Interfacial tension behavior of a nonionic surfactant in oil/water system; salinity, pH, temperature, and ionic strength effects

Since most of the world's oil reservoirs are in the second half lifetime, the use of Enhanced Oil Recovery (EOR) methods is inevitable. Interfacial Tension (IFT) is one of the effective parameters on EOR can be changed by surfactants. But surfactant injection is one of the costly methods and chemistry of the surfactant solutions such as salinity (one and two valence ions) and pH should be engineered. Furthermore, the temperature is an effective parameter affecting on IFT. In this study, the effect of salinity, especially hard salinity, temperature and pH on IFT between Triton X-100 surfactant and an Iranian oil sample has been investigated. In order to, evaluate the effect of salinity, different concentrations of NaCl, CaCl2, MgCl2, and Na2SO4 salts (0, 0.1, 0.5, and 1 wt%) were used in different concentrations of surfactant. IFT results showed that magnesium and calcium divalent cations had a greater effect on IFT reduction than monovalent sodium cation. Also, all the studied cations were more effective than sulfate as a divalent anion. The ionic strength of the solutions was inversely proportional to the IFT amounts. Less value of IFT in the presence of magnesium ions than calcium ions was due to the higher ionic strength of solutions containing magnesium compared with calcium. IFT results at three temperatures (20, 40, and 60 degrees C) proved that by increasing temperature IFT increased. Also, the effect of pH on IFT in three pHs including acidic, almost neutral and alkaline in the presence of surfactant was studied. Results indicated that IFT decreased with increasing pH, especially in concentrations lower than critical micelle concentration (CMC).