Comparative Effectiveness of Thermal Stability and Rheological Properties of Nanofluid of SiO2–TiO2 Nanocomposites for Oil Field Applications

Thermal stability is becoming a barrier for silica nanofluid use at high temperatures in several industrial applications including oil fields. Homoagglomeration of SiO2 nanoparticles (NPs), which leads to premature sedimentation of large NP clusters, is one of the reasons for the loss in thermal stability. However, this can be improved by incorporating a thermally conductive co-stabilizer, which not only reduces the homoagglomeration of SiO2–SiO2 NPs but also improves their rheological properties. Thus, this study reports the use of titania (TiO2) NPs in improving the thermal stability and rheological properties of silica nanofluids for high-temperature applications. TiO2 concentration was kept low and constant (0.1 wt %), whereas the SiO2 concentration was varied from 0.1 to 1.0 wt %. In nanofluid synthesis, water-soluble partially hydrolyzed polyacrylamide of 1000 ppm is used as a viscosity enhancer. Different techniques such as visual inspection, dynamic light scattering, ultraviolet–visible (UV–vis) spectroscopy, thermogravimetric analysis, and field emission scanning electron microscopy were used to characterize nanofluids. The thermal stability and rheological properties of HS nanofluids were not only affected by agglomeration and high temperature but also showed least dispersion (45 days). TiO2 inclusion controlled the rate of homoagglomeration in silica nanofluids, resulting in SiO2–TiO2 nanocomposites of least size, and better dispersion (71 days) and thermal stability (only 78% mass loss) were observed in HTS nanofluids. Thus, thermally stable silica nanofluids of improved flow behavior are proposed for oil field applications where conventional nanofluids may find limitations. Finally, the enhanced oil recovery potential of silica nanofluids is studied and compared with the ones of silica and titania at real oil field conditions of high temperature (90 °C) and saline environment of 5 wt % NaCl. The oil recovery potential of conventional silica nanofluids increased by 12% original oil in place, with the inclusion of 0.1 wt % TiO2 in the system.