--> Abstract: The Spraberry Trend, Midland Basin, Texas: Development, Innovation, and Reserve Growth Potential in a Mature Giant, by E. H. Guevara and N. Tyler; #91004 (1991)

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The Spraberry Trend, Midland Basin, Texas: Development, Innovation, and Reserve Growth Potential in a Mature Giant

GUEVARA, EDGAR H., Bureau of Economic Geology, Austin, TX, and NOEL TYLER, University of Texas at Austin, Austin, TX

The Spraberry trend area field is a stratigraphic trap about 60 mi long (N-S) and 40 mi wide (E-W) on a west-dipping monocline in the central Midland basin, west Texas. It contained 9500 MMbls of in-place oil at discovery in 1949; recovery efficiency in these solution-gas-drive, originally underpressured reservoirs is protected to be 8%. There are more than 10,000 wells in the field, which, in the 1980s, was among the most intensely drilled areas in the nation. Wells are mostly at 1 60-ac and locally at 40-ac centers. Rapid production declines prompted local waterflooding. The Spraberry trend has been the experimental site of significant technological innovations, among them imbibition flooding, drilling using air, horizontal wells, and development of naturally fractured reservoirs.

Main reservoirs occur in the Spraberry, Dean, and upper Wolfcamp formations (Lower Permian) at depths ranging from about 6000 to 9000 ft. They are naturally fractured, very fine-grained sandstones and siltstones in beds up to 14 ft thick, forming part of mid- to outer-fan, channel-fill and associated submarine-fan facies. Permeabilities average less than 1 md, and porosities are mostly less than 10%. Geochemical data suggest indigenous oils and short migration paths. Oils are paraffinic-naphthenic, light (36-40 degrees API), and low in sulfur (0.17%).

Entrapment is a product of reservoir pinch-out into slope and base-of-slope mud facies. Internal reservoir compartments result from channel-to-interchannel facies changes causing intrareservoir stratigraphic traps. Cumulative production of wells in sand-rich, channelized areas are locally six times greater than those of wells outside these areas. Additional reserves can be obtained in infill wells targeted at partly drained compartments by strategic placement with respect to natural fractures and sandstone depoaxes.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)