ABSTRACT: Complex Reservoir Geometries in the High Island A-467 Field, Offshore Texas
Gary J. Mitch, Paul L. Peterson
The High Island A-467 field, located 90 mi southeast of Galveston, Texas, has produced 160 bcfg of gas from 10 reservoir levels with remaining gas reserves estimated at 40 bcfg. The field formed upthrown to a major expansion fault that marks the southern boundary of a basin active in the late Pliocene through Pleistocene(?). During this interval, approximately 9000 ft of slope sediments were deposited downdip from a shelf margin located 20 mi north. Gas reservoirs formed in submarine fans deposited during lowstand wedge construction.
Production has exceeded annual EUR estimates based on original reservoir configurations mapped with well data and a two-dimensional seismic grid. Reinterpretation using a three-dimensional volume was undertaken to define accurately the productive limits and to assess remaining reserves. This was done by integration of stratigraphic cross sections, companion three-dimensional seismic traverses, and horizon amplitude (bright spot) maps. Reservoir limits were delineated using areal variation in bright spot maps, combined with geologic models for submarine fan deposition and data from 5 years of production. Previous single-reservoir horizon maps now contain complexities such as multiple reservoir levels, isolated channels, abrupt facies changes, and submarine erosion surfaces that may sea or leak. Following reinterpretation, several development and extension drilling opportunities were identified and drilled successfully.
Complex deep-water reservoir geometries can be interpreted with accuracy only where well and seismic data are abundant and closely integrated. Field studies such as this contribute to improved resource assessment and management, and they provide practical examples of reservoir configurations fur use in exploration prospect analysis.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990