Toward mechanistic understanding of interfacial tension behavior in nanofluid-model oil systems at different asphaltene stability conditions: The roles of nanoparticles, solvent, and salt concentration

Abstract

Surface phenomena between liquid-liquid phases like interfacial tension (IFT) can significantly affect the recovery factor in hydrocarbon reservoirs. Nanotechnology could be used as a chemical method for enhanced oil recovery (EOR) via IFT reduction and wettability alteration. Nanoparticles could draw the asphaltene molecules to the interface of crude oil and brine water to reduce IFT. Several researches were conducted on SiO2 nanoparticles due to their accessibility with low price and their good performance in wettability alteration. However, the mechanism of IFT changes under different conditions of asphaltene instabilities and in the presence of nanoparticles has not been fully understood yet. In this study, the stability of SiO2 nanofluid in the presence of different NaCl concentrations was evaluated by visual observation, spectral analysis, and measuring the size of the hydrodynamic diameter of the particles. Besides, Fourier transform infrared (FTIR) spectroscopy of asphaltene was measured. Then, the influence of different parameters, including asphaltene content, water salinity, and nanoparticle concentration on the IFT between synthetic oil and nanofluids, was measured by the pendant drop shape method using drop shape analysis apparatus. Furthermore, IFT changes due to asphaltene instability at different n-heptane content and the instabilities of SiO2 nanoparticles at higher salinities were discussed. The IFT between synthetic oil and brine was measured. Results showed that the IFT reduces (about 23 mN/m) at very high salt concentrations due to the presence of free salt ions attracted with the hydrocarbon phase. Also, increasing the instability of asphaltene to a particular n-heptane concentration reduces the IFT variation by NaCl concentration from 5 mN/m to 2.5 mN/m because less potential remains for asphaltene adsorption at the interface. In addition, the increase in n-heptane concentration leads to a decrease and then an increase in IFT. Furthermore, as the nanoparticles become unstable at high salinities, the IFT increases significantly. Moreover, the IFT difference between the case with nanoparticle and the case without it is about 20 mN/m.