ABSTRACT: Essential Elements of Significant Stratigraphic Exploration Plays in Ordovician to Lower Permian Carbonates in the Midland Basin

MAZZULLO, S. J.

Review of reservoir models suggest potential for a variety of stratigraphic plays in Ordovician to Lower Permian rocks in the Midland Basin (MB). Exploration in the Ellenburger, e.g., has traditionally focused on karst paleocaverns. The majority of fields and plays in the MB are also karst-related, but in contrast, they include buried hills, subunconformity truncation of porous dolomites, and intraformational porosity related to earlier episodes of karstification. Zonal subdivision of the Ellenburger is essential in mapping these plays, which can be complicated by structures, and is effectively approached by lithostratigraphic studies employing insoluble residues. Principal entrapment styles in Fusselman and Devonian strata in the MB likewise are represented by buried hills and subunconformity truncations, wherein similar recognition of paleogeomorphic features, and analysis of timing of dolomitization, are critical in reservoir predictions.

Lowstand-highstand cyclicity exerted contrasting controls on reservoir occurrence, particularly in slope facies in Pennsylvanian and Lower Permian rocks. Lowstand banks/reefs, typically associated with carbonate conglomerates, were deposited basinward of the highstand margins of the Horseshoe Atoll, Eastern Shelf, and Central Basin Platform (CBP). In contrast, potential reservoir facies in either dolomitized carbonate megabreccias or "turbidite" limestones were deposited in slope environments during highstands in Lower Permian strata. Both of these plays are readily mapped by paleofacies studies, fusulinid biostratigraphy, and analysis/prediction of porosity formation via petrography and geochemistry.

AAPG Search and Discovery Article #90947©1997 AAPG Southwest Section Meeting, San Angelo, Texas