Experimental investigations on synthesis, rheological characterization, and application potential of TiO2-PAM nanofluids for light paraffinic crude oil

Abstract

The performance of nanofluid is often affected by premature phase separation, agglomeration, and uncontrolled size. Single-step offers a synthesis of agglomeration-free, size-independent, and highly stable nanoparticles which neither demands for extensive sonication/energy but also uses a cost-effective precursor/accelerator. Thus, in this study, stable TiO₂ nanofluids of customized size (20 to 100 nm) and concentration (0.04 wt%-0.4 wt%) were prepared via a sol–gel method that involves (a) constant concentration (0.04 wt%) of TTIP + 0.5–1.5 ml of NH₄OH (type I nanofluids: T1, T2, and T3) and (b) constant concentration (1 ml) of NH₄OH + 0.1 wt%-0.4 wt% of TTIP (type II nanofluids: T4, T5, and T6). The nanofluids exhibited better zeta-potential (−53 to −69 mV) however, phase separation occurred due to NP settlement over the storage period of 80 d (−37 to −60 mV) as validated by the results of DLS, UV–vis, and electrical conductivity. Further, nanofluids were analysed for IFT reduction of 4 kinds of paraffin. Moreover, their spreading on the surface of shale, beach sand, and sandstone was checked via contact angle tests for wettability alteration in porous media. All nanofluids showed some wetting for rock surface however, the order of preferential wetting for shale, beach sand, and sandstone was T2, T3, and T1, respectively. With type II nanofluids, T4, T5, and T6 ranked for similar preferential wetting in shale, beach sand, and sandstone, respectively. Finally, viscosity and G′ tests were conducted at 30 and 90 °C, to understand the impact of thermal energy on the rheological properties of nanofluids. Nanofluids were viscous liquids with classical shear-thinning behaviour, and they exhibited a gel-like nature due to dominating G′ from low to high levels of strain (1–100 %). The thermal impact on viscosity and elastic nature of nanofluids was found variable as nanofluids of smaller particles had the least reduction in viscosity and G′ than the one of large particles or large concentration.