Residual Oil Distribution and Displacing Mechanisms of CO2 Asynchronous Injection and Production in Complex Fault Block Reservoirs and Pilot Test

The well pattern of complex fault block reservoir is not perfect, thus leading attic oil along the fault and corner oil away from the injection well and around the production well. The proposed CO2 asynchronous injection and production (CAIP) method is expected to significantly improve the sweep efficiency and ultimate recovery factor. Firstly, the new developed physical model and experimental method for CAIP flooding are established, and the difference of recovery between this model and conventional long core model by CAIP flooding is compared, and the recovery is also compared between continuous flooding and CAIP flooding. Then, based on the microscopic visual model of longitudinal heterogeneity, the microscopic residual oil types and sweep efficiency under continuous gas injection (CGI) and CAIP injection are compared. Finally, the remain oil contact behavior in pores of different size for CAIP injection is analyzed by nuclear magnetic test. The results show that, by the CAIP injection, oil recovery can be improved by 9.2% in complex fault block reservoirs than in conventional reservoirs. And compared with the CGI flooding, the recovery of complex fault block reservoirs can be improved by 13.3% by the CAIP injection. In the longitudinal heterogeneous reservoir, the residual oil after continuous gas injection is mainly columnar and isolated type, while the CAIP injection can significantly reduce the columnar oil and increase the microscopic swept efficiency, leading more oil be displaced in the low permeability area near the high permeability boundary. In addition, the NMR test shows that the CAIP can not only increase the utilization ratio of large pore oil, but also contact the previously uncontacted small pore oil. The research results can provide reference for development methods of other complex fault block reservoirs of the same type.