Hydrocarbon Potential of Northern and Central California Offshore
Ernest G. Hoskins, John R. Griffiths, 1971. "Hydrocarbon Potential of Northern and Central California Offshore", Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2, Ira H. Cram
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The continental shelf appears to have a granite basement from Point Conception to about Point Arena and a metasedimentary type of basement from Point Arena to the Oregon border. Remnants of thick marine Cretaceous and Eocene sections are present throughout the length of the shelf, but because of their erosional history, the poor potential for reservoirs, and the difficulties in mapping, they appear to merit little further exploration. Deep-marine beds deposited throughout the length of the shelf from early Miocene through early late Pliocene time appear to have by far the best potential for hydrocarbon reserves. This section generally includes thick sequences of shale and ample reservoir-quality sandstone. Hydrocarbon shows are common. The overlying Pleistocene beds are not considered as objectives.
The six basins present on the shelf, each of which has an onshore extension, began forming in late middle Miocene time. Generally they do not contain as thick a post-Eocene section as that in the producing onshore California basins.
The southern third of the offshore Santa Maria basin is similar to the onshore part and is considered to have about the same hydrocarbon potential; the northern two thirds is only slightly explored. The Outer Santa Cruz basin lacks large, mappable structural traps and extensive reservoir-quality sandstone beds; however, oil shows are common. The offshore half of the small Santa Cruz basin is considered to have about the same hydrocarbon potential as the onshore half, where production is minor. The Bodega and Point Arena basins contain most of the geologic constituents of major producing basins, but they also have 16 structurally well-located dry holes. Eel River basin, the largest and least explored of the shelf basins, has good structural- trap potential, and limited data suggest the presence of an objective Miocene-Pliocene section, but beneath deep water.
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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.