Identification and prevention of gas source in goaf: Stable carbon hydrogen isotope tracer method and numerical simulation of gas flow field

Gas disaster in goaf (by goaf, we mean the area behind the working face after coal mining) of coal mine has always been the key research object of mine safety. A large amount of gas will flood into the goaf during coal mining work, and accurate identification of its gas source is of great significance for clarifying the focus of gas prevention and optimizing mine gas control. In this paper, the 28 118 working face of the Tunlan coal mine is taken as the research object, and the distribution characteristics of carbon and hydrogen isotopes in desorption gas of each coal seam are revealed by field sampling and experimental determination. The results show that the main contribution form of gas source is the coal seam and the lower adjacent layer. The COMSOL numerical simulation software was used to study the distribution law of gas concentration in goaf under different extraction parameters of large-diameter boreholes. The optimal borehole spacing of large-diameter borehole technology was determined to be 20 m, the extraction negative pressure was 10 kPa, and the borehole diameter was 550 mm. On this basis, the comprehensive prevention and control technology of gas in goaf with large-diameter borehole and directional long borehole is proposed. Compared with buried pipe extraction, the proportion of gas concentration in goaf and lower adjacent layer is reduced by 41.5% and 40.2%, respectively, and the gas concentration in upper corner is reduced by 46.77%. The comprehensive prevention and control technology inhibits the emission of main gas sources in goaf and effectively reduces the gas concentration in upper corner, which fundamentally prevents the gas accumulation and overrun in working face.