## 3 Numerical Simulation Results and Analysis
This observation suggests that high-pressure water injection can effectively increase water volume, expand the wetting range, and shorten the injection time, thereby saving construction time. Figure 6 illustrates the temporal variation of seepage velocity around the borehole. The curve representing 4 Mpa exhibits a distinct inflection point at 18 h, while the 10 Mpa curve shows an inflection point at 24 h. The 15 Mpa curve displays inflection points at 18 h, 24 h, and 36 h, while the 20 Mpa curve exhibits inflection points at 24 h, 36 h, and 42 h. The 25 Mpa curve shows inflection points at 12 h and 24 h. All curves demonstrate a significant flattening after 42 h, indicating a slow decline in flow velocity within the coal seam surrounding the borehole. Therefore, 42 h represents the time threshold for injection pressure. Within this timeframe, the wetting effect of water injection is pronounced under all injection pressures, whereas the effect becomes less evident beyond 42 h.  
Figure 5: Cloud plot of seepage velocity around the radial direction of the borehole with time under different injection pressures. Analysis of Water Distribution Law of Radial Seepage in Borehole under Different Pore Water Pressure  
To better illustrate the wetting effect of coal seam water injection, a numerical simulation was conducted on a unidirectional injection borehole with a length of 85 m. A cross-section was set at a radial distance of 1.5 m from the injection borehole to analyze the temporal variation in moisture increase around the borehole under different injection pressures. The simulation results are presented in Figure 7.  
The simulation results demonstrate that the increase in moisture content within the coal seam under different injection parameters is reflected by the turbulent dissipation of the fluid. The red areas represent maximum dissipation, indicating a higher fluid flow around the borehole, while the blue areas represent minimal dissipation, indicating lower fluid flow. During borehole injection, the fluid initially passes through a solid section. At injection pressures of 4 Mpa and 10 Mpa, the fluid dissipation gradually decreases, resulting in a less effective moisture enhancement effect. At an injection pressure of 4 Mpa, as the injection time increases, the color contour plots clearly indicate a higher fluid flow dissipation within the injection borehole at 12 h, leading to a more pronounced moisture enhancement effect. At this point, the moisture increase within the borehole is approximately 0.4%. Under an injection pressure of 10 Mpa, the moisture enhancement effect is approximately 3-4 times greater. For injection pressures of 15 Mpa, 20 Mpa, and 25 Mpa, a certain degree of dissipation occurs at the borehole entrance as the water is injected at an injection time of 36 h. Higher injection pressures result in more pronounced dissipation. Notably, the moisture enhancement effect under 15 Mpa is approximately twice that of 10 Mpa. Furthermore, starting from an injection pressure of 15 Mpa, the analysis of color changes in the images reveals that fluid flows more easily during the early stages of injection, and the moisture increment increases with higher injection pressures. Taking the 12-hour injection time as an example, the moisture increment within the borehole under 15 Mpa is approximately 1.2%, which is higher than the 0.8% observed under 4 Mpa. Under 25 Mpa, the moisture increment within the borehole can reach 1.8%, which is higher than the 1.4% observed under 4 Mpa. Figure 6: Plot of radial seepage velocity with time in borehole.