Study of sodium electrolytes on phase behavior of the anionic surfactant/alcohol/model oil system and its application for alkaline-surfactant flooding formulation design

Abstract

In this study, the phase behavior of several anionic surfactants, i.e., one internal olefin sulfonate, the sodium dodecyl sulfate and the dodecyl benzene sulfonate, were conducted to investigate the influence of different sodium electrolytes on the optimal salinity of the anionic surfactant/alcohol/model oil system. The sodium activity at the optimal salinity was calculated by the PHREEQC software, which was found to be equal between different sodium electrolytes. Noticeably, the solubilization parameter of water or oil at the optimal salinity was not influenced by the anions, but largely dependent on the alcohol type, the oil type and the temperature. Furthermore, oleic acid was added into model oil to simulate the acid components in crude oil. The phase behavior results indicated that a larger fraction of oleic acid was active at higher pH with sodium hydroxide (NaOH), however, its solubilization parameter at optimal salinity was lower compared to that using sodium carbonate (Na2CO3). The phase behavior of alkali/crude oil was also performed by mixing different alkalis with a crude oil sample that consisted of high contents of water-soluble active soaps. It is found that the soap generated by NaOH is more lipophilic than that generated by Na2CO3. When sodium activity is used, the optimal salinity of alkali/surfactant/crude oil system can be accurately predicted by the improved mixing rule correlation. The findings of this study would be helpful for us to rapidly select the optimum formulation for alkaline/surfactant flooding process.