Pore Structure Characteristics of Deep Coal Reservoir and Its Control Mechanism on Two‐Phase Occurrence of Coalbed Methane

Deep coalbed methane (CBM) is an important field for increasing natural gas production. This study investigates the pore structure and fractal characteristics of the No. 15 coal seam in the Yushe‐Wuxiang block through integrated experiments, including high‐pressure mercury intrusion, low‐temperature nitrogen adsorption, and methane (CH ₄ ) isothermal adsorption. The primary controls on pore fractal parameters and their influence on gas occurrence states are elucidated. Results indicate that specific surface area and pore volume are predominantly provided by micropores (2.5~3.0 nm) and pores larger than 170 nm, respectively. Fractal dimensions D ₁ and D ₂ range from 2.4391 to 2.7068 and 2.2811 to 2.5789, controlled mainly by micropore surface area and maceral composition. A greater difference between D ₁ and D ₂ correlates with higher nitrogen adsorption capacity. CH ₄ is primarily adsorbed in micropores, with its maximum adsorption capacity governed by micropore‐specific surface area and volume. Free gas content shows positive correlations with micropore‐specific surface area and volume, as well as mesopore volume, whereas the overall storage capacity of free gas is ultimately determined by fracture development scale.