Effect of Miscibility Condition for CO2 Flooding on Gravity Drainage in 2D Vertical System

Abstract

In CO2 flooding process, gravity drainage and miscibility condition are the main factors on the efficiency of oilrecovery. In this study, we observed oil recovery for different miscibility conditions in vertical oil reservoir. This wasinvestigated in two dimensional vertical sandstone slab, where unstable gravity drainage phenomena can be formed.CO2 is injected at bottom into 100% saturated with oil and production port is open at top of the system. We haveperformed a series of experiments using continuous CO2 flooding for immiscible and near-miscible conditions. Fromthe experimental results, oil recovery at near-miscible condition is 3.77 times greater than at immiscible condition,particularly in vertical system. It indicated that applying the immiscible CO2 flooding is ineffective because of gravityoverride of CO2 and generation of CO2 channel at upper side in vertical reservoir. Meanwhile, the results revealedthat oil recovery increases considerably once miscibility is reached at outlet. That is, miscibility condition is found tobe a sensitive factor on oil recovery particularly in vertical oil reservoir.