With the continuation of oil production, the world’s light oil reserves are constantly shrinking. Global heavy oil reserves are still abundant; therefore, increasing light oil production has very important economic value. The exploitation of heavy oil is mainly hampered by its high viscosity and high pour point [
1]. Due to these obstacles, the traditional exploitation methods are no longer applicable [
2,
3,
4]. In order to improve its economic benefits, many technologies, such as chemical flooding, thermal flooding, and steam-assisted gravity flooding are used. Nevertheless, the utilization of these technologies can be very complicated for the following reasons. The viscosity reduction effect of chemical flooding agents varies greatly in different oil regions [
5]. Thermal flooding has the widest range of applications, but the oil viscosity remains higher after oil production [
6,
7]. Steam-assisted gravity flooding is limited by the various factors of layers of soil; therefore, the technique is still at the theoretical stage [
8,
9]. All the above technologies reduce the viscosity of heavy oil by physically reducing its viscosity for extraction purposes. Therefore, they cannot fundamentally solve the problem of the high viscosity of heavy oil, nor can they target the components affecting the high viscosity, such as resins and asphaltenes. Despite high levels of upgrading, the problem of high viscosity in heavy oil has not yet been solved effectively.
In traditional thermal recovery methods, during the process, the introduced high-temperature steam acts as a heat source to reduce the viscosity of the heavy oil contact layer in order to improve its fluidity, requiring increased energy input [
10]. When the temperature is lowered, the viscosity of heavy oil returns to its previous value. During the heat transfer process, the heavy oil is under high-temperature conditions; the large molecules are thermally cracked into smaller-sized lighter hydrocarbon molecules, which, in turn, reduce the viscosity of the heavy oil [
11,
12]. However, the degree of cracking is very low, and it is difficult to achieve the desired effect without the presence of a catalyst [
10]. Nowadays, the catalysts used for the aquathermolysis of heavy oil can be divided into six categories: water-soluble catalysts, oil-soluble catalysts, amphiphilic catalysts, minerals and zeolites, solid superacids, and dispersed nanoparticles [
13,
14,
15,
16]. The utilization of catalysts improved the viscosity reduction rate of heavy oil to varying extents, achieving satisfactory results. Chen et al. [
17] studied the transition metal catalysts used for the low-temperature cracking catalysis of heavy oil, the catalytic effect of which is most efficient at 180 °C. Suwaid et al. [
18] prepared oil-soluble transition metal-based catalysts (Fe, Co, Ni) to catalyze the hydrothermal decomposition of heavy oil at 300 °C. This approach enables high catalytic performance by simultaneously promoting the thermal decomposition and hydrogenation reaction of heavy components (rubber grease, asphaltenes, polycyclic aromatic hydrocarbons, long-chain alkanes, etc.). Li et al. [
19] catalyzed the hydrothermal cracking of heavy oil using a ZrO
2-TiO
2 catalyst modified with CTAB, achieving a 66.3% heavy oil viscosity reduction rate at 180 °C. The effect of alkyl chain length (C2, C4, C6, C8, C10, and C12), the counterion charge (chloride, thiocyanate, and tetrafluoroborate) of the ionic liquid, and skeletal group types (imidazolium, pyridinium, and thiazolium) on the catalysis of Mexican heavy oil and Canadian and Venezuelan pitch was investigated by Deepa et al. [
20]. A nanocatalyst for the low-temperature aquathermolysis of heavy oil was prepared by Li et al. [
21], achieving a 99.7% viscosity reduction rate. However, the mentioned reports are solely focused on the catalytic effect between the catalyst and the heavy oil; meanwhile, the interplay between the catalyst and the reservoir has been ignored. Studies show that the clay minerals in the reservoir can promote oil reserves from the source rock, while clay minerals mainly promote the conversion of kerogen [
22,
23]. Due to the properties of clay minerals, they readily undergo ion exchange and are able to act as catalyst carriers [
24]. Transition metal catalysts that are introduced into the reservoir will interact with the various mineral components found in the reservoir, forming new catalysts, which will increase the catalytic effect of aquathermolysis, while the viscosity of crude oil will decrease due to the increased hydrocarbon content. Therefore, it is of great significance to study clay-supported catalysts in order to enhance the conversion efficiency of crude oil into smaller-sized hydrocarbon molecules. Certain progress in the field of heavy oil aquathermolysis was achieved by Chen et al. [
25,
26,
27,
28,
29]. Transition metal ions were employed as a catalyst for the heavy oil aquathermolysis, achieving good viscosity reduction effects. Song et al. [
29] used cobalt tartrate as a catalyst, obtaining an improved viscosity reduction rate. The reduction of heavy oil viscosity at low temperatures was demonstrated by using ferric citrate as a catalyst [
30]. An 84.2% decrease in viscosity was reached by Hao et al. [
31] by employing a series of Mannich base-transition metal coordination complexes.
In this study, the physicochemical conditions of the catalytic decomposition of heavy oil by aquathermolysis were studied. On the basis of previous results, the effect of various minerals on catalysis was investigated. To simulate the catalysis of heavy oil, a combination of a clay mineral with the most optimal properties (sodium bentonite) and a transition metal complex with a catechol ligand was used. TGA/DSC, GC, and GC-MS methods were used to study the ongoing changes during heavy oil aquathermolysis. In addition, commonly used compounds were selected to simulate the material changes of heavy crude oil, and GC-MS was used to determine the individual fractions.