This report is an evaluation of the petroleum potential of the Cenozoic sedimentary rocks of the Imperial Valley. The Imperial Valley is within a broad zone of faulting that may be termed the "San Andreas rift." Diastrophism has produced structures comparable to those which form the traps for petroleum in the oil fields of California adjacent to the San Andreas rift.
About 7,000 cu mi (29,170 cu km) of siliceous clastic sedimentary rocks has been deposited in the California part of this complex basin. About 22 percent is of marine origin, in an area of 3,200 sq mi (8,290 sq km). Included are 455 cu mi (190 cu km) of coarse-grained clastic rocks that contain 125 cu mi (520 cu km) of sandstone suitable for petroleum reservoirs, and 1,060 cu mi (4,420 cu km) of fine-grained clastic rocks that might be source rocks for petroleum. The oxidizing freshwater environment of the nonmarine sediments and the shallow-water and apparently sterile environment of the marine sediments explain the absence of evidence of petroleum in the exposed sedimentary strata and the exploratory wells. Except for an unusual and unique source of petroleum (detrital oil shale transported from the eroded oil shale deposits of Colorado, Utah, and Wyoming, and distilled by the Salton Sea geothermal feild), the possibility of discovering significant petroleum reserves in the Imperial Valley area appears to be very slight.
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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.