Diagenetic Study of Upper Member of the Smackover Formation (Upper Jurassic), Columbia County, Arkansas
Karl F. Kalbacher, Austin A. Sartin
Reservoir quality trends in the upper Smackover member 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 altered only 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 McMahon 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 McMahon 25-12 was altered by marine-meteoric phreatic cementation that effectively occluded the pore space. Scanning-electron-microscope photomicrographs also reveal aragonitic needle-like structures in the Pruet McMahon 25-12 core. These structures are believed to have been preserved as a consequence of early cementation that 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 and migrated updip toward the site of Pruet McMahon 25-12. 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.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.