Petroleum Potential of Western Oregon and Washington and Adjacent Continental Margin
Dana B. Braislin, Douglas D. Hastings, Parke D. Snavely, JR., 1971. "Petroleum Potential of Western Oregon and Washington and Adjacent Continental Margin", Future Petroleum Provinces of the United States—Their Geology and Potential, Volumes 1 & 2, Ira H. Cram
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Western Oregon and Washington and the adjacent continental margin occupy the site of a Tertiary geosyncline. The oldest rocks in most of the geosyn- cline are early Eocene volcanic rocks, which are considered as "economic basement" with respect to oil production. Marine sandstone and siltstone of Eocene to Pliocene age reach a maximum thickness of 25,000 ft (7,620 m) and in places contain interbedded volcanic and nonmarine sedimentary rocks. A total of approximately 100,000 cu mi (416,700 cu km) of Tertiary marine and nonmarine sedimentary rocks is present with in the trough, of which 70,000 cu mi (291,700 cu km) is considered to have potential as petroleum source rock.
Interest in the oil and gas possibilities of this region is reflected in the drilling of about 560 wells since the turn of the century. Only within the last 10 years has exploration been directed toward the continental margin, where 14 wells now have been drilled. Although commercial production has not been obtained, a favorable geologic environment, including source rocks, reservoir rocks, and structure, is an incentive to future petroleum 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.