Simulation Study on Miscibility Effect of CO2/Solvent Injection for Enhanced Oil Recovery at Nonisothermal Conditions

Abstract

The minimum miscibility pressure (MMP) determines the main mechanism of CO2 flooding, which is either an immiscible or miscible process. This paper examines the recovery improvements of CO2 flooding in terms of both the injection temperature and solvent composition. The results show that a lower temperature injection and LPG (liquefied petroleum gas) mixture can considerably improve oil recovery due to the reduced MMP in the swept area caused by the injected solvent. For the pure CO2 injection at the reservoir temperature, oil recovery is 59% after 1.0 PV CO2 injection. The oil recoveries by CO2-LPG mixtures are improved to 73% with 0.1 mole fractions of LPG and 81% with 0.2 mole fractions of LPG. The recovery factor fromlow-temperature CO2 injection is 78%, which is 32% higher compared to the isothermal case. The recoveries obtained by low-temperature CO2-LPG injection increase up to 87% of the initial oil. Heat transfer between the reservoir and the formation of over/underburden should be considered in order to describe the processmore accurately. Additionally, the recovery factors from the heat transfer models are decreased by 4-12% in comparison with the original nonisothermal models.