Geochemical and isotopic characterization of coalbed gases in active excavation fields at Preloge and Pesje (Velenje Basin) mining areas

摘要

Coalbed gases in excavation fields of mining areas in the Velenje coal basin have been subjected to geochemical and isotopic monitoring since the year 2000, with the aim of obtaining better insights into the origin of coalbed gases. Results from active excavation fields in the mining areas Pesje and Preloge in the year 2013 are presented in this study. Composition and isotopic composition of coalbed gases were determined with methods utilizing mass spectrometry. The chemical and isotopic composition of coalbed gases in the Velenje Basin vary and depend on the composition of the source of coalbed gas before excavation, advancement of the working face, depth of the longwall face, pre-min-ing activity and newly mined activity. The basic gas components determined in excavation fields are CO2 and methane. The isotopic composition of deuterium in methane has been determined and used to characterize the origin of methane. The isotopic compositions of carbon and hydrogen in methane in the excavation fields show its biogenic origin, while a high Carbon Dioxide Methane Index indicates the bacterial and endogenic origin of CO2.