38 AAPG: Petroleum Geology of Northern Alaska (Posters)

COMPILATION OF SUBSURFACE INDICATIONS OF OIL AND GAS, NORTH SLOPE, ALASKA

Paper number: 38-6
Program: THEME SESSIONS
Time: 8:00 AM – 11:30 AM

Authors

Abstract

Over 14,000 records on oil and gas shows have been compiled from public data on more than 200 wells across the North Slope of Alaska. These data were derived from an area extending from the Belcher 1 (OCS 0917)well in the east to the Eagle Creek 1 well in the west, a distance of more than 500 miles, and from the Cabot (OCS 0742)well in the north to the Lisburne 1 well in the south, a distance of about 200 miles. For most wells, data were extracted directly from lithologic and mud logs, formation tests, and other reports; data from the older wells (1944-1953) in the National Petroleum Reserve in Alaska (NPRA) are more limited. We distinguished among the following wide range of oil show types, listed in order of decreasing strength: 1) mobile oil - from drill stem tests or 'bleeding' core, 2) staining, 3) fluorescence or visual cut, and 4) dead oil. For gas, the categories include 1) mobile gas, 2) gas show, 3) C2 concentrations >2,000 ppm, and 4) C1 >20,000 ppm. For each well, plots display the down-hole distribution of these show-types; regional trends are shown on a series of 5 north-south and 5 west-east cross sections. In addition, maps for each formation display the strongest show-type recorded at each well in order to illustrate the lateral distribution of hydrocarbon shows by formation.

Within the Ellesmerian sequence, strong oil and gas shows (i.e. show types 1 and 2 vs. 3 and 4) are found only along the Barrow arch and the strength of the shows deceases rapidly southward. Beaufortian rocks show a similar trend with the strongest shows limited to the Point Barrow area. Shows in the Brookian section exhibit significantly different patterns. The strongest oil shows are largely in the central portion of the North Slope, decreasing to the west. However, strong shows are also present near Point Simpson and Point Barrow. Gas shows within the Brookian are abundant in the central and southern portions of NPRA with moderate shows found in the north.