Research on the wetting interface characteristics between water molecules and bituminous coal based on pore evolution and molecular dynamic theory

Bituminous coal (BC) poses a challenge to the implementation of coal seam water injection technology due to its high hydrophobicity. To investigate the wetting interface characteristics between water molecules and BC, the wetting process of BC was analyzed based on pore evolution and molecular dynamic theory. It is found that there is a significant development of mesopores and macropores following wetting, resulting in a 2% increase in total pore volume and a 26.71% enlargement of the average pore diameter. Microscopically, during the surface wetting stage and initial internal permeation stage, water molecules exhibit strong pore expansion ability due to numerous hydrogen bond interaction sites. The number of hydrogen bond interaction sites between water molecules and coal molecules is positively correlated with the diffusion coefficient of water molecules. Additionally, the diffusion behavior of water molecules resulted in a 14.47 Å increase in the maximum pore size of bituminous coal in surface wetting system and a 6.93 Å increase in internal infiltration system, with significant increases observed in pores (>30 Å) for both systems. These research findings have revealed the wetting interface characteristics of BC, providing valuable theoretical guidance for optimizing coal seam water injection technology.