Petroleum processes in the Palaeozoic and Mesozoic strata between Tarnów and Rzeszów (SE Poland) : 2-D modelling approach

Two-dimensional modelling of hydrocarbon generation, expulsion, migration and accumulation pro- cesses in SE Poland between Tarnów and Rzeszów was carried out for five source rock horizons, i.e. the Ordo- vician, Silurian, Middle Devonian–Lower Carboniferous carbonates, Lower Carboniferous clastics, and Middle Jurassic. Five cross-sections in the study area allowed the reconstruction of timing and range of petroleum processes. The best source rocks related to the Ordovician and Silurian shales and mudstones reached “oil window” maturity within the entire study area and locally also reached the “gas window”. Generation of hydro- carbons was observed from all five source rocks, but the Ordovician and Silurian source rocks generated two and three times more hydrocarbons than the Lower Carboniferous and Jurassic source rocks, respectively. Expulsion took place only in case of the Lower Palaeozoic source rocks, but the volume of expelled hydrocarbons differed across the area. Hydrocarbons migrated from the Ordovician and Silurian source rocks to the Upper Jurassic (carbonates) and Upper Cretaceous (sandstones) reservoirs or to the Upper Palaeozoic carbonates in connection with the emplacement of the Carpathian thrust belt during the Miocene. Faults formed main migration pathways and hydrocarbons accumulated in structural and stratigraphic traps, located in the vicinity of faults. In places, traps are associated with a deep Miocene erosion surface. The onset of hydrocarbon generation took place during the Neogene, mainly the Miocene, but in the north, generation and expulsion started earlier – at the end of the Mesozoic.