BENSON, D. J., and E. A. MANCINI, Center for Sedimentary Basin Studies and Department of Geology, University of Alabama, Tuscaloosa, AL

Abstract: Diagenetic Influence on Reservoir Development and Quality in the Smackover Updip Basement Ridge Play, Southwest Alabama

Smackover reservoirs in the updip basement ridge play of south Alabama are developed over low to high relief paleotopographic highs on the pre-Mesozoic, "basement" surface. These reservoirs occur within shoal grainstones or microbial boundstone/bindstones that have been modified by intense diagenesis. Diagenetic patterns, which vary dramatically over short distances, are principally controlled by paleotopography and eustatic sea level fluctuations.

Diagenesis occurred in both eogenetic and mesogenetic environments. Eogenetic processes include grain micritization, precipitation of aragonite or Mg-calcite cements, physical compaction, precipitation of low-Mg calcite cements, dolomitization, dissolution, and precipitation of dolomite and aragonite cements. Mesogenetic processes include chemical compaction, precipitation of ferroan calcite, quartz, and ferroan dolomite cements, dissolution, emplacement of hydrocarbons, and precipitation of anhydrite and baroque dolomite cements.

The products of this complex diagenetic history are heterogeneous reservoirs, which consist of one or some combination of interparticulate, shelter, and vuggy porosity with lesser amounts of moldic and intercrystalline porosity. While diagenesis had a significant influence on reservoir quality, it did not significantly alter the geographic distribution of reservoir-grade rock. The primary controls on reservoir development are depositional and exploration strategies should seek to identify paleohighs with enough relief for the development of microbial reefs and/or grainstone shoals. 

AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana