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Assessing Undiscovered Oil and Gas Resources of the Eastern Great Basin in Parts of Nevada, Utah, Idaho, and Arizona

Lawrence O. Previous HitAnnaTop, Laura N. R. Roberts, and Christopher J. Potter
U.S. Geological Survey, Lakewood, CO

The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the Eastern Great Basin (EGB). USGS assessments of undiscovered oil and gas use the total petroleum system (TPS), which includes mapping the distribution of potential source rocks and known petroleum accumulations, and determining the timing of petroleum generation and migration. The assessment is geologically based and includes source and reservoir rock stratigraphy, timing of tectonic events and the configuration of resulting structures, formation of traps and seals, and burial history modeling. TPS is subdivided into assessment units (AU) based on similar geologic characteristics, and accumulation and petroleum type. For the EGB, the USGS defined the Phanerozoic TPS and three AU, and quantitatively estimated the undiscovered oil and gas resources within each AU. The three AU are (1) Neogene basins formed during Basin and Range extensional tectonics, (2) mountain ranges related to the same tectonic event, and (3) the Sevier thrust system of western Utah and southeastern Nevada. The oil and gas potential of each AU was based in part on burial and thermal history modeling. Model results showed several potential scenarios for petroleum generation and migration in the TPS based on varying depositional thickness, erosion amount, and heat flow. Model results showed that the Mississippian Chainman Formation entered the oil generation window during the Permian but generation ceased in late Mesozoic. Part of the Chainman began to generate oil again after additional burial in Neogene basins, but remained dormant in Neogene mountain ranges.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005