Law of water migration during spontaneous imbibition in loaded coal and its influence mechanism

The permeation process of water introduced by coal seam water injection forces the original fractures in the coal seam to communicate with each other or form a new fracture network， which provides a network channel for the flow of water in the coal seam. Water and gas interact with each other in the process of spontaneous imbibition. The imbibition process is an effective wetting process， and the wetting effect is closely related to the water trans⁃ port distance. To reveal the influence mechanism of water transport in the process of spontaneous imbibition of loaded coal， the self-developed water transport distance test system during spontaneous imbibition in the loaded coal is used to carry out the experiment of spontaneous imbibition in the loaded coal. The results show that water and coal become a system after water intrudes into the coal. The resistivity of coal sample changes suddenly， rapidly and gradu⁃ ally. In the process of isobaric imbibition， the greater the loading stress， the smaller the average pore diameter of the vertical capillary in the multi⁃branch capillary bundle model， and the greater the water transport distance. The wa⁃ ter transport distance in loaded gas⁃bearing coal is greater than that in the loaded non gas⁃bearing coal during the iso⁃ baric imbibition under the same loading stress. The capillary tube closed at one end and the capillary tube open at both ends with simultaneously spontaneous from both ends have a plugging effect. In the process of capillary imbibition with one end open， the greater the gas pressure around the capillary， the more obvious the plugging effect. In the process of isobaric imbibition， the smaller the adsorption equilibrium pressure is， the longer the liquid adsorption length of the horizontal capillary in the multi⁃branch capillary bundle model is. Also， the slower the water transport rate of the vertical capillary in the multi⁃branch capillary bundle model is， the better the wetting effect of water on the micro pores is. The research results provide a theoretical guidance for clarifying the wetting mechanism of gas⁃ bearing coal in the spontaneous imbibition process of coal seam water injection.