Synergistic Effect of Brine System Containing Mixed Monovalent (NaCl, KCl) and Divalent (MgCl2, MgSO4) Salts on the Interfacial Tension of Pure Hydrocarbon–Brine System Relevant for Low Salinity Water Flooding

Abstract

Interfacial tension (IFT) plays a vital role in the petroleum industry for enhanced oil recovery. In recent years, a new technology called “low salinity water flooding” has captured the attention of researchers because of its ability to alter IFT. However, the role of salt types and their impact on the IFT of pure hydrocarbon–water systems are not well understood which could help to develop robust models and processes. In the present investigation, we have considered both aliphatic (heptane) and aromatic (toluene) hydrocarbons along with set of nine mixed brine systems containing monovalent (NaCl, KCl) and divalent (MgCl2, MgSO4) salts with a wide range of compositions and concentrations for IFT studies which are otherwise not reported in the literature. Various combinations of monovalent salts (NaCl:KCl::25:75, NaCl:KCl::50:50, NaCl:KCl::75:25) divalent salts (MgSO4:MgCl2::25:75, MgSO4:MgCl2::50:50, MgSO4:MgCl2::75:25), and monovalent and divalent salts (NaCl:MgCl2::25:75, NaCl:MgCl2::50:50, NaCl:MgCl2::75:25) along with varying concentrations (0, 500, 750, 1 000, 2 000, 5 000, 10 000, 20 000 ppm) have been used. The experimental result reveals that combination of monovalent (NaCl) and divalent (MgCl2) salt in brine has significant impact on the reduction of the IFT of the n-heptane–brine system, and combination of divalent salts (MgSO4 and MgCl2) shows better impact on IFT reduction for the toluene–brine system. The mechanism of IFT variation at different salt concentrations and compositions has also been explained based on the Gibbs adsorption isotherm and specific ion effect based on the Hofmeister series. The study will be useful to understand the synergetic effect of these salts on the hydrocarbon–brine systems and also will help to develop robust models of IFT suitable for low salinity water flooding and other industrial operations.