Isotope geochemical features and layered quantitative method of coal seam group gas combined extraction

In view of the problem that it is difficult to measure the gas extraction of each coal seam alone by traditional device in the process of coal seam group gas combined extraction (CSGGCE), the calculation model of the mixing gas ratio is established and solved by using mathematical method, based on the definition of isotope value in gas isotope geochemistry and the ideal gas state equation. At the same time, the field test is selected in the Fengchun Coal Mine in Songzao Mining Area of China. The spatial distribution characteristics and differences of coal seam group are obtained, and the law of the CSGGCE mixing ratio is revealed with the variation of the extraction time, according to the discrete data of the separate and combined extraction gas components and isotope values. The results show that the coal seam gas has a thermal origin and a significant mantle-derived contribution. Compared with the traditional method, the CSGGCE mixing ratio obtained based on the isotope principle is dynamic. The mixing ratio is mainly controlled by the geochemical characteristics of the gas isotope in the initial stage of extraction and affected by gas deposit difference and physical space limitation as the extraction time increases, which is more in line with the actual situation of the CSGGCE in coal mines.