Stratigraphic Controls on Fluid Distribution: An Example from Prudhoe Bay, Alaska

Beverly A. Burns, Douglas Knock, and Robert S. Tye

Oil, gas, and water distribution in three drill sites (179 wells) studied in the Prudhoe Bay Field is controlled dominantly by sandstone and shale stratigraphy. Detailed reservoir description, encompassing genetic-stratigraphic correlations and three-dimensional reservoir modeling has provided a new look at the locations of remaining reserves in the upper Romeo and Tango intervals of the lvishak Sandstone.

Greater than 22 billion stock tank barrels constitute in-place oil reserves in Prudhoe Bay Field. Production in excess of nine billion barrels, in conjunction with waterflood and tertiary-recovery projects, has created a complex distribution of reservoir fluids. As oil is produced, the gas-cap expands and intersects laterally extensive shales to form gas underruns. Underruns are of great economic concern as they disrupt the NLOC and segregate oil lenses as well as causing high GOR wells. Recovering these oil lenses at low GORs requires precise analysis of in-place fluids, well placement, and completion strategy.

Core descriptions and stratigraphic correlations provided the basis for facies interpretations and the deterministic division of the strata into twenty-four reservoir layers (twelve sandstone and shale units). Isochore, fluid-distribution, and NLOC maps were compiled for the reservoir horizons. Stratigraphic, structural, and fluid data integrated within a three-dimensional model resulted in an improved fluid-distribution picture and revealed numerous development opportunities including infill wells, sidetracks, and recompletions.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California