Investigating the effects of fault reactivation and CO2 migration during combined CO2-EOR and sequestration within a mature oil reservoir

The investigation into the combined processes of CO2-EOR and geologic carbon sequestration was seen to be a viable solution to reducing CO2 emissions from the atmosphere, while boosting production from mature oil fields. However, the practicality of the combined process hinges on the determination of an optimum injection pressure to maximize the application of both methods. In addition, the success of these two operations is also contingent upon the dynamic sealing capacity of bounding faults, to allow hydrocarbon accumulation and trapping of injected CO2. Consequentially, the goal of this research is to optimize the implementation of combined CO2-EOR with simultaneous CO2 sequestration and investigate the enhancing/diminishing aspects of fault reactivation and CO2 migration. The study was approached from two scenarios; the first was the determination of an optimum injection pressure for the combined process, with the main focus on maximizing recovery from a mature oil field. The results saw a maximum cumulative recovery of 73.7090 Mbbls being facilitated at an optimal injection rate of 722 Scf/day. The second scenario entailed the investigation of the occurrence or lack thereof, of injection-induced fault reactivation at this predetermined injection rate of 722 Scf/day. Simulations reflecting the characteristics of fault reactivation were conducted, and are indicative of relations between fault opening stress, reactivation time, hydraulic fracture permeability, fracture propagation length, and leakage. Conclusively, the viability of the combination of CO2-EOR and sequestration were seen to depend on the technicalities of fault reactivation. In some cases, reactivation resulted in increases of accessible storage capacity, whereas, in other instances, it led to the leakage of the injected CO2.