Middle Ground Shoal Oil Field, Alaska1
Middle Ground Shoal oil field, in upper Cook Inlet, Alaska, is located beneath water with an average depth of 100 ft (30 m). The Shell MGS State No. 1, drilled in 1963, was the first offshore oil completion in Alaska. The field produces oil from a gross interval of about 2,800 ft (850 m) in the Tertiary lower Tyonek Formation. The productive interval has been separated into seven pools; the A pool is produced separately, but production from the B, C, and D and the E, F, and G pools, respectively, is commingled. Three production platforms are in use, and the field contains 31 producing wells, 23 injection wells, 1 shut-in gas well, and 8 abandoned or suspended wells. As of January 1, 1974, the field had produced 78,662,670 bbl of oil, 37,270,730 Mcf of gas, and 9,162,874 bbl of water. Because of declining reservoir pressures, pressure maintenance by water injection was started in 1969.
The structure at Middle Ground Shoal is a narrow anticlinal feature which strikes N10°E. Little or no paleostructural growth is thought to have occurred during deposition of the oil-bearing sandstone sequence. Channel fills and braided-stream deposits provide the reservoirs. The main productive interval in the field is the G pool, which is in the Hemlock Sandstone Member of the Tyonek.
Figures & Tables
With three previous volumes published by AAPG on structure of American oil fields, this publication takes 17 of these oil fields and describes them in detail. The reservoirs described in these 17 papers range in age from Devonian to Pleistocene; their litholgies are standstone, limestone, or dolomite; and the trapping mechanisms are structural or stratigraphic or a combination of the two. The North American oil fields described are distributed from Alaska and the McKenzie Delta area of Canada on the northwest, to the Gulf of Mexico and Southern Floriday on the southeast. This publication also includes an index to those North American oil and gas fields which have been described in previous AAPG publications.