摘要：Aim ing at severe heterogeneity, complex fluid distribution, multi-scale nature of fractures and cavities in fracture-cavity reservoirs, it is difficult to meet the development needs only by water injection for the high water-cut reservoirs. Nitrogen injection in the reservoir can improve the development effect and the crude oil recovery rate from the mechanism. Therefore, through different displacement experiments, the effects of nitrogen displacement, gas injection speed, crude oil viscosity, different water-gas ratios, and different injection methods on recovery factors were studied. The results show that some residual oil remains in the fracture-cavity model after water flooding. After gas injection, the liquid flow conditions can be improved to increase the recovery factor. There is an optimal gas injection rate, which allows the gas to enter the fractures and mix with the crude oil sufficiently, avoiding the occurrence of early breakthrough. The water-gas alternate flooding and water-gas mixed flooding were the best when water-to gas ratio of 1: 1 was used. Comparing the effects of different gas injection methods on heterogeneous conditions on recovery factors, it can be seen that the use of water-gas alternation and water gas-injection displacement can effectively improve the recovery factor.
