Asphaltene Aggregation Research Articles

Adsorption of Asphaltenes at Model Oil/Brine Interface: Influence of Solvent Polarity.

With the exploitation of heavy oil worldwide, the influence of asphaltene aggregation in the oil phase on the stability of crude oil emulsion has been paid more and more attention. Under this background, the effects of solvent polarity on model oil/brine water interfacial properties and emulsion stability are investigated in this study. It is demonstrated that there is a critical asphaltene concentration for the formation of a stable emulsion. This critical concentration is then found to increase from 80 to 500 ppm with the mixing ratio of methylnaphthalene to n-decane changed from 2:3 to 7:3. The dynamic light scattering experiment shows that the average aggregate size increases abruptly from 132.8 to 261.1 nm at 2:3 mixing ratio of methylnaphthalene to n-decane once the asphaltenes are added to above the critical concentration. Accordingly, the diffusion coefficient of the asphaltenes decreases sharply from 4.36 × 10-12 to 5.68 × 10-13 m2/s. Similar conclusions are also found for the other mixing ratios of 1:1, 3:2, and 7:3. Besides, the aggregation degree of asphaltenes weakens, and the diffusion coefficient enlarges at the same asphaltene concentration with the enhancement of the solvent polarity. Further, the interfacial experiments manifest that the equilibrium interfacial dilation modulus decreases from 38.42 to 23.65 mN/m with the mixing ratio of methylnaphthalene to n-decane increased from 2:3 to 7:3. It can thus be inferred that the structural strength of the interfacial film decreases with the enhancement of the solvent polarity.

Softeners doped with asphaltene dispersants acting in synergy with resins: Molecular mechanisms underlying asphalt rejuvenation

In confronting the global climate change, reusing waste asphalt materials stands out as a key strategy for the transportation sector to preserve natural resources and reduce the carbon footprint. Recycling additives or rejuvenators are usually required in this practice, especially for boosting the recycling rate. Given the imperative need for a general compositional design principle of rejuvenators, we previously proposed an innovative formulation concept by combining softeners with asphaltene dispersants, and reported that the use of dispersants largely reduced the total quantity of rejuvenators needed and thus would minimize the environmental impacts. The present study is aimed for probing the molecular mechanisms underlying this observation, with additional interest focused on the synergistic effect of the dispersants with resins and also on the impacts due to their self-association. Selection of representative materials consisted of three types of dispersants including an ionic liquid, a phenolic amphiphile, and an ester plasticizer, in combination with an aromatic oil as the softener. Long-time molecular dynamics (MD) simulation was employed to inspect the aggregation of asphaltenes. Quantum chemical (QC) computation was performed to provide insights into the source of different dispersing behaviors. The results indicated that the three dispersants all acted in concert with resins in dispersing asphaltenes. The dispersion characteristics of asphaltenes could be viewed as a net result of the two competing mechanisms of the dispersing capability and self-association of the dispersant used. The ionic liquid exhibited much higher propensity to self-association at increasing concentrations than the phenolic dispersant, and yet the optimum performance was achieved for both when they were added at low dosages. The ester plasticizer showed minimal self-association and yielded improved dispersion with increasing concentrations. In all cases, the dispersing functionality mainly originated from the presence or formation of significant electron-withdrawing sites, collectively due to the highly electronegative cation and anion, hydrogen bonding, and polar groups. Comparison of the dispersing power was also conducted from different perspectives. The findings are expected to provide molecular insights for formulating versatile and more environmentally benign asphalt rejuvenators.

Formation behaviors of gas hydrates in water-in-oil emulsions with the coexistence of asphaltenes and resins

Hydrate formation is one of the major flow assurance issues for the subsea multiphase pipelines. The effects of the interaction between heavy fractions of crude oil components on hydrate behaviors are still not well understood. In this study, the effects of resins on hydrate formation behaviors in asphaltene-containing emulsions were investigated using a high-pressure reactor apparatus. The results indicated that both resins and asphaltenes inhibited hydrate nucleation and increased the induction time. Furthermore, considerable synergistic effects of asphaltenes and resins on the hydrate formation behaviors were discovered in the water-in-oil emulsions, depending on the aggregation state of asphaltenes. The addition of resins was observed to disperse the asphaltene aggregates significantly and enhance the inhibitory effect of asphaltenes on hydrate nucleation. Additionally, the calculated results of gas consumption showed that the presence of resins can decrease the growth rate of hydrates in the asphaltene-containing emulsions. A potential mechanism was presented to illustrate how resins affect hydrate formation in an emulsion with varying asphaltene aggregation states. These findings offer a better knowledge of the synergistic effects between the heavy components of resins and asphaltenes and have potential application in the hydrate management of crude oil pipelines.

Microscopic mechanism of single-walled carbon nanotubes (SWCNTS) as a dispersant for alleviating asphaltene aggregation

The flow properties of crude oil have been seriously affected by the aggregation behavior of asphaltenes. The single-walled carbon nanotubes (SWCNTs) can exhibit positive alleviation effect as a dispersant for asphaltene aggregation, but the influence mechanism at the molecular level is still controversial. With the action of SWCNTs, the rate of asphaltene self-aggregation decreased, and the time to form asphaltene clusters came later. At the same time, the structure of asphaltene clusters became looser. Interestingly, when a small number of asphaltene molecules start to accumulate, the density of asphaltene molecules in the accumulation body is relatively low. In addition, the peak value of RDF between the SWCNTs and asphaltene is much higher than that between asphaltene molecules, which indicates that the interaction between SWCNTs and asphaltene molecules is stronger than that between asphaltene molecules, thus affecting the self-aggregation of asphaltene molecules. In addition to that, it is worth mentioning that in the vmd snapshot, we also observed that the aggregation mode of asphaltene would change to SWCNTs as the core. This work explains the decrease of asphaltene self-aggregation degree and speed with the addition of SWCNTs from the microscopic point of view, which is due to the strong interaction between SWCNTs and asphaltene molecules weakens the interaction between asphaltene molecules.

Properties of waste vegetable oil recycled asphalt-binder: a molecular simulation study

ABSTRACT The aging of asphalt-binder during long-term use is an important reason for the decline in road performance of asphalt mixtures. In this study, waste vegetable oil (fried for 1-2h) was investigated as a rejuvenator of asphalt-binder. The optimisation effect of waste vegetable oil on the performance of asphalt-binder with different aging degrees (RTFOT, PAV15/20/48h) was evaluated by testing their conventional physical properties, high-temperature properties, and low-temperature properties. The molecular dynamics method was used to construct models, and the diffusion properties, solubility properties, adsorption energy, and asphaltene aggregation were calculated. The influences of linoelaidic acid and oleic acid molecules on aged asphalt-binder molecules were evaluated. The changes in the functional groups of the aged asphalt-binder after the addition of waste vegetable oil were analyzed by infrared spectrometry, and the changes in the microstructure of the aged asphalt-binder surface were observed by scanning electron microscopy. The results revealed that waste vegetable oil could regenerate aged asphalt-binder and significantly improve their physical and high-/low-temperature properties. Waste vegetable oil molecules are compatible with aged asphalt-binder molecules, improve their diffusion behaviour, enhance their adsorption capacity, and slightly reduce the aggregation of asphaltenes. Overall, waste vegetable oil shows great potential for the regeneration of aged asphalt-binder.

Inhibition of asphaltene aggregation using deep eutectic solvents: COSMO-RS calculations and experimental validation

Asphaltene precipitation/deposition adversely affects various oil and gas processes, such as oil recovery, transportation, and petroleum processing. The resulting increase in viscosity of crude oil decreases distillate yields creating unstable phase separation. Deep eutectic solvents (DESs) have recently gained interest as inhibitors of asphaltene aggregation. The goal of the present study is to derive the mechanism of inhibition of petroleum asphaltene aggregation by a novel screening of DESs. An archipelago-based chemical structure of asphaltene was adopted for performing quantum chemical calculations. The structure was used in the conductor-like screening model for real solvents (COSMO-RS) model to screen potential DESs for asphaltene precipitation. It was found that DESs containing thymol were the most promising of the 153 DES combinations screened. The COSMO-RS predictions were validated experimentally using solubility data of asphaltene in DESs. Among the studied DESs, thymol-diphenyl ether provided the highest solubility for asphaltene, which was further validated using the experimental and the COSMO-RS predicted data. In addition, to characterize the structural interactions between asphaltene and DESs, Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) measurements were performed. It was found that strong interaction between asphaltene and the DESs is responsible for the higher asphaltene dispersion. The present approach opens pathways to rationally design and understand the impact of structural variation of DESs based on their interactions with asphaltene.

Effectiveness of inhibitors to prevent asphaltene aggregation: Insights from atomistic and molecular simulations.

The technological landscape for industrial processes handling asphaltene is evolving at a rapid pace due to the increase in the extraction of heavy crude oil. The main underlying challenges in this regard are the flow assurance, the recovery of the spent solvent, and the sophisticated extractor setup required to develop the process to an industrial scale. The number of studies focused on the handling of the asphaltene at the atomic and molecular scales is growing enormously in order to identify new sustainable solvents for the effective extraction of asphaltene from heavy crude oil or oil-bearing sands. This Perspective focuses on the importance of density functional theory and molecular dynamics simulations to explore the broader range of asphaltene inhibitors, e.g., nanoparticles, ionic liquids, and deep eutectic solvents, to prevent asphaltene precipitation. We provide a concise overview of the major accomplishments, analyze the aspects that require attention, and highlight the path-breaking studies having a significant impact on the process of chemical enhanced oil recovery from heavy crude oil reservoirs primarily based on atomistic and molecular simulations.

Experimental and Simulation Studies of Imidazolium Chloride Ionic Liquids with Different Alkyl Chain Lengths for Viscosity Reductions in Heavy Crude Oil: The Effect on Asphaltene Dispersion.

Heavy crude oil poses challenges in terms of extraction and transportation due to its high viscosity. In the pursuit of effective methods to reduce viscosity in heavy crude oil, this study investigates the potential of imidazolium chloride ionic liquids with varying alkyl chain lengths as viscosity reducers. The experimental results demonstrate that the addition of 1-dodecyl-3-methylimidazole chloride ([C12-MIM]Cl) leads to a maximum viscosity reduction of 49.87%. Solubility parameters were calculated based on characterization of the average molecular structure of the asphaltenes. The viscosity reduction effect is enhanced when the solubility parameter of the ionic liquid closely matches that of the asphaltene. The initial asphaltene deposition point of heavy crude oil is increased from 63% to 68% with the addition of 150 mg/L [C12-MIM]Cl. Furthermore, the average particle size of asphaltene deposits decreases from 79.35 μm to 48.54 μm. The viscosity of heavy crude oil is influenced by the aggregation of asphaltenes. The ability of ionic liquids, especially those with longer alkyl chains, to disperse asphaltene molecules and reduce viscosity has been confirmed through molecular dynamics and quantum mechanical simulations.

Effect of non-thermal effects in microwave heating on the rheology and chemical properties of petroleum asphalt

This study systematically analyses the rheological properties of typical petroleum asphalt heated by microwaves at different temperatures through viscosity, penetration, dynamic shear, low-temperature bending, and other rheological tests. The results show that the non-thermal effect of microwaves enhances the fluidity of petroleum asphalt in the high-temperature viscous flow state, becomes softer in the medium-temperature viscoelastic state, and becomes hard and brittle in the low-temperature glassy state. The effect of microwaves also causes some specific changes in the properties of bitumen, including softening point and glass transition temperature in the opposite direction, as well as a large difference in the response of bitumen of different viscosities. The chemical changes in microwave-heated bitumen were analyzed using component tests and microscopic observation. It was found that microwave heating homogenized and dispersed the asphaltene aggregates into small particles, with the heavy components significantly reduced and the light components increased.

Influence of Ionic Liquids on the Aggregation and Preaggregation Phenomena of Asphaltenes in Model Solvent Mixtures by Molecular Dynamics Simulations and Quantum Mechanical Calculations: The Effect of Cation’s Shape and Size

Influence of Ionic Liquids on the Aggregation and Preaggregation Phenomena of Asphaltenes in Model Solvent Mixtures by Molecular Dynamics Simulations and Quantum Mechanical Calculations: The Effect of Cation’s Shape and Size

Influences of molecular tail architectures of rejuvenators on their efficacies in restoring microstructures of reclaimed asphalt

The chemical structure of rejuvenators determines their rejuvenation performance. This work studied the influence of molecular tail architectures on efficacies of rejuvenators, through the combined use of molecular dynamics (MD) simulation and laboratory experiments. The solubility parameter was used to characterize rejuvenators changing in molecular tail structures. Then, microstructure changes of corresponding recycled asphalt were monitored with the confinement size of asphalt molecular diffusion. Accordingly, experiments were conducted for examining essential characteristics of rejuvenators with changing molecular tail structures and their efficacies in restoring mechanical properties of aged asphalt. The results show that the stronger interaction among molecular tails enhances cooperation effects of rejuvenator molecules, thus promoting higher efficacies and stabilities in separating asphaltene aggregates. This finally leads to greater reductions of elastic proportions within mechanical properties of aged asphalt. Moreover, the complex molecular tail structure of rejuvenators lowers down the molecular interaction. Thus, the surface tension of rejuvenators could be an indicator for predicting their efficacies.

Dispersion of asphaltene aggregates by zwitterionic surfactants: influence of cations structure

The precipitation and deposition of asphaltenes are significant challenges in the petroleum industry resulting in substantial costs. A practical approach to addressing this issue is to use chemicals as inhabiting and dispersing agents. Zwitterionic surfactants are interesting materials in this field. In this study, three zwitterionic compounds including 2-(1-methyl-1H-imidazol-3-ium-3-yl)butane-1-sulfonate (MIBS), 4-(pyridin-1-ium-1-yl) butane-1-sulfonate (PBS), and 4-(tributylammonio)butane-1-sulfonate (TBBS) were synthesized and characterized by FT-IR, NMR spectroscopy, thermogravimetric, and differential thermal analysis. The ability of these zwitterions to prevent asphaltenes precipitation was investigated using interfacial measurements, ultraviolet spectroscopy, quartz microbalance analysis, particle size analysis, and optical microscopy. The results showed that the MIBS zwitterion, which contains an imidazole cation, was the most effective in dispersing asphaltene aggregates compared to the other two zwitterions. For instance, the UV spectroscopy results showed that the dispersion indexes for MIBS, PBS, and TBBS were 52.8%, 29.9%, and 16.3%, respectively. In addition, the size of asphaltene particles reached from 2179 nm to 622, 1489, and 2038 nm for MIBS, PBS, and TBBS, respectively. Finally, a comparison between the performance of these zwitterions with sodium dodecyl sulfonate (SDS) and tetrabutylammonium hydrogen sulfate (TBAHS) showed the following trend: MIBS (90.5%)> PBS (79.4%) > TBAHS (75%)> SDS (73.9%) >TBBS (46%).

Insights into the effect of water content on asphaltene aggregation behavior and crude oil rheology: A molecular dynamics simulation study

In the production and transportation of crude oils, the interaction between asphaltene components and water is inevitable, significantly impacting asphaltene aggregation, deposition behaviors, emulsion stability, and rheological properties of crude oils. However, the comprehension of the oil-water interaction mechanisms and corresponding viscosity responses remains unclear. Hence, we performed molecular dynamics (MD) simulations to investigate the effect of varying water content on distinct asphaltene aggregation states and the rheological behavior of crude oils. The microscopic mechanisms underlying the aggregation and rheological properties were elucidated. Our MD results show that with the continuous introduction of water, the original bulk phase aggregation of asphaltenes undergoes a transition towards interfacial adsorption behavior, culminating in the formation of water-in-crude oil emulsions. The strength and driving forces of this interfacial adsorption are influenced by different polar functional groups of asphaltene. Besides, by elucidating the contributions of external molecular friction and internal structural deformation to the viscosity, two viscosity-influencing mechanisms are revealed. Furthermore, we delineate a physical viscosity scheme. These intriguing discoveries hold promise for advancing the comprehension of rheological behavior in crude oils with distinct aggregation states, providing theoretical guidance for efficient development of crude oils.

A mechanistic study of asphaltene formation and aggregation in presence of metallic-based nanoparticles

In this work, the effects of metallic-based nanostructures including iron oxide (Fe2O3), magnesium oxide (MgO) and zinc oxide (ZnO) on asphaltene precipitation and aggregation were explored. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and Brunauer, Emmett and Teller (BET) methods. Optical microscopy and asphaltene dispersant tests (ADTs) were utilized to discover the effects of nanoparticles on asphaltene stability and the size-growth of asphaltene aggregates in crude oil medium. The interactions of the asphaltene functional groups with metal oxide nanoparticles were evaluated at molecular scale by thermogravimetric analysis (TGA/DTG), FT-IR, and field emission scanning electron microscopy (FESEM). Results of different experiments exhibited that synthesized nanostructures in general postpone the asphaltene onset of precipitation (AOP) and reduce the size of asphaltene aggregates in unstable crude oil medium. MgO nanoparticles with a concentration of 300 ppm had the greatest effect on controlling the asphaltene precipitation and aggregation. The TGA/DTG analysis showed that the oxidation of pure asphaltenes occurs at a temperature of about 425 °C, while the oxidation temperature of asphaltenes adsorbed on ZnO and Fe2O3 nanoparticles occurs at around 330 °C, and for MgO nanoparticles at about 365 °C. In addition, the spectra obtained from the FT-IR analysis for asphaltenes without and with nanoparticles at the wavelengths of 1450 and 2900 cm−1 show the medium C–H stretching bonds that play the most important role in the adsorption of asphaltene on the surfaces of the nanoparticles. Also, the recorded FESEM images of the asphaltene and nanoparticles demonstrated the proper absorption of asphaltenes in the empty spaces between the structures of nanoparticles. According to the results from different experiments and intermolecular analyses, the performance of synthesized nanoparticles for retarding asphaltene precipitation and dispersing the asphaltene aggregates was in order of MgO (300 ppm) > Fe2O3 (300 ppm) > ZnO (700 ppm). The results of intermolecular analyses established the effective adsorption of the asphaltene particles onto the surface of the nanoparticles, which is caused by strong hydrogen interactions between the active sites of the asphaltene and nanoparticles. The findings of this study prove that metal-oxide nanoparticles can be utilized as an economically and environmentally-effective agents for controlling asphaltene formation and aggregation in crude oil.

Multi-component oil–water two phase flow in quartz and kerogen nanopores: A molecular dynamics study

Two-phase flow of oil and water frequently occurs within shale nanopores. Unique phenomena, like liquid–liquid slip at the oil–water interface, have been noted within the alkane-water system. However, in the case of realistic crude oil, the presence of highly polar components like asphaltene and toluene may introduce intricate migration behaviors near phase interfaces. Consequently, it is imperative to thoroughly explore the influence of these realistic crude oil components on flow behavior. This paper employs a comparative approach to examine the impact of polar components present in crude oil on two-phase nanoflow by molecular dynamic simulations. The investigation employs a mixed alkanes model (encompassing methane, propane, octane, and tetradecane) and a black oil model (comprising a range of alkanes, toluene, and asphaltene) to analyze the behavior of oil–water two-phase flow within quartz and kerogen nanopores, respectively. Four water adsorption layers near the quartz with an individual thickness of 0.23 nm and three alkane adsorption layers near the kerogen surface with an individual thickness of 0.45 nm were observed. Near the oil–water interface region, it indicated that toluene and asphaltene tend to accumulate, leading to a reduction of alkane aggregation in that region. Such aggregation of toluene and asphaltene imparts an interfacial viscosity increase of 2.67 to 3.47 times, substantially diminishing the enhancement of liquid–liquid slip. Based Hagen-Poiseuille equation, we proposed a simplified mathematical model in which the liquid–liquid slip was neglected and the oil–water interface region was omitted. Compared with the results from molecular dynamic simulations, such a simplified model is validated and effective for the description of oil–water two-phase nanoflows containing toluene and asphaltene, and ensures that the relative error of flow rate remains below 0.5 %. This study provides valuable insights into the two-phase flow of oil–water in nanopores, particularly measuring the effect of liquid–liquid slip under the different crude oil components conditions.

Studying the effects of asphaltene oxidation on wax crystallization and rheological properties in waxy crude oils

Oxidation in crude oil production is unavoidable. Oxidized asphaltenes, interacting with waxes during crystallization, profoundly alter wax precipitation and gel behavior in crude oils. This research evaluated the impact of asphaltene oxidation on the wax precipitation characteristics and rheological properties of waxy crude oils during the processes of crude oils extraction and transportation. A comprehensive structural characterization of the asphaltenes was conducted, revealing an increase in aromaticity and a reduction in the length and abundance of aliphatic chains following oxidation, accompanied by the formation of larger asphaltene aggregates. Subsequently, an investigation into the wax precipitation behaviors of waxy model oils showed that asphaltenes were involved in the crystallization processes of wax molecules, which had a minor impact on wax precipitation characteristics (crystallization and crystallization enthalpy). However, it had a significant influence on the rheological properties (pour point, flow curve and gel strength) of the systems. And it was also observed that the degree of influence was dependent on the structure and composition of the given asphaltenes and waxes. Asphaltenes with abundant aliphatic chains (before oxidation) tended to assume favorable positions during the crystallization process, which interfered to some extent with the normal growth of wax crystals and resulting in a transition from a “strong gel” to a “weak gel” network structure of wax crystals. Conversely, the oxidized asphaltenes with a high aromaticity exhibited a greater interference with wax crystal growth. This interference not only more effectively hindered the establishment of the wax crystal network but also prompted the formation of an “extremely fragile gel structure”.

Probing the interaction between asphaltene-wax and its effects on the crystallization behavior of waxes in heavy oil via molecular dynamics simulation

High content of asphaltenes and waxes leads to the high pour point and the poor flowability of heavy oil, which is adverse to its efficient development and its transportation in pipe. Understanding the interaction mechanism between asphaltene-wax is crucial to solve these problems, but it is still unclear. In this paper, molecular dynamics simulation was used to investigate the interaction between asphaltene-wax and its effects on the crystallization behavior of waxes in heavy oil. Results show that molecules in pure wax are arranged in a paralleled geometry. But wax molecules in heavy oil, which are close to the surface of asphaltene aggregates, are bent and arranged irregularly. When the mass fraction of asphaltenes in asphaltene-wax system (ωasp) is 0–25 wt%, the attraction among wax molecules decreases and the bend degree of wax molecules increases with the increase of ωasp. The ωasp increases from 0 to 25 wt%, and the attraction between asphaltene-wax is stronger than that among waxes. This causes that the wax precipitation point changes from 353 to 333 K. While the ωasp increases to 50 wt%, wax molecules are more dispersed owing to the steric hindrance of asphaltene aggregates, and the interaction among wax molecules transforms from attraction to repulsion. It causes that the ordered crystal structure of waxes can't be formed at normal temperature. Simultaneously, the asphaltene, with the higher molecular weight or the more hetero atoms, has more obvious inhibition to the formation of wax crystals. Besides, resins also have an obvious inhibition on the wax crystal due to the formation of asphaltene-resin aggregates with a larger radius. Our results reveal the interaction mechanism between asphaltene-wax, and provide useful guidelines for the development of heavy oil.

New insight into the role of the self-assembly of heteroatom compounds in heavy oil viscosity enhancement.

Unveiling the role of heteroatom compounds in heavy oil viscosity is pivotal for finding targeted viscosity reduction methods to improve oil recovery. This research investigates the impact of heteroatoms in asphaltene molecules by utilizing quantum chemical calculations and molecular dynamics simulations to analyze their electrostatic potential characteristics, pairwise interactions, and dynamic behavior within realistic reservoirs. Heteroatom compounds can influence the molecular-level properties of asphaltenes and thus impact the macroscopic behavior of heavy oils. Research results suggest that the presence of ketone and aromatic rings in asphaltene molecules leads to the unrestricted movement of pi electrons due to their collective electronegativity. Two distinct configurations of asphaltene dimers, face-to-face, and edge-to-face, were observed. Intermolecular interactions were predominantly governed by van der Waals forces, highlighting their significant role in stabilizing asphaltene aggregates. The distribution of asphaltene molecules in the oil phase can be summarized as the "rebar-cement" theory. In the heteroatom-free system, the face-to-face peaks in the radial distribution function exhibit significantly reduced magnitudes compared to those in the heteroatom-containing system. This emphasizes the pivotal function of heteroatoms in connecting molecular components to form a more compact asphaltene structure, which may result in a higher viscosity of heavy oil. These findings give insight into the significance of heteroatoms in bridging molecular components and shaping the intricate structure of asphaltene and advance our understanding of heavy oil viscosity properties.

Study of the precipitation trend of asphaltenes and waxes in crude oil using computational chemistry and statistical thermodynamics methods

Asphaltenes aggregation and waxes in petroleum were simulated considering five molecular structures containing functional groups: asphaltenes, resins, and non-polar hydrocarbons in a heavy oil crude. The properties of molecules were calculated using the density functional theory. The van der Waals constants associated with the pairwise interactions and the Hamaker constants for the dispersed phase (formed by asphaltenes and waxes) and the dispersion medium (created by non-polar hydrocarbons) were estimated. Sparse pass size as a function of its composition is calculated using Qyle groups and the Young–Laplace equation. We also assessed the potential colloidal pair corresponding to the interactions between the asphaltene and resin aggregates for different dispersion media, the attractive energies between the asphaltene molecules (−60 10–20 J ≈ ) are more than twice as high as the attractive energies concerning the rest of the molecules present ( × -30–10] 10–20 ≈ × J). It is predicted that attraction energy between the aggregates decreases with the increase of the presence of resin in the dispersed phase, This is explained by the fact that the increase in the concentration n of resin can lead to a decrease in the relative size d of the aggregates by up to 90 % (for n = 0.1, d = 0.1 and for n = 0.9, d = 0.1). This decrease in aggregate size is manifested in a theoretically calculated effective viscosity reduction of up to 50 %.

Viscosity reduction mechanism of surface-functionalized Fe3O4 nanoparticles in different types of heavy oil

In-depth investigation of the viscosity reduction mechanism of nanoparticle viscosity reducers in various heavy oil types holds key strategic significance for the rational exploitation of global heavy oil resources. In this work, the dispersion stability mechanism of three surface-functionalized Fe3O4 nanoparticles (NPs) in kerosene was first explored by molecular dynamics (MD) simulation. Then Studies showed that the differences in asphaltene aggregation structures in different types of heavy oils make their initial viscosities significantly different. The addition of NPs could effectively reduce the viscosity of heavy oil and increase the diffusion coefficient of asphaltenes. Importantly, there were differences in the viscosity-reducing ability and viscosity-reducing mode of the NPs in different types of heavy oil. In Oil1, the NPs increased the peak of the radial distribution function curve, the number of hydrogen bonds (2.25–8.63), and the cluster size between asphaltenes (3.72–6.40). However, these property changes of asphaltenes in Oil2 are opposite. The NPs effectively broke the hydrogen bond between asphaltene (number of hydrogen bonds from 22.87–12.50) and reduced its cluster size (8.17–3.25). Among them, Fe3O4-OA and Fe3O4-KH570 showed the most excellent viscosity reduction performance in Oil1 and Oil2, respectively. Finally, by calculating the surface electrostatic potential of each molecule and the weak interaction between molecules, the microcosmic mechanism of the difference in the viscosity-reducing ability and mode of the NPs in different types of heavy oil was revealed. Overall, the NPs effectively depolymerized the high-density aggregation structure of asphaltene, thereby achieving the purpose of reducing the viscosity of heavy oil. However, in Oil1, the viscosity-reducing performance of NPs was mainly related to their ability to adsorb asphaltenes and their dispersion stability. In Oil2, the viscosity-reducing performance of NPs was dominated by their ability to destroy hydrogen bonds between asphaltenes.