Deep saline aquifers offer substantial CO storage potential

and exploring the CO-water two-phase displacement mechanisms in tight sandstone is crucial for efficient and secure CO storage in saline aquifers. CO-water two-phase displacement experiments were conducted on two low-permeability sandstones with distinct pore structures. Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques were employed to quantitatively and visually analyze the distribution of gas and water phases during the drainage and imbibition processes. The study examined the impact of core pore size distribution

heterogeneity

and permeability variations on the two-phase displacement characteristics. The research indicates that in the drainage processes

CO is preferentially captured in larger pores

and cores with a larger proportion of large pores exhibit higher CO saturation. However

during the imbibition processes

CO captured in the cores with a higher proportion of micropores and lower permeability are less likely to be displaced by water

resulting in higher CO storage efficiency. The local permeability changes of rock cores have a significant impact on the final residual gas distribution

and areas with lower permeability have higher final residual gas saturation and storage efficiency. This study can further improve the theoretical system of reservoir selection

efficient storage

and safety assessment in CO saline aquifer storage projects.