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

Abstract

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.