Abstract
One of the main hazards occurring in post-mining areas is the uncontrolled migration of gases to the surface, which may pose a serious threat to life and health. These gases are mainly methane and carbon dioxide, in smaller amounts ethane and higher hydrocarbons, carbon oxide, hydrogen sulfide, and radon. Methane migrating into the lower levels of buildings, garages, cable ducts, and sewage systems reaching the concentrations of above 5% may cause an explosion hazard. The concentration of carbon dioxide over 4% also represents a serious threat to life. Moreover, carbon dioxide and methane, emitted into the atmosphere, constitute a considerable source of greenhouse gases. The methane could be utilized, yet it is necessary to develop effective capture and purification methods with the first step of determination being its migration routes. The paper presents the application of numerical modelling with the use of TOUGHv2.0 software, which enabled effective simulation of the multiphase flow, applying adsorption and diffusion phenomena. The results of gas migration modelling were compared to the outcomes of geological tests, and the obtained results were satisfying. It was observed that both geological investigation and computer simulations are proper tools for investigation of the phenomenon of gas migration and identification of gas hazard areas on the surface, constituting the basis for development of effective methane capture methods for further application.
Highlights
Methane occurring in coal seams has been a research subject for decades, mainly in the aspect of labour safety in mines [1,2,3,4]
The gas is contained within the coal in free or adsorbed form. Both forms occur in coal seams in equilibrium, depending on the pressure, moisture content in coal, and its sorption properties
The rising groundwater table creates a kind of a hydraulic press affecting the structure of the overburden as a result of discontinuance of dewatering workings and goafs. Such a phenomenon was observed in the area of coal mines of Lower Silesia Coal Basin and resulted in high concentrations of carbon dioxide and methane in sub-surface conditions [22,23]
Summary
Methane occurring in coal seams has been a research subject for decades, mainly in the aspect of labour safety in mines [1,2,3,4]. Disturbances to the equilibrium result in methane release from coal, often in large amounts, i.e., its transition into the free form and migration into the rock mass. The problem of mine gases migrating towards the surface and their emission into the atmosphere, after the closure of a hard coal mine, occurs in virtually all mining areas in Europe [17,18]. The rising groundwater table creates a kind of a hydraulic press affecting the structure of the overburden as a result of discontinuance of dewatering workings and goafs Such a phenomenon was observed in the area of coal mines of Lower Silesia Coal Basin and resulted in high concentrations of carbon dioxide and methane in sub-surface conditions [22,23]. The modelling of pathways of mine gas migration towards the surface constitute a novel approach to forecasting potentially hazardous zones
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