Chemical enhanced oil recovery in carbonate oil reservoirs using a combination of zwitterionic and cationic surfactants in the presence of different salts

In this study, mechanisms of surfactant mixture and different salts for enhanced oil recovery in carbonate oil reservoirs were investigated experimentally. Therefore, a novel idea of combining two different surfactants including cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and TR-880 as a zwitterionic surfactant was investigated. The efficiency of the surfactant mixture was investigated in the presence of different concentrations of magnesium chloride (MgCl2) and calcium chloride (CaCl2) and sodium chloride (NaCl). The efficiency of the prepared solutions for improving oil recovery was investigated through interfacial tension (IFT) and contact angle measurement, zeta potential measurements, micro-model experiments and core flooding experiments. Experimental results showed that critical micelle concentrations (CMC) value of CTAB surfactant and TR-880 is 350 and 1000 ppm, respectively. Experimental results showed that CTAB surfactant was more effective than the TR-880 in reducing IFT and contact angle values. In addition, the surfactant mixture prepared by CMC values of both surfactants was even more effective than the surfactants alone. In addition, optimum concentration of MgCl2 and CaCl2 was found to be 6000 ppm, however, MgCl2 was more compatible with surfactant mixture than CaCl2 in reducing IFT and contact angle. In this study, minimum IFT of 1.65 mN/m and contact angle of 49° were achieved at optimum MgCl2 concentration of 6000 ppm and 32,000 ppm NaCl in the presence of surfactant mixture. In addition, the values were further reduced to 1.25 mN/m and 41° when all three salts (6000 ppm MgCl2 + 6000 ppm CaCl2 + 26,000 ppm NaCl) were used in the presence of CMC values of both surfactants. The secondary oil recovery factor results showed that a solution prepared by 6000 ppm of MgCl2 and 32,000 ppm NaCl and CMC values of both surfactants resulted in maximum oil recovery factor of 76.36% in a micro-model set up. In addition, the maximum oil recovery factor of 79.70% was achieved during tertiary recovery in a core flooding system.