Experimental Analysis and Performance Investigation of Immiscible Super-Critical CO2 Flooding Processes in Tight Oil Reservoir

CO2 flooding, a promising technique of enhanced oil recovery, is widely used for its capability of boosting oil recovery, and reducing greenhouse gas emissions. In this study, the oil displacement performance of supercritical CO2 is tested in laboratory under immiscible flooding. The results show that: Supercritical CO2 improves oil recovery, by virtue of its low viscosity, high diffusivity, and easy dissolution. With the same pore volume (PV), supercritical CO2 flooding significantly boosted the oil recovery factor. The factor reached the maximum, when almost 1.5PV of CO2 was injected. As CO2 moved from the gas phase to the supercritical state, the oil displacement efficiency increased by 10%. To obtain the same oil recovery factor, non-supercritical flooding needed to inject more CO2 than supercritical flooding. Light hydrocarbon components (C1-7) in crude oil were gradually extracted before CO2 breakthrough, while heavy hydrocarbon components (C7+) were extracted mainly after CO2 breakthrough. In addition, supercritical CO2 flooding extracted more intermediate hydrocarbons than critical CO2 flooding. To sum up, supercritical flooding outperforms non-supercritical flooding in injection performance, oil displacement efficiency, and oil exchange rate.