Diagenetic Redox Compartmentalization of the Big Clifty Sandstone Reservoir in South Central Kentucky

Kort H. Butler
Western Kentucky University, Bowling Green, KY

The Big Clifty Sandstone Member of the Golconda Formation is one of several Chesterian sandstones deposited in the late Mississippian along the southeastern margin of the Illinois Basin which contains both conventional (lower gravity) and unconventional (bitumen and higher gravity) oil. Preliminary petrographic analysis of several cores indicates at least two diagenetic phases with calcite associated with replacement of framework grains and mesogenetic quartz cement.

Authigenic replacement of framework grains and cements by calcite and a lesser degree pyrite have created multiple intrastratal seals compartmentalizing and further sealing the reservoir in addition to the bounding stratigraphic traps. Sedimentary structures influence oil emplacement but in cored sections where framework grains have undergone more extensive calcite replacement reservoir seal boundaries are discordant with primary sedimentary fabrics. The precipitation of poikilotopic calcite and replacive pyrite is posited to be a result of an iron oxide sulfide redox reaction coupled with microbial mediated sulfate/methane redox producing excess bicarbonate buffering the pH. The absence of any Permian-Tertiary sediments within the southeastern margin of the basin and lack of near surface fault offsets greater than 100 meters makes reconstruction of paleohydrologic flow regimes and isotopic signature comparisons between the poikilotopic calcite problematic. The study minimally establishes that diagenetically sealed reservoirs are of local significance along the basin margin in contrast to the apparent lack of diagenetic seals in deeper parts of the basin.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013