Region 8, as defined by the National Petroleum Council's Committee on Future Petroleum Provinces of the United States, includes Wisconsin, Michigan, and the northern parts of Indiana and Ohio. The region includes three geologic provinces: the Wisconsin arch, the Lake Superior basin, and the Michigan basin. The Wisconsin and Lake Superior provinces have no established hydrocarbon production and offer little possibility of future production. The Michigan basin has been an oil- and gas-producing province for more than four decades and is the most likely area for future undis covered reserves.
The Michigan basin covers about 122,000 sq mi (315,980 sq km) and contains about 108,000 cu mi (450,040 cu km) of sedimentary rock. About 36,800 cu mi (153,350 cu km) of this volume is considered potentially productive. The consolidated rocks filling the basin include Cambrian, Ordovician, Silurian, Devonian, Mis- sissippian, Pennsylvanian, and remnant Jurassic sediments. The entire rock sequence, including the Jurassic, is estimated to be 14,000-15,000 ft (4,270-4,570 m) thick in the central part of the basin. Pleistocene glacial drift, ranging up to 1,000 ft (305 m) or more in thickness, blankets virtually all bedrock.
The Michigan part of the basin, specifically the Southern Peninsula, had produced nearly 552 million bbl of oil and 580 billion cu ft of gas through 1967. These hydrocarbons have come from about 600 individual pools, most of which are small. The bulk of oil and gas in past years has been produced from Missis- sippian and Devonian rocks. Silurian and Ordovician rocks also produce and in recent years have become increasingly important as drilling objectives. Cambrian rocks have not produced and their potential is not known. Large areas of the basin are still inadequately explored, especially to formations older than Devonian.
Several estimates were made of the volume of hydro carbons yet to be found in the Michigan basin. The first estimate, based on oil yield per cubic mile of sedimentary rock, is more than 1 billion bbl. The other estimates, based on actual hydrocarbon yield per square mile of proved area, range from about 673 million to more than 1.2 billion bbl. The latter figures apply only to the Southern Peninsula of Michigan and not the entire Michigan basin as defined. New pools, generally of small size, are found each year in the basin. Exploratory and development drilling always has been cyclic, and is closely related to the number and size of new discoveries. The gradual decline in exploratory drilling in recent years, the results of this drilling as reflected by the number and small size of discoveries, and the sagging annual production do not lend high confidence to the estimates of hydrocarbons yet to be discoverd.
Figures & Tables
Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2
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.