Migration mechanism of fine particles in aquifer during water injection

Water injection in aquifers to stabilize water level is a novel method to prevent shaft failure. However, with the progression of water injection, the flow rate of water injection decreases gradually. Through analysis, it is considered that the fine particles in sand migrate to form a dense structure, which hinders the increase of water flow. In order to investigate the migration mechanism of fine particles in the aquifer during water injection, experimental tests and numerical simulations were conducted in the present study. First, the physical experiment was designed, and it was shown that the water pressure difference between the two pressure gauges gradually decreased, while the water flow rate per hour slowly decreased. Furthermore, the permeability coefficient of sand near the outlet became smaller and smaller with the migration of fine particles, which indicated that the fine particles among sand grains migrated gradually from the water injection inlet to the outlet. Additionally, the water flow channels formed slowly. Then, the microscopic mechanism of fine particle migration was studied using particle flow code numerical simulation. During water injection, water pressure and porosity of sand decreased from the water injection inlet to the outlet, while the coordination number of particles increased on the whole. Contact force chain gradually strengthened near the outlet side during water injection. The trends of force chain distribution, the coordination number distributions and the evolution of porosity were consistent, which highlighted the process of fine particles migrating from the injection inlet to the outlet in the aquifer.