Optimization Approach of CO2 EOR Field Implementation Using Pilot Test Results by Including the Operational Considerations in a Complex Reservoir in Indonesia

Abstract Miscible gas injection is one of the promising methods to improve oil recovery. A CO2 gas injection pilot was successfully conducted in a highly complex heterogeneous reservoir in Indonesia. In this study, the result of the CO2 pilot test was used to find the optimum field development plan and address the key risk parameters. Compositional model of the field was validated using the latest production and pressure data. A recent pilot test has been accomplished as one of the early steps of field implementation of gas injection. Slim-tube simulation was carried out to compare the MMP against experimental measurement. Appropriate relative permeability curves were utilized to incorporate interfacial tension reduction due to miscibility. Then, sensitivity and optimization have been done to find the impact of operational parameters on oil recovery as the objective function. An AI-based proxy model was generated to relate influential parameters and the objective function and help us with risk mitigation. The field incorporates highly complex and heterogeneous formations and thus several modifiers besides local grids are applied in the model to describe the field performance. The recorded data during the pilot test were compared to the model results which exhibited high consistency. The estimated MMP from Slim-tube simulation was quite close to laboratory data. Some parameters such as pore volume injected, CO2 injection rate and Gas-oil ratio limit were included in the sensitivity parameters. Sobol analysis showed that maximum allowable GOR from operational point of view has the highest impact on objective function. Afterwards, response surface methodology (RSM) was applied to aid on building the proxy model. Different models were examined, and it was found that polynomial regression had the higher correlation factor of verification cases. Differential evolution methods have been applied to optimize oil production. The results showed that the oil recovery factor could be increased by 6% using miscible CO2 injection. Review of the model performance of injector well and nearby wells revealed that further improvement in oil recovery would be achieved by some squeezing and reperforation jobs of these wells. Results of this study will help to provide the roadmap and risk mitigation plan for CO2 field implementation by considering the operation issues including reservoir surveillance and flow assurance. Moreover, a comprehensive monitoring plan is suggested to integrate the well, reservoir and facilities which will assist to enhance the reservoir management and decision-making purposes.