Petroleum generation and migration in the Styrian Basin (Pannonian Basin system, Austria): an integrated geochemical and numerical modelling study

Abstract

Source rock analysis and numerical modelling techniques have been applied to evaluate the hydrocarbon potential of the Styrian Basin. Oil- and gas-prone sediments occur in the lower Miocene section (Ottnangian and Karpatian levels). Kinetic parameters indicate that hydrocarbons are generated at higher temperatures and within a narrower temperature interval from Ottnangian sediments than from Karpatian sediments. The thermal history of the basin is governed by Miocene magmatic activity due to subduction along the Carpathian front. Heat flow during magmatic activity in close vicinity to the volcanic centres was about 300 mW/m 2, decreasing to about 120 mW/m 2 at a distance of a few kilometres. After the magmatic activity the heat flow decreased and has remained at 60–85 mW/m 2 since the end of the middle Miocene. The increased heat flow resulted in an early Miocene (Karpatian to early Badenian) petroleum generation phase near the volcanoes. Because no traps were formed at that time, the generated hydrocarbons may have been lost. Thus the early magmatic episode had a negative impact on the hydrocarbon potential from a timing aspect. At some distance from the volcanoes, generation continued up to the end of the middle Miocene (early Sarmatian). Hydrocarbons generated during and since the middle Badenian have had a good chance of becoming trapped and forming accumulations. Only small amounts of oil formed after the middle Miocene. The numerical modelling of petroleum migration provides important information on its timing and pathways and predicts correctly the only drilled hydrocarbon occurrence in the Styrian Basin. The calculated gas to oil ratio is 0.5. The integration of all these data helps to define areas with high petroleum potential.