The strong hydrophobicity and low pore permeability of coal seams limit the effectiveness of practical applications in water injection. To reveal the interface characteristics and pore structure changes during the coal wetting process, the wetting process of bituminous coal (BC) was investigated using experimental and molecular dynamics simulation (MD) methods. The MD simulations of the large-scale surface wetting and internal infiltration systems constructed were in good agreement with the results of the contact angle and wetting heat tests. It shows that the formation of the wetting interface is primarily manifested in the surface wetting and initial internal infiltration stages. During these periods, the number of hydrogen bond sites between H₂O and BC molecules is positively correlated with the diffusion coefficient of H₂O. At the same time, the diffusion behavior of H₂O also contributes to the development of internal pores within BC. Macroscopically, there is a more pronounced development of mesoporous and macroporous, resulting in a 2% increase in total pore volume and a 26.71% enlargement of the average pore diameter. Microscopically, H₂O exhibits significant pore-expanding capabilities with the increasing pore size. Therefore, by increasing the number of hydrogen bond sites in the wetting interface, the wetting permeability of coal seam water injection can be improved, which provides valuable theoretical guidance for optimizing the coal seam water injection technology.
 

Coal seam water injection,Wetting interface,Pore evolution,Molecular dynamics simulation,Bituminous coal