Gas Hazard and Origin: Near-Surface Zone of the Upper and Lower Silesian Coal Basins

Abstract

Summary In 1991–2001 the all coal mines in the Lower Silesian Coal Basin (LSCB) were closed and remediated. In the middle of the 1990s mine restructuring process started at the Upper Silesian Coal Basin (USCB). At that time 65 coal mines were operational. In 2019 22 mines were still active. The main aims of this presentation are to determine the origin of soil gases in the USCB and LSCB and evaluate gas hazard caused by secondary migration of coalbed methane and carbon dioxide from Carboniferous coal-bearing strata to near-surface zone connected with the restitution of groundwater level to the original position (“piston effect”). For evaluating gas hazard surface geochemical survey and determining the origin of soil and coalbed gases, stable isotope analyses and simulation of generation of thermogenic gases by hydrous pyrolysis experiments were performed. Comprehensive geochemical, geological and hydrogeological studies carried out in the zones of closed mines in the USCB and LSCB allowed for detecting the surface range of occurrence of anomalous concentrations of methane and carbon dioxide at the surface, the mechanism of the flow of these formation gases into the near-surface zone and establish to what an extent the local population living in post-mining areas is hazarded.