Experimental verification of the water-methane displacement effect in gassy coal

To verify that water-methane displacement effect in gassy coal exists objectively, a pseudo-triaxial experimental system of water-methane displacement was independently developed and tested. First, methane was injected into the standard cylindrical coal sample until the methane adsorption equilibrium state was reached. Then, the methane in the coal sample spontaneously desorbed. Finally, water was injected into the coal sample. It is shown that: 1) water-methane displacement effect exists objectively; 2) water-methane displacement effect includes the process of free methane generated by competitive adsorption and displacement desorption effect, the consumption caused by methane pressure increase, and water driving methane; 3) competitive adsorption and displacement desorption between methane and water can generate free methane. Due to water injection, the increase of methane pressure leads to consumption of free methane. The net free methane of the combined action provides methane source for the water-methane displacement effect. [Received: August 19, 2017; Accepted: February 2, 2018]