Experimental research and industrial application of heat injection-enhanced coalbed methane extraction

As the main clean energy in coal seams, the efficient extraction and utilization of coalbed methane (CBM) will help to improve resource utilization and coal mine safety production. However, due to the strong adsorption characteristics of methane and the low permeability characteristics of coal seams, the recovery efficiency of CBM is particularly low. Based on the energy conservation equation, the theory of heat injection-enhanced CBM extraction was improved. The experiments of heat injection-enhanced CBM extraction were carried out in the laboratory and in the coal mine, and the desorption law of methane under different conditions and the promotion effect of heat injection on CBM extraction were studied. The laboratory experiment results show that the final desorption rates of coal samples under the three conditions of water injection desorption, natural desorption and thermal injection desorption are 12%, 37% and 81%, respectively. The quantitative calculation results show that the enhanced desorption by heat injection after natural desorption and water injection desorption can increase the desorption rate by 46% and 68% respectively, which proves that heat injection can enhance the desorption of methane and release the water lock effect. The field test results in Yangquan mining area show that the heat injection method can not only improve the desorption rate of CBM, but also shorten the extraction time of CBM. The heat injection method can increase the concentration of CBM and the daily gas production by 10 times and 100 times respectively, wherein the maximum concentration of CBM and the maximum daily average gas production are 98% and 123 m³/d, respectively. The effective heat injection radius of No.8 heat injection borehole is more than 5 m, and the extraction stage after heat injection is the efficient extraction period of CBM. The research results can provide reference for the field application of heat injection-enhanced CBM extraction and the prevention and control of local gas in coal mines.