Given the ever-increasing demand for and consumption of fuels around world, the exploitation, production, and processing of available hydrocarbon sources (heavy oil and natural bitumen) will bridge the gap of lack of supply. Consequently, their exploitation is not an easy task to achieve, because of high viscosity and low API gravity (high content of resins and asphaltenes, including heavy metals) [
1,
2]. A decrease of viscosity and density, as well as heteroatom and metal removal, are the main purpose of the hydrothermal upgrading process of heavy crude oil. Nowadays, many thermal methods, namely in-situ combustion (ISC), microwave heating (MWH), and dry pyrolysis, are applied for heavy oil recovery, despite the need for heating systems to heat the reservoir formation to reduce the viscosity of the oil, which often happens with a significant release of gases and coke formation, decreasing the yield of oil recovery [
3,
4,
5,
6,
7,
8]. The in-situ steam injection process has been used for decades to improve the rate of heavy oil recovery through three methods: steam-flooding, Cyclic Steam Stimulation (CSS), and, recently, Steam-Assisted Gravity Drainage (SAGD); of these, steam injection-based methods are the most widely applied [
9]. However, several investigations have been conducted to highlight and develop thermal techniques to achieve the goal of heavy oil recovery. Thermal methods, including steam injection, in-situ combustion, hot water injection, etc., are the most well-known techniques and are usually applied to the production and processing of heavy oils by reducing the viscosity and increasing the flow characteristics [
6,
10,
11]. As for in-situ combustion, although it has a high displacement capacity, its wide application is still limited due to its complexity, as well as the difficulty of controlling and predicting the burning front (e.g., combustion is unstable) [
12]. Other methods, such as ultrasound and magnetic physical treatments, have also been advanced but have not yet been fully commercialized [
13,
14]. Steam injection is by far the most widely used thermal method for heavy oil recovery. Nevertheless, in the process of its application, many problems have been discovered; for example, for every 2–5 barrels of water injected as steam, one barrel of oil is produced, giving it significant energy consumption with a high environmental impact [
15]. This implies that significant volumes of water and natural gas are needed for steam generation, which adds to the capital and operating cost. In addition, oil produced from steam-enhanced recovery processes requires the addition of expensive diluents to support pipeline transportation to refineries, as well as additional surface upgrading to meet refinery feedstock specifications. Therefore, any effort that helps to improve steam injection efficiency by solving or relieving one or more of the aforementioned problems is worth encouraging. Due to the search for new technologies for the improved recovery of heavy crudes, these processes have been studied and applied both conventionally and in a hybrid way in conjunction with solvents and catalysts. The application of catalysts during steam injection is intended to decrease the activation energy necessary for the production of hydrocarbons of lower molecular weight during the characteristic times of the process, thus achieving an in-situ improvement of the hydrocarbons. This allows an additional decrease in viscosity that could lead to a greater increase in the recovery factor. Studies have been reported on different metal-based catalysts (Fe, Co, Ni) [
16,
17,
18]; however, it has been shown that Ni is the most active catalyst for the hydrocracking and hydrogenation of heavy components, while inhibiting condensation and recombination reactions, as demonstrated by Muneer et al. in their study [
2]. Several studies of hydrothermal upgrading of heavy oil using different catalysts have been performed [
19,
20,
21,
22,
23,
24,
25,
26,
27,
28,
29,
30,
31,
32]. Hamedi-Shokrlu et al. [
19] studied the effect of nickel nanoparticles on the in-situ upgrading of heavy oil in aquathermolysis conditions. Based on the kinetic analysis, they concluded that nickel nanoparticles reduced the activation energy of the reactions corresponding to the hydrogen sulfide generation by approximately 50%. Hart et al. [
20] studied the in-situ catalytic (bimetallic) upgrading processes of heavy oil using a pelletized Ni-Mo/Al
2O
3 catalyst in the THAI process. The results revealed that the cleavage of the C-C, C-S, C-N, and C-C bonds is facilitated by the acid sites of the alumina support of the Ni-Mo/Al
2O
3 catalyst, while the metals (i.e., Ni) promote hydrogen-transfer reactions. By extension, different metal oxides have been tested for the valorization of bio-oil. Consequently, several studies have investigated the upgrading processes of bio-fuel production by the use of efficient catalysts. The results revealed that Ni-alloy catalysts are more attractive than single Ni catalysts in hydrodeoxigenation and other processes [
21,
22,
23,
24,
25,
26]. Given the literatures analysis mentioned above, the purpose of this study is to focus on the synthesis and use of nanoparticle catalysts based on the nickel oxides (Ni
xO
x) without support for viscosity reduction and in-situ hydrogenation heavy oil during the hydrothermal processes. Therefore, the content of this article consists of two parts; the first will be without the use of support for the hydrothermal processes of heavy oil. Therefore, three nickel-based catalysts (Ni
xO
x) have been synthesized; they were characterized using different techniques, such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), and X-Ray Diffraction (XRD) to evaluate their size, morphology, and the metal phases created. The characterization of the properties of the catalysts is very important for the design and manufacture at experimental and industrial scales, as well as for the optimization of the catalytic processes for their possible application at the industrial level. Thus, four experiments (including one (1) without and three (3) with Ni
xO
x nanoparticle catalysts) were carried out in a discontinuous reactor at 300 °C for 24 h of treatment of Ashalcha heavy crude oil from the Republic of Tartarstan (Russia). Characterization of the Ashalcha crude oil was also carried out in order to obtain a baseline of the physical and chemical properties and composition to establish a comparison of the upgrading performance and catalytic activity. Firstly, reaction tests in a reactor of Ashalcha crude oil without catalysts were carried out using only water. Secondly, reaction tests in the reactor were carried out with a catalyst ratio of 2% of the total weight of the heavy crude oil, and then distilled water. Characterization and evaluation of the efficiency and performance of the catalysts were carried out by analyzing the properties of the upgraded oil, including SARA fractions, viscosity, elemental analysis, gas chromatography, GC analysis of saturates, GC-MS measurement of aromatics, and NMR analysis of resins and asphaltenes.