Study of multicomponent sorptive gas flow in fractured porous media using in-situ synchrotron X-ray imaging technology

Abstract Carbon dioxide (CO 2 ) geo-sequestration in deep coal seams is a complex process, involving multicomponent gas diffusion, competitive gas sorption, and the associated mechanical deformation of the coal mass. There is no sufficient knowledge about these coupled underlying multi-physical behaviours, so an in-depth fundamental understanding of these processes is required. In this paper, we conducted in-situ core flooding experiments to study multicomponent gas flow dynamics in coal through microscale synchrotron X-ray imaging. Since xenon (Xe) and krypton (Kr) have high X-ray attenuation coefficients, they could be directly observed under X-ray imaging. Thus, we use Kr as analogues of methane (CH 4 ) and Xe to represent CO 2, due to similar sorption behaviours in coal. The high-resolution imaging results uncover the process of the multicomponent gas exchange and sorption, gas diffusion, and sorption-induced fracture deformation. We presented the direct evidence of competitive adsorption behaviours of different gas coal lithotypes types during the core flooding. The image data provide a method to quantify the mass transfer coefficients under different gas types and conditions, which further enable us to perform larger-scale gas Advection–Diffusion-Sorption modelling with lab-verified parameters. Moreover, we found that gas desorption by the mechanism of gas competition exchange is more dominant than sample depressurisation. When there are multiple sorptive gases, fracture deformation is not significant because gas adsorption and desorption have opposite effects on fracture aperture.