PARR, J. J., M. H. CLARK, and M. P. CANDELARIA, ARCO Oil and Gas Co., Midland, TX; K. A. Petty, University of Texas at Dallas, Dallas, TX; and G. J. PALKO, ARCO Oil and Gas Co., Midland, TX

ABSTRACT: Reservoir Characterization of Mississippian Sycamore Formation, Ardmore Basin, Oklahoma

The Sycamore Formation is a regionally extensive, low permeability oil reservoir in the Ardmore basin of southern Oklahoma. The Sycamore consists of two distinct members. The lower, nonreservoir member (<=80 ft thick) consists of glauconitic shale, and minor argillaceous-siliceous limestone. The upper member (<=400 ft thick) comprises the Sycamore reservoir, consisting of thin-medium bedded, peloidal silty turbidites or liquefied sediment-gravity flows. Regionally, the Sycamore thins southeastward by downlap from 480 ft to <150 ft. To the northwest, proximal flow units within the upper member rarely exceed 3 ft in thickness, and typically exhibit Bouma A-C-E or A-C sequences. Southeastward, distal flow units thin considerably, consisting of A or D-E sequences only. Primary se imentary structures indicate generally southeastward directed transport.Coincident with southeastward thinning is decreased siliciclastic content, and increased argillaceous and total carbonate content. Siliciclastic content in proximal facies reaches >60% rock volume. Porosity and permeability are best preserved in siliciclastic-rich facies and/or above subsea depths of -10,000 ft, below which porosity loss occurs due to compaction and cementation by calcite, microcrystalline silica and minor dolomite. Primary interparticle matrix porosity is commonly <6% but ranges locally to 25%. Minor secondary moidic porosity is locally developed. Matrix permeability is typically <1 md due to small pore throat size and high-tortuosity flow pathways. However, the brittle and thin bedded natu e of the upper Sycamore renders it fracture-prone. Where intensely fractured, permeability reaching several darcies significantly enhances reservoir producibility.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.