Formulation and Characterization of Quaternary Ammonium Compounds for Novel Application in Enhanced Oil Recovery

Enhanced oil recovery (EOR) is the process of residual oil production in the tertiary stage. It requires the injection of external energy sources such as gases, chemicals, and thermal energy in the reservoirs. Chemical enhanced oil recovery (CEOR) can boost the oil recovery significantly by improving the microscopic displacement of oil trapped in the pore spaces of the reservoir rock. Each type of chemical flooding depends on different mechanisms to enhance the oil recovery. Surfactant flooding aims to reduce interfacial tension, alter the wettability of rock to more water wet, and promote the displacement of oil in porous media. The surfactant performance can be affected by temperature, salinity, pH, surfactant concentration, and adsorption. Hence, a comprehensive study of fluid–fluid and rock–fluid interactions is required before any surfactant flooding process. This characterization study aims to evaluate the cationic surfactants, tetramethylammonium chloride (TMAC) and hexadecyltrimethylammonium chloride (HTMAC), which have the potential to be EOR fluids for carbonate reservoirs in harsh conditions. The surfactant solutions were prepared in seawater. TGA, FTIR, solubility and compatibility, IFT, contact angle, and zeta potential tests have been carried out to characterize these surfactants. The obtained results revealed that the cationic surfactants are stably compatible under harsh conditions. Moreover, the results demonstrated that HTMAC has high potential to be used as an EOR fluid by lowering the IFT from 21.4 to 0.16 mN/m and shifting the contact angle from 159.6 to 40° within 24 h of aging at a low concentration (100 ppm). In contrast, TMAC has little effect on IFT; it reduced IFT from 21.4 to 10.2 mN/m and could not alter the wettability to a water-wet condition. Further investigation has been done using a cosurfactant (SS-885) with TMAC to evaluate the effect of this mixture on IFT and contact angle. Using a low concentration (100 ppm) of the mixture reduced the IFT to an ultralow value (0.03) mN/m but had little effect on the contact angle.