Methane emissions and dynamics from adjacent coal seams in a high permeability multi-seam mining environment

Abstract

Reliable prediction of methane emission sources and dynamics from adjacent strata of longwall coal mining is critical for developing efficient methane capture designs to maximise emission reduction and improve mining safety. This paper presents an integrated field monitoring study that has resulted in many new insights into mine methane emissions and dynamics in a relatively high permeability, multi-seam mining environment. The field study comprised of measuring gas content pre- and post-mining at three different locations across the longwall panel, and continuous monitoring of seam pore pressure using fibre optic piezometers.The gas content profile pre- and post-mining enabled delineation of the gas emission zone. The lateral extent of the gas emission zone was found to be far beyond the goaf vicinity, which contradicts the baseline assumption of the conventional Flugge model used at the mine. Significant discrepancies were also found in the degree of gas emission between the measurement and the predictive modelling. For instance, the coal seam 62 m below the mining seam had no discernible gas released, whereas the Flugge model predicts a 24% gas emission. The causes underlying these discrepancies were analysed, and the methods to improve gas emission prediction were discussed. The monitored pore pressure change in different seams validates the gas content measurement results, and is also invaluable for characterising gas emission dynamics from seams in the roof and floor. Monitoring seam pore pressure change can therefore be an effective means to guide methane capture planning and design.