Diagenetic Study of Upper Member of the Smackover Formation (Upper Jurassic), Columbia County, Arkansas: ABSTRACT

Abstract

ABSTRACT Upper Smackover member reservoir quality trends in Columbia County, Arkansas are the result of regional variations in the intensity of diagenesis. Major controls on diagenesis were marine-meteoric phreatic cementation and later stage brine dissolution and cementation associated with the maturation of hydrocarbons. Carbonates only altered by brine dissolution have higher porosity and permeability values than carbonates affected by marine-meteoric phreatic cementation. Cores from wildcat tests 1-Neill 23-8 and Pruet McMahen 25-12, Columbia County, Arkansas were analyzed. The core from 1-Neill 23-8 was affected by late stage dissolution and partial cementation by baroque dolomite, anhydrite, and poikilotopic calcite. The core from Pruet McMahen 25-12 ws altered by marine-meteoric phreatic cementation which effectively occluded pore space. Scanning electron microscope photomicrographs also reveal arogonitic needle-like structures in the core of Pruet McMahen 25-12 core. These structures are believed to have been preserved as a consequence of early cementation which occluded pore space and created a closed diagenetic system. Chemical analyses of both cores and the diagenetic overprints indicate brine development occurred nearer the location of 1-Neill 23-8 wildcat test and migrated updip toward the site of Pruet McMahen 25-12 wildcat test. Based on the results of this study, it is proposed that regional diagenetic control in the study area can be related to the mobility and location of the Louann Salt.