Study on geometry and seepage evolution mechanism of fracture channels in granular filling coal

The seepage range of dynamic water in coal seam water injection technology directly determines the disaster prevention effect. However, in the process of coal formation, primary particles and secondary particles produced by mechanical crushing will fill in the fracture, which will increase the difficulty of water seepage. Therefore, it is of great significance to clarify the morphology and seepage evolution process of particle filling fracture channel for improving the effect of water injection and dust reduction in coal seam. In this study, a simulation experiment system was developed to explore the structural evolution of seepage channel in coal fracture. Then, computer graphics was used to quantitatively characterize the morphological structure changes of fracture channels. Finally, the permeability evolution law of fractures was explored in combination with the cubic law. The results show that the filling particle migration with water has a significant effect on the expansion and development of fracture channel structure and seepage capacity. After water injection migration, the geometry of water migration channel in fracture changed, which changed the void distribution in fracture and the migration path and space of fluid. With the particle migration out of the fracture, the original fracture structure of the coal sample is gradually opened. The seepage channel is expanded, and the gap width and permeability increase with the increase of water injection time and flow rate. With the increase of filling quality, the permeability of filling fracture in small particle size range decreases, and the permeability of filling fracture in large particle size range is opposite.