Influence of Sodium Metal Nanoparticles on the Efficiency of Heavy Oil Aquathermolysis

Abstract

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.

1. Introduction

Nowadays, with an increasing global energy demand and depleting conventional oil reserves, the share of unconventional hydrocarbon resources is increasing and the varieties of Enhanced Oil Recovery (EOR) methods are also expanding [1,2,3,4]. The need for such a diversity in EOR methods arises due to the challenges of unconventional hydrocarbons resources. The most widely produced unconventional hydrocarbons resources are heavy oil and natural bitumen. Moreover, this type of hydrocarbon is considered as the most abundant with huge reserves all over the world. However, modern heavy oil production technologies have some challenges such as low efficiency, feasibility and environmental issues [5]. The main issues of heavy oil recovery are their high viscosity, significant content of high-molecular-weight fractions such as resins and asphaltenes, low content of hydrogen to carbon ratio, significant number of heteroatoms and metals in the form of vanadyl and porphyrin complexes. Generally, the yield of light fractions is very low in such hydrocarbon resources. The conventional refinery and pipeline transporting systems are not ready for the processing of heavy crude oil mainly due to high viscosity, a significant amount of sulfur and metals. Currently, almost all produced heavy crude oil passes through partial upgrading units in order to meet the standards of traditional refineries, which are initially designed for conventional crude oil processing. In this regard, the desulfurization and demetalation of heavy crude oil, transformation of resins and asphaltenes into low-molecular-weight compounds or fractions such as saturates and aromatics during the upgrading of heavy oil are crucial for almost all enhanced oil recovery techniques, which aim to not only produce heavy crude oil, but also partially upgrade them. Moreover, the mechanisms of the most commonly applied recovery techniques are poorly studied or debatable among the scientists. Therefore, modification of the existing technologies and the development of new oil recovery techniques considering the mechanisms of the processes are crucial and relevant.

Advanced oil recovery technologies are based on the application of various chemical species, which mainly determine both the efficiency and feasibility of the project [5,6,7,8,9,10]. In the last century, there was a boom of nanotechnology, which is an inseparable part of many industries and various areas of human activity [11,12,13,14,15,16,17,18]. Today, nanotechnology is successfully assisting to enhance, even revolutionize, many industrial sectors and the petroleum industry is not an exception [19,20,21,22,23,24]. It is worth noting that the most widely applied nanoparticles in chemical EOR methods are SiO₂, TiO₂, Al₂O₃, graphene and ZnO. The specific surface area of the dispersed materials (including catalysts) is inversely proportional to the size of the particles. Hence, the transition from microscale into nanoscale (1–100 nm) sharply increases the activity of surface atoms in contrast to the volumetric atoms [25]. It is well-known that most of the processes in colloid systems are carried out on the interphase. Therefore, increasing the surface area leads to the intensification of these processes, and hence, nanoparticles (NPs) are considered more reactive than their volumetric analogs [26]. On the other hand, the distribution of NPs through porous reservoir rocks can be accomplished without any damage to the permeability of the rocks. Some of the NPs are even environmentally green and compatible with the terrigenous reservoir rocks [27]. Although the application of nanotechnology exhibits high efficiency, it is still a cost-effective technology. However, the cost of a solution based on nanotechnology primarily depends on the initial cost of precursors for the synthesis of nanostructures [23,24,28]. Moreover, there are some challenges regarding the chemical composition, particle size, polydispersity, surface charge, wettability and concentration of the nano dispersions, and the conditions of use (salinity and pH of reservoir water, reservoir temperature, composition of crude oil, type and properties of reservoir rock) may limit the use of nanofluids in EOR. The efficiency of nanoparticles in one reservoir does not guarantee its performance in another reservoir [26,29]. Inspired by the idea of finding appropriate nanostructure precursors that can promote the aquathermolytic upgrading of heavy oil and enhance the oil recovery factor, we met the work [1], where the possibility of the easy synthesis of Na nanoparticles and their application for viscosity reduction at room temperature was demonstrated. It is well-known that sodium remains a very active substance during various chemical processes. However, for the dispersion of nanoparticles we used an alike method, which was described in [30].

In the last century, alkali metals were initially used in the desulfurization of low-molecular-weight fractions of oil that contained sulfur-containing heteroatom compounds, i.e., thiophenes [31]. The application of sodium and potassium for the conversion of crude oil distillates rich with asphaltenes has been proposed as a second step after conventional hydrodesulfurization processes [32]. The alkali metals were aimed at contributing to the desulfurization of polynuclear aromatic compounds. Later, the general concept was expanded with including basic salts as well as alkaline earth metals [33,34,35]. One of the main issues of applying alkali metals in heavy oil upgrading is the regeneration of alkali metals. Therefore, it was decided to co-add H₂ with sodium, so that the sodium can be isolated from upgraded heavy oil in the form of a NaHS compound instead of Na₂S [36]. Since then, many studies have been conducted on the application of sodium to remove sulfur-containing compounds from heavy oil, natural bitumen and shale oil [37]. Lithium and sodium were used as alkali metals in the desulfurization, denitrogenation and demetalization of hydrocarbons. Although the conventional hydrodesulfurization of heavy crude oil and natural bitumen is highly effective, the high consumption of H₂ makes this approach challenging and cost-effective. In this regard, the desulfurization of heavy crude oil and natural bitumen with alkali metals is very attractive, particularly for highly sulfurous hydrocarbons such as Canadian natural bitumen, in which the content of sulfur prevails at 5 wt.% [38]. The heavy oil treatment processes using alkali metals were developed at temperatures above 250 °C. This contrast in temperature did not agree with the most fundamental investigations on the main catalysis of alkali metals, which were carried out in mild conditions [39,40,41,42].

Alkali metals promote the conversion of polycyclic aromatic hydrocarbons (PAH) of heavy oil by the formation of electron-accepting ions with aromatic compounds. The alkali metals are very strong donors of electrons, and the conversion can be described in the example of sodium oxidation (1) and adding electrons to the aromatic molecules (2) as follows:

Na → Na⁺ + e⁻(1)

aromatic + e⁻ → [aromatic^•]⁻(2)

Sodium is an electron donor, while the PAH molecule is an electron acceptor. It is possible that either one electron is donated Na⁺[aromatic^•]⁻ or two electrons to form a pair of ions (Na⁺)₂[aromatic]²⁻. The former can also be described as a radical anion, since the only donated electron is unpaired. The electron(s) donated to the PAH molecule is delocalized in the system of π-electrons [40]; these ion pairs can be isolated. In [43], the authors provide the crystalline structures for various combinations of alkali metals and aromatic compounds.

The nature of a solvent is mainly determining the disproportionation degree between anions of free radicals and dianions (3), where the dianion is favored by weakly polarizable solvents [44].

2Na + [aromatic^•]⁻ ⇌ (Na⁺)₂[aromatic]²⁻ + aromatic(3)

Such ion pairs are active in the hydrogen exchange reactions. Additionally, the aromatic ion is also involved in partial hydrogenation reactions. The Birch reduction is the well-known form of a partial hydrogenation reaction.

Birch reduction is a «hydrogenation» reaction of unsaturated hydrocarbons with alkali metals in liquid ammonia and alcohol as a co-solvent and hydrogen donor [45]. If the required reduction temperature is higher than −33 °C, organic amines can be used instead of ammonia.

Despite the enhanced oil properties of heavy oil after an alkali metal treatment, particularly with sodium [36,37], the advantage of using sodium remained unclear in terms of describing the reaction mechanisms. If the main advantage is the formation of a sodium–aromatic ion pair, then there is no need in a high temperature treatment. To sum up the literature review, it should be noted that the high efficiency of oil recovery and upgrading in the case of applying a suspension of alkali nanometals, particularly sodium, is based on the chemical reactions, which yield several advantages such as heat, hydrogen gas and sodium hydroxide.

In this study, we propose the application of Na nanometals, which were obtained by the ultrasonic dispersion of them in liquid phase paraffin, for the first time to promote the upgrading performance of the aquathermolysis of heavy oil and improve the mobility of heavy crude oil. Moreover, the chemical reaction of sodium nanometals with formation water yields hydrogen and sodium hydroxide. The first is involved in the hydrogenation of hydrocarbons, while the latter contributes to the desulfurization and utilization of carbon dioxide, which are the main gaseous products after the aquathermolysis of heavy crude oils.

2. Results and Discussions

The inert organic liquid-paraffin was selected as a continues phase to disperse sodium nanometals. The desired degree of dispersion was achieved in less than 30 s, and the formation of the suspension was followed by the change in color from gray to purple. The average particle size was 6.5 nm. The particle size distribution is presented in Figure 1. According to Figure 1, the character of particle distribution in the suspension is monomodal with the size range of 5–11 nm. Sodium nanofluid is characterized by a distribution different from the normal Gaussian distribution with a slight shift towards a smaller particle size. It is worth noting the high kinetic stability of the sodium nanodispersion for a long time, which was observed by the absence of precipitates during the storage of nanodispersion.

A large amount of gases is evolved after the aquathermolysis process. However, the presence of sodium nanoparticles and its well-known interaction with water [1] produces a significant amount of hydrogen and sodium hydroxide. Therefore, the analysis of evolved gases after the aquathermolysis of heavy oil samples in the presence of Na nanoparticles (Na-NP) showed an increase in the content of hydrogen (from 0.015 to 0.805 wt.%) and decrease in the content of hydrogen sulfide and carbon dioxide in contrast to the blank sample up to 99% and 94%, correspondingly (Table 1). The initial pressure was supplied by nitrogen, and hence, we detected its maximum content in both samples. The carbon dioxide was significantly reduced after a Na-assisted hydrothermal treatment, which shows its chemical transformation in the presence of exceeded free hydrogen gas. Hence, the hydrogenation of carbon dioxide in reservoir conditions can be considered as a possible technology for the particular utilization of carbon dioxide gas. The composition of gas samples was analyzed at a temperature and pressure of 32 °C and 11.3 bar, respectively. The aquathermolysis of heavy oil was carried out for 24 h at a temperature of 250 °C and the initial pressure supplied by nitrogen gas was 10 bar (at ambient temperature of 25 °C).

The hydrogen yield along the presence of sodium nanoparticles depends on the temperature of the aquathermolysis process [46]. Figure 2 illustrates the dependency of the hydrogen gas from the temperature of the process.

Figure 2 demonstrates a parabolic correlation of evolved hydrogen gas with the temperature of reaction. The absolute minimum was observed at a temperature of 250 °C, which means the evolved hydrogen as a result of the interaction between sodium and water is more involved into the hydrogenation of hydrocarbons. The relatively higher yield of hydrogen content at temperature ranges below 250 °C is probably due to the low consumption of hydrogen in conversion processes, the intensity of which is lower, below 250 °C. The increase in the content of hydrogen at higher temperature ranges (above 250 °C) can be explained by the prevail of dehydrogenation processes, which leads to the low consumption of hydrogen on the hydrogenation of oil and hence, a higher content in the composition of the evolved gas sample.

The results of the elemental analysis of heavy oil samples before and after the upgrading are summarized in Table 2. The data demonstrate an increase in the content of carbon, hydrogen and nitrogen, while the content of sulfur was decreased. It is well-known that C-S bonds have the lowest dissociation energy—66 kcal/mol, and they easily break down even at a temperature of 180 °C [47]. Therefore, the decrease in the content of sulfur in oil samples was expected. It is important to note that the sulfur is evolved in the form of H₂S (ref. Table 1).

The fractional composition of oil was determined by SARA-analysis, the results of which are provided in Figure 3.

The histograms in Figure 3 show the decrease in the content of resins and asphaltenes with adding sodium nanoparticles. The destruction products of these high molecular-weight molecules increased the saturated and aromatics fractions after hydrogenation of the cracked fragments. The obtained fractions were further analyzed by FT-IR and GC-MS to reveal the structural changes in the composition of the upgraded heavy oil sample. The FT-IR spectra of resins and asphaltenes are demonstrated in Figure 4 and Figure 5. Analysis of the spectra of asphaltenes isolated from the initial oil and oil subjected to the aquathermolysis process in the presence and absence of Na-nanoparticles shows that the intensity of peaks in the range of 900–660 cm⁻¹ corresponding to organic compounds with a terminal vinyl group, when modeling the process of aquathermolysis with sodium nanoparticles, is significantly reduced, which, according to our assumptions, corresponds to the process of hydrogenation of unsaturated hydrocarbons released by the reaction of metallic sodium with water. In addition, a sample with the addition of sodium nanoparticles has a peak corresponding to coumarins and isocoumarins, which are obtained in the presence of sodium salts of carboxylic acids.

The intensity of peaks is significantly reduced (even escaped) in asphaltene samples isolated from crude oil after a hydrothermal treatment in the presence of sodium nanoparticles, which supports the process of hydrogenation of unsaturated hydrocarbons. On the other hand, we identified an aromatic organic chemical compound—coumarin (C₉H₆O₂) in the spectra of asphaltenes of heavy oil upgraded with sodium NP. Coumarins are produced in the presence of sodium carboxylic salts.

The modeled aquathermolysis process led to the destruction of side chains of benzene derivatives, which can be followed from Figure 5. The peak in the range of 770–650 cm⁻¹ corresponds to 1,3-, 1,3,5- and 1,2,3- substituted benzenes escape after aquathermolytic upgrading in the absence and presence of Na-NP.

The GC-MS spectra of saturated and aromatics fractions of oil samples are presented in Figure 6 and Figure 7.

From the chromatograms of saturated hydrocarbons in Figure 6a, the decrease in the intensity of peaks in the retention time range of 25–65 min corresponds to the high-molecular-weight alkanes C32–C34 (Figure 6b), which can be explained by the hydrogen-donating capacity of sodium that plays a crucial role in the destructive hydrogenation of cycles and long chain hydrocarbons. Despite insignificant changes in the content of alkanes of different groups in Figure 6d, the given processes correlate with the results presented in Figure 6c. Particularly, there is an increase in the content of C12 hydrocarbons by almost 1.5 times, C13 by 3.5 times, as well as a decrease in the content of C26 by 1.2 times and the content of C32–C34 approaches to almost zero for oil after aquathermolysis in the presence of sodium nanoparticles. The obtained results are in accordance with the results reported in [47,48].

According to the spectra provided in Figure 7a, one can observe the generation of new peaks, which correspond to the alkylbenzenes with low-molecular-weight substituents. The detail changes can be observed on the histogram (Figure 7b), where the total content of C10–C18 alkylbenzenes is significantly increased. The transformation processes can be evaluated quantitatively by analyzing the histogram presented in Figure 7c, where the content of C10–C18 alkylbenzenes in crude oil was increased almost by two times after aquathermolytic upgrading in the presence of sodium nanoparticles compared to initial crude oil. All in all, the aquathermolysis process leads to dealkylation and increases the share of low-molecular-weight fractions. The presence of sodium nanoparticles further promotes this phenomenon.

The analysis of the chromatograms shown in Figure 8a allows us to conclude that there are no noticeable changes in this fraction when comparing the initial oil with oil subjected to non-catalytic aquathermolysis. However, when using sodium nanoparticles, peaks of a low-molecular fraction appear in the left part of the histogram, apparently formed by the decay of larger homologues as a result of destructive hydrogenation processes. It should be noted that, as can be seen from the histogram in Figure 8b, during aquathermolysis, the content of naphthalenes decreases with an increase in the proportion of trimethyl naphthalene.

The phenanthrenes spectra in the composition of aromatics are presented in Figure 9a. The results demonstrate no significant changes in the relative content of phenanthrenes and their homologues. However, the histogram in Figure 9c demonstrates the decrease in the content of trimethylphenanthrene under non-catalytic aquathermolysis, with intensification of this influence under sodium nanoparticles. The application of EOR methods is primarily aimed to increase the production of unconventional hydrocarbon resources such as heavy oil and natural bitumen, shale oil and shale gas [26]. Providing the necessary rheology characteristics to such hydrocarbon fluids is an important task, and aquathermolysis is considered as one of the solutions to the given issue.

The viscosity of the heavy oil samples before and after aquathermolytic upgrading in the absence and presence of Na NP was studied at various temperatures. The temperature-dependent dynamic viscosity of the oil samples is compared in Figure 10.

The results of the comparison study shows that temperature-dependent viscosity behavior is characterized by a descending curve with the maximum viscosity reduction observed in the temperature ranges of 10–30 °C. The further raise in temperature of the viscosity measurement provides a little decrease in the dynamic viscosity values. The curve characterizing temperature-dependent viscosity of heavy oil after non-catalytic aquathermolysis is close enough to the viscosity curve of the initial oil sample. This indicates the inefficiency of such an upgrading method on the rheology, which is reasoned by an insignificant transformation of resins and asphaltenes. Moreover, the light fractions are lost under thermolytic upgrading. The sodium nanometals contribute to the generation of free hydrogen protons, which are involved into the destructive hydrogenation of resins and asphaltenes, mainly on the weakest C-S bonds. This process in the presence of sodium nanometals provides the hydrodesulfurization of heavy crude oil and decreases the molecular weight of asphaltenes. The products of destructive hydrogenation processes form low-molecular-weight hydrocarbons. Finally, the viscosity of the upgraded heavy oil measured at a temperature of 20 °C was reduced by 51.2%.

3. Materials and Methods

The object of this study is the heavy crude oil (Table 3) produced from the Ashal’cha reservoir, Tatarstan Republic, Russia. The reservoir is located on the western slope of the South Tatar Arch and is distributed in the wide stratigraphic range starting from the Ufa Stage of Upper Permian to the Frasnian Stage of Upper Devonian, from the day surface to the depth of 1884 m. The reservoir rocks are mainly characterized by sandstone and the pay zone with a thickness of 34 m is in the depth of 110 m from the top of the Sheshminskiy horizon. The sandstones are fine- and medium-grained, highly porous and unconsolidated. The average oil saturation percentage of the reservoir rocks is 13 wt.% Many oil wells have industrial scale production rate potential. The reservoir is developed by Public Joint Stock Company (PJSC) Tatneft using various enhanced oil recovery methods. The reservoir is served as a polygon for the industrial scale application of newly emerged technologies and processes. However, the main heavy oil production technology remains as Steam Assisted Gravity Drainage (SAGD) and its modifications.

The hydrothermal experiments in the absence and presence of sodium nanoparticles were carried out in a high pressure–high temperature (HP-HT) reactor with a stirrer manufactured by Parr Instruments Company. The volume of the reactor was 300 mL, and it was coupled with Gas Chromatography (GC) «Chromatec Crystal 5000.2» [49] to analyze the composition of the gaseous products after hydrothermal upgrading and sodium assisted upgrading. The gas measurements were carried out according to the international technical standards GOST 23781 «Natural combustible gases. Chromatographic method for determination of component composition», maintained by the Euro Asian Council for Standardization, Metrology and Certification (EASC).

The initial given pressure and temperature was 10 bar and 250 °C, respectively. The reaction time for all samples was set for 24 h. The model system composed of heavy crude oil and water with the mass ratio of 70:30 was stirred at a constant speed of 200 rpm in an inert nitrogen medium. The concentration of sodium metal suspension (50% of sodium dispersed in paraffin) in the oil bulk was 2%. The suspension was prepared by cutting metallic sodium into pieces, which were loaded in liquid paraffin. The paraffin was previously degassed by an ultrasonic homogenizer as per [30]. The mixture was heated up to the melting point temperature of sodium, and the sodium pieces were melted up to the formation of spherical shiny particles. Then, the dispersion of sodium particles in liquid degassed paraffin was carried out under an ultrasonic homogenizer. After the formation of a gray–purple suspension, the content of the beaker was cooled down in a cooling water bath. The obtained nanosuspension of sodium was analyzed by the Dynamic Light Scattering (DLS) method using 90Plus Brookhaven Instruments.

The upgrading performance of sodium was evaluated by GC-analysis, elemental analysis, SARA-analysis, GC-MS and FT-IR analysis methods. The viscosity measurements were carried out to study the mobility and rheology of crude oil after upgrading.

The elemental composition of upgraded crude oil was analyzed by the X-ray fluorescence spectrometer method in an M4 Tornado manufactured by «Bruker», the results of which allow us to quantitatively compare the mass ratio of elements such as C, H, N, O and S in oil samples before and after the upgrading.

The composition of heavy oil samples was roughly grouped into four fractions as per the ASTM D4124: Saturates, Aromatics, Resins and Asphaltenes (SARA). The asphaltenes were isolated from crude oil by precipitating them in n-hexane. Then, the precipitates are filtered and the residue of asphaltene fragments from the filter are extracted in a Soxhlet by warm polar solvent-toluene. In its turn, the filtrates were separated in a special chromatography column filled with the neutral adsorbent-Al₂O₃ previously calcined at 450 °C into saturated hydrocarbons, aromatics and resins by using diluent solvents with different polarity.

The isolated saturates and aromatics fractions were further analyzed by the GC-MS system, which is the combination of GC «Chromatec-Crystal 5000» (Moscow, Russia) with a Mass-Selective detector «ISQ» (Dayton, OH, USA). The obtained spectra were processed using the Xcalibur application. The capillary columns used during the measurement were 30 m in length and 0.25 mm in diameter. The gas carrier was helium with the flow rate was 1 mL/min. The temperature mode was set as follows: from 100 °C to 150 °C with a heating rate of 3 °C/min, from 150 °C to 300 °C with a heating rate of 12 °C/min followed by its isotherm until the end of the analysis. The energy of electrons was 70 eV, and the temperature of ion source was fixed at 250 °C.

The viscosity of the initial heavy oil sample and after upgrading was measured in a rotational viscometer Fungilab Alpha L, coupled with a thermostat «Microprocessor Control MPC» from the Huber manufacturer. A TL5 spindle was used for the measurement of all samples, which required 6.7 mL of heavy oil sample. The viscosity values were measured in the temperature ranges of 10–60 °C with the step of 10 °C.

4. Conclusions

In this study, we modeled for the first time the aquathermolysis of heavy oil samples at reservoir conditions in the presence of nanoliquids based on the sodium nanoparticles. The results of the investigation showed that hydrogen formed as a chemical product of sodium nanoparticles and water interaction is involved in the aquathermolysis reaction, particularly the hydrogenation of hydrocarbons. This was justified by the GC-MS data. The yield of hydrogen after the thermo-chemical upgrading processes increased from 0.015% (blank sample) to 0.805%. The reaction temperature of 250 °C is a favorable condition for the hydrogenation of hydrocarbons, and the given temperature in the reservoir can be supplied by the existing industrial steam generators. The further increase in the process temperature leads to the increase of hydrogen content in the composition of the evolved gas cap, which means hydrogen is not involved in the reduction of hydrocarbons. In addition, dehydrogenation reactions occur, as evidenced by the evolvement of hydrogen in gaseous products of non-catalytic upgrading under identical conditions.

The second product of the chemical reaction of metallic sodium with water-sodium hydroxide contributes to hydrodesulfurization and the particular utilization of carbon dioxide, which remained as corresponding salts in the separated water phase after the upgrading process. The hydrodesulfurization and carbon dioxide utilization degree was 99% and 94%, correspondingly.

The group-composition analysis of heavy oil samples before and after upgrading in the presence of sodium nanoparticles revealed a decrease in the content of resins and asphaltenes by 13.22 and 8.15 wt.%, respectively. The destruction products of high-molecular-weight fragments of oil increased the contents of saturated and aromatics fractions, which justifies the upgrading performance of sodium nanoparticles during steam injection techniques.

The analysis of saturated hydrocarbons by GC-MS revealed a reduction in the intensity of C32–C34 peaks, which indicates the hydrogen-donating capacity of sodium in the destructive hydrogenation of cyclic and long hydrocarbon chains. The aromatic fraction of upgraded heavy oil was characterized by a significant content of C10–C18 alkyl benzenes with relatively low-molecular-weight substituents. One of the main reasons of increasing low-molecular-weight fractions, which was observed in FT-IR spectroscopy, is the transformation of resins and asphaltenes during the aquathermolysis of heavy oil in the presence of sodium nanoparticles.

The hydrothermal upgrading of heavy oil in the presence of sodium nanoparticles reduced the viscosity of heavy oil samples by 50%. The obtained data are the initial step toward enhancing our understanding on the heavy oil upgrading performance of sodium nanoparticles during steam stimulation techniques. It is assumed that the injection of sodium suspension into the reservoir formations is a promising method of in situ upgrading, which can not only irreversibly decrease the viscosity, but also enhance oil recovery. However, further comprehensive studies are required to better understand the possible mechanisms of the sodium-assisted processing of heavy oil, and their influences on the structural and chemical composition of crude oil. In addition, laboratory and field test data are needed to understand the effect of sodium nanofluids on the reservoir properties.

Author Contributions

Conceptualization, V.E.K. and A.V.V.; Methodology, A.V.V.; Formal analysis, F.A.A.; Investigation, S.A.T. and A.A.K.; Resources, N.A.N. and A.V.D.; Data curation, V.E.K. and F.A.A.; Writing—original draft, F.A.A. and A.V.V.; Writing—review & editing, F.A.A.; Supervision, A.V.V.; Project administration, V.E.K. and A.V.V.; Funding acquisition, N.A.N. and A.V.D. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Data available upon request.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

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Figures and Tables

Figure 1. The particle size distribution of sodium in nanosuspension.

Figure 2. The content of evolved hydrogen gas depending on the temperature of the process.

Figure 3. Fractional composition of oil before and after processing.

Figure 4. IR spectra of asphaltenes oil before and after processing.

Figure 5. IR spectra of resins before and after processing.

Figure 6. GC-MS of saturated hydrocarbons. C10–C32—the number of carbon atoms in n-alkanes; iC13–iC18—iso alkanes oil before and after processing.

Figure 7. GC-MS spectra of (a) aromatics fractions and relative contents of alkylbenzenes (b,c) before and after processing.

Figure 8. GC-MS spectra of (a) naphthalenes before and after processing, and (b) the relative content of them in the composition of aromatics fractions.

Figure 9. GC-MS spectra of (a) phenanthrene and its homologues in the aromatic fraction, (b,c) relative content of phenanthrene types.

Figure 9. GC-MS spectra of (a) phenanthrene and its homologues in the aromatic fraction, (b,c) relative content of phenanthrene types.

Figure 10. Temperature-dependent dynamic viscosity of oil samples.

Table 1

The content of evolved gases after the aquathermolytic upgrading of heavy oil in the absence and presence of sodium nanoparticles.

Sample	Content, wt.%
	C1	C2	C3	C4	H2	CO2	H2S	N2	O2	Sum
Blank sample	0.016	0.017	0.019	0.029	0.015	0.154	0.099	99.58	0.071	100
HTT+Na-NP	0.017	0.024	0.025	0.041	0.805	0.009	0.001	99.02	0.063	100

Table 2

Elemental analysis of the source oil and after aquathermolysis with and without a catalyst.

Sample	Content, wt.%
	C	H	N	S	H/C
Initial crude oil	81.49	12.08	0	4.60	1.77
Blank sample	82.02	12.15	0.02	4.48	1.77
HTT+Na-NP	82.12	12.8	0.04	4.40	1.86

Table 3

Basic properties, SARA fractions and elemental analysis of Ashalcha heavy oil.

Density (g/cm 3 @20 °C)	Viscosity (mPa·s@20 °C)	SARA Composition, wt.%				Elemental Analysis, wt.%
		Asphaltenes	Saturates	Aromatic	Resins	C	H	N	S	H/C
0.952	4895	6.5	28.2	42.98	22.32	81.49	12.08	0	4.60	1.77

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