Abstract: ：This paper focuses on the research of water flooding mechanism in fracture-cavern reservoirs by visualized physical simulation. The effects of different injection fluids, injection directions and injection angles on flooding, and the oil and water distributions before and after water injection are obtained directly. The experiment of gas injection to enhance oil recovery has also been conducted. The results indicate that the location of fractures and caverns has a significant impact on water flooding, and gravity differentiation plays an important role in the fracture-cavern model. The formation and distribution of remaining oil is mainly affected by channel irregularity and gravitational capture. Residual oil mainly distributes in the“attic storey”, in which the top caves and head of bottom caves the residual oil is difficult to flood. They are also the main displacement space of gas injection. Once the water channel was formed during the displacement, remaining oil in caves would be difficult to displace. Changing the way of water injection or injection media, such as gas injection, is possible to further displace the remaining oil in caves, so that to enhance the recovery. Sequent gas injection experiments demonstrate that remaining oil in the attic storey can be driven obviously by changing the way of gas injection.

Key words: fracture-cavern reservoir, visualized physical simulation, water flooding mechanism, affecting factor analysis