Study on 3D spatial characterization analysis and water injection seepage numerical simulation of coal micro-pore/fracture

Abstract

ABSTRACT To establish a geometrical model to characterize the true microscopic pore and fracture structure of a coal mass and to further study the seepage law of water injection into the coal mass, after three-dimensional X-ray scanning of a coal sample, a three-dimensional reconstruction of the coal sample and a pore network model based on part of the coal sample were generated by means of Avizo three-dimensional visualization software. We conducted a quantitative statistical analysis of the pore numbers, pore throat numbers, coordination numbers and other parameters, and the characteristics of the microporosity connectivity and development degree of the coal were analyzed in depth. ANSYS finite element software was used to simulate the model of water injection seepage under a pressure of 4 MPa. The results show that the pore size distribution of the gas fat coal is irregular: the analyzed sample has a total of 651 pores, a total of 655 pore throats, surface fractal dimensions concentrated at 1.40, and a volume fractal dimension of 2.44. Additionally, 80% of the pore radii range from 0–6 μm, and more than 58% of the pores have coordination numbers of 1–7. Thus, a complex pore topology is observed. Along the water seepage path, the seepage pressure gradually decreases.