Relationship between oil recovery and CO2 storage efficiency under the influence of gravity segregation in a CO2 EOR system

Integrating the technologies of EOR and CO2 sequestration could economically bring large quantities of CO2 storage capacity and increase recoverable oil, which could be called "green oil''. Gravity segregation, particularly in CO2 gas flooding, is an important factor for the successful application of CO2 flooding. A major goal of this study was to analyze how miscibility conditions and CO2 injection rate affect both oil recovery and CO2 storage efficiency under an environment of gravity segregation. This paper presents experimental observations of both EOR and CO2 sequestration for CO2 flooding in immiscible and near-miscible conditions at various CO2 injection rates using two-dimensional vertical Berea sandstone slabs (20 9 20 cm). The experiments were run under immiscible and near-miscible conditions with various CO2 injection rates. CO2 was injected continuously up to a maximum three-pore-volume injection into sandstone saturated with n-decane. From the results, both oil recovery and CO2 storage efficiency in the near-miscible conditions were much better than the immiscible conditions in the case of a vertical system containing a gravity segregation environment. Ultimately, in the relationship between oil recovery and CO2 storage efficiency, from this study, we propose that they behaved similarly, with a trend corresponding to the CO2 injection rate in immiscible conditions, whereas they showed the opposite relationship in near-miscible conditions.