Geochemical and stable carbon isotopic composition of coal-related gases from the SW Upper Silesian Coal Basin, Czech Republic

Gas associated with Carboniferous coal seams and younger Miocene sediments in the SW Upper Silesian Basin in Czech Republic shows wide compositional variation. Coal-related gas extracted from cross-measure degassing boreholes, as well as gas released during canister desorption of coal samples from three different mines was analyzed to evaluate the genetic origin and the influence of sorption/desorption processes on the gas composition. Analyses comprised the compositional and stable carbon and isotope composition of coal-related gases. The isotopic composition of gas from cross-measure boreholes indicates thermogenic origin in the southern part of the basin and microbial CO2 reduction and mixed type origin in the northern part. Gas from canister desorption shows similar origins, but larger compositional and isotopic variation. No consistent isotopic fractionation due to desorption could be observed. Differences in geochemical composition of thermogenic gases could indicate a contribution of gas migrated from deeper formations below the Carpathian overthrust.