Genetic correlation of source rocks and natural gas in the Polish Outer Carpathians and Paleozoic–Mesozoic basement east of Kraków (southern Poland)

Abstract

Natural gas-source rock correlations in the Polish Outer Carpathians and Paleozoic–Mesozoic basement in the Kraków–Brzesko–Nowy Sącz area (southern Poland) have been established. In the Dukla and Sub-Silesian units, mixed kerogen Type-II/III or III/II occurs. The organic matter is immature or low-mature. The Oligocene Menilite beds of the Silesian Unit are rich in TOC and contain gas-prone Type III kerogen of low maturity. In the Paleozoic–Mesozoic basement, the TOC content and residual hydrocarbon potential vary in the Middle and Upper Devonian strata, Mississippian carbonate and clastic facies and Middle Jurassic strata. The Paleozoic strata are capable of thermogenic hydrocarbon generation, while organic matter in the Middle Jurassic rocks is generally immature. Gaseous hydrocarbons accumulated both in the Silesian and Dukla units of the Polish Outer Carpathians and in the Mesozoic basement are genetically related to thermogenic and microbial processes. The Outer Carpathian natural gas was generated mainly from the Type-II/III kerogen of the Oligocene Menilite beds. The thermogenic gases from the Mesozoic basement were generated from Devonian and Mississippian (carbonate) Type-II and mixed II/III kerogens and probably from Silurian/Ordovician Type-II kerogen and Middle Jurassic Type-III/II kerogen occurring at more than 7 km depth. Microbial methane migrated into the Outer Carpathian flysch succession from the Miocene strata of the Carpathian Foredeep.