Reservoir Architecture--A Critical Element in Extended Conventional Recovery of Mobile Oil in Heterogeneous Reservoirs

Noel Tyler, Robert J. Finley

The greatest challenge facing development geologists is our limited understanding of the internal reservoir framework and its control on hydrocarbon recovery. All reservoirs are heterogeneous, and even in only moderately heterogeneous reservoirs as much as half the mobile oil is commonly not recovered. Such geologic complexities are magnified in low-permeability reservoirs and reservoirs with weak drive mechanisms where conventional primary and secondary yields may be only 15% of the in-place mobile oil.

Sedimentological research during the last 20 years has defined models that support exploration and therefore focus on external geometry of reservoirs. These models understate the importance of the internal reservoir framework and are inadequate to explain internal reservoir seals and resultant compartmentalization as it controls hydrocarbon recovery. Development of models describing internal reservoir architecture, that is, facies composition, extents, three-dimensional geometries, orientations, and relations with surrounding facies, is critical for guiding well placement and completion interval to maximize hydrocarbon recovery from heterogeneous reservoirs.

Reservoir architecture, a product of sedimentation style, governs mobile oil recovery efficiency. Wave-reworked depositional systems with simple architectures have high mobile oil recovery efficiencies. In contrast, strongly channelized systems with complex architectures, including fluvial, fluvial-dominated deltaic, and submarine fan reservoirs, have low to moderate mobile oil recovery. Carbonate reservoirs display a smaller range of mobile oil recovery efficiencies; however, large volumes of unrecovered mobile oil remain in highly stratified, laterally discontinuous platform carbonates in the Permian basin. In Texas reservoirs with complex architectures, 35 billion bbl of mobile oil will remain unrecovered at abandonment; nationally, this important and moderate-cost resource may be 0 to 100 billion bbl.

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