Abstract: The prospects for exploration of unconventional accumulations in tight rocks of Bilche-Volytsya unit (Carpathian foredeep, Ukraine)

POLUTRANKO, ALEXANDER*, MYROSLAV ZAZULYAK, YAROSLAV LAZARUK.

In the Carpathian foredeep there are only a few areas where the rocks of late catagenesis capable of generating a gas of so-called Lower zone of gas accumulation are developed. Here they rest at the depth range of 3.6 to 4.8 km (Hhushiv block) and 6.5 to 7.5 km (Krukenytsya deep), respectively. Stratigraphic column which is under conditions of late catagenesis consists of Neogene clastics as thick as 1.2 km. The area closed by the isotherm of 160 degree C is equal to 160 sq. km. The gas resources of this area are estimated at 277 billion m3; at that estimate, the gas saturation is 58%. Paleozoic basement rocks are more interesting both in the AHP zone of gas fields (Zalouszany, Pynyany) and also at the smaller depth. In the Zalouzany field the highest excessive formation pressures are located at the top of basement. In the sedimentary cover the methane accumulations are located in relation to maximal overpressures for each of productive horizons of AHP zone. The gas is replaced by water if the AHP falls. In upper horizons without AHP, gas is absent; it is located peripherally to the fluid unloading zone that has a normal or abnormal low pressure.

In the Hrushiv block the sediments of late catagenesis zone with AHP is sealed by tight rocks of basement at depths of 3.5-4.0 km. CH₄ migration is possible from Lower zone of gas accumulations located in the central part of the Krukenytsya deep to the upper part of the Hrushiv block.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria