The mechanism and relief method of the coal seam water blocking effect (WBE) based on the surfactants

In order to study the mechanism and relief method of coal seam water blocking effect (WBE) to improve the efficiency of gas drainage, the causes and the influencing factors of the coal seam WBE are analyzed, and the critical micelle concentration (CMC), surface tension, viscosity and contact angle changes of the surfactants on the surface of coal are investigated. The capillary force and viscous hysteresis effect are the two reasons for WBE, which is affected by five factors: physical property, surface tension, contact angle, viscosity and intruding depth. The surfactants can reduce the surface tension of water, which decreases with the increasing surfactant concentration. Moreover, the anionic and nonionic surfactants to be reduced are higher than the cationic ones. The contact angle of the surfactant solution on the coal surface decreases with time. The greater the degree of coal metamorphism, the bigger the equilibrium contact angle, and the less the adhesion work of the surfactant solution on the coal surface. The anionic, cationic and nonionic surfactants all reduce the capillary force, and the anionic surfactant has the largest reduction amplitude of the capillary force. Therefore, the surfactant SDS can be selected as the best additive for removing the WBE, the reasonable concentration of which is 0.022%. The results reveal the mechanism of the WBE and provide a method to remove the WBE. (C) 2017 Published by Elsevier B.V.