Investigation of Smart Water Injection into Water-Wet Carbonate Reservoirs

In recent years, smart water injection as an efficient method of oil extraction has received particular attention from different researchers. Concentration and salt type are important and influential factors in the thermodynamic equilibrium properties such as interfacial tension (IFT) and wettability. In this study, salt type performance on the physical and chemical properties of reservoir rock, changing the balance into the desired direction, and increasing oil production have been investigated in the smart water process injection. IFT and contact angle measurements and core flood test were performed to achieve the goal. Initially, rocks from the Baba Koohi outcrop in Fars province were prepared. Then, scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectroscopy were performed. The effect of NaCl, KCl, Na2SO4, and MgCl2 salts and the combination of MgCl2 / NaCl salts with the same ionic strength of 0.7 on the wettability alteration of water-wet dolomite carbonate rock has been investigated. The effect of the above salts on the IFT reduction has also been investigated. In addition, with the help of IFT and contact angle values, the spreading coefficient was calculated to select the appropriate injection salt for the core flooding tests. Finally, flooding experiments were performed with the cores with close permeability and porosity. According to the results obtained from the measured contact angle, the type of salt does not significantly affect changing the wettability of water-wet carbonate rocks. Despite the IFT reduction in the presence of salt, this effect on the spreading coefficient was insignificant. However, the injection of an aqueous solution containing MgCl2 salt resulted in the extraction of 6.1% of the original oil in place (OOIP) in the tertiary stage, which indicates the complexity of the dominant mechanism during smart water injection into the carbonate reservoirs. Besides, the results of this study show that aging time is a practical and useful parameter in oil extraction.