The offshore area of southern California from south of the Channel Islands to the Mexico boundary and from the shoreline to the continental margin, but excluding the present offshore oil fields that have been extended from onshore fields, is estimated to contain 75 billion bbl of oil in place. This oil is contained in 17,780 cu mi (74,090 cu km) of rock above the basement, primarily in 5,323 cu mi (22,180 cu km) of basinal sedimentary rocks of Pliocene and late Miocene age.
This area is in the Peninsular Ranges province, which also includes the prolifically oil-productive Los Angeles basin. The offshore area is similar in structural grain, stratigraphic sequence, and geologic history to the Los Angeles basin; therefore, the well-known geologic conditions and oil-content values of that basin are used as norms in evaluating the offshore area by application of appropriate discounting factors to each offshore basin. Eleven of the factors responsible for the oil accumulations onshore are rated, depending on less favorability or less certainty of effectiveness, for each offshore area, and the reduced ratings are applied to the volume of rock as compared to the Los Angeles basin volume of similar rock.
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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.