Possible Future Petroleum Potential of Lower Miocene-Oligocene, Western Gulf Basin
H. L. Tipsword, W. A. Fowler, JR., B. J. Sorrell, 1971. "Possible Future Petroleum Potential of Lower Miocene-Oligocene, Western Gulf Basin", Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2, Ira H. Cram
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Sedimentary rocks downdip from present lower Miocene production in Louisiana and Texas, and in the Texas offshore area on strike with this producing trend, offer the best potential for major future petroleum reserves in lower Miocene-Oligocene beds of the western Gulf basin. These prospective beds are present in an area about half the size of the present lower Miocene trend; the area is divided into two roughly equal parts— a probable producing area where an environment favoring hydrocarbons is known to have existed, and a possible producing area where such an environment reasonably can be inferred.
Future lower Miocene-Oligocene discoveries should be found under conditions similar to those controlling present production—-where reservoirs are typically sandstone and traps are usually associated with salt domes, fault closures, anticlines, residual highs, and, in some places, stratigraphic changes. Depositional environment is critical, the ideal habitat for petroleum being a thick section of deltaic or shallow-neritic sandstone inter- bedded with marine shale. Depositional environment limits the extent of production downdip, because deep- water shale succeeds sandstone.
Miocene-Oligocene strata of Mississippi, Alabama, and Florida are thin, nonpetroliferous carbonate rocks. They give little promise for future discoveries, although thicker, deeper reef-carbonate rocks may be present east of the Mississippi delta.
Additional reserves will be found from the Rio Grande to southeastern Louisiana within present producing trends, where the most productive areas in successively younger intervals commonly are found progressively downdip and northeast along strike. Production from the middle Oligocene Frio and the lower Miocene beds is especially prolific.
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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.