Foam assisted gas drive is a potential EOR technology for fracture-vuggy reservoirs. Fractures are the main flow channel of fluid in fracture-vuggy reservoirs. They developed in an expanding-aperture or shrinking-aperture way during the reservoir formation process. In order to systematically study the flow characteristics and displacement effect of foam-assisted gas drive in fracture-vuggy carbonate reservoirs, this article describes a fracture similarity model and microscopic visualization model with both equal-apertures and variable-apertures, and carried out physical simulation experiments on foam-assisted gas drive.The results show that the foam assisted gas drive easily formed gas-liquid slugs in small-aperture fractures. Gas could easily break through the foam slug and form a gas dominant channel after a little compression; The foam was accumulated in the form of multiple small slugs in large-aperture fractures, resulting in a superimposed accumulation effect. The displacement effect of large-aperture fractures was better than that of the small-aperture fractures. The foam slugs would be deformed with the change of aperture in variable-aperture fractures. The higher the degree of foam accumulation, the stronger the stability and the better the EOR. In the fractures, the foam displacement front changed in the following four forms: micro-scale foam accumulative types,small-scale foam accumulative type, mesoscale foam slightly deformed type and large-scale foam seriously deformed type. The stability decreased from the first form to the last form. In the lipophilic fractures, the flow of gas and liquid interface at the foam
displacement front basically conformed to a Poiseuille velocity distribution. The trend of the gas phase breaking through the gas-liquid interface was more obvious with the increasing imbalance of additional pressure on the curved liquid surface.