Nonconventional Drilling in Prudhoe Bay Field

Douglas B. Dickey

Nonconventional wells are an important part of the development plan for the Prudhoe Bay field. Each of four types, (1) high angle, (2) horizontal, (3) inverted high angle, and (4) drain hole, have specific applications in the field. Geologic criteria for well selection include vertical permeability heterogeneities, faulting, structural dip, and reservoir geometry. Initial production rates are up to five times that of a conventional well.

The original justification for the wells included increased productivity, reduced gas and water coning, additional oil recovery, access to thin or geometrically isolated reservoir intervals, and increased drainage areas. These benefits are tempered with the increased drilling and completion costs, limited workover potential, and surveillance complexity.

At Prudhoe Bay, nonconventional wells have been drilled in peripheral areas, the gravity drainage area, for gas injection in the West End development area and are planned for minor reservoir development. Five horizontal wells, eight high angle wells, two inverted high angle wells, and two drain holes have been drilled to date. The recently developed inverted high angle wells can be used to optimize well placement as the well is drilled. The production performance of these wells is impressive, with the benefits of accelerated production and additional recovery in the peripheral areas.

The economics of the nonconventional wells are dependent on the future cost of workovers, the actual additional recovery, the long-term performance, and the future price of oil. In the near term, the wells have proven to be highly productive or to have very high injectivities, and are valuable as a means to reach peripheral accumulations that would otherwise not be developed.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.