The effect of adsorption-induced swelling on porosity based on the transient coal swelling model

Coal swelling induced by gas adsorption is a well-known phenomenon. In order to enhance coalbed methane production and greenhouse gases sequestration, adsorption phase should be understood deeply, and it is the most basic and the most important. Experimental measurements performed in this work on three samples from Kaiping Basin using carbon dioxide. Basing on Gibbs adsorption model, the steady-state swelling model is developed, which also assume that the change of the coal surface free energy induced by adsorption is equal to the change of energy caused by adsorption deformation. The mass balance equation of gas in porous media is combined with the steady-state swelling model. The dynamic variation of porosity and internal gas pressure of coal are integrated into the transient swelling model. The steady-state model and transient model are applied to describe the experimental volumetric strain. The results show good agreement between the models and the experimental strain data. The coal pore tests with different probe scales are also used to investigate the true pore size distribution and porosity, which provide more accurate parameter values. According to the transient swelling model, the effects of porosity on adsorption-induced swelling are further analyzed