One-Pot synthesis of modified-cationic surfactants for enhanced oil recovery applications in carbonate reservoirs

In this study two cationic surfactants, dodecyltriethylammoniumbromide (C(12)TEAB) and hexadecyl-triethylammoniumbromide (C(16)TEAB) were prepared. The formation of synthezied surfactants were confirmed using FTIR and HNMR spectroscopy. Electrical conductivity, interfacial tension and surface tension methods were used to determine the critical micelle concentrations (CMC) of these surfactants. To understand the behavior of synthesized surfactants in harsh environments, the CMC was measured in deionized water (DIW), sea water and petroleum formation water. Using electrical conductivity technique, for C(12)TEAB surfactant the CMC values of 4000 ppm, 2000 ppm and 850 ppm were recorded in DIW, sea water and formation water respectively. For C(16)TEAB surfactant, the CMC values of 420 ppm, 190 ppm and 115 ppm were obtained in DIW, sea water and formation water respectively. The similar CMC results were obtained using the interfacial tension (IFT) and surface tension (ST) methods. Reduction of IFT between crude oil and formation water and also alteration of wettability of petroleum reservoir of carbonated rock from oil-wet (large contact angle) to water-wet (small contact angle) are two major factors affecting chemical enhanced oil recovery (EOR). Interfacial tension (IFT), surface tension (ST) and contact angle measurements were carried out using an IFT-PDSA-06 apparatus (Apex Technologies Company, Iran). The IFT and ST of these surfactants were also carried out in DIW, sea water and formation water. For C(12)TEAB surfactant, the IFT values of 0.051 mN/m, 0.036 mN/m and 0.023 mN/m were recorded in DIW, sea water and formation water respectively. The IFT values of 0.044 mN/m, 0.026 mN/m and 0.0126 mN/m were measured for C(16)TEAB surfactant in DIW, sea water and formation water respectively. The effect of temperature on IFT was studied for both surfactants. When temperature increases, IFT decreases. The reduction of IFT continues up to 55 degrees C, then the IFT increases with increasing temperature. For C(12)TEAB surfactant, the ST values of 44.9 mN/m, 38.8 mN/m and 31.8 mN/m were obtained in DIW, sea water and formation water respectively. In similar measurements for C(16)TEAB surfactant, the recorded ST values were 33.95; 32.9 and 32.22 mN/m in DIW, sea water and formation water respectively. In wettability alteration study both surfactants altered the contact angle from oil-wet to water-wet conditions. Using formation water and C(12)TEAB surfactant, the contact angle varied from 96.4 degrees to 54.5 degrees. In similar study using C(16)TEAB surfactant the contact angle changed from 92 degrees to 46.1 degrees. The contact angles of these surfactants in DIW and sea water were also measured and reported. The results of IFT and wettability studies demonstrated excellent potential application of synthesized surfactants in EOR process in carbonate petroleum reservoirs.