Size Of Asphaltene Aggregates Research Articles

Large-scale molecular dynamics simulation and aggregate behavior research on asphalt

In this comprehensive study, a molecular dynamics (MD) model consisting of approximately 150,000 atoms was developed within the Strategic Highway Research Program (SHRP) framework to investigate the behavior of AAA asphalt, focusing on asphaltene aggregate dynamics behavior over a simulation time span of 0.282 microseconds. The findings reveal that the model achieves a stable state in terms of both energy and microstructure without significant changes or the formation of densely clustered molecules, despite the extensive simulation period. Notably, the patterns of asphaltene aggregation were found to significantly influence the MD system energy, with variations ranging from loosely organized structures due to dispersed asphaltenes to more structured, energy-efficient clusters formed by encapsulated asphaltene pentamers. The size of asphaltene aggregates emerged as a pivotal factor, affecting their encapsulation and leading to distinct formation patterns. Furthermore, the research highlighted that increasing shear rates prompt the depolymerization of asphaltene aggregates, shifting from large-scale structures to smaller ones and adapting dynamically to the flow conditions by aligning parallel to the shear direction. This study underscores the critical impact of asphaltene aggregate behavior and shear rates on the structural integrity and distribution within the asphalt model, offering profound insights into the MD of asphalt materials.

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.

A molecular dynamics approach to investigate effect of pressure on asphaltene self-aggregation

Asphaltene aggregation is a serious issue in the oil industry that negatively affects the production, transportation, and exploitation of oil, causing considerable costs. In the past few years, the experimental analysis of asphaltene aggregation has been a fascinating topic; however, a laboratory study that can assess the asphaltene aggregation behaviors at high pressures will be a costly and high-risk project. In this paper, molecular dynamics (MD) simulations are used to investigate the influence of pressure on the asphaltene aggregation phenomenon. The employed asphaltene in this research is Gachsaran asphaltene (obtained from an Iranian oilfield) with archipelago geometry. The aggregation number, radial distribution function (RDF), potential of mean force (PMF), cohesive energy, solubility parameter, mean square displacement (MSD), diffusion coefficient, relative concentration, potential energy, and radius of gyration are analyzed based on the data and results obtained from the output trajectory files. It is concluded that the number and the average size of asphaltene aggregates significantly decrease with increasing pressure because the pressure delays the growth of asphaltene aggregates by enhancing the asphaltene solubility parameter. The associated energies of asphaltene molecules at 35, 90, and 135 bar are calculated to be −15.7834, −15.7571, and −15.7249 kJ / mol, respectively. It is found that the tendency of asphaltene molecules to aggregate reduces upon an increase in pressure. Face-to-face interactions are more likely than T-shaped and offset stacking for this asphaltene sample because of the more aromatic nuclei in the asphaltene structure than the aliphatic chains, which increase the strength of the π-π interactions. It is also observed that by increasing pressure, the movement and vibration of asphaltene increase and then decrease by further increase in pressure. According to the asphaltene onset envelope diagram, the asphaltene molecules at 35 bar are located in the solid–liquid region. As the pressure increases to 90 bar, the asphaltene passes the upper asphaltene onset point zone. It can be concluded that when asphaltene is in the solid–liquid region, the mobility and displacement of molecules increase with increasing pressure. In the upper asphaltene onset point zone, the tendency of molecules to move is reduced. The MD results are consistent with the laboratory data.

The study on interactions between stabilizers and asphaltenes

Asphaltene stabilizers are the main means to inhibit the flocculation and sedimentation of asphaltenes in crude oil exploitation, transportation, and refining operations. In this work, the interactions between asphaltenes and 2-dodecyl benzene sulfonic acid, 4-dodecyl benzene sulfonic acid, 4-dodecyl aniline, 4-dodecyl phenol, polyisobutylene succinic imide benzene boric acid and polyisobutylene succinic imide benzene sulfonic acid were studied by XPS, XRD, DLS, TEM and SEM methods. The aggregation behavior of asphaltenes in the absence and presence of stabilizers was characterized by analyzing asphaltene’s particle size, surface composition, and aggregate microstructure. It was observed that the interactions between asphaltene and stabilizers decreased asphaltene aggregate size in solution, and that the polymeric stabilizer with an acidic group was superior to the small-molecule stabilizer with an acidic group, but both better than chemicals with basic groups. It was found that stabilizer adsorption on asphaltenes affected the O, N, S contents of asphaltene surface and prompted formation of protonated pyridinic N+ and nitrogen-oxide -R-N+-O-, which further revealed that an acid-base reaction was the most effective at stabilizing asphaltene-stabilizer complexes, followed by π-π interactions and hydrogen bonds. We also found that the synergistic effects of π-π and acid-base reactions stimulated the transformation of 2-dodecyl benzene sulfonic acid adsorbed on asphaltene from the vertical state at low concentrations to the tiled arrangement at high concentrations. XRD results showed that adsorption of stabilizers on asphaltene increased the distance of asphaltene aromatic sheets and decreased the aggregation number of asphaltene to below the critical aggregation number of asphaltene tactoids.

Impact of conjugated polymer addition on the properties of paraffin-asphaltene blends for heat storage applications: Insight from computer modeling and experiment.

Adding carbon nanoparticles into organic phase change materials (PCMs) such as paraffin is a common way to enhance their thermal conductivity and to improve the efficiency of heat storage devices. However, the sedimentation stability of such blends can be low due to aggregation of aromatic carbon nanoparticles in the aliphatic paraffin environment. In this paper, we explore whether this important issue can be resolved by the introduction of a polymer agent such as poly(3-hexylthiophene) (P3HT) into the paraffin-nanoparticle blends: P3HT could ensure the compatibility of aromatic carbon nanoparticles with aliphatic paraffin chains. We employed a combination of experimental and computational approaches to determine the impact of P3HT addition on the properties of organic PCMs composed of paraffin and carbon nanoparticles (asphaltenes). Our findings clearly show an increase in the sedimentation stability of paraffin-asphaltene blends, when P3HT is added, through a decrease in average size of asphaltene aggregates as well as in an increase of the blends' viscosity. We also witness the appearance of the yield strength and gel-like behavior of the mixtures. At the same time, the presence of P3HT in the blends has almost no effect on their thermophysical properties. This implies that all properties of the blends, which are critical for heat storage applications, are well preserved. Thus, we demonstrated that adding polyalkylthiophenes to paraffin-asphaltene mixtures led to significant improvement in the performance characteristics of these systems. Therefore, the polymer additives can serve as promising compatibilizers for organic PCMs composed of paraffins and asphaltenes and other types of carbon nanoparticles.

Experimental and theoretical study of the influence of solvent on asphaltene-aggregates thermo-oxidation through high-pressure thermogravimetric analysis

This study is focused on the understanding of n-C7 asphaltene-aggregates oxidative behavior under high-pressure conditions. For this aim, different asphaltene model solutions were prepared using three asphaltene concentrations (0.1, 1.0, and 10 wt%) on three xylene isomers. The experimental results revealed that the asphaltene aggregate size increase in the order o-xylene < m-xylene < p-xylene. Also, molecular dynamics (MD) simulations were carried out to explain the aggregation differences. It was found that the –CH3 location in the xylene has a substantial impact on the aggregation state. The o-xylene molecules surrounding the asphaltene aggregates oriented them –CH3 groups towards the aggregates, increasing their interaction energy and reducing the aggregation size. Further, the oxidative experiments of the aggregates showed that the oxygen chemisorption decreased as the asphaltene aggregate size increased, reducing their reactivity. Contrasting the xylene isomers, for concentrations >1.0 wt%, the mass gained by oxygen chemisorption increased in the order: p-xylene < m-xylene < o-xylene. This study improves our understanding of the relationship between the aggregation and thermal oxidation of crude oils, characterizing the physical behavior to propose alternatives that reduce asphaltene aggregation and improve the oxidative kinetic.

Experimental study on pore-scale mechanisms of ultrasonic-assisted heavy oil recovery with solvent effects

Production from heavy asphaltenic oil reservoirs poses several challenges that require new and innovative techniques for improved production and recovery. The main objective of this study is to experimentally investigate the influences of ultrasonic waves and solvent on oil viscosity, asphaltene precipitation behavior, and recovery of a heavy asphaltenic crude oil. This study is divided into two main parts. In the first part, crude oil samples were subjected to ultrasonic radiation with a frequency of 20 kHz and varying output powers (30, 60, and 100 W) for various durations. The viscosity of each oil sample was measured immediately after stopping ultrasonic radiation and also after 24 h of irradiation. An optimum time for ultrasound radiation was determined when the cooled-down radiated oil reached a minimum viscosity. We then measured the viscosity of the ultrasonically treated oil samples blended with a solvent (i.e., n-heptane) to assess the synergetic effect of ultrasonic radiation and solvation on the oil viscosity. In the second part, the application of ultrasonic radiation on the asphaltene aggregates and oil recovery was examined using solvent flooding in a transparent porous medium. Four sets of experiments were undertaken where the solvent was injected into the micromodel saturated with the untreated and ultrasonically treated oil free from or blended with the solvent. The results showed that ultrasonic treatment decreased the size of asphaltene aggregates and consequently reduced the viscosity of the crude oil. As a result, the suspension of asphaltene in the ultrasonically treated oil increased and reduced its tendency to precipitate at the optimum radiation time. Furthermore, the results indicated that the combined use of ultrasound and solvent had the greatest reduction in the oil viscosity compared to the untreated crude oil with ultrasonic waves or solvent.

Multi-alkylated aromatic amides amphiphiles effectively stabilize the associated asphaltene particles in crude oil

As an economic and efficient method, asphaltene dispersants are widely used to inhibit the precipitation of asphaltenes in the crude oil tank. In this study, a series of multi-alkylated aromatic amides (MAA) amphiphiles containing benzene rings and a different number of alkyl side chains were synthesized and evaluated as asphaltene dispersants for the Saudi crude oil. After adding 500 ppm MAA-3, the initial flocculation point of the oil sample is significantly increased from 42.48% to 70.94%, the size of asphaltene aggregates is reduced from 3.99 ± 0.2 μm to 1.45 ± 0.2 μm, and the viscosity of the oil sample has increased by 21.77%. The influence of the number of alkyl side chains on the performance of asphaltene dispersants was also studied. The result shows that increasing the number of the alkyl side chain is beneficial to improve the performance of dispersant, and the MAA has the best performance of dispersing asphaltenes at the number of alkyl side chains of 3 (MAA-3). The molecular simulation (MS) further verified the experimental results from the perspective of interaction energy.

Combined experimental and molecular dynamics investigation of 1D rod-like asphaltene aggregation in toluene-hexane mixture

The aggregation behavior of asphaltene in the toluene-hexane mixture is systematically investigated using experimental techniques such as optical microscopy and Fourier-transform infrared spectroscopy (FTIR) combined with molecular dynamics (MD) simulations. The optical images of various asphaltene concentrations are processed to determine the size of asphaltene aggregates. FTIR is performed within our work in order to understand the formation of aggregates and its interaction with the solvent mixture. MD simulations are employed to achieve atomistic insights into the aggregation behavior of asphaltene. The end-to-end distance of the asphaltene molecule is calculated for various asphaltene concentrations in the toluene-hexane mixture. The dynamical properties of the asphaltene aggregates such as the diffusion coefficient and shear viscosity are calculated. Further, an in-depth analysis of the density contours is performed to probe the clusterization of asphaltene. Thus obtained structural and dynamical properties of the asphaltene aggregates in the toluene-hexane mixture are compared with our experimental findings. Our results thereby highlight the importance of the combined experimental and theoretical study to achieve deeper and better insights into the aggregation behavior of asphaltene in toluene-hexane mixture.

Influence of ultrasonic treatment on kinetic of asphaltene aggregation in toluene/heptane mixture

This article illustrates the results of a study of ultrasonic dispersion’s influence on kinetic of asphaltene aggregation in a toluene/heptane mixture. The study was carried out by the method of dynamic light scattering. This optical method allows to measure the size of nano- and submicron particles in liquid medium. This method allows to measure the dependence of the average size of asphaltene aggregates during primary and secondary asphaltene aggregation. The primary aggregation was studied in a solution of asphaltenes in toluene and was initiated by the addition of heptane. Secondary aggregation of asphaltenes was initiated by ultrasonic dispersion of a mixture of toluene/heptane/asphaltene, in which primary aggregation finished and which contained asphaltene floccules. The effect of stabilization of asphaltene aggregates was experimentally detected after multiple ultrasonic dispersions.

Experimental and DFT studies on the effect of carbon nanoparticles on asphaltene precipitation and aggregation phenomena

• CNPs were synthesized for controlling asphaltene precipitation and aggregation. • FESEM and FTIR demonstrate uniform adsorption of asphaltene on surface of CNPs. • DFT modeling proves the strong hydrogen interaction between CNPs and asphaltenes. • CNPs represent biocompatible and affordable asphaltene inhibitor-dispersant. In this study, a new class of carbon nanoparticles (CNPs) is synthesized for inhibition/dispersion of asphaltene precipitation and aggregation in unstable crude oil. The microscopy and asphaltene dispersant experiments are carried out to assess the effects of CNPs on asphaltene precipitation and aggregation. Also, density functional theory is applied to describe the mechanisms of asphaltene adsorption onto the CNPs surfaces. Experimental results demonstrate postponement of asphaltene onset of precipitation from 26 to 37 vol% n-C 7 in the presence of 400 ppm of the CNPs which is ascribed to the extra high specific surface area of the CNPs. DLS analysis shows the average size of asphaltene aggregates adsorbed onto the CNPs reduces from 1730 nm in the blank oil to 255 nm in treated oil with CNPs. The results of DFT modeling demonstrate the strong hydrogen interaction between functional groups of the CNPs and active sites of asphaltene. Also, π–π interactions occur between electron cloud of aromatic rings of asphaltene and CNPs with minimum equilibrium distance of 2.94 Å. The adsorption energy for the most stable complex of asphaltene and CNPs in the gas and solvent phases are −91.22 and −107.64 kJ/mol, respectively, confirming the strong chemisorption of asphaltene over the CNPs. This research reveals that synthesized CNPs with specific features such as high surface area, potential of covering the external shell with a wide variety of functional groups, low toxicity and cost, and environment-friendly can be successfully implemented as an efficient inhibitor and/or dispersant for asphaltene handling strategies.

Molecular dynamics simulation to investigate the effect of polythiophene-coated Fe3O4 nanoparticles on asphaltene precipitation

Asphaltene precipitation is one of crucial problems in oil industry that negatively affects oil production, transportation, and processing, imposing high costs. In recent years, numerous experimental studies have been conducted to analyze inhibition of asphaltene precipitation using nanoparticles. In this study, molecular dynamics simulations are employed for the first time to investigate the effect of Fe3O4 and polythiophene-coated Fe3O4 nanoparticles on asphaltene aggregation phenomena. In addition, the structure of asphaltene is determined based on elemental analysis, 1HNMR, 13CNMR, and FTIR. The number of molecules and average size of asphaltene aggregates in the presence of nanoparticles show a considerable decrease in aggregation, compared to the case without nanoparticles due to delay in growth of asphaltene aggregates. Asphaltenes tend to adsorb on surface of nanoparticles as a result of interaction forces. Consequently, smaller and/or fewer aggregates of asphaltene precipitate on the quartz surface. The simulation results show a good match with the experimental data.

Investigation of asphaltene aggregate size: influence of Fe3O4 nanoparticles, asphaltene type, and flocculant

Investigation of asphaltene aggregate size: influence of Fe3O4 nanoparticles, asphaltene type, and flocculant

Developing a novel colloidal model for predicting asphaltene precipitation from crude oil by alkane dilution

This research aims to propose a thermodynamic model for predicting asphaltene precipitation upon diluting a crude oil with a paraffinic solvent. To this end, a thorough mathematical formulation was carried out to derive a novel micellization model based on the associative properties of asphaltenic compounds. It was assumed that asphaltenes exist in the oil both as monomeric molecules and aggregated cores; with stabilization latter by attachment of resin on its periphery. The aggregation equilibrium was established by taking into account asphaltene's lyophobic tendency, heat of resin adsorption, and interfacial tension between micelle and oil media which is the main driving factor contributing to Gibbs free energy of micellization. In this study, the mean diameter of asphaltene aggregates at different dilution ratios was incorporated into the framework of modeling approach, by measuring particle size distribution of asphaltenes at varying n-heptane fractions. The data density of pure asphaltene for an Iranian crude-oil sample was used in calculations. The proposed model favorably predicted the precipitation trend of the crude oil diluted at varying fractions of n-heptane. This model shows that taking into account the size of asphaltene aggregates can significantly improve the prediction accuracy of the micellization model, compared to the simple model, with normalized root-mean-square error of 9.4 and 28.7, respectively. A detailed sensitivity analysis was performed to gain insight into physical implication of the model parameters.

Effect of asphaltene structure on its aggregation behavior in toluene-normal alkane mixtures

Colloidal behavior of asphaltene in normal alkane-toluene mixture has been under research over the past decades. However, the influence of asphaltene composition and its structure on asphaltene aggregation in such mixtures has not been fully understood yet. In this study, the colloidal behavior of asphaltene in normal alkane-toluene mixture was investigated using image processing approach. Three different types of asphaltenes were extracted from Iranian oil reservoirs. Asphaltenes were characterized by elemental analysis, X-Ray Diffraction (XRD), and Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The effects of asphaltene concentration, type of normal alkane, ratio of normal alkane to toluene, and structure of asphaltene on onset of asphaltene flocculation (OAF) and aggregates size were investigated. The onset of asphaltene flocculation decreases with increasing asphaltene concentration. A mathematical model was developed to predict OAF for different normal alkanes and asphaltenes. The proposed mathematical model has an exponential form with two constants, which should be tuned using experimental data. The results indicate that as asphaltene concentration increases, larger aggregates are formed with an average (AS) size between 8 and 15 μm and some aggregates greater than 100 μm may be formed. Moreover, the structure and composition of asphaltene is determinant of aggregates’ size. The lowest aggregates size refers to asphaltene C with the lowest number of fused rings, polarity, and aromaticity, which is the most stable asphaltene with the smallest aggregates size. Asphaltenes A and B have almost the same size as polarity and aromaticity both contribute to the aggregates size. The aggregates formed by n-C7 (AS≈ 7.5 to 8.5 μm) are larger than those of n-C10 (AS≈ 8.5 to 12 μm) and n-C16 (AS≈ 9 to 14 μm). In addition, increasing the ratio of normal alkane to toluene increases the size of asphaltene aggregates up to a maximum value and then gradually decreases.

Laboratory evaluation of a novel multifunctional chemical solution for asphaltene precipitation and aggregation problem: Comparison with an industrial chemical solution

Asphaltene deposition in the near-wellbore area and within the pipelines reduces productivity and is costly. There are usually 2 methods to remedy this hardship that are using dispersants or inhibitors to preventing asphaltene deposition or using solvents when asphaltene deposits on inner surface of pipes or in the porous media. In this study, additive called AUT Force 110 has been developed and its properties have been inspected. This solvent has multifunctional efficiencies (MS) such that can be used as asphaltene inhibition and dispersion and dissolve asphaltene deposits. Furthermore, its performance is compared to an industrial solvent called PL5001 (CS). Analyzing the fourier-transform infrared spectroscopy (FTIR) of the two additives were found to have polar functional groups of hydroxyl, thiol, carbonyl and carboxylic acid in their molecule. The existence of various functional groups gives the MS molecule the ability to interact with adjacent molecules through hydrogen bonding. In addition, aliphatic compounds were observed in the MS molecule with a low carbon number, which leads to its compatibility with crude oil. In contrast, the CS consists mainly of aromatic rings. Two carbonyl and ether functional groups were also observed in its molecular structure, which are very low in concentration compared to polar compounds of MS. Then, the confocal microscopy imaging was used to observe asphaltene aggregates with precipitant. The crude oil and n-heptane were combined in a ratio of 1–30 volumes. The addition of 100 ppm MS reduced about 87% of the mean diameter of asphaltene aggregates; while this reduction was less than 70% by adding CS. Also, adding MS narrowed the dispersion range of the asphaltene particles diameter to 2–16 μm. The carboxylic acid and thiol functional groups play important roles in asphaltene dispersion in MS system. Both MS and CS delayed the onset of asphaltene precipitation, however MS has greater asphaltene inhibition power as well as improving the rheological properties of crude oil and n-heptane solution due to the reduction in the size of asphaltene aggregates, the interaction of MS with asphaltene, and the reduction of the interaction between the asphaltene-asphaltene molecule besides the polar nature of MS. Turbiscan test was also used to measure the solvation power of two additives. The solubility number of MS was lower than that of CS and was reported to be a good solvent, indicating that it has better solvation power than CS. Because MS has the ability to hydrogen bond with asphaltene molecules as both donor and acceptor. Secondly, its aliphatic chains cause steric hindrance, which contributes to the stability of asphaltenes within MS.

New insights into the interactions between asphaltene and a low surface energy anionic surfactant under low and high brine salinity

Hypothesis: The hyperbranched chains on the tail of low surface energy surfactants (LSES) causes lowering of surface free energy and rock wettability alteration, offering significant improvement in oil recovery in asphaltene oil reservoirs.Experiments: Oil sweep efficiency was determined by fluid displacement in pure brine and LSES-brine solutions in a microfluidic pattern that was representative of a sandstone cross-section. Interfacial tension (IFT), wettability alteration, Raman and X-ray photoelectron spectroscopy (XPS) were used to measure the changes of asphaltene interactions with oil-aged substrate after surface treating with brine and surfactant-brine solutions.Findings: The hyperbranched LSES yielded a significant increase in the original-oil-in-place (OOIP) recovery (58%) relative to brine flooding (25%), even in the presence of asphaltene. Raman spectra showed the LSES-brine solutions to be capable of causing change to the asphaltene aggregate size after centrifugation treatment.

Investigation into mechanisms and kinetics of asphaltene aggregation in toluene/n-hexane mixtures

Determining the rate of asphaltene particle growth is one of the main problems in modeling of asphaltene precipitation and deposition. In this paper, the kinetics of asphaltene aggregation under different precipitant concentrations have been studied. The image processing method was performed on the digital photographs that were taken by a microscope as a function of time to determine the asphaltene aggregation growth mechanisms. The results of image processing by MATLAB software revealed that the growth of asphaltene aggregates is strongly a function of time. Different regions could be recognized during asphaltene particle growth including reaction- and diffusion-limited aggregation followed by reaching the maximum asphaltene aggregate size and start of asphaltene settling and the final equilibrium. Modeling has been carried out to predict the growth of asphaltene particle size based on the fractal theory. General equations have been developed for kinetics of asphaltene aggregation for reaction-limited aggregation and diffusion-limited aggregation. The maximum size of asphaltene aggregates and settling time were modeled by using force balance, acting on asphaltene particles. Results of modeling show a good agreement between laboratory measurements and model calculations.

Experimental study of asphaltene deposition: Focus on critical size and temperature effect

Asphaltene by far is the most problematic part of crude oil that could separate from oil body as a result of any change in system equilibrium. It can deposit at any point along oil flow path which in turn impose series restrictions, and subsequently create major impact on production from economic perspective. In this study, the influence of oil composition, flow rate, and for the first time, temperature on the intensity of deposition process are experimentally investigated. An in-house deposition unit apparatus was utilized which is based on the measurement of pressure drop across the capillary tube. The results indicate that in overall, temperature and oil composition change toward less soluble asphaltene, accelerate deposition process while flow rate enforces further restriction on process. In addition, by devising novel centrifugal based deposition experiments, critical size concept is more effectively addressed. The concept argues that there is a critical value for asphaltene aggregate size, beyond which the deposition will not occur. This critical size is not necessarily influence by hydrodynamic drag like forces.

The effect of nonylphenol on asphaltene aggregation: A molecular dynamics approach

ABSTRACTMolecular dynamics (MD) simulations were performed to study the occurrence time of each stage of asphaltene aggregation from single molecules to a large flocculate with and without nonylphenol (NP) molecules as asphaltene dispersants. NPs reduce the size of asphaltene aggregates, and curb the clustering of nanoaggregates when they are added to the simulation box at nanoaggregation nucleation stage. These dispersants are able to break clusters into their constituent nanoaggregates when they are added at higher concentrations. Moreover, asphaltene–NP interactions change the structure of asphaltene flocculates from globular into filamentary.