Comparative Analysis of Pore Structure and Methane Adsorption Capacity in Deeply Buried Coal and Coal‐Bearing Shale: A Case Study of the Huoshiling Formation in the Wangfu Sag, Southern Songliao Basin

ABSTRACT Deep coalbed methane and coal‐bearing shale gas represent strategic frontiers in unconventional natural gas exploration, where the co‐production of these resources has emerged as a vital development trend. However, these deeply buried reservoirs exhibit strong heterogeneity and complex pore structures, and studies quantitatively characterizing their fractal features and the specific controls of these features on methane adsorption capacity remain relatively limited. To address this, this study integrates low‐pressure CO 2 adsorption, low‐temperature N 2 adsorption, and high‐pressure methane isothermal adsorption experiments to comparatively analyse deeply buried coal and coal‐bearing shale samples from the Huoshiling Formation in the Wangfu Sag, southern Songliao Basin. The results indicate that deeply buried coal possesses a significantly higher methane adsorption capacity (average Langmuir volume of 8.99 cm 3 /g) compared to coal‐bearing shale (5.26 cm 3 /g), primarily due to the dominance of micropores which contribute 95.22% of the total specific surface area. Fractal analysis reveals that the adsorption capacity of deeply buried coal is strictly controlled by micropore heterogeneity, showing strong positive correlations with the micropore fractal dimension ( D C ), total organic carbon, and vitrinite content. Conversely, the adsorption capacity of coal‐bearing shale is principally governed by mesopore development and clay mineral content, exhibiting a significant positive correlation with the mesopore surface fractal dimension ( D N −1 ) rather than micropore parameters. These findings elucidate the distinct adsorption mechanisms in deep coal measures and provide a theoretical basis for interval selection in the co‐production of coal‐measure gas.