Tectonic coals in coal seams may affect the process of enhanced coalbed methane recovery with CO₂ sequestration (CO₂-ECBM). The main objective of this study was to investigate the differences between supercritical CO₂ (ScCO₂) and intact and tectonic coals to determine how the ScCO₂ changes the coal’s properties. More specifically, the changes in the tectonic coal’s pore structures and its gas desorption behavior were of particular interest. In this work, mercury intrusion porosimetry, N₂ (77 K) adsorption, and methane desorption experiments were used to identify the difference in pore structures and gas desorption properties between and intact and tectonic coals after ScCO₂ treatment. The experimental results indicate that the total pore volume, specific surface area, and pore connectivity of tectonic coal increased more than intact coal after ScCO₂ treatment, indicating that ScCO₂ had the greatest influence on the pore structure of the tectonic coal. Additionally, ScCO₂ treatment enhanced the diffusivity of tectonic coal more than that of intact coal. This verified the pore structure experimental results. A simplified illustration of the methane migration before and after ScCO₂ treatment was proposed to analyze the influence of ScCO₂ on the tectonic coal reservoir’s CBM. Hence, the results of this study may provide new insights into CO₂-ECBM in tectonic coal reservoirs.

The effect of different acids on the pore structure and fractal characteristics of micropores and mesopores was determined with the help of low-temperature liquid nitrogen adsorption, X-ray diffraction, and the Frenkel–Halsey–Hill (FHH) model by using Yuwu coal as a sample and placing it in acidic environments, such as HF, HCl, HNO₃, and CH₃COOH. The results show that the acidization effects of HF and CH₃COOH are separately dominated by the micropore and mesopore formation effects, while HCl and HNO₃ mainly play their roles in expanding mesopores. After acidization, the surface fractal dimensions D₁ and D₁′ of micropores and mesopores in coal are always negatively correlated with the total specific surface area S_BET, specific surface area S_mic of micropores, and specific surface area S_mes of mesopores. After being acidized by HF, D₂ is negatively correlated with the total volume V_tot and the corresponding micropore volume V_mic, while acidization with HCl and HNO₃ leads to the opposite result. After being acidized by CH₃COOH, D₂ has a negative correlation with V_tot and a positive correlation with V_mic. The structural fractal dimensions D₂′ of mesopores in samples acidized by HF and CH₃COOH are positively correlated with both the volume V_tot and mesopore volume V_mes, while it is the opposite for samples acidized by HNO₃. D₂′ of coal samples acidized by HCl is negatively correlated with V_tot while positively correlated with V_mes.