Pore alteration of Yanchang shale after CO2-brine-rock interaction: Influence on the integrity of caprock in CO2 geological sequestration

The integrity of the caprock is a pivotal element influencing the security of CO2 geological sequestration. The CO2-brine-rock interaction can alter the pore structure of the caprock, thereby influencing its sealing capability. In this study, CO2-brine-rock interaction experiments were conducted on Yanchang shale from the Ordos Basin, China. The changes in the shale pore structure and mineral composition before and after the interaction were characterized using low-pressure N2 adsorption (LPN2A), low-pressure CO2 adsorption (LPCO2A), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results showed that the pore volume (PV), specific surface area (SSA), and fractal dimension (D) of the shale decreased after the CO2-brine-rock interaction. The formation of siderite precipitates is the main reason for the reduction in shale pore volume, which can enhance the sealing capacity of the caprock. The findings of this study provide critical insights and theoretical support for the implementation of CO2 geological sequestration projects in the Ordos Basin, China, potentially enhancing their safety and effectiveness.