Effect of the NiO/SiO₂ Nanoparticles-Assisted Ultrasound Cavitation Process on the Rheological Properties of Heavy Crude Oil: Steady State Rheometry and Oscillatory Tests

This manuscript has the primary objective of demonstrating the changes in the rheological behavior of heavy crude oils (HO) in response to the application of ultrasound cavitation assisted with NiO-functionalized SiO₂ nanoparticles (SiNi1). A HO with an asphaltene mass fraction of 17.0% was used for the tests which were carried out at 25 °C and 1 atm with a fixed ultrasound frequency and power of 37 kHz and 400 W, respectively. The viscosity measurements were performed on four different samples: the HO in the absence of nanoparticles and ultrasound irradiation (sample A), the HO alongside ultrasound irradiation (sample B), the HO with the addition of nanoparticles (sample C), and, finally, the HO in the presence of the mentioned nanomaterial and ultrasound irradiation (sample D). It was observed that a single treatment, whatever it is, only slightly changed the original HO rheology, while the cooperative action of ultrasound cavitation and nanoparticles addition induced several measurable differences with respect to the HO: The viscosity was reduced up to 50–60%, depending on the applied shear rate; the power per unit of volume dissipated during a hysteresis cycle was decreased of about the 70%; the sample elasticity was measurably reduced, and accordingly, the relaxation time measurable for the original HO was not detectable anymore. These findings can be explained by hypothesizing that the original HO viscoelastic microstructure is broken down by the proposed combined treatments as the asphaltenes may stably adsorb on the nanoparticles and the subsequent size reduction process of the asphaltene aggregates is enhanced by the ultrasound irradiation.