The present review paper discusses the different aspects related to the chemical transformation of oil components through ultrasound assistance. Ultrasound intensifies heat and mass transfer processes in oil production and treatment, which is used to separate water–oil emulsions, optimize pumping, clean the bottomhole zone, and more. The main reason for the positive effect of ultrasound is the cavitation phenomenon, which forms vapor–gas bubbles that cause changes in the structure and properties of dispersed phases, intensifying processes such as dissolution, extraction, and emulsification. The inhomogeneities in the medium being processed also reduce resistance to bubble formation and increase the intensity of technological processes. It is believed that ultrasonic treatment of heavy oil influences the colloid structure of oil. Such effects were observed in several studies. Despite the widespread use of ultrasound in oil processing, the chemical transformation of hydrocarbons during ultrasonic treatment remains an understudied area, particularly for heavy oil. Furthermore, the transformation mechanism of high-molecular-weight fragments of oil under ultrasonic energy is still poorly understood. Heavy oil can benefit greatly from ultrasonic treatment, both after production for pipeline transportation or plant processing and in the reservoir. This is due to the improved mobility of oil in rock and the chemical transformation of high-molecular components, such as resins, asphaltenes, and paraffins. These transformations contribute to the overall improvement of heavy oil processing, making it a crucial area for further research and development. In this review paper, we will explore the latest innovations in oil processing, specifically focusing on the chemical transformation of oil components through ultrasound assistance. This will include a comprehensive analysis of the underlying mechanisms of ultrasonic treatment and their impact on the chemical composition of oil. The review will also include a discussion of the current state of the art and future directions for research in this field, highlighting the potential for further advancements in the use of ultrasound in oil processing.

Aquathermolysis is a promising process for improving the quality of heavy oil under reservoir conditions. However, the application of catalysts during the process can significantly promote the transformation of the heavy fragments and heteroatom-containing compounds of crude oil mixtures into low-molecular-weight hydrocarbons. This research paper conducted a comparative analysis of the catalytic effectiveness of water-soluble metal salts like NiSO₄ and FeSO₄ in the process of aquathermolysis to upgrade heavy oil samples extracted from the Ashal’cha reservoir. The temperature of the experiment was 300 °C for a duration of 24 h. Compared to the viscosity of the native crude oil, the Fe nanoparticles contributed to a 60% reduction in viscosity. The viscosity alteration is explained by the chemical changes observed in the composition of heavy oil after catalytic (FeSO₄) aquathermolysis, where the asphaltene and resin contents were altered by 7% and 17%, accordingly. Moreover, the observed aquathermolytic upgrading of heavy oil in the presence of FeSO₄ led to an increase in the yield of gasoline fraction by 13% and diesel fraction by 53%. The H/C ratio, which represents the hydrogenation of crude oil, increased from 1.52 (before catalytic upgrading) to 1.99 (after catalytic upgrading). The results of Chromatomass (GC MS) and Fourier-transform infrared spectroscopy (FT-IR) show the intensification of destructive hydrogenation reactions in the presence of water-soluble catalysts. According to the XRD and SEM-EDX results, the metal salts are thermally decomposed during the aquathermolysis process into the oxides of corresponding metals and are particularly sulfided by the sulfur-containing aquathermolysis products.

Ultrasound technologies are well-known for their ability to intensify the heat and mass transfer processes. Hence, ultrasonic treatment processes are widely applied for the separation of oil–water emulsions, optimization of oil pumping processes, cleaning the bottomhole zone, etc. However, the main phenomenon under the positive influence of ultrasonic waves on such processes is the cavitation bubbles implosion on the water–oil boundary. It is well-known that ultrasound energy contributes to the reversible viscosity reduction in heavy oil systems. However, it is possible to exhibit chemical destruction of the weakest carbon–heteroatom bonds in the structure of the asphaltenes. This study investigates the influences of controllable ultrasound waves with frequency ranges of 20–60 kHz under the exposure time of 60 s on the rheology of a heavy crude oil sample produced from the Ashalcha reservoir (Tatarstan Republic, Russia). The specific feature of this study is the application of multi-frequency ultrasonic exposure with a wide spectrum of side harmonics with the frequency up to 400 kHz. The results of the Saturates, Aromatics, Resins and Asphaltenes (SARA) analysis method support the chemical consequences of ultrasonication of crude oil. The content of resins under the irradiation of ultrasound waves altered from 32.5 wt.% to 29.4 wt.%, while the number of aromatics hydrocarbons raised from 24.3 wt.% to 34.1 wt.%. The Gas Chromatography—Mass Spectroscopy (GC-MS) analytical analysis method was applied to qualitatively compare the composition of saturated and aromatics fractions between the initial and upgraded heavy crude oil in order to show the chemical destruction of asphaltene bonds after the ultrasonic treatment. It was demonstrated that ultrasound waves allowed chemical conversion of asphaltene fragments that led to irreversible viscosity reduction. The viscosity of the heavy oil sample under the favorable ultrasonic irradiation conditions reduced from 661.2 mPa·s to 178.8 mPa·s. This advantage can be used to develop enhanced oil recovery methods and partial upgrading processes in downstream conditions.

The purpose of this study is to enhance the quality of heavy oil through refinement using aquathermolysis with the simultaneous injection of steam and thermally stable nonionic surfactants (NS). To achieve this, the NS R-PPG of the nonionic type was synthesized, and the optimal product structures were characterized using infrared (IR) methods. Furthermore, the thermal stability of the synthesized NS R-PPG was investigated in line with the requirements for surfactants used in heavy oil applications. Subsequently, the study delved into investigating the hydrothermal upgrading of heavy oil with a catalyst, involving the joint participation of steam and surfactants at a temperature of 250 °C. Additionally, we assessed the improved oil characteristics resulting from the experimental process through SARA analysis, elemental analysis, GC, and viscosity reduction evaluations. The experimental results demonstrated distinct effects concerning the presence and absence of surfactants on heavy oil. Based on these findings, we conclude that surfactants play a crucial role in dispersing asphaltene clusters, thereby facilitating the decomposition process under mild thermobaric conditions, leading to a noticeable increase in the content of light fractions. Furthermore, as per the results of the elemental analysis, surfactants contribute significantly to the desulfurization of heavy oil. Overall, the incorporation of surfactants during hydrothermal upgrading resulted in an irreversible reduction in the viscosity of heavy oil, thereby enhancing its overall quality.

In this study, for the first time we investigated the in situ upgrading performance of Na metal nanoparticles, which were obtained by dispersing small pieces of sodium in liquid paraffin up to certain dispersity. In situ aquathermolytic reactions were modeled in a high pressure–high temperature reactor coupled with a Gas Chromatography (GC) system at a temperature of 250 °C for 24 h using a heavy oil sample, produced from the Ashal’cha reservoir, Republic of Tatarstan (Russia). The mean particle size of Na nanoparticles was 6.5 nm determined by the Dynamic Light Scattering (DLS) method. The nanoparticles were introduced to the reaction medium with a concentration of 2 wt.% The upgrading performance of Na nanoparticles was evaluated by several analytical methods such as Gas Chromatography (GC), elemental analysis (CHNS), SARA, Gas Chromatography–Mass Spectroscopy (GC-MS), FT-IR spectroscopy and viscosity measurements. It was revealed that Na nanoparticles interact with water to yield hydrogen gas, the concentration of which increases from 0.015 to 0.805 wt.% Moreover, the viscosity of upgraded heavy oil was reduced by more than 50% and the content of low-molecular-weight hydrocarbons in saturated and aromatics fractions was increased. The Na nanoparticles contributed to the utilization of hydrogen sulfide and carbon dioxide by 99 and 94 wt.%, respectively.

Catalytic thermolysis is considered to be an effective process for viscosity reduction, the conversion of high-molecular components of oil (resins and asphaltenes) into light hydrocarbons, and the desulfurization of hydrocarbons. In this paper, we conducted non-catalytic and catalytic thermolysis of a heavy oil sample isolated from the Ashalcha oil field (Tatarstan, Russia) at a temperature of 250 °C. Fullerene C60 nanoparticles were applied to promote selective low-temperature thermolytic reactions in the heavy oil, which increase the depth of heavy oil upgrading and enhance the flow behavior of viscous crude oil. In addition, the influence of water content on the performance of heavy oil thermolysis was evaluated. It was found that water contributes to the cracking of high-molecular components such as resins and asphaltenes. The destruction products lead to the improvement of group and fractional components of crude oil. The results of the experiments showed that the content of asphaltenes after the aquatic thermolysis of the heavy oil sample in the presence of fullerene C60 was reduced by 35% in contrast to the initial crude oil sample. The destructive hydrogenation processes resulted in the irreversible viscosity reduction of the heavy oil sample from 3110 mPa^.s to 2081 mPa^.s measured at a temperature of 20 °C. Thus, the feasibility of using fullerene C60 as an additive in order to increase the yield of light fractions and reduce viscosity is confirmed.