Imbibition Characteristics and Mechanism of Surfactant Water in Gas-Bearing Coal

In coal seams with high gas content, gas impeded pore wetting, resulting in a poor wetting effect and weak gas-liquid competitive adsorption during water imbibition. Although surfactant water was widely used to enhance coal wettability, existing studies mainly focused on surface wettability, while the internal imbibition-driven wetting and associated gas displacement in gas-bearing coal remain poorly understood, limiting its application in coal seam gas control. A gas-bearing coal imbibition testing system was developed to quantitatively characterize the imbibition characteristics of the surfactant water. For both water and surfactant water imbibition, the gas displacement amount increased with gas pressure, but the gas displacement ratio decreased. Under constant surfactant water concentration, higher gas pressure inhibited gas desorption in the pore with one end open and the other end closed (Pooc), but promoted it in a pore with both ends open (Pobe) due to restricted diffusion in the Pooc and enhanced gas migration in the Pobe. For the same gas pressure, higher surfactant concentrations increased both the gas displacement amount and the ratio. Phase-field simulations confirmed that surfactant water imbibed farther and exhibited stronger wetting effects compared with water. When coal seams primarily consisted of open-ended pores with limited connectivity, gas control could be achieved by synergistically combining permeability enhancement measures with surfactant-water injection technology. The results provided theoretical support for the application of high-gas coal seam surfactant water injection in gas control.