Abstract:

To investigate the influence of coal bedding angle on enhancing CO₂ injection-enhanced coalbed methane recovery efficiency, coal samples from Mine 6 in Sijiazhuang, Jinzhong, Shanxi Province were studied. Using a flow displacement experimental system, CO₂ displacement of CH₄ experiments were conducted under different bedding angles. The variation patterns of displaced gas composition, gas flow rate, displacement efficiency, and storage capacity with bedding angle were analyzed during the displacement process. The results indicate: An increase in the angle between the bedding plane and the seepage direction significantly prolongs the breakthrough time of CO₂. The steeper the bedding angle, the slower the rate of change in outlet gas composition. The relationship between inlet and outlet flow rates follows the pattern 0 > 30 > 60 > 90°. The relationship for outlet CH₄ flow rate aligns with outlet flow rate in the early stage of the experiment, shifting to 90 > 60 > 30 > 0° in the later stage. At the end of the first displacement stage, CH₄ recovery rates followed 0 > 30 > 60 > 90°. By the end of the second stage, recovery rates shifted to 30 > 0 > 60 > 90°. Upon completion of the entire displacement process, the 30°-layered coal achieved the highest CH₄ recovery rate of 67%. The 30° bedded coal exhibited the lowest displacement ratio and the most effective replacement. Throughout the displacement process, CO₂ penetration consistently followed the pattern 0 > 30 > 60 > 90°, and non-0° bedded coal had not reached adsorption equilibrium for CO₂ by the end of displacement. Furthermore, the 90° bed coal achieved a storage rate of 81.59%, demonstrating the best storage effectiveness. These findings provide crucial insights for optimizing CO₂ injection strategies to enhance coalbed methane extraction.

Key words: bedding angles, CO₂ displacement of CH₄, recovery rate, displacement ratio, storage effectiveness