Production characteristics and adsorption control mechanism of CO2-rich CBG wells

To investigate the productivity laws of coalbed gas (CBG) wells in carbon dioxide (CO₂)-rich coalfield, the Haishiwan coal mine in Yaojie coalfield, Gansu Province, China, which is rich in CO₂ of different concentrations in CBG, was selected as the study area. Using numerical simulation technology, the production capacity of CBG wells was simulated, and the thermodynamic factors influencing gas adsorption differences on production capacity were discussed. Numerical simulation indicates that with the increase of CO₂ concentration, the gas breakthrough time is prolonged, and the gas production first increases and then decreases. Research considers that changes in CBG production capacity result from the combined effects of temperature and pressure on gas adsorption. At shallow coal seams, pressure is the dominant factor that promotes gas adsorption, resulting in increased gas content and production. However, due to the competitive adsorption of CO₂ and methane (CH₄), CO₂ preferentially adsorbs on coal, hindering desorption. Therefore, gas breakthrough in CBG wells with high CO₂ concentration is slower, but the production period is longer. On the contrary, high temperatures inhibit gas adsorption in deeper coal seams, reducing gas content and promoting CH₄ desorption. Therefore, CBG wells with low CO₂ concentration have faster gas breakthroughs, but overall production is lower. The findings of this study help to better understand the drainage characteristics of CO₂-rich CBG wells and provide guidance for developing such resources.