Contrasting Styles of San Andres Reservoirs: Vacuum Versus Slaughter Fields, Middle Permian, West Texas and Southeast New Mexico

Vacuum and Slaughter Fields contain two major San Andres (middle Permian) reservoirs in west Texas and southeast New Mexico. Both are dolomitized. Vacuum has produced more than 355 million barrels of oil and Slaughter more than 1,200 million barrels of oil (Koperna and Kuuskraa, 2006). However, the reservoirs are very different in their (1) paleogeographic position, (2) stratigraphic position within the San Andres, (3) internal reservoir geometries, and (4) pore types and permeability. Vacuum occurs at the San Andres shelf margin, whereas Slaughter is in the shelf interior. The San Andres Formation is ~1400 feet thick, and the main oil column in Vacuum is in the upper 500 feet of the San Andres, whereas as the oil column in Slaughter is in the middle part of the San Andres, 450-750 feet below the top San Andres. The upper San Andres is dominated by nonporous, lagoonal evaporites at Slaughter. At Vacuum, the best reservoir is in basinward prograding ooilitic grainstones, whereas the Slaughter reservoir is dominated by relatively flat lying burrowed wackestones and packstones. Molds, intercrystalline and intergranular pores are present at Vacuum, whereas Slaughter is dominated by small intercrystalline pores. Average porosity in the Vacuum reservoir is ~7.4% with permeability commonly varying from 1-100 mD. Slaughter has higher average porosity (~11%), and more uniform, but lower permeability, generally 0.2-30 mD. As a result, the two fields have different production characteristics.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California