Enhanced Oil Recovery (EOR) by Combining Surfactant with Low Salinity Injection

When injecting low salinity (LS) water, it is believed that destabilization of oil layers adhering to mineral surfaces could be a contributing mechanism to enhanced oil recovery (EOR). Surfactant flooding is a proven EOR technique by increasing the capillary number. The combination of LS water at reduced capillarity can avoid retrapping of destabilized oil and exceed recoveries of either of the techniques applied alone. In this study, we have used an alcohol propoxy sulfate mixed with an internal olefin sulfonate to compare the oil recovery in a low salinity surfactant (LSS) flooding process at moderately low IFTs to that of an optimal salinity surfactant (OSS) injection process at ultralow IFT. The surfactant formulation was selected on the basis of an initial screening phase using a North Sea crude oil and diluted seawater. Its effect on oil recovery efficiency in different injection scenarios was investigated using crude oil aged Berea sandstone cores. The results showed comparable recoveries for the LSS flooding at a capillary number 2 orders of magnitude lower than that for the surfactant flooding at ultralow IFT. In addition, retention values in the latter case were around 60% higher than for the LS case. On the basis of this, it appears that the LSS process may be more economically efficient than an OSS injection process at ultralow IFT.