USGS Central Energy Team website:
http://energy.cr.usgs.gov/oilgas/noga/
Powder River Map

Figure 1. Powder River Basin Province of northeastern Wyoming and southeastern Montana.


Powder River Basin Province Assessment Team:
Romeo M. Flores (Task Leader; flores@usgs.gov), Larry O. Anna, Gordon L. Dolton, James E. Fox, Christopher D. French, Ronald R. Charpentier, Troy A. Cook, Robert A. Crovelli, Timothy R. Klett, Richard M. Pollastro, and Christopher J. Schenk.
Reference Cited
Dolton, G.L., and Fox, J.E., 1996, Powder River Basin Province (033), in Gautier, D.L., Dolton, G.L., Varnes, K.L., and Takahashi, K.I., eds., 1995 National Assessment of United States Oil and Gas ResourcesóResults, methodology, and supporting data: U.S. Geological Survey Digital Data Series DDS-30, one CD-ROM, Release 2.
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