Study on evolution characteristics of coal fracture structure and fluid migration law under the action of water-loaded particles

The amorphous particles such as coal rock contained in the coal seam enter the fracture channel with the pressure water during the water injection process, which directly affects the structural characteristics of the fracture channel, and then changes the seepage behavior of the pressure water in the fracture structure. In order to clarify the migration behavior of water-loaded particles in the process of coal seam water injection, clarify the evolution characteristics of fracture structure and the law of fluid migration, the traditional cubic law is used to describe the linear seepage process inside the filling fracture. Combined with the capillary model, a fracture seepage damage model considering filling particles is constructed, and the hydraulic transmission characteristics in the fracture channel filled with particles are revealed by mathematical analysis. Subsequently, the coal seam fracture images were collected by a high-definition camera, and the image processing was used to ensure that the fracture geometry was consistent with the actual coal seam fracture distribution. COMSOL was introduced to construct a two-dimensional numerical solution model. The migration process of water-loaded particles in single fracture and fracture network environment was numerically simulated, and the migration trajectory and deposition position of particles at different flow rates were analyzed to reveal the interaction between particles and fluids. The results show that the flow velocity in the fracture depends not only on the porosity, but also on the particle diameter and hydrodynamic viscosity. In a single fracture, the higher flow velocity prolongs the migration distance of particles, but the particle distribution is more dispersed. The lower flow velocity enhances the vortex effect and promotes the aggregation and deposition of particles. In the fracture network, the migration behavior of particles is more complex, and the migration of particles is affected by the main fracture and the secondary fracture.