EOR by Low Salinity Water and Surfactant at Low Concentration: Impact of Injection and in Situ Brine Composition

Low salinity water (LSW) and low salinity surfactant (LSS) core flooding experiments were performed to study the impact of ionic composition on oil recovery from aged Berea sandstone cores. Surfactant adsorption in packed beds, contact angles, interfacial tension (IFT), critical micellar concentration (CMC), and end-point relative permeabilities were used to better understand wettability alteration. In the samples aged with the same in situ brine with (Ca2+ + Mg2+)/Na+ = 0.033, both endpoint relative permeabilities of LSW flooding and contact angles showed LSW with only sodium chloride made the samples more water-wet than LSW with divalent-contained brines. Oil recovery was also highest in LSW injection with only sodium chloride. In tertiary LSS of the same core samples, according to both flooding and contact angles, LSS with only sodium chloride showed more water wetness. Characterization measurements showed that, at higher Ca2+/Na+ ratio, CMC and IFT were lower whereas surfactant adsorption was higher. Further, at similar conditions, LSW and LSS made the core sample more water-wet than high salinity water (HSW) and high salinity surfactant (HSS). At low surfactant concentration, LSS recovered as much oil as HSS did.