Petroleum geology of the Transcarpathian Basin, NE Pannonian Basin, Ukraine

The Transcarpathian Basin (TB) is part of the Neogene transtensional sedimentary basin superimposed on the Inner Carpathian thrust–fold belt and stretches across eastern Slovakia, westernmost Ukraine and northern Romania. The TB is part of the much larger Pannonian super-basin, which evolved as a back-arc system behind the Carpathian arc during Miocene times and covers many Central and Eastern European countries including Ukraine. This study highlights the geological structure of the TB in the context of its petroleum systems and its hydrocarbon potential. This overview paper is based on both published and unpublished industrial data ranging from sedimentary, petrophysical and petrographic datasets of cores and well-logs, acquired in various wells drilled in the Ukrainian sector of the TB. The hydrocarbon-bearing sub-basins include the Mukachevo, Solotvyno, Mara and East Slovakian with the first two located in Ukraine. Within the Ukrainian part of the TB, commercial hydrocarbon accumulations are associated with Paleogene and Miocene (Badenian, Sarmatian and Pannonian in age in Paratethys nomenclature) reservoirs. The basin fill is mainly represented by the Badenian sedimentary sequence with thick evaporites that became the driver for salt tectonics in the Solotvyno sub-basin. In the Mukachevo sub-basin, younger sedimentary rocks of Sarmatian, Pannonian and Middle Pliocene age dominate, including pronounced volcanic units. In the Ukrainian segment of the TB, gas pools were discovered between 300 and 1750 m depth. Productive units are mainly composed of stacked sandstones alternating with shales, clays, siltstones and tuffaceous rocks sealed mostly by Middle Badenian evaporites.