The long and narrow San Joaquin Valley of California represents a Late Cretaceous to Pleistocene basin of deposition. Many sediment sources around the periphery have filled the basin with coarse clastic materials to a thickness of more than 40,000 ft (12,190 m). Numerous local and regional uplifts and structural deformations have combined with the varied deposi- tional sources to create extreme structural and strati- graphic complexity. San Joaquin is the largest onshore basin in the state and contains 94 oil fields and 16 gas fields with proved reserves of 7.8 billion bbl of oil and 11.18 trillion cu ft of gas. I estimate that these proved reserves represent only 70 percent of the potential recoverable reserves of the basin. Of the 30 percent that remains, one fourth should be found in the north half of the basin. I estimate that the remaining three fourths will be distributed in the southern half of the basin in the following manner: "East Side," 5 percent; "South End," 5 percent; "Palorna Deep," 10 percent; "West Side," 10 percent; Bakersfield arch, 25 percent; and "Central Valley," 45 percent. Severe land problems plague the last three areas. Deeper drilling and a new exploration attitude will be required to find these additional reserves in stratigraphic and hidden structural traps.
Figures & Tables
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.