Evaluation of Development Effect for CO2 Flooding After Water Flooding in Low Permeability Reservoirs-A Case Study of a Well Group in Hei46 Block, Jilin Oilfield

China is rich in low-permeability oil resources. But due to the complex pore structure and strongly heterogeneity in reservoirs, it is difficult to form an effective replacement system, and the recovery of water flooding is low. CO2 flooding is a new green idea to increase production by combining the advantages of improving the recovery of low-permeability reservoirs and achieving greenhouse gas emission reduction. At present, most of the research is focused on experimental effect evaluation and theoretical analysis, and it is difficult to form practical experience to effectively guide oilfield development. Therefore, the development effect of long-cycle WAG injection and short-cycle WAG injection after water flooding was analyzed by dynamic analysis, taking a well group in Hei46 block, Jilin Oilfield, as an example. The study results showed that the formation pressure decreases in the late stage of water-driven development, and the continuous injection of CO2 for a long period of time to recover the formation energy also directly leads to serious gas channeling. The oil decreases and water cut rises more quickly with worse development effect instead. Continuous gas injection followed by continuous water injection to inhibit gas breakthrough can only partially restore productivity. Compared to long-period WAG injection, short-period WAG is the most important way to achieve oil productivity, control gas breakthrough and improve development effect. Based on the above research results, four measures are proposed to promote the development effect. The results of the study can provide an empirical reference for the development of CO2 flooding in the late stage of water flooding for similar low permeability reservoir in China.