Reserves of ultimately recoverable oil and gas in the Mid-Continent (17.3 billion bbl and 130.0 trillion cu ft, respectively) are nearing depletion. Production through 1967 of 14.9 billion bbl of oil and 81.4 trillion cu ft of gas dictates this conclusion. A detailed review of Mid-Continent geology indicates that future potential oil and gas reserves of 1.7 billion bbl and 44.5 trillion cu ft, respectively, remain to be found. These figures represent the total of "probable," "possible," and "speculative" potential reserves as defined by the Potential Gas Committee.
The Texas Panhandle and Oklahoma should furnish 54 percent (932.0 million bbl) of the estimated new potential oil reserves; Kansas, 32 percent (561.3 million bbl); Nebraska, 12 percent (201.8 million bbl); and Missouri and Iowa, 2 percent (26.6 million bbl). The Pennsylvanian System is believed to contain the most important potential reservoirs—32.7 percent (563.0 million bbl) of the estimated new oil reserves—followed by the Middle and Upper Ordovician, 20.4 percent (352.3 million bbl); the Lower Devonian-Silurian, 16.7 percent (286.9 million bbl); the Mississippian, 13.8 percent (237.0 million bbl); the Cambrian-Lower Ordovician, 12.2 percent (210.0 million bbl); the Permian, 2.3 percent (39.0 million bbl); the Middle and Upper Devonian, 1.9 percent (32.5 million bbl); and the Cretaceous, about 0.5 percent (1.0 million bbl).
Old established producing areas should continue to furnish new potential reserves as a result of infill drilling and stepouts, but at a decreasing rate. Potential reserves attributed to reservoirs in southeast Kansas and northeast Oklahoma (Pennsylvanian, Mississippian, Middle Devonian, Silurian, Middle Ordovician, and Cambrian-Lower Ordovician) and southern Oklahoma (Cretaceous, Permian, Pennsylvanian, Mississippian, Lower Devonian-Silurian, Middle Ordovician, and Cambrian- Lower Ordovician) are optimistic estimates based on anticipated exploration activities.
The Cambridge arch in Nebraska, the northern shelf of the Anadarko basin, and the Hugoton embayment should furnish significant new potential reserves from Pennsylvanian rocks. The pre-Pennsylvanian section should become the most important future reservoir as exploration for structural traps continues in the deeper parts of the Anadarko and Ardmore basins, the Hugoton embayment, and the Salina and Forest City basins.
The Texas Panhandle and Oklahoma should furnish 75.3 percent (33,543 billion cu ft) of the estimated new potential gas reserves; northern Arkansas, 19.3 percent (8,600 billion cu ft); and Kansas, 5.4 percent (2,400 billion cu ft). The Lower Devonian-Silurian section is the most important future reservoir, containing 38.0 percent (16,900 billion cu ft) of the estimated new potential gas reserves. It is followed by the Pennsylvanian, 24.5 percent (10,900 billion cu ft); the Mississippian, 17.7 percent (7,900 billion cu ft); the Cambrian-Lower Ordovician, 10.8 percent (4,810 billion cu ft); the Middle Ordovician, 6.0 percent (2,685 billion cu ft); and the Permian, 3.0 percent (1,348 billion cu ft).
The deeper parts of both the Anadarko and Arkoma basins should furnish significant new reserves from Pennsylvanian and pre-Pennsylvanian strata. The Hugo- ton embayment should furnish new reserves from Permian, Pennsylvanian, and Mississippian rocks. Structural traps will be of primary importance, initially, in the deep Anadarko basin. Stratigraphic traps will be important in the Arkoma basin and the Hugoton embayment.
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.