Significant Improvement in Oil Recovery and CO2 Storage by Carbonated Water Injection (CWI)

CWI can alleviate many of the shortcomings of conventional CO2 floods. As a single phase (water and dissolved CO2), carbonated water (CW) does not exhibit fingering problem when injected into the reservoir since the mobility contrast between oil and CW is less than what it would be in the CO2-oil system. Consequently, a much better sweep efficiency (compared to CO2 flooding) can be obtained and hence CO2 would be distributed within a larger part of the reservoir. Furthermore, the higher density of carbonated water (compared to water) prevents CO2 gravity override eliminating the risk of leakage of CO2 through cap rock. In this paper, we present the results of a series of coreflood experiments using sandstone cores and real crude oil. The brine used in the coreflood experiments represented Seawater which is usually injected in oil reservoirs. The experiments were carried out to compare the performance of CWI with plain (conventional) water injection and CO2 flooding. The results of both secondary (pre-waterflood) CWI and tertiary (post-waterflood) CWI reveal that CWI is an efficient oil recovery method compared to conventional waterflooding and leads to safe storage of significant quantity of CO2 as a dissolved phase.