Impact of Micro-Dispersion Formation on Effectiveness of Low Salinity Waterflooding

Low salinity water injection (LSWI) is considered as a promising technique for improving oil recovery. Several mechanisms have been proposed for improving oil recovery by LSWI mainly based on core flood experiments, but these experiments are difficult to interpret and many conflicting results have been reported in the literature. While much attention has been paid to the role of rock mineralogy, important fluid/fluid interactions have been overlooked. A few attempts for identifying the significance of oil characteristics have been reported in the literature but the results have been inconclusive. Using our state-of-the-art flow visualisation and fluid/fluid characterisation capabilities, we have recently reported a physical phenomenon taking place when low salinity brine comes in contact with a crude oil, which revealed spontaneous formation of micro-dispersions of water in oil (SPE 166435 and SPE 169081). The micro-dispersions are associated with indigenous surface active components of crude oil. Migration of low salinity water into crude oils is also associated with perturbation of indigenous surface active materials, which can in turn modify the wettability of the system. Here in the current work, we aimed to quantitatively evaluate whether micro-dispersion formation plays a dominant role in the mechanisms by which LSWI may lead to improved oil recovery. A number of coreflood experiments have been designed and performed in which the propensity of different crude oils to form micro-dispersions was determined. In a specially designed mixing cell, low salinity brine was contacted with crude oils and the resultant micro-dispersions were remove prior to coreflood tests. Using pre-contacted and unadulterated crude oils, the performance of tertiary LSWI was examined. The results demonstrate the impact of mutual interactions between the aqueous and oleic phases. The results clearly shows that the amount of oil recovered by LSWI for the two cases varies significantly which indicate that the observed micro-dispersions play a crucial role in the performance of both high and low salinity water floods. Removing the micro-dispersions influences the wetting characteristics of cores through the association of the micro-dispersions with natural surface active components of crude oil. The results show that depriving crude oil from these compounds results in more water wet behaviour, which is in line with general consensus about how LSWI would change the wettability.