Study on multi-scale characterization and fractal characteristics of coal pore structure in Wuyang Coal Mine of Luan Mining Area

In order to explore the microscopic pore structure characteristics and fractal law of coal reservoir in Wuyang Coal Mine of Lu 'an mining area, the coal samples of No.3 coal seam in Wuyang Coal Mine were selected, and the microscopic morphology, pore structure and surface complexity were characterized by scanning electron microscopy (SEM), low temperature liquid nitrogen adsorption experiment and FHH fractal model. The results show that the matrix of coal sample is relatively dense, mainly develops pores and dissolution pores, and is accompanied by micro-fractures. The pore structure is mainly mesoporous with an average pore diameter of 8.255 nm. The pore volume is mainly concentrated in the range of 10-50 nm and > 50 nm. The nitrogen adsorption isotherm is type IV and has a H3 hysteresis loop, indicating that the pore morphology is mainly slit-like pores formed by irregular particle accumulation. FHH fractal analysis shows that the pore structure has obvious segmentation characteristics. The surface fractal dimension (D1) of the low pressure zone is higher (reflecting the roughness of the pore surface), and the fractal dimension (D2) of the high pressure zone structure is relatively low (reflecting the pore size distribution tends to be concentrated). The research shows that the coal reservoir in Wuyang Coal Mine has formed a multi-scale pore system dominated by mesopores, accompanied by macropores and fissures. The mesopores dominate the gas adsorption capacity, while the macropores and fissures provide channels for gas migration. The synergistic effect of the two determines the adsorption-diffusion-seepage characteristics of the coal reservoir.