Experimental investigation of wettability alteration, IFT reduction, and injection schemes during surfactant/smart water flooding for EOR application

In recent years, the application of smart water and surfactant in order to improve oil recovery has attracted special attention in carbonate reservoirs. In this research, the effects of various salts in smart water and two surfactants of Cetyl Trimethyl Ammonium Bromide (CTAB) and Sodium Dodecyl Sulfate (SDS) on the wettability alteration of carbonate rock and IFT were studied. Besides, along with micromodel flooding, core flooding tests were conducted to assess the amount of oil recovery at reservoir conditions as an injection scheme was used. In this regard, the results illustrated that the presence of CTAB or SDS in seawater (SW) can act better in contact angle reduction compared to smart water. Also, a four times increase in the concentration of SO42- and removing Na+ from SW reduced the contact angle to 68 & DEG; and 71 & DEG;, respectively, being the best possible options to alter the carbonate surface wettability to more water-wet states. Moreover, in the second-order process in which the rock section was first placed in SW, and then was put in the smart solution (with or without surfactant), CTAB had a great effect on the wettability alteration. In the case of IFT reduction, although SW4Mg(2+), compared to other ions, better decreased the IFT to 17.83 mN/m, SW + SDS and SW + CTAB further declined the IFT to 0.67 and 0.33 mN/m, respectively. Concerning different ions, divalent cations (Mg2+ and Ca2+) show better results in improving oil recovery factor. However, the combination of SW and surfactants has a more positive effect on boosting oil recovery, as compared to smart water flooding. It should be mentioned that the first-order injection is better than the second-order one since SW is flooded at first, and then, after the breakthrough, smart water is injected into the micromodel. In addition, the core flooding tests showed that SW + CTAB and SW + SDS in tertiary injection increased the oil recovery to about 59 and 57%, respectively, indicating that the presence of CTAB could be more effective than that of SDS.

Automated summary

In recent years, the use of smart water and surfactants to enhance oil recovery in carbonate reservoirs has gained significant attention. This study investigated the impact of various salts in smart water and two surfactants (CTAB and SDS) on wettability alteration and interfacial tension (IFT) in carbonate rock. Micromodel and core flooding tests were conducted to evaluate the oil recovery under different injection schemes. The results showed that CTAB or SDS in seawater (SW) had a stronger contact angle reduction effect compared to smart water. Increasing the concentration of SO42- and removing Na+ from SW resulted in more water-wet states. Divalent cations (Mg2+ and Ca2+) showed better performance in improving oil recovery. The combination of SW and surfactants had a more positive effect on boosting oil recovery compared to smart water flooding. The first-order injection scheme was more effective than the second-order injection scheme. SW + CTAB and SW + SDS in tertiary injection increased the oil recovery to about 59% and 57%, respectively, with CTAB being more effective than SDS.