Study on heterogeneous characteristics of topology structure of low-rank coal seepage pores in Ordos Basin

The microscopic connected pore clusters of coal are the decisive factor of coal permeability, and its special topological structure heterogeneity is the fundamental cause of coal permeability anisotropy. In order to reveal the heterogeneous characteristics of the topological structure of connected pore clusters, X-ray μCT scanning is performed on low-rank coal in Ordos Basin, and the micro-spatial structure model of coal pores was reconstructed. The largest connected pore cluster was extracted using AVIZO software, and its equivalent pore network topology was constructed. The relationship between the pore shape factor and the small diameter and surface area of the pore is analyzed, and the change law of the connection characteristics and the fractal dimension in space is discussed. The results show that: the pore shape factor has an exponential relationship with the equivalent diameter, and a linear relationship with the pore surface area. The larger the seepage pore space inside the connected pore cluster, the more irregular its shape and the stronger the heterogeneity. The Euler number of each section of the connected pore group of low-rank coal varies greatly, the connectivity has stronger heterogeneity, the degree of pore dispersion is higher, but the roughness is lower.