3D Reconstruction of Pore and Fracture Structures in Crushed Soft Coal with Low Permeability and Its Permeability Analysis: Implications for the Design of CO(2) Injection and CH(4) Production

[Image: see text] In order to improve the CO(2) injection and CH(4) production efficiencies during the CO(2)-ECBM process, it is necessary to clarify the relationship among the complexity of pore and fracture structures, the typicality of the fluid migration path, and the heterogeneity of reservoir permeability. In this study, crushed soft coal with low permeability from Huainan and Huaibei coalfields of China was taken as the research object. First, the three-dimensional (3D) visualization reconstruction of pore and fracture structures was realized. Second, the equivalent pore and fracture network model was constructed. Finally, the permeability evolution and its anisotropy of the coal reservoir were dynamically demonstrated. In this study, the implication of surface porosity on the heterogeneity of pore and fracture structures was first discussed, followed by the implication of coordination number on the anisotropy of fluid flow, and finally, the influence of the anisotropy of fluid flow on the CO(2)-ECBM process was discussed. The results show that the equivalent pore and fracture network models of the reservoir structure can be constructed based on the digital rock physics technology. The analysis results of porosity, interconnected porosity, typical path of fluid migration, absolute permeability, and surface porosity of each sample have good consistency in characterizing the complexity of pore and fracture structures and the heterogeneity of permeability. The average coordination numbers of RL and LZ samples are 5.99 and 5.78, respectively, and the number of pores and throats is well-balanced, which indicates that LZ and RL collieries are suitable for the development of CO(2)-ECBM industrial tests. When the interconnected pores and fractures are mainly developed vertically and horizontally, the construction of drilling technology of the CO(2)-ECBM process should be mainly designed for vertical wells and horizontal wells, respectively. This study has important theoretical and practical significance for the industrial testing and commercialization of CO(2)-ECBM technology in crushed soft coal with low permeability.