Andrew G. Alpha, 1971. "Petroleum Potential of Sierra Nevada and Eastern Desert, California", Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2, Ira H. Cram
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Area 9 of Region 2 (Pacific Coast) encompasses the Sierra Nevada, western Great Basin, and Mojave Desert geomorphic provinces. Hydrocarbons are unknown as seeps or shows in wells. As a future oil province, this area appears to be of low order of importance because of intensive tectonism, plutonic activity, and varied degrees of metamorphism imposed on the Paleozoic section; a paucity of Mesozoic strata; and the limited areas of marine Tertiary rocks. Hydrocarbon entrapment is possible in the Great Basin and in the limited areas of possibly marine Tertiary rocks adjacent to the San Andreas fault and along the Colorado River.
Post-Cambrian, pre-Mississippian sequences, where present, are mainly carbonate rocks deposited in a mio- geosynclinal environment. As a result of the Antler orogeny, which occurred largely in Nevada from latest Devonian to Early Pennsylvanian time, Mississippian and Pennsylvanian rocks adjacent to this orogenic belt are made up of coarse clastic material, as they are also in the Inyo Mountains. However, carbonate rocks are predominant eastward. Post-Cambrian to Permian rocks have reservoir characteristics in the Great Basin province.
The Sonoma orogeny of Late Permian and Early Triassic time resulted in the deposition of coarse clastic materials which could serve as reservoir beds in the Great Basin province. The Nevadan orogeny, associated with the Sierra Nevada and Mojave Desert plutonic events, and the Sevier orogeny on the east during Late Jurassic and Early Cretaceous time, resulted in removal of rock material from most of this area, particularly the Mojave Desert. Jurassic beds are clastic with good reservoir character but are limited to the easternmost part of the area. Cretaceous strata, if deposited, subsequently were removed.
These orogenies and the Laramide orogeny in latest Cretaceous and early Tertiary time involved much of the area in extensive thrust faulting and associated faulting and folding, and, during Tertiary time, Basin- Range block-faulting was superimposed on this structural complex.
Tertiary deposition was terrestrial, and volcanic activity was widespread. Sedimentary rocks of middle to late Tertiary age are confined to long narrow basins and contain much terrestrial clay, sand, and gravel; thicknesses of units are varied.
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The geology of the entire United States, including the continental shelf and slope, was studied by petroleum geologists to determine its petroleum potential. Prospective areas of the 11 regions were assessed qualitatively and, usually, quantitatively.
The prospective basinal area covers approximately 3.2 million sq mi (statute; 8.3 million sq km) and contains approximately 6 million cu mi (25 million cu km) of sedimentary rock above basement or 30,000 ft (9,144 m). Other less prospective areas are, in the aggregate, large.
The prospective area has not been explored adequately. Many high-potential areas are indicated by the geology and extent of exploration, particularly in parts of Alaska, California, Colorado, Louisiana, Mississippi, Montana, New Mexico, North Dakota, Oklahoma, Texas, Utah, and Wyoming, and in parts of the offshore of Alaska, California, Louisiana, and Texas. The prospective Atlantic, Florida, and Alaska continental shelves, and the entire continental slope, barely have been touched by drilling, and other prospective areas and depths on land and the continental shelf remain largely unexplored.
Estimates of potential crude oil reserves of the basinal area only, exclusive of known reserves, range from 227 to 436 billion bbl of original oil in place. The potential probably exceeds the mean of 332 billion bbl. Approximately 32 percent of the oil in place would be recoverable at known rates of recovery. Ultimately, the rate of recovery may reach 60 percent.
Estimates of potential natural gas reserves exclusive of known reserves range from 595 to 1,227 trillion cu ft of recoverable natural gas. The gas potential also probably exceeds the mean of 911 trillion cu ft.
The ultimate petroleum potential of the United States, including known reserves, may exceed 432 billion bbl of crude oil, 1,543 trillion cu ft of natural gas, and 49 billion bbl of natural gas liquids.
Finding and developing the large petroleum potential will require a great amount of drilling because a significant percentage of the visualized undiscovered crude oil and natural gas is in stratigraphic traps, combination stratigraphic and structural traps, reefs, and complex structural situations. Estimates of future domestic demand call for accelerated exploration. To the extent that policies of industry and government militate against accelerated exploration, particularly drilling, a high percentage of the petroleum resources of the United States will not be reduced to possession.