Salinity Tolerance and Solution Property Correlations of Petroleum Sulfonate-Cosurfactant Blends

Abstract A petroleum sulfonate (Petrostep 465/420) was combined with commercially available ethoxylated and other cosurfactants. Salt tolerance, phase volume behavior, interfacial tensions, and viscosities were measured; correlations among these parameters are presented for the 21 systems studied. Salinity tolerance levels as high as 120 g/kg NaCl, optimal salinities as high as 95 g/kg NaCl, and ultralow interfacial tensions on the order of 1 × 10-4 mN/m were exhibited by some systems. Optimal salinities were accompanied by ultralow interfacial tensions and lower microemulsion viscosities only when the range of salinity over which the three-phase region persisted was narrow. Furthermore, some systems were characterized by almost 95% microemulsion volume at optimal salinity. The width of the three-phase region decreased as the middle-phase microemulsion volume at optimal salinity increased. Consequently, the microemulsion viscosities were lower for systems that displayed a narrower three-phase region. It was also concluded from our results that optimal salinity does not necessarily occur at the middle of the three-phase region. For most of the systems studied, it occurred at lower values. The plots for the interfacial tension versus solubilization parameter were similar to those reported by Reed and Healy.13 The interfacial tension between the microemulsion phase and the excess phases was correlated with the excess phase volumes. We also found that the interfacial tension between the excess oil and brine was close to and parallel to that between the microemulsion and excess brine phases.