Contrary to sandstone reservoirs, carbonate reservoirs have an oil-wetting nature. Water flooding of these fractured reservoirs with low permeability matrix blocks is not recommended unless a wettability alteration process is possible. Imbibition is an oil recovery mechanism for these types of reservoirs, if the rock matrix is water wet and there is enough water in fractures in contact with the matrix. Heavy matrix oil, high interfacial tension (IFT), oil-wet matrix sample, and limited contact area of matrix with water in fractures, requires additional effort to enhance the oil recovery by capillary imbibition. Surfactants can be injected into naturally fractured reservoirs to improve the capillary imbibition recovery performance. A well-known surfactant is Hexadecyl Trimethyl Ammonium Bromide (C 16TAB), which is an appropriate type of surfactant for these kinds of reservoirs. However, due to its high cost, it is rarely used in the real case
studies. In the present paper a simple and inexpensive method has been proposed for synthesizing this surfactant. Surfactant at different concentrations have been dissolved in high salinity brine, and the interfacial tension (IFT) between the aqueous solution and the oil has been measured by pendent drop method. In addition, the contact angle between the oil and the aqueous solution is measured by sessile drop method, and during the experiment, photos were taken every two seconds in order to analyse the IFT and the contact angle obtained. It has been found that reduction of IFT continues up to critical micelle concentration of the surfactant. Furthermore, a correlation has been obtained to predict the IFT between the oil and the high salinity aqueous solution containing different surfactant concentrations. Finally, the best surfactant concentration is obtained for reservoir case studies.