Asphaltene Solubility Research Articles

Modeling of asphaltene precipitation - part I: comparative study for asphaltene precipitation envelope prediction methods

The solubility of asphaltenes in crude oils is predominantly influenced by variations in temperature, pressure, and oil composition. These alterations can precipitate asphaltene deposition, resulting in diminished permeability, obstruction of wells and auxiliary surface facilities, and ultimately, a reduction or cessation of production. Therefore, it is imperative for upstream and downstream processing engineers to comprehend and predict asphaltene phase behavior to implement effective preventative and remedial strategies and minimize costs. Asphaltene precipitation can be predicted through the application of solubility and colloidal theories. In this study, cubic equations of state and cubic-plus-association equations of state are utilized as solubility theory-based methodologies. The advanced versions of the Peng-Robinson (APR78) and Soave-Redlich-Kwong (ASRK) cubic equations of state are compared with cubic-plus-association (CPA) equations of state using Multiflash software to predict fluid and asphaltene phase behavior. The simulation results demonstrate a strong correlation between the ASRK model and the CPA model, with a minor deviation from the results of the APR78 model. This observation suggests that these models can effectively predict asphaltene behavior and yield acceptable results when compared to experimental data for fluid and asphaltene. Considering the likelihood of asphaltene deposition within wells, hence, it is recommended to develop a model to determine the locations and quantities of deposition.

Molecular simulation of asphaltene clustering in toluene and n-heptane: Thermodynamics and dynamics aspects

This study investigated the thermodynamic and dynamic properties of asphaltene molecules in Toluene and n-Heptane using the OPLS-AA force field in the GROMACS package at 300 K and 1 bar. The results indicate that van der Waals (vdW) interactions have a significant influence on thermodynamics, accounting for around 88–90 % of the total interaction energy between asphaltene molecules, while Coulombic (Coul) interactions contribute approximately 10–12 %. Stable asphaltene aggregates form at concentrations equal to or greater than 8 asphaltene molecules in 4000 molecules of Toluene. The interaction energy between asphaltene chains, which promotes aggregation, is much weaker than the interaction between aromatic rings. Longer chains exhibit more attractive vdW interactions and more repulsive Coul interactions. The presence of heteroatoms (sulfur and oxygen) hinders the parallel and symmetrical interaction of asphaltene molecules. Density profiles and two-dimensional maps were used to analyze the spatial arrangement of asphaltenes. A total interaction energy equal to or more positive than −300 kJ/mol for asphaltene-liquid interactions is introduced as a criterion for classifying a liquid as an asphaltene precipitator. The polarity of the solvent was inferred not to affect asphaltene solubility. In n-Heptane, asphaltene molecules aggregated to form a dense nucleus, while in Toluene, sharp peaks in the density profiles indicated the formation of clusters of varying sizes via asphaltene aggregation. Systems containing 64 and 32 asphaltene molecules had the highest probability of forming clusters comprising 10–16 and 12–16 asphaltene molecules, respectively. In Toluene, the average cluster sizes ranged from 1.4 to 6.1 molecules, depending on asphaltene concentration. Cluster size analysis showed variations in both size and stacking architectures, including face-to-face stacked and T-shaped aggregates. The proportion of face-to-face stacked structures was higher than T-shaped structures in both Toluene and n-Heptane, with the ratio of face-to-face stacked to T-shaped aggregates estimated at ∼2.9. While thermodynamic equilibrium was well attained, simulation times longer than 150 ns are recommended to achieve dynamic equilibrium.

A new insight into H-donor’s positive effect on thermal cracking process at molecular level

Thermal cracking reactions of vacuum residue (VR) at 420 ℃ with different reaction time were carried out to evaluate an industrial H-donor’s effect on thermal cracking process at molecular level. The mass distribution, conversion ratio, asphaltene and coke yields were analyzed to evaluate the changing rules. Aromatic structures of H-donor were analyzed and its typical structures were speculated, and the bond energy of those model compounds were calculated. It can be concluded that the >460℃ fractions from a refinery stream have abundant H-donors. From analyzing the structures of asphaltenes for the feed and products, it can be learned that H-donors not only can modify the asphaltene structures but also can improve the asphaltene solubility.

Experimental Evaluation of Kinetic Behavior of Asphaltene Particles: Effect of Temperature, Shear Stress, and Inhibitors

Summary Asphaltene deposits under a variety of temperatures and shear stresses in reservoirs, wells, and crude oil transmission pipelines, and it is currently one of the most serious problems in the oil industry. The size of asphaltene particles strongly affects the deposition rate. The particle size is mainly determined by aggregation rate that depends on shear rate and temperature. Therefore, different shear rates of 127 s–1 and 254 s−1 were applied within Couette flow at 25°C, 45°C, and 65°C, and the particle size was analyzed by using an optical microscope. Crude oil viscosity and asphaltene solubility were determined using a capillary tube viscometer and IP143 procedure, respectively. In this work, the effects of four additives, namely, dodecyl benzene sulfonic acid (DBSA), nonyl phenol (NP), salicylic acid (SA), and benzoic acid (BA), were studied on the aggregation of asphaltene particles in a light crude oil. The additives were chosen based on their functional groups. Moreover, asphaltene functional groups were determined using a Fourier transform infrared (FTIR) analyzer to better understand the behavior of inhibitors in preventing the aggregation of asphaltene particles at different conditions. DBSA, BA, and SA were inhibitors, and NP behaved as a promoter. According to the results, the presence of acidic groups, SO3H in DBSA and COOH in SA and BA, increases the interaction of inhibitor with asphaltene and so reduces the aggregation of asphaltene particles. The stronger acidic group of DBSA improved its performance compared to other inhibitors. Both increasing temperature and increasing shear stress resulted in higher collisions of asphaltene particles and thus lowered the efficiency of inhibitors at a constant concentration.

Understanding the Aggregation of Model Island and Archipelago Asphaltene Molecules near Kaolinite Surfaces using Molecular Dynamics.

The solubility of asphaltenes in hydrocarbons changes with pressure, composition, and temperature, leading to precipitation and deposition, thereby causing one of the crucial problems that negatively affects oil production, transportation, and processing. Because, in some circumstances, it might be advantageous to promote asphaltene agglomeration into small colloidal particles, molecular dynamics simulations were conducted here to understand the impacts of a chemical additive inspired by cyclohexane on the mechanism of aggregation of model island and archipelago asphaltene molecules in toluene. We compared the results in the presence and absence of a kaolinite surface at 300 and 400 K. Cluster size analyses, radial distribution functions, angles between asphaltenes, radius of gyration, and entropic and energetic calculations were used to provide insights on the behavior of these systems. The results show that the hypothetical additive inspired by cyclohexane promoted the aggregation of both asphaltenes. Structural differences were observed among the aggregates obtained in our simulations. These differences are attributed to the number of aromatic cores and side chains on the asphaltene molecules as well as to that of heteroatoms. For the island structure, aggregation in the bulk phase was less pronounced than that in the proximity of the kaolinite surface, whereas the opposite was observed for the archipelago structure. In both cases, the additive promoted stacking of asphaltenes, yielding more compact aggregates. The results provided insights into the complex nature of asphaltene aggregation, although computational approaches that can access longer time and larger size scales should be chosen for quantifying emergent meso- and macroscale properties of systems containing asphaltenes in larger numbers than those that can currently be sampled via atomistic simulations.

The Effect of Temperature on the Size and the Deposition of Asphaltene Particles

Summary The deposition of asphaltene as a main component of crude oil is considerably affected by temperature. Despite the studies on influencing factors on deposition and size of asphaltene particles, no experimental research was previously conducted on the simultaneous impact of temperature on asphaltene particle size and deposition. In this study, the asphaltene deposit mass was measured within a Couette device at various temperatures ranging between 20 and 65°C under a constant angular velocity. Furthermore, the asphaltene particle size was simultaneously measured to investigate the relationship between deposition mass and asphaltene particle size and also to validate the concept of critical particle size. A digital microscope was used to measure the size of unstable asphaltene particles in oil. Asphaltene solubility and oil viscosity were measured to understand the deposition mechanisms. The analysis of microscopic images indicated that larger asphaltene particles are produced at higher temperatures. Although the total mass of the deposit was decreased with temperature, the deposition fraction, defined as mass fraction of total unstable asphaltene particles that deposit, was increased. Higher fraction of deposition was found for larger particles that is in contradiction to the previously introduced critical particle size concept. Additionally, the effect of solubility was found to be dominant in comparison with viscosity from the point of view of the total mass of the deposit. For the oil sample investigated in this study, a 45°C increase in temperature reduced the total mass of the deposit by 46.84%.

New optical microscopy method for determining the influence of feedstock composition on the morphology of microcarbon residue test petroleum cokes

Predicting the petroleum coke or petcoke morphology tendencies of Delayed Coking feeds is paramount to optimizing refinery operation and profitability. Herein, we report a new analytical methodology employing cross-polarized light optical microscopy (CPL-OM) of Microcarbon Residue Test (MCRT) cokes, followed by image segmentation and statistical analysis to determine several structural parameters, i.e., average area, average Feret maximum, and percentage of isochromatic domains with Feret maximum <8 μm (Feret is defined as the maximum distance between the two parallel planes of a given coke particle). Several advantages over previous CPL-OM methods include using more extensive data sets and machine-learning software to accurately segment images to yield better statistics, eliminating isochromatic domains on edge to reduce error, and stitching multiple images to account for larger domains. The new CPL-OM-image segmentation-statistical analysis procedure was effectively used to determine the influence and predict the morphology of MCRT cokes based on Delayed Coking feed properties (C7-asphaltenes percentage/MCRT percentage ratio and the asphaltene solubility parameter) and in blends of vacuum resids. The structural parameters Feret Max. Percentage <8 μm and average area showed excellent agreement within the errors of the technique. This technique represents a convenient analytical tool to qualitatively rank Delayed Coking feedstocks in terms of coke morphology tendencies.

Comparative Static and Dynamic Analyses of Solvents for Removal of Asphaltene and Wax Deposits above- and below-Surface at an Iranian Carbonate Oil Field.

During production from oil wells, the deposition of asphaltene and wax at surface facilities and porous media is one of the major operational challenges. The crude oil production rate is significantly reduced due to asphaltene deposition inside the reservoir. In addition, the deposition of these solids inside the surface facilities is costly to oil companies. In this study, the efficiency of different solvents in dissolving asphaltene and wax was investigated through static and dynamic tests. The analysis of solid deposits from the surface choke of one of the Iranian carbonate oil fields showed that they consisted of 41.3 wt % asphaltene, and the balance was predominantly wax. In addition, the asphaltenes obtained from the surface choke solid deposits had a more complex structure than that of asphaltenes extracted from the crude oil itself. The static tests showed that xylene, toluene, gasoline, kerosene, and gas condensate had the highest efficiencies in dissolving solid deposits; conversely, diesel had a negative impact on dissolving solid deposits. Static tests on pure asphaltene showed that, among the tested solvents, gas condensate and diesel had a negative effect on the solubility of asphaltene. The dynamic core flooding results showed that asphaltene deposition inside the cores reduced the permeability by 79-91%. Among the tested solvents, xylene, gasoline, and kerosene resulted in the highest efficacy in restoring the damaged permeability, and higher efficiency was obtained with an equivalent solvent injection rate of 1 bbl/min versus 3 bbl/min.

Quantitative determination of petroleum hydrocarbons in oily sludge following efficient n-heptane separation

Accurate analysis of the main chemical components of oil-bearing sludge is an important prerequisite for effective soil remediation and resource reuse. However, precise analysis of the extract components is difficult to achieve because of the mutual interference of saturates, aromatics, and resins, collectively called SAR, and asphaltene that are introduced during chloroform extraction. In this study, SAR was efficiently extracted using n-heptane, while asphaltene components were retained in soil because of their insolubility in n-heptane. The maximum yield of SAR extraction was 27.0%, indicating an increase of 1.75% compared to chloroform extraction. The extracted SAR components were separated by chromatography and the main structural units and components were analyzed. The results show that saturates, aromatics, and resins have a single component, a high content of major components, and contain fewer impurities using n-heptane extraction. Moreover, the solubility of asphaltene was inhibited during the effective extraction of SAR components with n-heptane and did not influence the subsequent analysis of SAR component. Efficient SAR extraction, accurate SAR component analysis, and high efficiency asphaltene separation was achieved using n-heptane-extraction-assisted pyrolysis. This provides a new method for the component analysis of oily sludge and promotes its efficient separation.

Aggregation of Asphaltene Subfractions A1 and A2 in Different Solvents from the Perspective of Molecular Dynamics Simulations

The aggregation behavior of model molecules of asphaltene subfractions A1 and A2 dissolved in heptane, toluene, and tetrahydrofuran (THF) were studied using molecular dynamics simulations. The proposed asphaltene molecular models are based on previously studied structures with two new models, including a highly aromatic model with a prominent island-type molecule and another molecule with a prominent archipelago-type architecture. The aggregation mechanisms in toluene, THF, and heptane solvents were studied. The results in heptane and toluene were consistent with the solubility of asphaltenes and their subfractions in these solvents. The size of the aggregates is well-correlated with aromaticity. When considering THF, large aggregates are broken down into smaller aggregates. This could lead to the mixture of high, medium, and low molecular weight distribution bands usually observed when gel permeation chromatography (GPC) analyses are conducted on asphaltene samples in THF. The size distribution extracted from the simulations shows a bimodal distribution with profiles similar to the size distribution profiles usually found in GPC analysis for asphaltene samples in THF. The distributions of dipole moments of the aggregates against the number of molecules in aggregates were constructed in both THF and toluene and reveal that the dipole moment of the aggregates vanishes when the number of molecules increases as a result of a random structure of the aggregates. The contributions of different molecular interactions to the aggregation mechanism, such as π stacking, van der Waals, and hydrogen bonds, are described.

Biodiesel as Dispersant to Improve the Stability of Asphaltene in Marine Very-Low-Sulfur Fuel Oil

Since the implementation of the sulfur cap legislation in 2020, marine very-low-sulfur fuel oil, often known as VLSFO, has become a crucial source of fuel for the contemporary shipping industry. However, both the production and utilization processes of VLSFO are plagued by the poor miscibility of the cutter fraction and the residual fraction, which can result in the precipitation of asphaltene. In this study, biodiesel was chosen as a cutter fraction to improve the stability and compatibility of asphaltene in VLSFO because of its environmental benefit and strong solubility. The average chemical structure of asphaltene derived from the marine low-sulfur fuel oil sample was analyzed using element analysis, FTIR, 1HNMR, and time-flight spectroscopy. The composition of biodiesel was analyzed using GC-MS. It was found that the asphaltene had a feature of a short side chain, low H/C ratio, high aromaticity, and a high proportion of heteroatoms. Both laboratory experiments and molecular dynamic simulations were applied to investigate the dispersion effect and mechanism compared with other dispersants. The dispersion effect of biodiesel was studied using measurements of the initial precipitation point (IPP), dispersion improvement rate, and morphology of asphaltene in the model oil. Experimental results revealed that biodiesel was fully compatible with heavy fuel oil and that it can postpone the IPP from 46% to 54% and increase the dispersion improvement rate to 35%. Molecular dynamics (MDs) simulation results show that biodiesel can form strong interactions with the fused aromatics structures and heteroatoms in the asphaltene; such interactions can increase the solubility of asphaltene and acts as a “connection bridge” to promote the dispersion effect of asphaltene molecules.

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.

High-Field (3.4 T) Electron Paramagnetic Resonance, 1H Electron-Nuclear Double Resonance, ESEEM, HYSCORE, and Relaxation Studies of Asphaltene Solubility Fractions of Bitumen for Structural Characterization of Intrinsic Carbon-Centered Radicals

Petroleum asphaltenes are considered the most irritating components of various oil systems, complicating the extraction, transportation, and processing of hydrocarbons. Despite the fact that the paramagnetic properties of asphaltenes and their aggregates have been studied since the 1950s, there is still no clear understanding of the structure of stable paramagnetic centers in petroleum systems. The paper considers the possibilities of various electron paramagnetic resonance (EPR) techniques to study petroleum asphaltenes and their solubility fractions using a carbon-centered stable free radical (FR) as an intrinsic probe. The dilution of asphaltenes with deuterated toluene made it possible to refine the change in the structure at the initial stage of asphaltene disaggregation. From the measurements of samples of bitumen, a planar circumcoronene-like model of FR structure and FR-centered asphaltenes is proposed. The results show that EPR-based approaches can serve as sensitive numerical tools to follow asphaltenes' structure and their disaggregation.

An Integrated Review on Asphaltene: Definition, Chemical Composition, Properties, and Methods for Determining Onset Precipitation

Summary Asphaltene is a solid oil component with a wide range of molecular compositions and structures, making it one of oil’s most complicated components. The deposition and precipitation of asphaltene in several places along the oil production line, such as the wellbore, reservoir, flow lines, tubing, and the separation unit at the surface, of the most prevalent flow assurance challenges. Changes in pressure, composition, and temperature cause asphaltene to precipitate out of the oil continuum. Variations in operation condition are caused by various recovery processes (gas injection, natural depletion, and chemical injection) in addition to the creation and blending of various oils during transportation. This paper presents a complete review of asphaltene precipitation (AP) and deposition (AD), which in turn helps in understanding the governing mechanisms and thermodynamic behaviors in this field. This study consists of several stages: analyzing the current state of asphaltene research (asphaltene characteristics, chemical nature, molecular structure, asphaltene crude oil phase behavior, solubility factors, and other factors); describing the phases of asphaltene (from its stability through its deposition in the reservoir pores, facilities, wellbore path in addition to the reasons for their occurrence); clarifying the rheology and asphaltene flow behavior in the reservoir; and finally examining the advantages and disadvantages of most widely used strategies for determining onset AP. In addition, some measured Iraqi asphaltene data are demonstrated and analyzed. This work will contribute to better knowledge of asphaltene and will serve as a reference for future studies on how to properly investigate and simulate asphaltene.

Asphaltene genesis influence on the low-sulfur residual marine fuel sedimentation stability

• Genesis and structure of asphaltenes affect the stability of residual marine fuel. • Thermodestructive asphaltenes reduce the stability of residual marine fuel rapidly. • There is a residual marine fuel stability rank (TSA) from the asphaltenes genesis. This paper describes the results of studies carried out to determine the influence of asphaltene genesis on the low-sulfur residual marine fuel sedimentation stability, based on RMG 380 commercial fuel as an example. The composition and structural features of potentially acceptable residual components of marine fuels asphaltenes (vacuum residues, asphalt, visbreaker residues, heavy pyrolysis resins) and crude oil (for comparison) asphaltenes – 9 types in total – were comprehensively characterized by FT-IR, XRD, SEM, XRF, CNH analyses. The gross formulas of the examined asphaltenes were established by determining the molecular weight and elemental composition. The dependence of asphaltene genesis influence on stability was assessed by adding them in an amount of 1 to 5 wt% into RMG 380 marine fuel base compositions of constant composition according to “total sediment aged” (TSA) index. It was determined that when the asphaltene content of the studied stock types increases above 4 %, the stability of the fuel compositions, and consequently the asphaltene solubility, in the base hydrocarbon system (based on RMG 380 as an example) decreases in the following series: Asphalt → Vacuum residue → Crude oil → Visbreaker residue → Heavy pyrolysis resin.

Effect of Temperature on Asphaltene Precipitation in Crude Oils from Xinjiang Oilfield.

During the production of crude oil, asphaltenes are prone to precipitate due to the changes of external conditions (temperature, pressure, etc.). Therefore, a series of research studies were designed to investigate the effect of temperature on asphaltene precipitation for two Xinjiang crude oils (S1, S2) so as to reveal the mechanism of asphaltene dissolution. First, the changes of asphaltene precipitation were intuitively observed by using a microscope. The results demonstrated that the asphaltene solubility increased with the increase of temperature and the dispersion rate of asphaltene particles increased with the decrease of particle size. Second, the variation of asphaltene precipitation with temperature was quantified by a gravimetric method. The results suggested that the different asphaltenes showed different sensitivity to temperature within the temperature range 25–120 °C. Third, a hypothesis was proposed to explain these results and proved that the asphaltene aggregate structure was an important factor for asphaltene stability. The crystallite parameters of asphaltenes were obtained by X-ray diffraction (XRD) to describe the structural characteristics. The results revealed that the layer distance between aromatic sheets (dm) of asphaltenes derived from S1 oil and S2 oil were 0.378 and 0.408 nm, respectively, which implied that the asphaltene aggregates derived from S2 oil were looser than those of S1 oil. Therefore, high temperature could facilitate the penetration of resins into asphaltene aggregates and ultimately improve the dispersion of asphaltenes. Finally, molecular dynamics (MD) simulation was used to verify the conclusions. Based on the molecular dynamics method, asphaltene aggregate models were developed. The compactness and internal energy of each model were calculated. The results showed that the asphaltene dispersion capability was proportional to the porosity and internal energy.

Application of the UNIFAC Model for the Low-Sulfur Residue Marine Fuel Asphaltenes Solubility Calculation

Since 2020, 0.5% limits on the sulfur content of marine fuels have been in effect worldwide. One way to achieve this value is to mix the residual sulfur and distillate low sulfur components. The main problem with this method is the possibility of sedimentation instability of the compounded residual marine fuel due to sedimentation of asphaltenes. In this paper, the application of the UNIFAC group solution model for calculating the solubility of asphaltenes in hydrocarbons is considered. This model makes it possible to represent organic compounds as a set of functional groups (ACH, AC, CH2, CH3), the qualitative and quantitative composition of which determines the thermodynamic properties of the solution. According to the asphaltene composition, average molecular weight (450–2500 mol/L) and group theories of solutions, a method for predicting the sedimentation stability of compounded residual marine fuels was proposed. The effect of the heat of fusion, temperature of fusion, molecular weight, and group composition on the solubility of asphaltenes in marine fuel has been evaluated. The comparison of the model approach with the data obtained experimentally is carried out. The results obtained make it possible to predict the sedimentation stability of the fuel system depending on the structure and composition of asphaltenes.

In-situ upgrading of heavy crude oils via solvent deasphalting using of nickel oxide nanoparticles as asphaltene co-precipitants

The use of NiO nanoparticles as asphaltene co-precipitant additives is studied to improve the upgraded oil's properties and potentially reduce the solvent-to-oil ratio for the in-situ upgrading of heavy oils via solvent deasphalting. Asphaltene content, solubility profile, and C7-deasphalting laboratory experiments were carried out to evaluate the efficiency of the nanomaterial. Results showed that nickel oxide nanoparticles increased the amount of asphaltenes in the 15–18% range with respect to the case without additive at the same solvent-to crude ratio. In the presence of the NiO nanoparticles, improvements on the upgraded crude oil properties were found with an average 17.1°API gravity (16% increase) and a viscosity of ∼2370 cSt (∼16% reduction) vs. the case without additive. These results demonstrate the usefulness of using nickel oxide nanoparticles to further enhance the upgraded crude oil properties for heavy oil upgrading via solvent deasphalting. Based on elemental analysis and spectroscopic techniques (scanning transmission electron microscopy with high angle annular dark field detection, energy dispersive X-ray analysis, Mid- and Far-FT-IR, and X-ray photoelectron spectroscopy), it was found that NiO nanoparticles acted as nucleation sites (agglomerants). A carbon-containing layer from the asphaltene fraction encapsulates the nickel oxide nanoparticles. A plausible mechanism for the interaction of the nanostructured NiO with the C7-asphaltenes was proposed that involves the formation of nanosized Ni-O-carboxylate or phenolate species on the surface of the nickel oxide nanoparticles.

An Integrated Simulation Approach for Wellbore Blockage Considering Precipitation, Aggregation, and Deposition of Asphaltene Particles

Summary Asphaltene deposition triggers serious flow assurance issues and can significantly restrict the production capacity. Because of the complexity associated with asphaltene deposition that includes several mechanisms acting simultaneously, an accurate prediction of asphaltene blockage along the wellbore requires integration of asphaltene precipitation, aggregation, and deposition. In this work, an integrated simulation approach is proposed to predict the asphaltene deposition profile along the wellbore. The proposed approach is novel because it integrates various deposition patterns of particulate flow (which depends on hydrodynamics) with aggregation processes to investigate how the distribution of asphaltene particle size varies (governed by molecular dynamics) after being precipitated out of the oil phase (controlled by thermodynamics). To improve the predictability capability of simulations, a direct input from the wellbore flow simulator is used to update the velocity profile after the wellbore radius changes beyond a certain predefined threshold. The fraction of asphaltene precipitation is determined using the asphaltene solubility model and combined with aggregation models to feed into deposition calculations. Wellbore blockage was examined for two cases with and without the aggregation mechanism included. A sensitivity analysis was carried out to study parameters that affect the severity of blockage, such as range of pressure-temperature along the wellbore, flow velocity, and radial distribution of asphaltene particles. The simulation approach proposed in this paper provides an in-depth understanding of the wellbore flow assurance issues caused by asphaltene deposition and thus provides useful insights for improving the predictions of production performance.

Vanadium and nickel distributions in Pentane, In-between C5-C7 Asphaltenes, and heptane asphaltenes of heavy crude oils

After selective solvent extraction, the volatile and non-volatile vanadium and nickel distributions for two Venezuelan heavy crude oils and the NIST Standard Reference Material SRM 8505 were determined for the Entrained n-pentane (C5) maltenes, In-between C5-C7 asphaltenes, and n-heptane asphaltenes. The fractions were analyzed via the asphaltene solubility profile, size exclusion chromatography (SEC), High-Temperature Gas Chromatography coupled with Inductively Coupled Plasma Mass Spectrometry (HTGC-ICP-MS), and atmospheric pressure photoionization Fourier-transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). Results showed that petroleum elution is strongly correlated to high hydrogen deficiency and increased heteroatom levels. The solubility decreased in the following order: Entrained C5 Maltenes, In-between C5-C7 asphaltenes, and C7 asphaltenes. Qualitative HTGC-ICP-MS shows that 51V traces of the first two asphaltene fractions showed a bimodal (Venezuelan crude oil 1 and NIST SRM 8505) or a multimodal distribution (Venezuelan crude oil 2). On the other hand, the 51V signal intensities for C7 asphaltenes were the lowest among all samples studied. FT-ICR MS revealed that the chemistry of vanadyl and nickel porphyrins is multimodal in terms of DBE. N4O1V1 and N4O2V1 classes exhibited abundant homologous series with DBE values of ≤22; when sulfur was incorporated, e.g., N4O1S1V1 class, the DBE increased by 4–6 units. Ni-containing porphyrins showed two major homologous series, pointing toward a bimodal chemical nature. We hypothesized that this compositional feature could be why the bimodal and multimodal distributions of boiling points were found in the studied heavy crude oil fractions.