(396e) Modeling Gas Adsorption-Induced Swelling of Coals

Gas adsorption-induced swelling of coals can impact the recovery of coalbed methane and design of CO₂sequestration processes. The swelling of coals can alter the cleat permeability and affect the flow behavior of gas in the coalbed reservoir. Studies have indicated that the cleat permeability is related to coal mechanical properties and changes to permeability can be estimated based on volumetric strain measurements on coals.

Pan and Connell (2007) presented a theoretical model to investigate adsorption-induced swelling of coals. In this study, we implemented the Pan and Connell swelling model through application of the simplified local-density (SLD) adsorption model. The theoretically rigorous SLD model, when combined with the Pan and Connell swelling model, was found capable of representing precisely the swelling behavior of coals due to adsorption of gases such as carbon dioxide, methane and nitrogen. The relation between strain and surface potential was found to be linear for all three gases mentioned above, confirming similar observations in the literature. An analysis of the literature data on swelling and its treatment with the SLD/Pan-Connell model will be presented. Further, the effect of coal swelling on changes to cleat permeability will also be presented.

Reference:

Pan, Z; Connell, L; 2007. A theoretical model for gas adsorption-induced coal swelling, International Journal of Coal Geology, 69, 4, 243-252.