Comparative analysis of pore structure and fractal characteristics of micropores in medium and high rank coals——Taking the typical mining area of western Guizhou and eastern Yunnan as an example

In order to clarify the micropore pore structure characteristics of medium and high rank coal reservoirs, based on low temperature CO₂ adsorption test and surface/volume fractal theory, the structure and fractal characteristics of medium and high coal rank micropores (0.40∼2nm) were analyzed. The results show that with the increase of coal metamorphism, the pore size of coal reservoirs changes from 0.55∼0.8nm to 0.5∼0.7nm, and the pore size is 0.5∼0.9nm. Microporous pores have good fractal characteristics, D_av1av2 indicating stage the pore volume heterogeneity increases with the pore size in the pore range. Dav2 is positively correlated with the maximum vitrinite reflectance, indicating that the pore volume heterogeneity increases with the pore size in the micropore range. The heterogeneity of the surface area of the adsorption pore is far more complicated than the volume heterogeneity, D_as1< D_as2⩾D_as3, indicating that the surface heterogeneity of the micropore decreases with the decrease of the pore size and tends to be stable; As the degree of metamorphism of coal increases. And the study shows that the influence of coal rank on surface heterogeneity decreases with the decrease of pore size. (paper)