Enhanced Oil Recovery (EOR) by Combined Low Salinity Water/Polymer Flooding

Recently, low salinity brine injection has been given a great interest as a technique for enhanced oil recovery (EOR) by waterflooding. Varying experimental results have been reported in the literature, from many promising results to limited or no effects of low salinity. The application of low salinity water in combination with other established EOR processes (e.g., surfactant flooding and polymer flooding) is of great interest. The combined processes involve dampening capillarity to avoid trapping of mobilized oil, reducing residual oil saturation (S-or), and altering frontal stability and sweep. In this article, we address the questions of timing of LS injection and the added benefit of polymer injection. Secondary-mode (at initial water saturation) and tertiary-mode (after seawater residual oil saturation) low salinity waterflooding experiments were performed on outcrop Berea sandstone core material. The main results are the oil recovery efficiencies of these two different flooding modes. These results show an increase in oil recovery of about 13% of the original oil in place (OOIP) in secondary-mode compared to tertiary-mode low salinity waterflooding. Moreover, the effect of polymer injection was found to be more positive when low salinity was initialized from the start of water injection (secondary mode). In this case, the final recovery factor increased to about 90% OOIP. Possible mechanisms for low salinity and low salinity polymer injection are discussed.