Visualization characterization of minerals touched by interconnected pores and fractures and its demineralization effect on coal permeability during CO2-ECBM process based on X-ray CT data

Abstract

The purpose of this study is to visually reconstruct the minerals touched by connected pores and fractures and reveal their demineralization process, which is of great significance for the analysis of permeability evolution during CO2-ECBM process. Two samples collected from Qinshui basin were taken as the research object. Firstly, the definition, reconstruction, and demineralization processes of such minerals were realized, and the evolution of pore network model under different demineralization efficiencies was discussed. Then, the analysis of geological and mathematical models for permeability evolution was realized with the pore network model as the geological carrier, and the influence of such minerals under different demineralization efficiencies on coal permeability was discussed. Finally, the application and its mechanism of demineralization process in CO2-ECBM process were further discussed. The results show that the minerals touched by interconnected pores and fractures extracted can be divided into five groups with the same volume, that is the demineralization efficiency is 20%, 40%, 60%, 80% and 100%, respectively, and each group can be independently removed from sample to merge into the pore and fracture space. The differences in spatial distribution between the aggregate phase of pore, fracture and mineral and the mineral phase touched by interconnected pores and fractures indicate that the presence of minerals touched by interconnected pores and fractures will have a great influence on the connectivity of pore and fracture. The connectivity of pore and fracture gradually increases with the increase of demineralization efficiency, and only the removal of such mineral can produce good connectivity. With the increase of demineralization efficiency, pore and fracture are completely interconnected, and pore volume and throat area significantly increase, which can form better pore network model. With the gradual increase of demineralization efficiency, the minerals in interconnected pore and fracture are gradually reduced, and the secondary porosity is gradually increased, which leads to the gradual expansion of the size of pore and fracture, and the gradual increase of the connectivity. The demineralization of the minerals touched by interconnected pores and fractures during the CO2-ECBM process is conducive to the realization of engineering of CO2-ECBM technology.