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

Abstract

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.

Adsorption Factors in Enhanced Coal Bed Methane Recovery: A Review

“…However, even though CO 2 is preferentially adsorbed increasing the percentage of CO 2 in the gas mixture makes it more difficult to desorb methane [99]. This phenomenon occurs because CO 2 alters the coal pore sizes via internal and external expansion effects [137]. The injection of pure CO 2 also results in swelling of the coal such that methane extraction is inhibited.…”

“…Compared with non-pressurized methods, pressure-based techniques can show initial fracturing and tend to indicate higher gas release volumes [133]. Increases in the adsorption pressure promote expansion of the coal matrix that in turn reduces the cleat apertures and closes pre-existing fractures [39,[134][135][136][137]. These phenomena decrease the permeability of the coal and inhibit methane production [24,118].…”

The Effectiveness of the Continuous and Cyclic Method on CO<sub>2</sub>-ECBM

“…During the last stage of the process, the conditions stabilize, and no traces of methane are detected in the outflow. As the adsorption of CO 2 increases, there is also a corresponding increase in porosity [27]. As the permeability of coal decreases, the rate of CO 2 flow gradually slows down, leading to a breakthrough at the outlet, and results in a CO 2 concentration of 90% [28].…”

Multiscale model for flow and transport in CO2-enhanced coalbed methane recovery incorporating gas mixture adsorption effects

“…The two coordinates x and y represent now micro and macroscale (or fast and slow coordinates respectively) so that we have y = x/ε. We postulate the ansatz similar to (12) with the same derivation rule as (13).…”

“…In this paper, we aim at clarifying this issue by developing a new multiscale model for flow and transport in dual porosity coalbed methane reservoir, which is coupled with the three-scale poromechanical model reported in a previous work [8]. Modeling of the coupling between transport and poromechanics problems in coal seam is well reported in the literature and classically described by dual porosity type models combined with Langmuir isotherm to compute gas adsorption in the coal matrix [9,10,11,12,13]. Moreover, modeling of CO 2 -enhanced coalbed methane recovery has showed important improvement of methane production curve and matrix swelling phenomena inducing cleat closure [10,11,12,14].…”