Abstract: The pore structure characteristics of tight rocks have an important impact on the displacement behavior between CO₂ and water, as well as the flow characteristics of CO₂. The residual water saturation will ultimately affect the efficiency and safety of CO₂ geological storage. Therefore, it is of great significance to further explore the CO₂-H₂O two-phase displacement characteristics of tight cores. In this study, the two-phase displacement characteristics and its influencing factors of natural low-permeability cores from deep reservoirs in Ordos Basin were visualized using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques. After qualitative and quantitative characterization of core pore structure, it is found that displacement patterns are closely related to core pore structure. Cores with strong heterogeneity and anisotropy are more conducive to the formation of fingering phenomena, while cores with large porosity and high permeability show piston-like displacement pattern. Fingering phenomena contributes to the migration of gas phase and can lead to the premature breakthrough of CO₂, resulting in high residual water saturation and low displacement efficiency.

Key words: CO2 geological storage, displacement efficiency, pore structure characteristics, relative permeability, nuclear magnetic resonance