Effect of gravity segregation on CO2 flooding under various pressure conditions: Application to CO2 sequestration and oil production

This research evaluates the effect of gravity segregation on CO2 sequestration and oil production during CO2 flooding under immiscible, near-miscible, and miscible conditions. The core experiment results show that CO2 flooding recovery was seriously affected by gravity under immiscible conditions, while under miscible conditions, this influence was not apparent. Visual experiments show when immiscible, gravity restricts the oil and gas front’s stability, and different gas injection strategies have evident differences in the swept region; when miscible, gravity has almost no effect on the swept region. These results indicate that when CO2 immiscible flooding is implemented, the reservoir thickness affects the choice of gas injection direction. However, for miscible flooding, the reservoir thickness and gas injection direction are not essential for developing CO2 flooding. In immiscible conditions, gas injection velocity greatly restricts the CO2 gravity flooding recovery; in miscible conditions, the velocity is no longer the main influencing index of CO2 gravity flooding recovery. For CO2 sequestration, gravity segregation is conducive to increasing CO2 sequestration potential. As the pressure increases, the influence of gravity on CO2 sequestration weakens. Regardless of whether there is gravity effect, the best oil recovery and gas sequestration potential of CO2 flooding is obtained under miscible conditions. •The combined effects of miscibility and gravity on CO2-EOR and storage are clarified.•For immiscible CO2-EOR, reservoir thickness affects the choice of injection strategy.•For miscible CO2-EOR, reservoir thickness and injection direction are not essential.•The best recovery and sequestration of CO2-EOR is obtained under miscible conditions.