Experimental Study on the Effect of CO₂ Injection Pressure on the Migration Characteristics and Extraction Effects of...

To study the effect of CO₂ injection pressure on gas migration characteristics and coalbed methane (CBM) extraction, a platform for the experimental replacement of CH₄ with CO₂ was used to conduct experiments on the replacement of CH₄ under different CO₂ injection pressures and analyze the gas transport characteristics and CH₄ extraction during the experiment. The results reveal that the rate of gas migration out of the coal seam accelerates with increasing gas injection pressure, as determined by comparisons of the migration rates between adjacent monitoring points. The change trend of the CH₄ desorption rate under different gas injection pressures is divided into slow decline, sharp decline, and stability stages, and the maximum value of the effective diffusion coefficient increases from 2.3 × 10^-5 to 3.4 × 10^-5 and 4.6 × 10^-5 cm²/s as the gas injection pressure increases from 0.6 to 0.8 and 1.0 MPa. Similarly, the change pattern of coal seam permeability can be divided into slow decline, sharp decline, and stability stages. After the gas injection pressure was increased from 0.6 to 0.8 and 1.0 MPa, the CH₄ desorption volume increased from 90.2 to 94.1 and 97.8 L, whereas the coal seam CO₂ sequestration volume increased from 269.2 to 274.2 and 322.8 L, respectively. In contrast, the CH₄ extraction efficiency increased from 76.9 to 80.2 and 82.9%, respectively. The research results have important reference value and practical significance for optimizing the CO₂ injection pressure and improving the CBM extraction.