Specific gas emissions in Bowen Basin longwall mines, Australia

Abstract

Longwall coal mines in the Bowen Basin of Australia are highly productive and gassy, comprising many coal seams above the working seam. Predictive modelling of specific gas emission (SGE) using the conventional Winter model developed in Germany or other European based models often results in significant discrepancies from reality. To improve methane emission prediction and management, significant efforts on measuring gas release from different coal seams were made at three longwall mines by safely drilling core holes into the goaf. The vertical extent of the gas emission zone and the proportion of gas released from different coal seams were quantified. It was found that the Winter model significantly underestimates gas emissions for coal seams 75–150 m above the mining seam. This discrepancy is likely due to the intensive goaf drainage using large-diameter vertical wells in the high production Bowen Basin longwall mines. The Winter model also appears inadequate in estimating the height of the gas emission zone at different mines where the extraction thickness differs. Finally, a new empirical model for predicting the degree of gas emission from roof coal seams is developed for Bowen Basin mines and other mines with similar mining conditions. The measured post-mining gas content data and the newly developed model in this paper can provide guidance to the design of goaf drainage boreholes and capacity, as well as assessing coal mine methane and abandoned mine methane resources.