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Assessment of Undiscovered Oil and Gas Resources in Selected Rocky Mountain Basins

Groat, Charles G.
U. S. Geological Survey, Reston, VA

The U.S. Geological Survey (USGS) provides periodic assessments of the oil and natural gas endowment of the United States. Understanding the petroleum resources in our country is needed for strategic planning, formulating economic and energy policies, evaluating lands in the purview of the Federal government, and developing sound environmental policies.

In 2002, the USGS completed an assessment of undiscovered, technically recoverable oil and gas resources in five geologic basins in the Rocky Mountain Region. The assessed basins are the Montana Thrust Belt, Powder River Basin, San Juan Basin, Southwestern Wyoming, and the Uinta-Piceance province. The assessment was done in accordance with the requirements of the Energy Policy and Conservation Act Amendments of 2000. The assessment of each province is based on the geologic elements of each Total Petroleum System defined in the province, including hydrocarbon source rocks (source-rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing).

Using this geologic framework and the geologic models for each assessment developed in 2002, the USGS estimated a mean of 183 trillion cubic feet of undiscovered gas (TCFG), a mean of 2.3 billion barrels of oil, and a mean of 3.2 billion barrels of total natural gas liquids in the six provinces. About 92 percent (169 TCFG) of the total mean undiscovered gas resource (183 TCFG) was interpreted to be continuous using the geologic models in 2002, and about 8 percent (14 TCFG) was conventional. Of the 169 TCF of undiscovered continuous gas, about 42 TCFG (or 25 percent) was estimated to be coal-bed gas. Of the remaining 127 TCFG of continuous gas at the mean, about 82 TCFG are in Southwestern Wyoming Province, about 26 TCFG are in the San Juan Province, and about 19 TCFG are in the Uinta-Piceance Province. More than half (8.5 TCFG) of the total conventional gas (14 TCFG) was in the Montana Thrust Belt Province.