ABSTRACT: Delineation of a Deep-Water Channelized Fan Interval Using 3-D Horizon Slice, Offshore Texas

Gary J. Mitch, Paul L. Peterson

The High Island A-467 field is located in the Pliocene producing trend, 90 mi southeast of Galveston, Texas. Gas is produced from 10 reservoir zones ranging in depth from -6500 to -10,000 ft. Reservoir sands were deposited in upper slope submarine fan complexes.

The late Pliocene (Globoquadrina altispira) I-2 producing zone is a 200-ft-thick interval containing multiple reservoirs formed from deposition of sand in several channel systems and their associated deposits. Delineation of the I-2 reservoir system has been possible with the combination of a three-dimensional seismic volume, well log interpretation, and production or test data.

Construction of an amplitude strength (bright spot) map on the I-2 seismic event reveals trends in gas-charged areas that can be linked to reservoir geometry through depositional models and production behavior. Areas in the reservoir system containing gas-filled channels are revealed by elongate and parallel amplitude trends which, using well logs and sidewall core samples, are shown to contain fine-grained, fining-upward cycles that pinch out laterally. These channelized fills, which are 25-100 ft thick, occupy staggered stratigraphic positions, suggesting a degree of compensation during sedimentation. Areas of interchannel deposition, where gas charged, lack distinctive amplitude trends but are characterized by increases in amplitude strength over broad areas. Wells in these areas c ntain thinner and more heterogeneous gas reservoirs. Producing characteristics between the channel and interchannel facies differ in decline history, drive mechanism, and gas-oil ratios, necessitating this type of reservoir delineation for efficient exploitation of reserves.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990