Impact of CO2 and methane adsorption and emission on coal's mechanical properties and pillar stability: Implications for ECBM and CO2 sequestration

This study investigates the effects of carbon dioxide (CO2) and methane (CH4) adsorption and emission on the mechanical Properties of coal and the stability of underground mines. Given the significance of the coal industry and its associated environmental and safety challenges, optimizing extraction methods and effective gas management is essential. In this research, the impact of CO2 and CH4 on the peak strength (PS), elastic modulus, and axial strain of coal samples under various laboratory conditions was examined. The results indicated that CO2 gas adsorption had more significant negative impacts on the engineering properties of coal, notably reducing its strength. Key findings reveal that CO2 adsorption significantly degrades coal's engineering properties more than CH4. Specifically, CO2 at 15 and 30 bar injection pressures reduced compressive strength by 57.80 % and 57.15 %, and Young's modulus by 77.67 % and 22.03 %, respectively. In contrast, CH4 reduced compressive strength by 27.9 % and 41.7 %, and Young's modulus by 18.06 % and 19.91 % at the same pressures. This reduction is influenced by factors such as gas pressure, coal type, cleat structure and orientation, moisture content, and other relevant parameters. Overall, the stability of coal pillars exposed to CO2 decreases, which should be carefully considered when designing enhanced coalbed methane recovery (ECBM) methods and CO2 storage projects in coal seams. Furthermore, the study highlights that gas emission from both depleted and non-depleted coal layers reduces coal strength, increasing the risk of gas explosions, spontaneous combustion, and pillar instability. These findings emphasize the need for thorough assessments of gas effects on mine stability and underscore the importance of further research in this area.