Geological Characterization of Permian Submarine Fan Reservoirs of the Driver Waterflood Unit, Spraberry Trend, Midland Basin, Texas

More than 350 well logs and core and production data were used to geologically characterize oil reservoirs of the Driver waterflood unit of the Spraberry Trend in the Midland Basin, West Texas, and to assess the relationship between reservoir stratigraphy and oil recovery. Results of this research indicate that to improve oil recovery from the Driver unit, and from the Spraberry Trend in general, selection of completion intervals and strategic infill drilling locations should be determined by both reservoir stratigraphy and natural fractures.Fifteen log-defined genetic-stratigraphic operational units composed mainly of sandstone and siltstone were delineated in the approximately 1,000-ft- (305-m-) thick, predominantly shale and carbonate Spraberry Formation of Permian (Leonardian) age. Sandstone and siltstone of this lithostratigraphic unit accumulated in submarine fans, forming upward-thickening sequences in the lower (Jo Mill submarine fan system) and upper (Driver and Floyd submarine fan systems) Spraberry. Areas of Spraberry submarine fans having greater net thickness of sandstone and siltstone form NNW- to NNE-trending belts. These sand-rich areas contain the main oil reservoirs of the Driver unit; they consist of low-permeability (less than 1 md), low-porosity (less than 8 percent to approximately 14 percent) sandstones and siltstones capping submarine fans of the lower and upper Spraberry.Historically, selection of well locations and completion intervals in the Driver unit has been based on the assumption that oil production is largely controlled by natural fractures in homogeneous, laterally extensive, sheet-like reservoirs. However, production data show trends that are generally correlative with axes of maximum sandstone and siltstone in operational units, suggesting that reservoir stratigraphy strongly influences oil production. Complex facies architecture of Spraberry reservoirs produces vertical and horizontal reservoir heterogeneity. Stacking of submarine fans results in multilayered, or stratified, oil accumulations in which reservoir rocks are separated vertically by shales and carbonate mudstones. Oil accumulations are also laterally compartmentalized because the main reservoirs occur in sand-rich belts generally parallel to the basin axis.The current low recovery efficiency of approximately 10 percent is attributed to reservoir heterogeneity that results in incompletely drained hydrocarbon zones. In performing well recompletions and strategic infill drilling, operators must consider stratigraphic heterogeneity in order to produce oil from untapped or only partly drained reservoir compartments. New well logs and core are necessary for identification and characterization of oil-saturated zones and natural fractures. These reservoir management strategies are also applicable to similar oil reservoirs, such as the Dean Sandstone of the Midland Basin.
Edgar H. Guevara

Guevara, E. H., 1988, Geological Characterization of Permian Submarine Fan Reservoirs of the Driver Waterflood Unit, Spraberry Trend, Midland Basin, Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 172, 44 p.

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The University of Texas at Austin, Bureau of Economic Geology
Report of Investigation