Observations of water-in-oil micro-dispersions as a displacement mechanism in secondary and tertiary low salinity waterflooding

Summary Low salinity waterflooding (LSW) is considered one of the most efficient techniques to improve oil recovery; it is cost-effective and easily deployable in oil fields. The previous experimental work investigating LSW was performed mainly at the core scale and on micromodels where there are limitations to investigating the mechanisms responsible for the low salinity effect on a natural rock. In this experimental study, a key mechanism of low salinity waterflooding was investigated in both secondary and tertiary modes in carbonates at reservoir conditions. In situ development of water-in-oil micro-dispersions was observed. The development of water micro-dispersions was more prompt in secondary LSW due to the direct contact between oil and low salinity brine. Whereas in the tertiary experiment, the high salinity brine slowed down the formation of these micro-dispersions. The analyses showed that, in comparison with tertiary mode, LSW resulted in higher oil recovery in the secondary mode. The results highlight the differences between LSW modes by investigating the pore-scale displacement mechanisms and interfacial interactions between rock, crude oil, and high and low salinity brine and their impact on oil recovery.