LAUSR

Abstract The paper presents the variability of methane emissions into mining excavations and the atmosphere in the Upper Silesian Coal Basin (USCB) (Poland) against the background of natural and mining factors. Emissions of methane from exploited coal seams have become a serious problem in the USCB due to the growing methane hazard in coal mines and emissions of methane into the atmosphere. In the mid-nineties 753 million m3 of methane was emitted annually from the USCB mines. Despite a significant drop in coal production over the next 20 years, methane emissions have not decreased sharply; on the contrary, in recent years they have begun to grow, and, in 2016, reached the level of 933 million m3 per year. This represents an increase of 180 million m3 per year since the mid-nineties. One of the important reasons for this phenomenon is the constantly increasing depth of coal exploitation, which in many mines now exceeds 1000 m; this is the depth corresponding to the deep methane zone, where the volume of accumulated methane in the coal seams is particularly high. Factors influencing the volume of methane emissions in relation to mine workings can be divided roughly into two groups: natural (geological) and anthropogenic (mining-related). Natural factors include methane content in coal seams, gas pressure, the presence of free gas in fault zones, related fissures and porous sandstone, the migration of methane through faults and fissures, and the presence of a continuous and impermeable Miocene overburden. Mining factors include the depth of exploitation and the concentration of coal production as expressed in terms of the length, height, and advance of walls. The interdependence of these factors means that, despite the decline in coal production, methane emissions, both total and specific, are increasing. This problem cannot be neglected, especially since it may grow worse in future. One measure to prevent the growth of methane emissions and the associated hazard may be the intensification of mine methane drainage and the economic use of captured mining gas, which is already done in the USCB.