Oil Fields of Cook Inlet, Alaska: ABSTRACT

Abstract

Significant increases in petroleum production continue in the Cook Inlet basin of Alaska, moving the state closer to being the fifth leading oil producer in End_Page 563------------------------------ the United States by 1971. Five fields account for a total present output of more than 145,000 b/d. Swanson River, Middle Ground Shoal, Granite Point, McArthur River, Foreland, Dolly Varden, and Trading Bay collectively have estimated producible reserves in excess of 750 million bbl. One of 15 geologic basins in the state, the Cook Inlet basin has an area of 9,500 sq mi lying approximately 45 percent offshore, 15 percent in tidal areas, and 40 percent onshore. The basin's Cenozoic stratigraphy generally is represented by a maximum thickness of 25,000± ft of nonmarine Tertiary rocks. Mesozoic limestone, marine clastic sedimentary rocks, and volcanic rocks unconformably underlie the Tertiary. Major structure and fault systems trend north-northeast. Tectonism occurred throughout the Mesozoic and Cenozoic and continues into the Recent as in other areas of the circum-Pacific tectonic belt. Faulting and folding are most prominent in the northwestern part of the basin close to the Alaska Range--a range which includes dioritic and granitic mountains with numerous active volcanoes. Oil has been found in the classic anticlines. Production is from sandstone and conglomerate beds of the Kenai Group including the middle Kenai and Hemlock Formations. Faulting and stratigraphic variations in part control accumulation and fluid properties. All reservoirs contain undersaturated oil close to bubble-point pressure requiring early secondary recovery efforts. Oil gravities range from 25° to 56°API. Average daily production per well is about 1,400 bbl. End_of_Article - Last_Page 564------------