The current study explores the performance of homolog series of gemini imidazolium ionic liquids with different spacer lengths, [C4im-Cn-imC4][Br2], n = 2, 4 and 6, for reducing interfacial tension in the presence of NaCl, MgCl2 and their mixture. The studied system was crude oil-water for which interfacial tension reduction is crucial in the chemical enhanced oil recovery. Results show a drastic interfacial tension reduction in the presence of the gemini ionic liquids due to their strong amphiphilic nature. Results also demonstrate a remarkable synergism in the presence of NaCl and MgCl2 salts, stronger with their mixture, that causes the maximum interfacial tension reduction to the extent of 67.1, 79.6 and 71%, for n = 2, 4 and 6 respectively, at the corresponding critical micelle concentrations and stronger for the mid-size spacer of n=4. The greater performance of the ionic liquids in the presence of salts can be attributed to a more adsorption and compact arrangement of ionic liquids at the interface by salting out effect and neutralizing electrostatic repulsion between the ionic liquids head groups. This abnormal variation in the interfacial tension implies the influence of high salinity brines in the reservoirs, which is important in operational and economical points of view and that saline waters could be used for injection in crude oil reservoirs in enhanced oil recovery using ionic liquids as green materials.
