Effect of CO₂ injection pressure on enhanced coal seam gas extraction

The CO₂ displacement of coal seam gas can simultaneously promote gas extraction and CO₂ sequestration, with gas injection pressure being a key factor influencing both efficiency and safety. This study examined the impact of varying CO₂ injection pressure on gas extraction and sequestration. The findings indicated that higher CO₂ injection pressures reduced the gas injection and extraction time costs, increased the equilibrium pressure and coal seam temperature, and decreased carbon sequestration efficiency. As the CO₂ injection pressure increased, the CH₄ cumulative desorption capacity and desorption rate rose by 4.98%, the time to reach the residual gas content critical value (TLV of 2 m³/t) shortened by 62.04 min, and the maximum CO₂ storage per unit mass of coal increases by 3.6 m³/t. Increasing the injection pressure enhanced gas desorption and CO₂ sequestration. A higher CO₂ injection pressure resulted in a higher CH₄ yield rate and a reduced CO₂ injection rate in the later stages. Therefore, it is advisable to reduce the CO₂ injection pressure during the low efficiency desorption stage.