Heterogeneity and Controlling Factors of Pore and Fracture Structure Collected from Coal Seam 10 in Xinjiang

Heterogeneity of pore and fracture structures has become an important factor affecting the migration of methane and water in coal reservoirs. However, controlling factors of pore and fracture structure collected from coal seam 10 in Taliqike Formation, Kubai Coalfield, Xinjiang need to be studied. In this paper, carbon dioxide adsorption, cryogenic liquid nitrogen, and high-pressure mercury intrusion, as well as coal microscopic components, were used to study pore volumes and characterize pore diameter distribution heterogeneity. By the theory of single weight and multiple fractal formations, the heterogeneity of the pore fracture structure of coal reservoir is expressed, and the influencing factors of the heterogeneity of the pore fracture structure and the pore volume are also discussed. The results are as follows. (1) Micro-pore distribution presents a distinct bidirectional state, with the main peak at approximately 0.6 nm and 0.85 nm. Ro,max has an obvious influence on micro-pore volume. The single-fractal dimension of micro-pore is not affected by a micro-pore volume but is influenced by other factors such as Ro,max and microscopic composition. The heterogeneity of the low-value area controls the heterogeneity of micro-pore diameter distribution. (2) For lower Ro,max samples, mesopores of these samples are ink bottle-shaped pores, and the pore connectivity is poor. In contrast, meso-pore of higher thermal evolution coal samples are mostly simple pores, such as parallel plates. The main mesopores are 10–100 nm pores, accounting for 75% of the total meso-pore volume. For the single fractal dimension, D1 is greater than D2, which also shows that the heterogeneity of a pore structure greater than 4 nm is much stronger than that of a pore structure less than 4 nm in these samples. (3) For lower Ro,max samples, double S-shaped curves with distinct hysteresis loop are obtained, while samples of higher Ro,max samples show parallel curves, suggesting that macro-pore of this type of sample develops parallel plate-like pore. There is a positive relationship between D−10–D0 and D−10–D10, while D0–D10 and D−10–D0 have a weak correlation. With the increase of 2–10 nm pore volume, pore distribution heterogeneity of lower value area (D−10–D0) weakens. This indicates that pore volume is an important factor affecting the multifractal variation.