The effect of sodium carbonate on reducing the interfacial tension of petroleum sulfonate

Abstract

In current chemical flooding technology, surfactant and polymer (SP) rather than alkali, surfactant and polymer (ASP) flooding is preferred, because the addition of alkali in ASP flooding has been linked to environmental problems. However, in the absence of added alkali, the interfacial performance of petroleum sulfonate (PS) in SP flooding is greatly impaired. Therefore, an important task in SP flooding is to understand the interaction between PS and alkali in reducing interfacial tension (IFT), with the goal of finding a more eco-friendly alternative to alkali. In this study, PS was separated according to its composition: sodium PS, unsulfonated oil, inorganic salt and water. A comparison of the effects of Na2CO3, NaCl and ethanolamine on IFT showed that the electrolyte property of Na2CO3, rather than its alkalinity, played a major role in reducing the IFT. The unsulfonated oil was found to be an indispensable component of PS. A subsequent analysis showed that the unsulfonated oil and the hydrophobic chains of PS had similar carbon numbers, which explained the improved adsorption of PS at the oil-water interface. The oil-water partition coefficient and the minimum cross-sectional area of PS were also studied. The effect of NaCl on the oil-water partition coefficient was stronger than that of Na2CO3, and the effect of Na2CO3 on the minimum cross-sectional area was slightly stronger than that of NaCl. These results demonstrate the potential of NaCl to replace Na2CO3 in supporting the PS-mediated reduction of IFT in SP flooding.