3D microfracture network and seepage characteristics of low-volatility bituminous coal based on nano-CT

Abstract Microfractures in the coal reservoir contribute greatly to the exploitation of coalbed methane. In this study, the 3D microfracture structure of low-volatility bituminous coal is characterized by using nano-computed tomography (nano-CT), and the seepage characteristic of the single-phase water flow in the microfracture network is simulated by Avizo and Comsol. The result shows that the low-volatility bituminous coal HB02 has significant structural heterogeneity and is dominated by type D microfractures on the nanoscale. By pore network modeling analysis, the connected microfracture network consists of 4945 pore bodies and 7194 pore throats, and the connected porosity is 1.96%. Additionally, as the pore diameter increases, the coordination number of the connected pores increases, but the shape factor decreases, indicating that larger pores have a better permeability and much rougher surface. Seepage simulation shows that the permeability of the microfracture network are strong anisotropic, and the microfracture structure has strong controlling effect on seepage. The permeability value in the horizontal (X-axis and Y-axis) direction is higher than that in the vertical (Z-axis) direction.