The seepage characteristics of coal under the hydraulic-mechanics coupling conditions considering the variation of porosity

In order to study the seepage law of coal under the hydraulic-mechanics coupling conditions, the seepage characteristics under different axial stresses and water pressures were carried out using the multifield coupling seepage test system. Results show that the porosity increases as the water pressure rises. Stress is the basis factor of leading to changes in seepage properties. The relationship model between water pressure and porosity was established. The UDF program of porosity variation with water pressure was loaded into FLUENT for the dynamic numerical simulation study of seepage. The simulation results show that at a certain water pressure, the greater the axial stress is loaded, the greater the velocity as well as the range of infiltration within the coal will be. When the stress conditions are fixed, with the increases of water pressure, the seepage velocity and the range of infiltration are also greater. It can be seen that stress and water pressure have a significant influence on water injection seepage. Comparing the simulated results of permeability with the experimental results, it is found that the simulated results with fixed porosity bring larger deviations compared with the experimental ones. The simulation results considering the variation of porosity are closer to the experimental results.