DefinePK

Abstract

The purpose of the study is to improve methods for predicting methane emissions from adjacent coal seams to longwall goafs. To assess prediction efficiency, an analysis was carried out of the existing methods for calculating the parameters of gas emission zones in overlying and underlying coal seams. Different methodologies were analyzed that are used by both companies developing Russian coal basins and those operating in top coal-producing countries (China, the USA, and Australia). As a result of the analysis, it was concluded that the methodology described in one of the coal mining regulations currently in force in Russia does not take into consideration a number of important factors that have a significant impact on methane emissions to longwall goafs. The article demonstrates that it is necessary to take into account such parameters as panel width and the depth of cover. To confirm that the depth of cover affects the permeability of underlying and overlying coal seams in the zones of stress relief, numerical models describing such zones were developed using the finite element method. Numerical modelling was carried out using a 2D rock mass model that included three coal seams (underlying, overlying, and the one being developed), mine workings, and a goaf. The Mohr-Coulomb model was used to describe rock behaviour under stress. By comparing stress distribution patterns at depths of cover of 300, 500, and 900 m with a 300-m distance to the overlying seam and a 50-m distance to the underlying seam, it was concluded that the extent of the gas emission zone created by the underlying seam significantly exceeds the value specified in regulations (35 m) and depends on the depth of cover. It was also established that the effect of stress relief (i.e. an increase in the effective porosity and permeability of the seam) on the seam being overmined increases along with growth in the depth of cover. This dependence is explained by the fact that changes in stresses under the goaf become more significant at greater depths. The novelty of the study consists in identifying a significant effect of stress relief on permeability that manifests itself and great depths of cover and in providing a rationale for improving the methodology for predicting methane emissions from coal seams being overmined at Russian mines by taking into account changes in effective porosity that depend on the depth of cover.