Lessons Learnt on the Feasibility of HC and CO2 WAG Application in a Giant Offshore Carbonate Reservoir

Abstract We explore challenges in modeling complex processes involved in hydrocarbon (HC) and CO2 water-alternating-gas (WAG) injection. It includes the topics of sector model utilization, the effect of well spacing on ultimate recovery, and the impact of utilizing a tuned Equation of State (EoS). Furthermore, reservoir simulation topics such as grid size and run times are highlighted. Understanding these challenges is crucial for effectively assessing the optimum EOR method. We offer a detailed analysis of the intricate relationship between field-scale effects, well-spacing, SCAL, and EoS in EOR modeling, addressing recoveries and economic scenarios, providing valuable insights for petroleum engineers and researchers to improve EOR strategy accuracy and efficiency. A high-level economic analysis is presented together with a discussion of some of the technical challenges that may need to be addressed in implementation of a WAG scheme. Results showed the importance of addressing field-scale effects and optimizing well-spacing for efficient EOR methods. Highlighting the role of Special Core Analysis (SCAL) data and EoS parameters in improving EOR predictions. It has been demonstrated that SCAL plays the highest role in the ultimate recovery, even beyond small scale EOR effects. Higher recoveries have been seen up to 3-7% by using an EoS fully tuned to the appropriate lab data. Fluid modelling through EoS is crucial for determining recovery volumes in gas WAG configurations. An uncertainty workflow has been applied that showed that different sectors in the field are sensitive to different parameters. EOR economics were compared to the base case water injection economics and different scenarios have been studied in order to maximize value out of the EOR. The economic viability of the project utilizing HC/CO2 WAG is inferior when compared to the base case of water injection. This is primarily attributed to the favorable mobility ratio to water injection in the base case, compared with the substantial costs associated with the HC/CO2 WAG approach. Additionally, imposing plateau restrictions impairs the economic inefficiency of HC/CO2 WAG, as any additional production it offers occurs at a later stage.