Numerical Simulation Study of Radial Seepage Evolution of Coal Seam Water Injection Borehole

Abstract

Coal seam water injection is widely used to reduce dust pollution and mitigate rock burst disasters. Evaluating its effectiveness depends on understanding the water content and distribution within the coal seams. Therefore, understanding the water content and its distribution after injection is crucial for optimizing the injection param. A theoretical model based on hydromechanical interaction and seepage theory was developed to analyze changes in injection pressure, permeability, and water content. Numerical simulation was used to analyze the wetting radius and seepage rates under different injection pressures and axial stresses. The results showed that the effective wetting radius increased with higher injection pressure, which improved the penetration range and effectiveness of water injection. At 4 MPa pore water pressure, the wetting front was 6 m from the borehole and increased to 10 m at 25 MPa. The seepage velocity within the coal seam also increased with higher injection pressures, reaching a maximum of more than 23.75 m/s at 25 MPa, which was about 4.9 times higher than the 4.85 m/s observed at 4 MPa. The application of various axial stresses gradually increased the internal porosity of the coal, which extended the influence of water pressure and improved the effectiveness of water injection. As a result, the moisture content of the coal increased significantly. At 30 MPa axial stress, the wetting range increased by 20% compared to 10 MPa. These results have significant practical value for the design and implementation of coal seam water injection param under field conditions.