GIPSON, MACK, Jr., and C. D. GULLETT, University of South Carolina, Department of Geological Sciences, Columbia, SC; and D.G. NEESE, Maxus Energy Corp., Dallas, TX

ABSTRACT: Reservoir Characteristics of the Danube Basin: A Brief Comparison with the East Slovakian Basin, Czechoslovakia

The Danube Basin is characterized primarily by a succession of Neogene and Paleogene litharenites, sublitharenites, biocalcarenites, and shales. Detailed petrographic analyses were made of representative Miocene samples from the Pontian, Pannonian, Sarmatian, Badenian, and Karpatian formations for the purpose of assessing reservoir potential. The arenite grain skeletons consist of monocrystalline quartz, potassium and plagioclase feldspars, highly altered feldspars, and volcanic lithic fragments;

the biocalcarenites consist of mixed skeletal and non-skeletal grains. The arenites are cemented by silica, silica and feldspar overgrowths, patchy calcite, and argillaceous matrix; the biocalcarenites are cemented by calcite and micritic matrix. The pore system in the arenites is predominantly secondary, consisting of moldic pores, developed in degraded feldspars and lithics; intercrystalline porosity is common in kaolinite vermicules and chlorite rosettes. Porosity is highly variable, ranging from 3-31 percent, however, there exists a general decreasing trend in porosity with increased depth of burial. Illite is the dominant clay mineral, followed by smectite, chlorite, and kaolinite, respectively. Mixed-layer illite/smectite and zeolites are present in trace-to-minor amounts. The D nube Basin contrasts sharply with the East Slovakian Basin (ESB), namely: (1) is mineralogically more mature, having only minor amounts of volcaniclastics, whereas the ESB is characterized by abundant volcaniclastics, (2) has a well-developed pore system--conversely, the ESB is summarily "tight", (3) contains only trace amounts of zeolites, as compared to the abundant zeolites in the ESB, (4) has good-to-excellent porosity present virtually basin-wide, whereas, the ESB contains only locally significant porosity, and (5) contains relatively small amounts of minerals that could pose problems with "conventional" drilling/completion fluids. The ESB contains, abundant, potentially "troublesome" minerals.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.