A novel hybrid nano-smart water with soluble chlorides and sulphates and silica-montmorilant-xanthan nanocomposite for EOR: Insights from IFT and contact angle measurements and core flooding tests

Injection of smart water mixed with various oil-water interfacial tension (IFT) reduction agents such as nanoparticles (NPs) into oil reservoirs is a proven enhanced oil recovery (EOR) method. A novel silica-montmorilant-xanthan was used to formulate novel hybrid nano-smart water solutions for EOR. Performance of the hybrid nano-smart water solutions as dispersion media at optimum salinity and NC concentrations was assessed. Stability, IFT, zeta potential, and wettability alteration of the solutions were assessed to find the optimum concentrations. Two groups of single and binary salts were used in the smart waters. Smart waters with individual NaCl, KCl, MgCl₂, CaCl₂, Na₂SO₄, MgSO₄, CaSO₄, and K₂SO₄ salts at concentrations of 1000, 2000, 4000, and 10,000 ppm in one group. Smart waters with a combination of each of the chlorates with various sulphates with equal ratios (1000/1000, 2000/2000, 4000/4000, and 10,000/10,000 ppm) in distilled water in another group. Smart waters with a combination of each of chlorates with various sulphates with equal ratios in distilled water in another group. Then the effects of the solution of these salts on IFT and contact angle in water-oil-sandstone and water-oil-carbonate systems were investigated. The optimum concentration of K₂SO₄+MgCl₂ for the sandstone sample was determined as 1000/1000 ppm with 1000 ppm of the NC. The optimum concentration of MgSO₄ for the carbonate sample obtained was 10,000 ppm with 250 ppm of the NC. The lowest IFT (15.42 mN/m) was obtained for the nanofluid with an NC concentration of 250 ppm. The results suggest that the salt-in effect and nano-film formation are behind the IFT reduction. Contact angle at the same NP concentration decreased from 109° (preferentially oil wet) to 33° (strongly water-wet) in the carbonate sample. For sandstone, the contact angle at the same NC concentration increased from 77° (preferentially water-wet to 117° - preferentially oil wet). Finally, we used the optimum formulas for core flooding to examine the performance of the prepared hybrid nano-smart water solutions. Using these novel hybrid nano-smart waters yields oil recoveries of up to 54% and 60% of the Oil Originally in Place (OOIP) in carbonate and sandstone samples, respectively.