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• The joint effects of ultrasound and solvation on oil viscosity were investigated. • The analysis of asphaltene structure by using FTIR and microscopy techniques. • The lowest viscosity was found for irradiation-then-dilution-treated crude oil. • Ultrasonic solvation reduced the ratio of aromatic rings to aliphatic chains. Production from heavy oil reservoirs faces challenges, such as accumulating heavy hydrocarbon materials like asphaltenes near the wellbore, resulting in low recovery rates. To enhance recovery and prevent formation damage, methods often focus on reducing oil viscosity. Solvents and ultrasonic waves have proven effective in this regard, though challenges related to asphaltene aggregation and structural changes persist. This study explores the impact of simultaneously applying ultrasonic radiation and solvents on crude oil's viscosity and asphaltene structure. Toluene and n-heptane, representing aromatic and paraffinic solvents, were employed. Viscosity measurements and Fourier transform infrared spectroscopy tests were conducted on sonicated crude oil diluted with solvents and solvent-diluted crude oil subjected to sonication. Results were compared to untreated and separately treated crude oil samples. The study found that the most effective viscosity reduction method involved blending sonicated oil with toluene under optimal radiation time and concentration conditions. Two primary mechanisms for viscosity reduction were identified. Firstly, there was the dissolution and aggregation of asphaltene clusters. Secondly, chemical changes in asphaltene molecular structure were observed, altering the ratio of aromatic rings to aliphatic chains. This research offers potential insights into how ultrasonication and solvation interact to modify crude oil structure. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights In this study, the influence of ultrasonic waves on the viscosity and thermal behaviour of a crude oil with high asphaltene content at different irradiation times and powers/frequencies was investigated. It was found that the ultrasonic radiation significantly reduced the oil viscosity before the oil cooled down. The viscosity was then remeasured after the irradiated oil cooled down to the ambient temperature to evaluate the reversibility in viscosity at various time intervals. For each ultrasonic frequency, an optimum irradiation time was found at which the cooled-down irradiated oil reached a minimum viscosity. For the ultrasonic radiation with a frequency of 46 kHz and an output power of 50 W, it was found that the permanent viscosity loss of the cooled-down oil irradiated for an optimum time of 8 min was 10 %. The effects of ultrasonic irradiation on thermal behaviour of the oil were analysed using thermogravimetric and differential thermal (TGA/DTA) methods to evaluate the relation between changes in viscosity and thermal properties of the oil. It was found that the weight loss of the irradiated-oil was more than that of the non-irradiated oil at the end of both the pyrolysis and oxidation stages. [ABSTRACT FROM AUTHOR]