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Influence of Facies Architecture on Hydrocarbon Recovery from Naturally Fractured Submarine Fan Reservoirs, Central Spraberry Trend (Permian), Midland Basin, TX

Edgar H. Guevara, Noel Tyler

The Spraberry formation of the central Spraberry trend consists of very fine-grained, terrigenous clastic intervals intercalcated in a shale-carbonate section. The lower Spraberry comprises a basal upward-coarsening sequence, consisting of two upward-coarsening sandy units, overlain by an upward-fining unit. The middle Spraberry is composed predominantly of shale and carbonate; it includes six thin, mostly upward-fining sandy units. The upper Spraberry comprises six generally upward-coarsening sandy units representing two upward-coarsening sequences.

The sandy unit, vertically segregated by intervening shales and carbonates, shows moderate lateral variations in thickness and sand content; gamma-ray facies maps of individual beds show pronounced lateral variation. These terrigenous clastics represent distal midfan to fringe deposits of a submarine fan, and associated basin-plain facies.

The Spraberry in the central Spraberry trend is a multipay play. The most productive reservoirs are thicker and coarser grained beds capping the upward-coarsening, progradational fan sequences of the upper and lower Spraberry. These naturally fractured, solution gas drive reservoirs have undergone local imbibition waterflooding since 1961. Besides the elusive fracture permeability in these tight reservoirs, the less than 10% recovery is attributed to reservoir heterogeneity. When reservoirs are isolated, hydrocarbon zones are not thoroughly drained by well completions or are affected by fracture treatments or waterflooding. To improve recovery from Spraberry trend fan sequences, strategies must incorporate selective completions for injection and production that consider the facies-con rolled reservoir heterogeneities.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.