Anthony D. Shinn, 1971. "Possible Future Petroleum Potential of Upper Miocene and Pliocene, Western Gulf Basin", Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2, Ira H. Cram
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Synergetic depositional and . deformational phenomena have resulted in large concentrations of oil and gas in the upper Miocene and Pliocene sections of the Gulf Coast geosyncline. Most of these accumulations have been found trapped in the sandstone and sand- stone-shale magnafacies. The gulfward limit of future exploitation can be determined reasonably from present data, and should extend to water depths of 600 ft (180 m). Any significant future discoveries are most likely to be in the offshore. Development of these facies in Louisiana is approaching maturity, but there should be limited extensions gulfward and eastward of present production. Offshore Texas is largely unexplored, but results of drilling have been disappointing.
Exploration for turbidites in the shale magnafacies gulfward of present trends is a challenge both to explorationists and to management. Turbidites will be difficult to locate and drilling will be expensive. They must be thick and prolific reservoirs in order to be commercial—but it is possible that such thick sequences are present.
A possible future source exists in the shale magnafacies where turbidite sandstone reasonably can be expected on the updip flanks of salt structures and in the lows between them. The search for reservoirs of this type, particularly in the younger sections, will involve operations beyond the continental shelf in water depths that increase abruptly from 600-ft (180 m) depth. Exploration in the older beds will require increasingly deeper drilling. Exploration for turbidites requires complex seismic techniques and the best efforts of geologists, paleontologists, and geophysicists. No realistic estimate of favorable sedimentary-rock volume in the shale magnafacies is possible at this time.
Present economics barely have justified the oil industry's exploration of the sandstone and sandstone-shale magnafacies in water less than 600 ft deep. Thus, more costly exploration in the deeper waters beyond the continental shelf will depend on increased incentives. Otherwise, economic considerations may jeopardize all future exploration in the Gulf of Mexico.
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.