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ABSTRACT: Gravity prospecting for Pennsylvanian carbonate reservoirs of the Northern Shelf of the Permian Basin

FAGAN, JOSEPH P., JR. and ROBERT NEESE

San Andres carbonate reservoirs of the Northern Shelf of the Midland Basin constitute one of the biggest plays in Texas. Most of the production is assembled with the older Abo Reef trend. The San Andres is a primarily carbonate facies stratigraphic unit that varies in thickness from about 1,300 ft along the Matador Arch to about 2,000 ft along the eastern margin of the reef trend near Reeves Field. Regionally, the San Andres is predominately composed of dolomite, laminated anhydrite and dolomite, massive bedded anhydrite and limestone. Some salt and red beds are also present.

The San Andres carbonates are underlain by the Glorieta Formation and overlain by the Grayburg Formation. Both of these are siliciclastic rich, and subsequently have contrasting densities with the San Andres. This density contrast can be exploited with high-sensitivity gravity data. Traditionally, gravity prospecting has not been considered a primary exploration tool. However, in areas where a significant density contrast exists between reservoir and non-reservoir rock, as in this portion of the Midland Basin, gravity methods should be considered as an inexpensive aid in delineating productive trends. Several known fields correlate very well with attributes of the gravity data set.

The geophysical principles used in the Midland Basin can also be extended elsewhere. While the geologic framework can be very different, the basic geophysical model can be transferred from the Midland Basin to another. As such, gravity prospecting can be a powerful, yet inexpensive, tool for exploration geologists.

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