An experimental investigation into the spontaneous imbibition of surfactant assisted low salinity water in carbonate rocks

Surfactant assisted smart water injection is one of the areas of research interests in enhanced oil recovery. Simultaneous use of smart water and surfactants has drawn great attention in last decades. Majority of studies highlight co-injection of cationic surfactant and sea water/low salinity water. Therefore, this paper opens a new approach by examining the effect of diluted sea water, termed as dSW, containing Sodium Dodecyl Sulfate (SDS) on spontaneous imbibition in carbonate media. Reservoir core plugs and oil samples were provided, saline waters were synthesized in laboratory and different tests were accomplished. It was observed that the brine spiked in Mg2+ is able to improve water wetness of calcite by reducing contact angle from 114 degrees to 42 degrees and reduction in interfacial tension (IFT) from 34.2 to 13.9 mN/m. Measurement of oil properties before and after imbibition, showed that Mg2+ plays the main role in increasing microscopic sweep efficiency and improving ultimate oil recovery. Moreover, faster imbibition rate and higher capillary number was gained by increasing Mg2+ concentration. Ca2+ was found to be a disturbing ion as it led to incompatible condition in the fluid system. We confirmed that in the presence of excess Ca2+, SDS molecules not only aggregate in the bulk of solution, but also another form of incompatibility, known as salt bridge, was occurred. It was also demonstrated that activity of SO42- was concealed in the presence of SDS.