Capillary trapping characteristics of CO2 sequestration in fractured carbonate rock and sandstone using MRI

Capillary trapping is a prominent short-term trapping mechanism that achieves the maximum storage capacity and ensures the integrity of CO₂ sequestration in deep saline aquifers on an industrial scale. To maximize capillary trapping, fluid injection scenarios need to be investigated, and the fluid flowing characteristics in porous reservoir media need to be acknowledged. In this study, magnetic resonance imaging (MRI) technology was used to examine the distribution of three fluid pairs in fractured carbonate rock and sandstone under reservoir conditions, and the relative permeability and capillary pressure were determined based on their capillary end saturation profiles. The initial gas saturation increased with the injection rate, and the fractured structure created a preferential flow channel that affected the saturation distribution. Differences in interfacial tension and wettability lead to different capillary pressures. The low interfacial tension of the scCO₂/water fluid pair and its strong water-wet properties in sandstone caused high relative permeability and residual gas saturation. These results imply that the influence of the fluid injection method and reservoir properties on capillary trapping characteristics should be investigated in detail before implementing CO₂ geological sequestration.