Underground gas production and migration induced by mining subsidence

Abstract : Since 2009, Ineris works on a former mining area of Lorraine coal basin (East of France) where gas emissions occur at surface. Local authorities reported dangerous gas emissions in the local school and in dwellings. Ineris has been mandated to diagnose the gaseous phenomena (origin of the emitted gas and mechanisms of the emissions). The gas emitted at the surface is strongly enriched in CO2 and depleted in O2. It does not contain methane and is not from old coalmines origin. It is produced in shallow rock formations of the unsaturated zone located above the local aquifer. The gas flows to the surface through crevasses resulting from deep mining activities. Here, we observed how geomechanical, hydrogeological and geochemical processes can interact to enable underground processes of gas production and migration.