Geology and Discovery of Prudhoe Bay Field, Eastern Arctic Slope, Alaska: ABSTRACT

Abstract

The Prudhoe Bay field is one of the largest oil fields in North America with estimated reserves of 5-10 billion bbl. Reconstruction of the geologic history suggests that the combination of geologic controls on the field probably will not be found elsewhere. Hydrocarbons are present in Jurassic and Permo-Triassic sandstone and Pennsylvanian-Mississippian carbonate reservoirs. These strata, locally folded into a west-plunging, faulted anticlinal nose, are truncated by a pre-Cretaceous unconformity resulting in the subcrop of progressively older reservoirs on the northeast. Most of the hydrocarbons are trapped below the unconformity in the Permo-Triassic Sadlerochit Formation. This reservoir is present in the field area as a uniform wedge of alluvial-deltaic sandstone and conglomerate. The pre-Cretaceous clastic reservoirs were derived from the ancient Beaufort arch, north of the present coastline. In contrast, the unconformably overlying Cretaceous and Tertiary sandstone and marine shale were derived from uplifts on the steep south flank of the basin, near the present Brooks Range. In 1944, the U.S. Navy initiated the first extensive Arctic exploration program. This program was carried on for 10 years at a cost of over $55 million. Drilling was conducted principally in 2 areas, the Barrow high and the Arctic Foothills belt. The Umiat field, on a foothills anticline, was the largest oil discovery with estimated reserves of 20-100 million bbl in Cretaceous sandstones. The high finding costs experienced by the Navy tended to discourage industry exploration. In 1963, several wells were drilled jointly by BP Exploration Company (Alaska) Inc. and Sinclair Oil and Gas Company, in an attempt to extend the foothills Cretaceous play. BP-Sinclair and Union Oil Company of California each later drilled unsuccessful Paleozoic tests near the Arctic coast. In 1964 Humble Oil and Refining Company joined Richfield Oil Corporation (now Atlantic Richfield) in evaluation of federal acreage south of Prudhoe Bay. Regional seismic data and federal leasing policy in existence at that time caused Humble to shift the exploration effort from the federal acreage to the eastern ARctic coastal area. The major part of the Prudhoe Bay structure was leased jointly by Humble and Richfield, and by BP at the State of Alaska sale in July 1965. The ARCO-Humble Prudhoe Bay No. 1 State was completed as the discovery well in June 1968. End_of_Article - Last_Page 1969------------