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Neogene Sandstone Reservoirs of the East Slovakian Basin: Zeolites and Clay Minerals from the Alteration of Volcanics

REED, JOHN K., and MACK GIPSON, Jr., University of South Carolina, Columbia, SC

Petrographic analyses of core samples from wells in the East Slovakian basin indicate that alteration products of volcanic materials cause porosity loss in sandstone reservoirs. The reservoirs, which produce natural gas, are part of a shallow marine to continental basin fill with interbedded volcaniclastics, tuffs, and volcanites. Abnormally high heat-flow values have been recorded in the basin fill, which reaches up to 7 km in thickness. Both clay minerals and zeolites are found to restrict porosity. Kaolinite, smectite, illite, chlorite, and mixed-layer clay minerals are all identified in various combinations. Zeolites identified include phillipsite, erionite, clinoptilolite, and analcime. These minerals are related to the occurrence of volcanic rock fragments in the reservoir sands and interbedded volcanics, and they occur as diagenetic replacement minerals and cements. The effects of these minerals are compounded by the initial poor reservoir quality caused by immature sediments and calcite cement. Reservoir productivity would probably be increased if drilling and completion practices in the basin reflected the potential effects of the clay minerals and zeolites.


AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)