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Sedimentologic Controls on Production in Giant Eolian Reservoirs in Western U.S. Overthrust

Patricia A. Henderson, Lee F. Krystinik

The Jurassic Nugget Sandstone is a 1,500-ft (457-m) thick eolian reservoir that produces prolifically throughout the Wyoming Overthrust belt. Nugget fields exhibit exceptional, but predictable reservoir anisotropy. Based on detailed core, log, and production analyses, this study documents Nugget reservoir behavior as a strongly layered system with preferred directional permeability.

Anschutz Ranch East and Painter Reservoir fields contain numerous fieldwide vertical permeability barriers that are interpreted as amalgamated inland sabkhas (interdunes) associated with significant diastems. The inland sabkhas contain internal erosion surfaces and abundant eolian ripples, and they are commonly disturbed by burrowing or salt growth. Carbonate and silicate cements render the inland sabkha deposits tight, creating vertical permeability barriers (Kv <= 0.001 md).

Strongly preferred directional permeability parallels dune strike. Dune orientations determined from dipmeter logs and oriented cores relate directly to production rates and premature breakthrough of injected fluids. Preferred permeability along the predominant dune axis can be 5-50 times greater than permeability across dune cross-bedding.

Detailed well data documenting dune orientation and diastems should be used early in field development to determine appropriate spacing and the well pattern. By incorporating these concepts into a reservoir management plan, eolian reservoirs can be more efficiently exploited.

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