Effect of NiO/SiO2 nanofluids on the ultra interfacial tension reduction between heavy oil and aqueous solution and their use for wettability alteration of carbonate rocks

One of the important factors in enhanced oil recovery (EOR), which leads to better oil flow in reservoirs and increases the recovery efficiency of the reservoirs, is the reduction of surface tension (S.T) and interfacial tension (IFT). The effect of NiO and SiO2 nanoparticles and their nanocomposites as NiO/SiO2 on the reduction of oil/water interfacial tension was investigated for the heavy oil of Soroush field located in Iran with a density of 0.965 g/cm(3) and viscosity of 1310 cP at 22 degrees C. NiO and SiO2 nanoparticles were produced by sol-gel-hydrothermal process and NiO/SiO2 nanocomposites were synthesized by co-precipitation-hydrothermal method. The interfacial tension of water/Soroush oil was measured to be 29.02 mN/m, as the reference, in the absence of nanoparticles. Water-based nanofluid of 30 wt% NiO/SiO2 and 28 wt% Fe@ NiO/SiO2 nanocomposites that benefits the synergism of the Fe promotor, decreased the IFT to 1.28 mN/m and less than 1 mN/m, respectively. In addition, the key factors such as concentration, aging time and salinity affect were studied in variation of S.T and IFT. It was found that 8 v/v% of the 30 wt% NiO/SiO2 diluted in water had the best efficiency in reducing the S.T and IFT, while preheating time of nanofluids and salinity of water that the nanofluid dissolved in had negligible impacts on surface and interfacial tension. Moreover, as the 30 wt% NiO/SiO2 nanocomposites were essentially hydrophobic, novel hydrophilic and eco-friendly nanocomposites of 30 wt% NiO/SiO2 were also synthesized through smart surface modifications by polyethylene glycol (PEG 6000) and polydimethylsiloxane. It was shown that the surface-modified nanocomposites could reduce the S.T and IFT significantly and alter the wettability of a strong oil-wet carbonate rock to water-wet condition.