Prudhoe Bay Western Peripheral Development Using Three-Dimensional Seismic: Case Study

Chuck G. Guderjahn

The western periphery of the Prudhoe Bay field, known as the West End or Eileen area, is characterized by a relatively gentle southwestern regional dip cut by numerous normal faults with up to 500 ft of throw. These faults displace the Permian-Triassic reservoir sandstones against Jurassic shales. A detailed structural map was interpreted from three-dimensional seismic data acquired in 1984 and 1985.

Three distinct and coherent trends of faulting are evident from the data: north-south, northwest-southeast, and east-west. These faults were aliased by the earlier two-dimensional data grid and could not be connected in a coherent manner consistent with suppositions of the stress directions. The added detail to the structural maps will allow development of narrow, oil-filled horst blocks and should prevent drilling of dry holes in narrow grabens as has occurred prior to the three-dimensional data acquisition. Seventy-two 80-ac wells and up to four horizontal gas injectors are planned for the area, with drilling commencing from new surface facilities in 1988.

Upon the successful completion of a horizontal and an 88° high-angle well from existing facilities, the utility and shortcomings of the data interpretations were illuminated. The high-angle well encountered only 40% of the prognosed oil column, which is believed to be a consequence of an unpredicted permafrost thickening. Thus, as with two-dimensional data, the uncertainty in the estimate of the velocity field is the dominant factor in estimating subsurface structure.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.