The water-alternating-gas process (WAG) was originally proposed to improve sweep efficiency during gas injection and it combines the advantages of gas and water flooding, better microscopic displacement efficiency and improved macroscopic sweep, respectively. Carbon dioxide is an attractive gas to be used in the Enhanced Oil Recovery (EOR) process, mainly, when the oil in place contains some dissolved CO2 which is produced in the gas phase. The WAG-CO2 can be an attractive recovery method in reservoirs with oil containing CO2. Also, it is a manner to store CO2, representing a viable solution to the greenhouse gas problem. In WAG process simulation, it is necessary to shut-in and shut-off the injector wells alternately in order to change the injection fluid. This procedure results in an elevated simulation time compared to the EOR process with injection of a unique fluid. A numerical approach is investigated to physically represent the WAG process with reduced computational time. In this approach, denominated as Pseudo WAG process, water and CO2 are simultaneously injected into the simulation model, maintaining the same amount of injected fluid. The possibility of the Pseudo WAG process to adequately represent the WAG-CO2 is analyzed using a compositional simulator. To execute the simulations, it is necessary to have equations of state (EOS) that properly represent the oil phase behavior. EOS tuning is based on PVT experimental data of oil available in literature. The EOS is validated before being used in a simulation model. Results indicate that WAGCO2 is an effective method to recover oil containing CO2. The Pseudo WAG process is capable of adequately representing the WAG-CO2 process in terms of production parameters, such as cumulative oil and water productions. The numerical approach of the Pseudo WAG process significantly reduces the simulation time compared to the WAG process. This approach can be useful to simulate WAG-CO2 processes in heterogeneous reservoirs in order to reduce the CO2 emissions into the atmosphere.

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