Quantitative determination of CH4 production and CO2 storage in coal mine goaf: A CO2-ECBM recovery model that considers zonal permeability

Injecting CO 2 into a coal mine goaf can not only recover residual CH 4 but also satisfy the effect of CO 2 geological storage in abandoned mines. To reveal the gas–solid couplings during CO 2 -enhanced coalbed methane (CO 2 -ECBM) recovery in abandoned mines, this study summarizes the occurrence of methane in a coal mine goaf, including falling, fracture, and bending subsidence zones, coal pillars, and surrounding rocks. The zonal permeability is then assessed and validated. Furthermore, a fully coupled CO 2 -ECBM model of coal deformation and CH 4 -CO 2 competitive adsorption and seepage is established. Finally, a series of scenario-based numerical simulations are conducted to quantitatively investigate CH 4 production and CO 2 storage in a coal mine goaf. The results showed that CO 2 injection into the coal pillars enhanced gas production from the coal pillars by 94% after 300 d. The efficiency of CO 2 injection into coal pillars for storage is very low compared with that of gas recovery. The total CO 2 storage in the goaf was 71200 Nm 3 after 3000 d of injection when the main storage spaces of CO 2 were the coal pillars and falling zone. The results of this study have implications for the coupling of coal, CH 4 , and CO 2 , particularly for the quantitative determination of CH 4 production and CO 2 storage in coal mine goafs.