Simulation and test of enhancement of gas drainage through CO₂ injection into coal seam of low permeability

In view of the difficulty of gas extraction and low drainage efficiency in coal seam of low permeability, based on multi component gas competitive adsorption of CO₂-CH₄, simulation and test for improving seam gas extraction rate through CO₂ injecting CO₂ into coal seam were carried out. A fluid-solid coupling model considering gas-water phases and Klinkenberg effect of CO₂ injection into coal seam for enhancement of gas drainage was established, parameters of gas pressure, gas content and gas extraction rate after coal seam CO₂ injection were analyzed by using COMSOL software and applied in engineering test. The results show that mathematical model of fluid-solid coupling is reliable and reasonable. Gas pressure and gas content in CO₂-injected coal seam decreased faster than those without CO₂ injection. After the field test, the gas concentration increased by 2.02 times and the pure gas extraction volume increased by 3 times. Gas extraction increased after CO₂ had been injected in coal seam, which promotes obviously the gas extraction.