Full‐Scale Pore Structure of Deep Coals and Its Relationship on Coal Facies: A Typical Case and Experimental Study

The pore structure of coals significantly affects storage and migration of coalbed methane (CBM). In this study, high‐pressure mercury intrusion (HPMI), low‐temperature N 2 adsorption (LT‐N 2 A), low‐temperature CO 2 adsorption (LT‐CO 2 A), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) tests were employed to characterise the full‐scale pore structures of the Jurassic Xishanyao Formation (J 2 x) and Badaowan Formation (J 1 b) coals. Additionally, the influence of coal facies on pore structure was confirmed using maceral and proximate analysis. The results indicate that pore structures and coal facies of J 2 x and J 1 b coals exhibit distinct differences with regularities. The J 2 x coals are associated with arid forest swamps and upper delta plains, while J 1 b coals correspond to humid forest swamps and lower delta plains. Vitrinite content, ash yield, volatile yield, micropore proportion, vitrinite/inertinite ratio (V/I), and gelation index (GI) increase from J 2 x to J 1 b coals. In contrast, inertinite content, fixed carbon, mesopores and macropores proportions, texture preservation index (TPI), and vegetation index (VI) decrease. These changes suggest variations in plant types, water cover, and redox conditions in the paleoenvironment. From J 2 x to J 1 b coals, the increase in water cover, the reduction of woody plants, and the enhancement of reducing conditions lead to corresponding changes in pore structure.