Understanding CO2 Gas Production Above a Partly Flooded, Former Coal Mining Area

Abstract : INERIS has worked for several years on the characterization of O2-defficient and CO2-enriched gas production and migration processes above a partly flooded, former coal mining area. To understand the origin of this gas production, a borehole 90 meters deep was drilled next to the area of gas emmanation. Several investigations were conducted to improve the understanding of the gas production mechanisms in relation to the presence of water. This paper deals with the results of experiments conducted in situ and tests done in the laboratory. One hypothesis is based on the results obtained: marcasite, which has been observed in rock samples, is oxidized by contact with air that migrates through mining fractures in the rock. CO2 is produced through carbonate dissolution because of the production of acidic fluids in the water. Noxious gas emissions can occur during drops in the atmospheric pressure, leading to gas migration through foundation cracks, allowing CO2 to enter into houses.