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University of Texas at El Paso, El Paso, Texas

Abstract: The Role of Internal Mound Stratigraphy in the Rowan and Hope Northwest (Pennsylvanian Reef) Field, Nolan County, Texas

The Rowan and Hope Northwest (Pennsylvanian Reef) Field, Nolan County, Texas was discovered in 1954 and is an excellent model showing the role of internal stratigraphy in hydrocarbon productivity of Pennsylvanian Carbonate "reefs" common to the shelves of the Permian Basin. Understanding the complex nature of deposition and development in the growth of these algal mounds is key for high success rates in drilling and developing these features. "Topping into" a "reef' with the expectation of a single oil/water contact, has probably left significant oil and gas reserves lying below in the interior and lower portions of the features.

The Rowan and Hope Northwest (Pennsylvanian Reef) Field is analogous with other Pennsylvanian carbonate buildups in the basin and clearly shows a feature with vertical and horizontal compartmentalization resulting from growth/death boundaries and facies changes within the mound. These features should be thought of as "mound (or reef) complexes", dominated by three basic areas: (1) mound core, (2) rubble/tallus, and (3) back reef flats. These areas are predictable and hold different potentials for productivity within the feature. Mounds uplifted and exposed to extensive subarial erosion, can be the occasional "rock sponges" that led to the common misunderstanding of the nature of trapping within the mounds. Mound complexes not experiencing a full uplift may have areas within the complex that have been for a time exposed and solutioned as a result of sea level oscillations.

AAPG Search and Discovery Article #90918©1999 AAPG Southwest Section Meeting, Abilene, Texas