Experimental research on the mechanisms of improving water flooding in fractured-vuggy reservoirs

Fractured-vuggy reservoirs have extremely complex reservoir characteristics, leading to a large amount of remaining oil not being recovered after water flooding. In order to solve the problem of the low recovery in fractured-vuggy reservoirs, we utilized 3D printing technology to fabricate two-dimensional and three-dimensional experimental models based on the typical reservoir structure. A series of experiments with different models on improving water flooding is conducted to study the production improvement effect. The difference in oil-water distribution or oil saturation distribution before and after improved water flooding is also compared, and the mechanism is analyzed. The results show that the oil-water gravity differentiation is the most critical factor affecting the remaining oil distribution, and changing the injected pressure or its propagation direction is the root of improving water injection. Reversing injection-production wells, increasing injection strength, water plugging, and cyclic water injection can effectively increase the sweeping scope or displacement efficiency. The attic oil, residual oil in filling medium, bypass remaining oil, and water cone remaining oil can be produced by one or more improving water flooding methods. This paper provides effective measures and mechanisms for the efficient and rapid development of fractured-vuggy reservoirs. •Different dimensions and characteristics of experimental models are designed and manufactured by 3D printing technology.•Various improved water flooding methods have been applied in the experiments of fractured-vuggy reservoirs.•The mechanisms of improving water flooding are revealed by experiments.•The methods of improving water flooding for various types of remaining oil are obtained.