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Gas diffusion plays a key role in CO 2-enhanced recovery of coal bed methane (ECBM), where more than one types of gases coexist and multicomponent gas diffusion occurs. Such process is now usually described by non-coupled two-component gas diffusion equations which exclude the interactions between gases. Self-diffusion and mutual diffusion of CO 2-CH 4 mixture are investigated through molecular simulation for the first time. The self-diffusion coefficients of CO 2 and CH 4 decrease with gas concentration but increase with temperature. The mutual diffusion coefficients of binary gas mixture of CO 2-CH 4 in coal are computed through Maxwell-Stefan diffusion theory. A 2D diffusivity matrix |D| (with diagonal element D i and non-diagonal element D ij) is obtained to depict the mutual diffusion of the gas mixture. It is found that CO 2 (CH 4) diffusion is coupled with CH 4 (CO 2). The diffusion coupling strength of CO 2 and CH 4 decreases with increasing gas

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Montmorillonite (MMT) constitutes most of fine-grained sedimentary rock, such as shale, mudstone, and siltstone. It is also applied in underground storage of carbon dioxide, petroleum drilling engineering, and material engineering. Although adsorption and mechanical behavior in MMT−H 2 O−CO 2 is widely studied, little is known about interplay between them. In this work, we have investigated the interplay between mechanical behavior and adsorption in MMT with different proportion of H 2 O and CO 2 content under super critical condition by molecular dynamic (MD) method. With respect to the calculated results, adsorption of H 2 O and CO 2 can diminish stiffness of MMT. Meanwhile, diffusion of H 2 O and CO 2 weakens because of stronger constrains deriving from geometry structure and hydrogen bond as the system undergoing compression test. Moreover, motion of H 2 O is restrained by CO 2 molecules as self-diffusion coefficient decrease with the increase of CO 2 . Hydrated MMT is more sensitive to deformation vertical to clay sheet which is confirmed by comparing changing tend of potential energy and stress. Process of adsorption can yield the stiffness of MMT structures while compression loading can slow down diffusion motions of adsobates. This impact we have revealed here is meaningful to understand mechanical properties of swelling MMT.