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Abstract: Carbonate Facies, Sequence Characteristics, and Reservoir Potential of Devonian Formations, Eastern Nevada and Adjoining Areas


Most of the oil produced in Nevada to date is from Devonian reservoirs. The Sevy and Simonson dolomite formations and the Guilmette Limestone represent approximately the Lower, Middle and Upper Devonian platform carbonates of Eastern Nevada and adjoining areas. Total thickness is ~1500m. Surface gamma-ray profiles are used to correlate between surface sections and to subsurface well logs. Interpretation of measured sections resulted in identification of 21 mappable stratigraphic sequences.

The Sevy contains 3 sequences, capped by an exposure surface and overlain by a 5-10m quartz sandstone (Oxyoke Member). The tops of the first and last of the four Simonson sequences contain ~60-m-deep karsted zones.

The Guilmette Limestone is generally more variable, containing ~140 shallowing-upward cycles each characterized by open shelf limestones at the base and supratidal dolomites at the top, combined into bundles representing 12 sequences. The Guilmette contains one interval of stromatoporoid buildups, up to 50m thick, and an overlying intraformational quartz sandstone ranging up to 100m. A single sequence, the Alamo Breccia, averages ~60m thick and was deposited over a minimum of 4000 sq km, created by a meteor impact.

The karsted intervals, cyclic platform limestones, buildups, quartz sandstones, and breccia all represent potential subsurface conventional and/or fractured reservoirs.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria