Formation mechanisms of residual water in CO2-water-rock systems: Effects of the CO2 phase

This study focused on the effects of the CO₂ phase on the formation mechanisms of residual water. Based on nine groups of core-flooding experiments, the order of residual water saturation was gaseous CO₂ > supercritical CO₂ > liquid CO₂, and a quantitative power function relationship between residual water saturation and displacement time for different CO₂ phases was proposed. The experimental results show that when CO₂ transitions from the gaseous phase to the supercritical phase and then to the liquid phase, the decrease in the interfacial tension and cosine value of the contact angle in two-phase flow can lead to a decrease in residual water saturation. Meanwhile, an increase in the viscosity ratio of two-phase flow weakens the viscous fingering phenomenon and can also lead to a decrease in residual water saturation. However, the logCa-logM stability phase diagram reveals that the viscous force is the primary factor influencing all core-flooding experiments.