Surface free energies parameters in carbonate rock/nonacidic crude oil/brines systems.

Since knowing the effect of salt type is a vital parameter during smart-water injection for enhanced oil recovery (EOR) purposes, surface-free energies on the carbonate surface contacted by crude oil and different aqueous solutions with 0.7 ionic strength (about the ionic strength of seawater) are studied for solutions containing NaCl, Na2SO4, KCl, CaCl2, MgCl2, and MgSO4. For this purpose, the interfacial tension (IFT) of crude oil/aqueous solution and contact angle of oil/rock/brine are measured concomitant with the calculation of works of cohesion (WC) and adhesion (WA) as well as spreading coefficient (SC). Maximum equilibrium IFT reduction was observed for MgSO4 (from 22.7 to 12.71 mN.m−1). Besides, the calculated adsorption times using the exponential decay model reveal that the chloride salts of MgCl2 and KCl has the minimum and maximum adsorption time of 1600 s and 3400 s, respectively. Moreover, the contact angle measurements demonstrate that it is possible to change the wettability condition of rock surface from strongly oil-wet to strongly water-wet (about 20°) using Na2SO4 while the other utilized salts can change the contact angle from 170° to neutral wetness condition of 100°. The obtained results show that the best SC was obtained for DW due to its significant wettability alteration capability (from strongly oil-wet toward neutral state) compared with brine solutions. To sum up, according to the results it can be concluded that solution congaing MgSO4 can introduce the lowest IFT value and the highest wettability alteration from the initial strongly oil-wet state toward a neutral state, while Na2SO4 solution leading the lowest contact angle of about 20° which is the most favorable condition (strongly water-wet). [ABSTRACT FROM AUTHOR]