Microbial Gas System in the Polish Part of the Carpathian Foredeep between Pilzno and Przemyśl

The main purpose of study is to determine the molecular and isotopic composition and origin of gaseous hydrocarbons in the Miocene strata of the Polish part of the Carpathian Foredeep between Pilzno and Przemyśl. We carried out analyses of molecular composition and stable carbon isotope composition of methane, ethane, propane and carbon dioxide and stable carbon isotope composition of methane. In the autochthonous Miocene strata of the Carpathian Foredeep natural gas is accumulated in the Badenian and Lower Sarmatian reservoirs. It is dominated by methane from the microbial carbon dioxide reduction and occurrence in the marine environment. During the microbial and initial phase of low-temperature thermogenic and/or diagenetic processes the ethane and propane were produced. The molecular and isotopic compositions of accumulated gases are similar which indicates homogeneity of generation processes within the full Miocene succession. Gases was generated in claystone/mudstone horizon migrated to the overlying sandstone horizon which was covered by another claystone/mudstone bed.