Scale Effect of Coal Porosity and Permeability Characteristics Based on CT 3D Reconstruction from a Microperspective

In order to explore the impact of the scale effect on the coal seepage from a microscopic perspective, CT scanning experiments were carried out on coal samples selected from the Zhangcun Coal Mine in Shanxi Province. The scanned images were processed by means of the Avizo software, and the real pore fracture model of coal samples was established through the three-dimensional reconstruction technology. Based on the qualitative characterization of pores and fissures in the model, the microstructure of pores and fissures in coal is analyzed. The influence of the scale effect on the porosity and permeability characteristics of a coal seam is discussed by numerical simulation of the representative pores and fissures. The results show that the fractures in the coal sample are developed and have strong connectivity. 87% of the fractures are longer than 5000 mu m and wider than 1000 mu m. The permeability of coal samples is between 0.079 and 0.298 mD. With the increase of the scale of coal samples, the change process of the permeability can be divided into three stages: gradually increasing, slowly decreasing, and keeping steady. From the microscopic perspective, the porosity and permeability of coal samples are in accord with the cubic function relationship.