Micro-Pore Structure and Fractal Heterogeneity of Deep Coal Seam

Deep coalbed methane (CBM) is not only an important alternative resource but also plays a crucial role in ensuring energy security and optimizing energy structure in China. However, with the progress of exploration, the gas adsorption characteristics and heterogeneity of the coal reservoirs’ pore structure have become critical factors influencing the enhancement of CBM production capacity. This study investigates the micropore structure and fractal characteristics of medium-to-high rank coal samples from deep coal seams in the Benxi Formation, Ordos Basin. The primary objective is to examine the impact of thermal maturity on the evolution of micropore structures and their effect on methane adsorption. A series of coal samples with varying thermal maturities were analyzed using CO₂ adsorption. The results reveal that thermal maturity leads to a decrease in both specific surface area and pore volume, attributed to the collapse and compaction of pre-existing pores. Despite this, new micropores are formed at higher coal ranks, although their development is insufficient to fully offset the loss of pore volume. Fractal analysis demonstrates that thermal maturity reduces surface heterogeneity, rendering micropore structures more irregular and complex. These findings indicate that thermal maturation significantly influences the evolution of the pore structure, which, in turn, affects methane storage potential in deep coal seams.