Law of water migration inside the water-injected coal base on the joint analysis of cross-scale CT images

The size of the CT scan specimen and the analytical scale of the CT image are mutually restricted, making it impossible to achieve high-precision imaging for the larger-sized specimens currently used in the laboratory for water injection experiments. Accordingly, the subsequent simulation analysis mostly studies the micro-and meso- scale models. Research on the macro-and meso-scale models that are close to reality is scarce. To solve the above mentioned problems, the method of cross-scale CT image joint analysis was used to reconstruct the pore and fracture structural model of a cubic specimen with a side length of 10 cm and a cylindrical specimen with a diameter of 1 cm and a height of 1.5 cm. The cube and cylindrical specimens with the same sampling point are assumed to have the same pore size distribution, and the parameters of the small pores in the unidentified area of the cube specimen are converted. Accordingly, a composite model that combines the geometric structure of the pores and fractures of the cube specimen and the conversion parameter data is formed. The mercury intrusion method was also used to verify the accuracy of the pore parameters of the CT scan reconstruction analysis. Subsequently, the CT images were digitized and imported into the simulation software to establish a large-scale simulation model considering the distribution of pores and fractures and the contribution of small pore parameters and compared with the analytical results of the isotropic model and the connected pore and fracture model. The accuracy of the composite model combining geometric structure and conversion parameter data is determined. The law of water migration in the water injection process of different pore and fracture structure types is also revealed.