Research on Displacement Technology for a Binary Heterogeneous System in Fractured-Vuggy Reservoirs

As one of the primary development schemes for fractured-vuggy reservoirs, nitrogen flooding following water flooding has become the prioritized injection option for these reservoirs due to its relatively low cost and superior enhanced oil recovery (EOR) effect. However, once gas channeling occurs, the degree of crude oil utilization in the formation decreases significantly, preventing the effective utilization of subsequent gas injection. We developed a binary heterogeneous system with equal density and viscosity for conformance control applications in fractured-vuggy reservoirs. We evaluated the stability of this binary heterogeneous system using density and viscosity measurements. The feasibility and EOR were validated through full-diameter core flooding experiments and visualized displacement experiments conducted under various injection medium conditions in fractured-vuggy reservoirs. Evaluation results confirm that our developed binary heterogeneous system exhibits a liquid drainage half-life greater than 5.5 h following 60-day aging, indicating sustained stability under reservoir conditions. Experimental results from full-diameter cores and visualized displacement in fractured-vuggy reservoirs demonstrate that, compared with CH4 and CO2, this binary heterogeneous system achieves superior oil mobilization and effectively displaces remaining oil. It enhances oil recovery by 9.75% to 11.94% above water flooding and nitrogen injection. This study presents a novel development strategy for EOR in fractured-vuggy reservoirs, which has significant theoretical implications and practical value for conformance control in such complex systems.