Petroleum play types and source rocks in the Pannonian basin, insight from the Slovak part of the Danube Basin

Abstract

The Danube Basin represents a Miocene depocenter located on the NW margin of the Alpine-Pannonian-Carpathian region and is considered a partial sub-basin of the larger Pannonian Basin System. The gradual opening of the northern Slovak part of the basin during a 4-stage rifting event between the Badenian, Sarmatian (Langhian, Serravallian) to Pannonian (Tortonian) time reflected not only on the sedimentary fill and the development of volcanic fields but also on individual elements of the petroleum system. The presence of effective petroleum systems is supported by several gas and condensate deposits together with abundant hydrocarbon shows. The study offers new insight into the petroleum plays in Danube Basin based on new and vintage reflection seismic lines and organic geochemistry data. The novel findings reveal that within the older sub-basins (Blatné and Želiezovce) the main source rock is the lower Badenian mudstone with mixed Type III/II kerogen. Paleogene shales with Type II kerogen together with Pre-Cenozoic basement Type III/II rocks cannot be excluded. In the younger sub-basins (Komjatice and Gabčíkovo-Győr) the main source rocks are upper Badenian – Sarmatian, and Pannonian mudstones with Type III/II kerogen. Two gas play groups are defined. 1) Plays in older sub-basins characterized by structural traps mostly in the Badenian reservoirs. 2) Plays in younger sub-basins characterized by stratigraphic and structural traps in Sarmatian and Pannonian reservoirs. Non-hydrocarbon gas risk arises from CO2 and N2 contents sourced from buried volcanic fields. The volume of inert gasses trapped in particular sub-basins is dependent on the timing and type of volcanism. It is lower in the older sub-basins and higher in the younger ones, at the same time, the risk is lower in stratigraphically highest reservoir intervals.