The Ozark and Lincoln fold areas of Missouri (Fig. 43) include 74 counties comprising approximately 45,400 sq mi (117,590 sq km). The part south of the Missouri River, consisting of 52 counties (33,100 sq mi or 85,730 sq km), covers the Ozark area and is largely unprospective as a hydrocarbon province. Possibilities are limited to the counties adjacent to the Mississippi River where oil might be found in Cambrian rocks, but the potential of these rocks is impossible to evaluate at this time. The 22 counties (12,300 sq mi or 31,860 sq km) north of the Missouri River, including the Lincoln fold area, have a cover of post— Lower Ordovician rocks which makes them more attractive for oil prospecting. However, the absence of the Maquoketa Shale and of the Silurian reefs—present in Illinois on the east and south—limits possibilities for oil accumulation in northeastern Missouri. St. Charles County north of the river and St. Louis County south of the river have similar potentials and constitute a third possible area of interest. At present, the only production is from the Florissant field in St. Louis County; it produces from the Kimmswick Limestone of late Middle Ordovician age. Total production to January 1, 1968, was approximately 700,000 bbl of 35° gravity oil. Future production of petroleum probably will not amount to more than 2-3 million bbl (from the Florissant field and the development of other small fields in the post—St. Peter rocks).
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.