Source rock features and thermal transformations in Kössen Formation

Abstract

According to the results of oil-to-source rock correlation, heavy oils discovered in Nagylengyel were generated by Kössen Formation. Based on trend values of Rock-Eval data and organic sulfur to carbon atomic ratios, the lower part of Kössen Formation in Rezi-1 drilling shows high hydrocarbon potential and the presence of of sulfur-rich, IIS type kerogen. Using the burial history of Kössen Formation in Bak-Nova trench and kinetic constants corresponding to IIS kerogen, thermal transformation generating heavy oil came to an end in Upper Cretaceous time at temperature of 70°C. This early generation of oil is due to the presence of sulfur-rich, IIS type kerogen. The primary migration of heavy oil caused by overpressure coincides with the beginning of decomposition of asphaltenes being in heavy oil. Microfracturing of Kössen Formation was due to the volume increase of oil presenting in pores, which was the consequence of asphaltene decomposition. Thermal transformation of kerogen in Kössen Formation ended with gas generation at higher maturity levels corresponding to vitrinite reflectance of 1.3 % at least.