IZOTOVA, T. S., and I. V. POPADYUK, Ukrainian State Geological Research Institute, Lvov, Ukraine

ABSTRACT: Oil and Gas in Jurassic Reefal Complexes of the West Ukrainian Carpathian Foredeep

Upper Jurassic (Oxfordian-Tithonian) reef-bearing carbonates are developed throughout the Ukrainian part of the Carpathian foredeep. These occupy an up to 50-km-wide area in which they

attain thicknesses of 500-1000 m, occur at depths ranging between 1 and 7 km, and are covered Early Cretaceous to Miocene sediments. Upper Jurassic strata can be differentiated into reef-core, pre-reef, and back-reef facies.

Reservoir development occurs in the karstified, crestal parts of reefs (e.g., Kakhanovka and Letnya fields) and also in detrital back-reef carbonates (Rudky and Lopushnya fields). The potential of this oil and gas play is not yet exhausted, particularly in the area of back-reef facies development under the Carpathian thrust sheets.

Reservoir prediction is difficult due to insufficient core control and therefore is based on sedimentological log analyses. Different facies types are characterized by consistent well-log parameters, including shale content, primary and secondary carbonate texture, structure of associated lithotypes, etc. Different facies types can be correlated with characteristic log parameters. Nine facies types are recognized according to the scheme of J. L. Wilson. This opens the possibility to construct regional facies maps, to trace in time and space the development of the actual reef belt, and thus to enhance reservoir prediction. Sedimentological log analysis, combined with seismic criteria, proved to be an effective tool in the analysis of carbonate prospects, as evidenced by the discovery o the genetically unique Lopushnya field.

Regional paleosedimentological reconstructions of the Upper Jurassic basin form the basis for evaluating the remaining hydrocarbon potential of the back-reef facies domain in the Ukrainian part of the Carpathian foredeep and the adjacent Romanian territory.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.