Theoretical model quantifies swelling in coal under gas adsorption, suggesting implications for permeability and methane extraction.
The volumetric response of coal with gas depletion in coalbed methane (CBM) reservoirs is a widely recognized fact. The adsorption-induced swelling has a significant impact on coal permeability, controlling the production efficiency of CBM. This phenomenon has received considerable implications on enhanced coalbed methane (ECBM) due to the injectivity of CO2. Previous research quantifies the adsorption-induced strain by applying the theory of surface energy assuming an isothermal process. Indeed, the heat is released during the adsorption process, modifying the thermal field at the adsorbate-adsorbent interface. The isosteric heat of adsorption measures the strength of the gas-solid interactions, which should be taken into consideration when quantifying the energy change at the adsorbate-adsorbent interface. This study introduces a theoretical model of adsorption-induced strain through an energy approach considering the heat released during adsorption. Following the modeling work, experimental investigations on volumetric changes of coal with respect to different gases were conducted. The measured swelling and shrinkage results fit in close agreement with the theoretical framework. Describing and predicting the deformation behavior of coal plays a significant role in controlling and utilizing coal mine gases. This model can be applied to permeability predictions, stress characterization, and coupled thermal-hydrological-mechanical-chemical (THMC) simulation of CBM production.
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Zhang et al. (2025) studied this question.
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