Geological and Geochemical Controls on Oil Occurrence and Future Exploration Potential, Pripyat Basin, Byelarus

J. L. Clayton, G. F. Ulmishek, S. Monk, P. G. Lillis, V. A. Bogino, Z. L. Pozniakevich, and M. B. Keller

The Pripyat Basin is a Late Devonian rift characterized by typical fault-block structure. It contains two thick, synrift salt formations that separate the Devonian stratigraphic succession into subsalt, intersalt, and post-salt sections. Oil production is mainly from carbonate reservoirs of the intersalt and subsalt sections, and is limited to the northen half of the basin. A number of oil shows have been encountered in the southern part of the basin, but no commercial production has been established. The Pripyat basin is unique among ancient rifts in that some very thermally immature oils and source rock are preserved, despite present-day burial depths of as much about 4 km. Sulfur content of the oils is from 0.1 to 4.9% and API gravities are 10 to 40°. Accumulation of heavy, sulfur-rich oil in the central part of the basin are probably due to early generation from sulfur-rich kerogens in the source rocks. Based on carbon isotope ratios (range -27 to -34^pmil) and biomarker analyses, three genetic oil-types are recognized, derived from organic-rich rocks contained within the Devonian intersalt and subsalt sequence. Thermally mature oils, restricted to the northern margin of the basin, are due to either higher temperature gradients in that area during or shortly after rifting or recent heating due to implacement of a magmatic body in the crust below the northem zone. Future exploration success, especially in the thermally immature southern part of the basin, depends on detailed understanding of the source rock distributions and oil generation/expuls on kinetics.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California