--> ABSTRACT: Lithologic and Geologic Characteristics of Silurian-Devonian and Woodford Formations, Northern Midland Basin, Texas, by Louis J. Mazzullo and S. J. Mazzullo; #91026 (2010)

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Lithologic and Geologic Characteristics of Silurian-Devonian and Woodford Formations, Northern Midland Basin, Texas

Louis J. Mazzullo, S. J. Mazzullo

The Silurian-Devonian section in the subsurface of the northern Midland basin consists of limestones, dolomitic limestones, and dolomites, with local interbeds of dark and red shales as well as terra rosa (weathered layers). These rocks were deposited in a spectrum of environments from high-energy grainstone shoals to low-energy lime mud facies. Dolomites probably represent early postdepositional replacement of limestones, perhaps in mixing zones bordering subaerially exposed lowlands. A readily mappable correlation does not appear to exist between dolomite occurrence and localization along the main Fusselman formation and Upper Silurian-Devonian pinch-outs in the study area. The overlying Woodford formation consists of a basal sandstone member deposited in transitional m rine environments; these sands are overlain by the euxinic shales typical of the Woodford formation.

Production from the Silurian-Devonian section is from porous and fractured limestones as well as dolomites. Production occurs at the tops of the Fussleman and Devonian sections along their respective pinch-outs, as well as within the carbonate section overlying the Fusselman. Lithofacies distributions are important facets of reservoir occurrence in these sections, the prolific reservoir facies being the grainstones and dolomites. The random distribution of these facies accounts for the widespread production in the area. Reservoirs typically are developed on structural closures with magnitudes ranging from 50 ft to several hundred feet, although several fields are "spoon-type" traps along erosional pinch-outs.

AAPG Search and Discovery Article #91026©1989 AAPG Southwest Section, March 19-21, 1989, San Angelo, Texas./