Hydrophilic Polyether Surfactants for Enhancing Carbon Dioxide Breakthrough across Aqueous Barriers

Summary

Numerous experimental and numerical investigations have demonstrated that carbon dioxide (CO2) enhanced oil recovery (EOR) technology is one of the most promising methods for tight oil development. However, after hydraulic fracturing, the residual water phase will occupy micronano pore throats and form aqueous barriers, which will adversely affect CO2 injectivity, pressure transmission, and oil mobilization. In this work, we established a determination method to quantitatively evaluate the process of CO2 breakthrough across aqueous barriers under different reservoir conditions. The effects of permeability, confining pressure, injection pressure, CO2/water/rock reaction, and hydrophilic polyether surfactants (e.g., C4EO3PO6 and C4PO6) on CO2 breakthrough were systematically investigated. The results show that reservoir permeability has a pronounced influence on the breakthrough process. As permeability decreased from 0.0952 md to 0.0387 md, the breakthrough time increased from 31.42 minutes to 251.93 minutes. Within a short period, the weakly acidic environment formed by CO2 dissolution in water had only a minor effect on reservoir permeability and porosity. The C4EO3PO6-assisted CO2 injection strategy provides a chemical approach to accelerate CO2 breakthrough. Adding 1 wt% C4EO3PO6 to CO2 increased the breakthrough rate by 49.0–62.0%. Compared with C4PO6, the breakthrough rate increased by 7.4–19.9%. Subsequent CO2-C4EO3PO6 injection improved cumulative oil recovery and enhanced the mobilization of oil in micropores. After four injection cycles, the cumulative recovery was increased by 18.25%, and the recovery of oil in micropores reached 26.39%, which was 51.71% higher than that of CO2 injection. These results indicate that C4EO3PO6-assisted CO2 injection can weaken the adverse effect of aqueous barriers, accelerate CO2 breakthrough, and improve the mobilization of bound oil. This work provides a strategy for CO2 injection development under complex reservoir conditions.