Physical chemistry mechanism of influence of liquid water on coalbed methane adsorption

Abstract

Free emission of mine gas brings out serious environmental pollution. Abundance of coalbed methane resource should be exploited, so cognition of coal adsorption characteristic has significance on the exploration and development of coalbed methane. Preparation of water injection coal sample and its isothermal adsorption experiment were carried out under simulated reservoir condition using coal samples from Feicheng mine in Shandong province of China. The experimental results indicated liquid water in coal has remarkable influence on coalbed methane adsorption. Then on the view of physics and chemistry, the essence of coal matrix adsorbing methane and the influence mechanism of gaseous and liquid water were analyzed, and the differences on adsorbing methane abilities of dry coal samples, equilibrium moisture samples and water injection samples were explained quantitatively. The conclusion is that the change of wetted coal matrix adsorbability is the fundamental reason for liquid water influencing coal adsorbability, comparing with dry or equilibrium moisture coal, which also effects on coalbed methane adsorption volume. The surface potential of wetted coal matrix, the long range force between coal and methane and methane density all can prove the change.