Future Petroleum Potential of Western and Central Pennsylvania
William S. Lytle, Louis Heyman, Dana R. Kelley, Walter R. Wagner, 1971. "Future Petroleum Potential of Western and Central Pennsylvania", Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2, Ira H. Cram
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The exceptionally low density of deep penetration shows that the Appalachian basin in Pennsylvania remains largely unexplored and geologically unknown. It still can be considered one of the major domestic areas with significant potential for new petroleum reserves. The thickness of the Paleozoic section ranges from less than 5,000 ft (1,520 m) in northwestern Pennsylvania to possibly 30,000 ft (9,140 m) northeast of Harrisburg. The sedimentary section averages 12,000 ft (3,660 m) in thickness in the Appalachian Plateau province and 25,000 ft (7,620 m) in the Valley and Ridge province. The upper part of the section is mostly clastic rocks, but the lower part is carbonate with some clastic rocks. Only half of the stratigraphic section has been evaluated in 40 percent of the 26,000-sq mi (67,340 sq km) Appalachian Plateau area in Pennsylvania. In the other 60 percent of the area, more than 10,000 ft (3,050 m) of favorable section associated with a wide variety of structures remains to be adequately appraised by drilling.
During the past 100 years, interest has been focused essentially on the sandstone reservoirs—i.e., the multiple, shallow Upper Devonian producing units and the Oris- kany and Medina. Where these rocks are present in areas of exploration for deeper reservoirs, they are an added incentive. Where productive, they may be the deciding factor in making an exploratory venture profitable. However, most unevaluated potential Paleozoic strata in the Appalachians consist of a great variety of carbonate rocks that have an equal variety of potential reservoir zones, nearly all of which have contained shows of gas locally. Barrier- and patch-reef zones and porous oolitic, algal, fossiliferous, dolomitized, and calcarenitic zones can be identified; some are apparently of large areal distribution and others are discontinuous. These zones are the prime targets for future exploration.
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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.