## 3 Results and Discussion
### Effect of Wettability on Flow in Pore Media
Figure 8: Flow snapshots of CH\({}_{4}\) at breakthrough and stabilization in porous media with different wetabilities: (**a**) Flow snapshots of CH\({}_{4}\) at breakthrough in porous media with different wetabilities; (**b**) flow snapshots of CH\({}_{4}\) at stabilization in porous media with different wetabilities. Figure 9: Velocity snapshots of CH\({}_{4}\) at breakthrough and stabilization under different wettability conditions with \(\theta_{c}=\pi/6\) and \(\pi/3\) (the upper part shows the breakthrough moment, and the lower part shows the stabilization moment): (**a**) Flow snapshots at breakthrough and stabilization for porous media with a contact angle of \(\theta_{c}=\pi/6\); (**b**) flow snapshots at breakthrough and stabilization for porous media with a contact angle of \(\theta_{c}=\pi/3\). To quantitatively analyze the CH4-water displacement process under different wettability conditions, the saturation (Sn) curves of methane at breakthrough and after reaching stability under different contact angles are plotted, as well as the methane concentration curves over time. As shown in Figure 10a, both at breakthrough and after stabilization, as the contact angle gradually increases, more water is displaced from the pores, increasing the CH4 saturation and improving displacement efficiency. However, an exceptional case occurs at \(\theta_{c}=\pi/3\), caused by backflow due to the formation of preferential paths, which can also be observed in Figure 10a. From Figure 10b, it can be observed that under different wettability conditions, CH4 saturation in the initial stage of entering the porous media generally shows a pattern of initial growth followed by stabilization. Additionally, this growth interval increases with the contact angle. With smaller contact angles, capillary forces are stronger, binding the fluid in smaller pores and making it less mobile. As the contact angle increases, capillary forces weaken, allowing the fluid to move and diffuse more easily within the pores, leading to a rapid increase in the saturation of the non-wetting phase (CH4). Figure 10: Relationship between non-wetting phase CH4 saturation, contact angle, and time: (**a**) Relationship of non-wetting phase CH4 saturation at breakthrough and stabilization in porous media with different wettabilities; (**b**) relationship between non-wetting phase CH4 saturation and time under different wettability conditions. Based on the analysis of Figures 8-10, it is evident that when the porous media is hydrophilic, capillary force is the main driving force. The CH\({}_{4}\)-water two-phase flow pattern is primarily capillary fingering with low displacement efficiency. When the porous media is neutral, both the capillary force and viscous force work together, resulting in a two-phase flow pattern which includes both capillary fingering and viscous fingering. Thus, the CH\({}_{4}\) displacement efficiency is improved. When the porous media is hydrophobic, viscous force becomes the main driving force, and the two-phase flow pattern completely shifts to viscous fingering, significantly enhancing CH\({}_{4}\) displacement efficiency. Therefore, in the actual CH\({}_{4}\) extraction process, the extraction efficiency can be improved by altering the wettability of the coal seam.