Asphaltene Flocculation Research Articles

Effect of asphaltene flocculation size on deposition using a modified quartz crystal microbalance in-house setup and microscopic image analysis: Model oil, inhibitory and nanoparticle solutions case studies

Asphaltene deposition phenomenon is a challenging event that may occur during the oil production process, causing difficulties such as formation damage and wettability alteration. To overcome these challenges, inhibitors and nanoparticles are commonly used as treatments. The size of asphaltene flocculation is a critical factor in the deposition process. In this study, we investigated the effect of asphaltene flocculation size on deposition using the quartz crystal microbalance (QCM) method in both model oil and inhibitory solutions containing Linear alkylbenzene (LABs), Sodium laureth sulfate (SLES), and 4-Dodecylbenzenesulfonic (DBSA), as well as solutions with nanoparticles such as TiO2 and SiO2. A novel in-house setup was designed to overcome experimental challenges and microscopic images were used as a visual approach for better interpretation of results. Our findings showed that TiO2 and SLES had the greatest performance in postponing flocculation points among nanoparticles and inhibitory solutions, respectively. We also observed that inhibitors were more effective in delaying the flocculation point as the concentration of heptane in the model oil decreased, with a weakened effect at higher heptane concentrations. Based on the interaction of forces, we obtained an average surface area of 17.5 square micrometres as the required value for aggregate deposition. Furthermore, inhibitory solutions showed a much lower growth rate and smaller aggregates compared to normal solutions.

Effect of temperature on the appearance of flocculated asphaltene in an unperturbed unstable American shale oil: Insights from a colloidal modeling

This work aimed to study the onset of flocculation of asphaltenes using optical microscopy and to evaluate the effect of temperature on the destabilization of an unstable undisturbed American shale oil. After magnetic stirring for 24 h, the flocculated asphaltene was redispersed. Increasing the temperature to 40 °C led to asphaltenes flocculating. After heating, the sample was cooled back to room temperature. We calculated the precipitate volume from microscopy data and found that after cooling the system had a larger precipitate volume than in the previously studied scenarios. When comparing the volumes of precipitates before and after cooling, it is possible to observe that the volume of smaller particles does not vary significantly in each class, but the volume of larger particles increases with cooling, indicating an irreversible phenomenon. Statistical analysis of the optical microscopy results allowed a detailed analysis of the phenomenon. To study the colloidal effect, a theoretical analysis was performed based on Hamaker theory and De Gennes scaling theory, presenting compatible results when the parameters of the repulsive term were adjusted. When the parameters of both the attractive term and the repulsive term of the model were kept constant, greater stability was verified with the increase of temperature. Conversely, it was observed that the reduction of the parameter related to the length of the alkyl chains can explain the experimental macroscopic behavior of the shale oil here studied and also some different behaviors reported in the literature, i. e., increasing of flocculated volume with increasing temperature. This size reduction of the length of the alkyl chains can be attributed to a desolvation effect. Hence, the appropriate parameterization of the model showed great potential to mimic the behavior of increasing and also decreasing stability with the increase of temperature. The sets of parameters were related to reaction-limited aggregation (RLA) and diffusion-limited aggregation (DLA), which allowed to interconnect the discussion on experimental stability of asphaltenes, molecular simulation, and the theoretical discussion. Furthermore, the proper use of this theory seems to be a promising way to represent microscopic interactions in asphaltene systems, including previous results from the literature. This work presents (i) an experimental case that shows reversibility of asphaltene flocculation only with magnetic stirring; (ii) the effect of temperature on the stability of asphaltenes, and also (iii) brings a contribution with the volume of precipitate, making it possible to conclude on the irreversibility in the thermal cycle applied. In addition, the proper use of this modeling can predict the stability changes as a function of temperature, being a promising way to represent microscopic interactions in asphaltene systems, including previous results from the literature.

EVALUACIÓN DE UNA UNIDAD HPHT ACOPLADA CON SONDA NIR PARA DETERMINAR EL INICIO DE LA PRECIPITACIÓN DE ASFALTENOS BAJO DIFERENTES PRESIONES

Asphaltenes are characterized as the crude oil fraction with the highest molar mass and polarity, presetting mainly (poly) aromatic groups. The flocculation and deposition of asphaltenes causes large losses to the oil industry. Understanding the phase behavior of asphaltenes under conditions closer to those found in reservoirs is important. Therefore, LMCP/UFRJ started operating a high-pressure high-temperature (HPHT) unit coupled to a near-infrared spectrometer probe that can use different flocculants. This work describes the development of a procedure as well as the validation of the results obtained from this unit. Due to the complex composition of crude oil, model systems (MS) were prepared with asphaltenes extracted with n-pentane (C5I) and n-heptane (C7I). The experiments were carried out at atmospheric pressure, titrated with n-heptane, and at 100 and 300 bar titrated with propane. As expected, C7I asphaltenes were more unstable, presenting lower precipitation onset than C5I asphaltenes under ambient conditions and higher pressures. However, for both MS, the stability increased with rising pressure when using propane as a solvent. The proposed method to evaluate asphaltenes precipitation onset was effective for MS in toluene and dead crude oil, and is a promising alternative for investigation of different types of crude oil.

Prediction of Refractive Index of Petroleum Fluids by Empirical Correlations and ANN

The refractive index is an important physical property that is used to estimate the structural characteristics, thermodynamic, and transport properties of petroleum fluids, and to determine the onset of asphaltene flocculation. Unfortunately, the refractive index of opaque petroleum fluids cannot be measured unless special experimental techniques or dilution is used. For that reason, empirical correlations, and metaheuristic models were developed to predict the refractive index of petroleum fluids based on density, boiling point, and SARA fraction composition. The capability of these methods to accurately predict refractive index is discussed in this research with the aim of contrasting the empirical correlations with the artificial neural network modelling approach. Three data sets consisting of specific gravity and boiling point of 254 petroleum fractions, individual hydrocarbons, and hetero-compounds (Set 1); specific gravity and molecular weight of 136 crude oils (Set 2); and specific gravity, molecular weight, and SARA composition data of 102 crude oils (Set 3) were used to test eight empirical correlations available in the literature to predict the refractive index. Additionally, three new empirical correlations and three artificial neural network (ANN) models were developed for the three data sets using computer algebra system Maple, NLPSolve with Modified Newton Iterative Method, and Matlab. For Set 1, the most accurate refractive index prediction was achieved by the ANN model, with %AAD of 0.26% followed by the new developed correlation for Set 1 with %AAD of 0.37%. The best literature empirical correlation found for Set 1 was that of Riazi and Daubert (1987), which had %AAD of 0.40%. For Set 2, the best performers were the models of ANN, and the new developed correlation of Set 2 with %AAD of refractive index prediction was 0.21%, and 0.22%, respectively. For Set 3, the ANN model exhibited %AAD of refractive index prediction of 0.156% followed by the newly developed correlation for Set 3 with %AAD of 0.163%, while the empirical correlations of Fan et al. (2002) and Chamkalani (2012) displayed %AAD of 0.584 and 0.552%, respectively.

Effect of kerosene aromaticity as a solvent on bulk and interfacial properties of Brazilian heavy crude oil with high asphaltene content

AbstractThis study investigated the effect of solvent aromaticity on asphaltene stability and interfacial behaviour using typical diluted heavy oils, which better represent the chemical diversity of petroleum components than previous studies that used simple solvent mixtures with low asphaltene concentrations. A Brazilian crude with high viscosity and asphaltene content was diluted with two kerosenes, one containing only saturated compounds (KeS), and the other a saturates/aromatics mixture (KeSA) to maintain total aromaticity in the oil mixture upon dilution. Viscosity, asphaltene stability, interfacial tension, and elasticity of the oil mixtures were measured, and correlated with emulsion stability, regarding the differences in solvent aromaticity and aromatics/saturates ratio. The results showed that the different kerosene compositions affected bulk viscosity and asphaltene flocculation, but had a lesser effect on oil/brine interfacial tension due to the high asphaltene content in the diluted oil. The elastic modulus decreased at higher dilutions with KeS, while it remained consistent for KeSA mixtures, which supported the differences obtained in emulsion stability, at solvent concentrations within the optimal aromaticity ratio reported for simple solvent mixtures. Interfacial segregation of the aromatics in KeSA was also observed, which has not been reported in previous studies using complex solvents. These findings suggest that the trends reported with model oils, such as heptol with added asphaltenes, can also be applied to more realistic complex oil mixtures with higher asphaltene concentrations. Nevertheless, it was suggested that maintaining the aromatic content may not be enough to prevent asphaltene flocculation upon dilution, due to the concurrent increase in saturates.

The influence of vegetable additives on the flocculation of asphaltenes in oil dispersed systems

The study examines the existing asphaltene flocculation inhibitors in oil dispersed systems — oil-soluble surfactants of various nature. It is proposed to use cheap surfactants of vegetable origin as flocculation inhibitors — phosphatide concentrate and sodium sulfosuccinate. The process of flocculation of asphaltenes on model mixtures of asphaltenes of different concentrations with toluene and precipitants, as well as the influence of the proposed inhibitors on the aggregative stability of the mixtures, was studied. The flocculation starting point (onset point) of each mixture was determined by the photocolorimetric method.

Особенности состава смол тяжелых нефтей и их влияние на стабильность асфальтенов

Peculiarities of heteroatomic components content and distribution in resins have been studied by the example of heavy oils of Tatarstan and Samara region fields. Peculiarities of structural and group composition of extracted fractions from resinsare shown. Resin fractionation allowed to determine the degree of influence of the heterorganic component content on the asphaltene flocculation. Kinetic studies using UV spectroscopy showed that the maximum efficiency of inhibition of asphaltene deposition for the high-molecular-weight organo-nitrogen bases was detected, which is superior to the original petroleum resins.

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.

Asphaltene Thermodynamic Precipitation during Miscible Nitrogen Gas Injection

SummaryFor many years, miscible gas injection has been the most beneficial enhanced oil recovery method in the oil and gas industry. However, injecting a miscible gas to displace oil often causes the flocculation and deposition of asphaltenes, which subsequently leads to a number of production problems. Nitrogen gas (N2) injection has been used to enhance oil recovery in some oil fields, seeking to improve oil recovery. However, few works have implemented N2 injection and investigated its effect on asphaltene precipitation and deposition. This research investigated the N2 miscible flow mechanism in nanopores and its impact on asphaltene precipitations, which can plug pores and reduce oil recovery. First, a slimtube was used to determine the minimum miscibility pressure (MMP) of N2 to ensure that all of the experiments would be conducted at levels above the MMP. Second, filtration experiments were conducted using nanocomposite filter membranes to study asphaltene deposition on the membranes. A filtration apparatus was designed specifically and built to accommodate the filter membranes. The factors studied include N2 injection pressure, temperature, N2 mixing time, and pore size heterogeneity. Visualization tests were conducted to highlight the asphaltene precipitation process over time. Increasing the N2 injection pressure resulted in an increase in the asphaltene weight percent in all experiments. Decreasing the pore size of the filter membranes increased the asphaltene weight percent. More N2 mixing time also resulted in an increase in asphaltene weight percent, especially early in the process. Visualization tests revealed that after 1 hour, the asphaltene particles were conspicuous, and more asphaltene clusters were found in the test tubes of the oil samples from the filter with the smallest pore size. Chromatography analysis of the produced oil confirmed the reduction in the asphaltene weight percent. Microscopy and scanning electron microscopy (SEM) imaging of the filter membranes indicated significant pore plugging from the asphaltenes, especially for the smaller pore sizes. This research highlights the severity of asphaltene deposition during miscible N2 injection in nanopore structures so as to understand the main factors that may affect the success of miscible N2 injection in unconventional reservoirs.

Numerical analysis of asphaltene particles evolution and flocs morphology using DEM-CFD approach

The agglomeration and fragmentation of asphaltenes which dictate particle size distribution (PSD) play an important role in deposition behavior of asphaltene. However, the physics underlying the agglomeration/fragmentation processes is grossly missing in the available literature. In this paper, Discrete Element Method (DEM) in combination with a coalescence model is coupled with Computational Fluid Dynamics (CFD) to simulate agglomeration/fragmentation considering asphaltene particles as real/irregular objects in the absence of deposition process. The evolution of asphaltene particles, asphaltene particle size distribution (PSD), and morphology of asphaltene flocs have been examined during the simulation. Also, the effect of fluid velocity (Vf), primary particle concentration (N0), inter-particle bond strength (Fb), and energy barrier (Ub) have been investigated. During asphaltene flocculation, mean floc size increases until a steady-state condition is attained where floc size and mass fractal dimension approximately remains unchanged. The size of asphaltene flocs increases up to 40 μm and fractal dimension values change in the range of 1.45–1.75. Higher Vf leads to the steady-state condition is attained more rapidly along with smaller floc sizes and higher fractal dimensions. Increasing N0 results in faster growth of asphaltene flocs, however, the stable mean asphaltene floc size is approximately insensitive to N0. The presence of larger flocs at higher N0 eventuates the smaller fractal dimensions. As Fb increases, the frequency of small particles decreases, and PSD shifts to larger sizes. Consequently, smaller fractal dimensions are obtained. The floc growth is insensitive to Ub at initial times, whereas the steady-state condition is reached more quickly with a smaller stable floc size for higher values of Ub. The fractal dimension shows a weak dependency on the energy barrier.

The effect of shear rate on aggregation and breakage of asphaltenes flocs: Experimental study and model-based analysis

The study of the effect of shear stresses on the aggregation and breakage of asphaltene flocculation is one of the important issues that little research has been done on it. In this paper, the effect of shear rate on the behavior of asphaltene particles of samples including medium and heavy oil in the colloidal state before and after precipitation has been investigated using viscometric method. The physical and chemical properties of dispersed oil systems depend on the particles of asphaltene dispersed in the colloidal state that form complex structural units (CSUs). The size of CSU for two medium and heavy oils was estimated by the Manzhai et al. equation using viscosity data in terms of temperature (T) at different shear rates. By increasing the shear rates from 10 S−1 to 200 S−1, the CSU radius decreases from 155 to 46.1 nm and from 6.64 to 1.27 nm for Azadegan (representative of medium crude oil) and model (representative of heavy crude oil) samples, respectively. Using the generalized Pal–Rhodes equation, the viscosities of heavy oil samples containing different extracted asphaltene contents are predicted at different shear rates. The shape factor at shear rates of 10 and 300 was 6.106 and 4.356, respectively, which indicates that it is approaching the spherical state by increasing the shear rate. Finally, to calculate the effective volume fraction of asphaltene particles in the unsteady state, using the viscosity data of the toluene and crude oil solution and applying the Lobe equation, the viscosity of the background (free-asphaltene) was calculated. With the viscosity of the background and the viscosity data of heptane and crude oil, the amount of effective volume fraction of asphaltene particles was calculated by the Gillespie equation. These values are obtained for three modes: different shear rates, different volume ratios of heptane, and in the presence of two novel inhibitors of cocamide diethanolamine and dodecylbenzene sulfonic acid.

Direct Visualization of Ultrasonication Induced Asphaltenes Removal in Carbonate Rock Using Confocal Imaging

Asphaltenes deposition is a major issue in the petroleum industry as it can have a detrimental impact on hydrocarbon recovery efficiency. Therefore, it is imperative to study the fundamental mechanisms controlling the asphaltenes flocculation and deposition in reservoirs allowing us to prevent and possibly eliminate such problem. Hitherto many studies have highlighted ultrasonication as a potential remediation technique but no investigation has been able to provide direct visual evidence of the phenomena. The primary objective of this study is to visualize the deposition of asphaltenes and their subsequent removal by ultrasonication in Indiana Limestone using state of the art confocal microscopy. To do so, we performed a comprehensive series of experiments by flooding Indiana Limestone core samples with crude oil and later passing ultrasonic waves through the flooded sample. Four core samples of Indiana Limestone each displaying different permeability were used, these are referred to as A2, B2, C4, and D4. At each stage of experiment series of images were captured by confocal microscopy depicting asphaltenes deposition and it’s post-sonication distribution. The images were further segmented allowing us to compute changes in the asphaltenes content before and after sonication. The comparison of confocal scans reveals that the ultrasonic irradiation is highly efficient in removing asphaltenes from the low permeability core samples, whereas in the case of highly permeable cores, rather than preventing it promoted the asphaltenes flocculation. Surprisingly, an increase in asphaltenes content was observed after ultrasonication in high permeability core samples.

The role of direct asphaltene inhibitors on asphaltene stabilization during gas injection

There are a large number of investigations, which evaluate the impact of the liquid-based inhibitors on the asphaltene stabilization. In those studies, a specific volume of inhibitor was added to the oil sample and the asphaltene precipitation is then studied. However, this method is indirectly applicable to processes like gas injection. For that reason, in this work, the metal oxide nanoparticles (GO, TiO2, SiO2, and MgO) have been considered in the liquid-free mode as direct asphaltene inhibitors (DAIs) on asphaltene stabilization for the duration of miscible CO2 injection. The dissolution of DAIs in CO2 was investigated by measurement of cloud point pressure to evaluate the pressure/temperature conditions, need for certifying that the CO2/DAIs mixtures have the single-phase condition. Afterwards, the impact of DAI was studied on asphaltene precipitation and deposition by static and dynamic approaches. Results show that the total size of asphaltene particles which precipitated during injection of miscible CO2/DAIs mixture is significantly lower than that for immiscible pure CO2 injection. The amount of asphaltene deposition significantly decreased during injection of miscible CO2/DAIs mixtures compared to immiscible pure CO2 injection. Additionally, themetal oxide nanoparticles hinder the phase separation of asphaltenes kinetically and prevent growth. It is conducted by stabilizing the colloidal suspension of the asphaltene particles, which are in sub-micrometre size to significantly slow the asphaltene flocculation onset.

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.

Investigation of asphaltene dispersion stability in slurry-phase hydrocracking reaction

Asphaltene precipitation is known as a challenging issue to fully upgrade heavy oils. In this study, asphaltene dispersion stability and sediment formation for a slurry phase hydrocracking reaction of vacuum residue was investigated with changes of temperatures (405–435 °C), LHSV (0.20–0.45 hr-1), pressures (80–180 bar) and superficial gas velocities (0.4–2.2 cm/s) in a bench-scale continuous system. The characteristics of dispersion stability were examined with the solubility parameters at the flocculation point (UV titration), the structure of the asphaltenes (H-NMR), and sediment content in the liquid product (Hot filtration). As results, it was found that the dispersion stability of asphaltene was mainly dependent on the VR conversion. In particular, at about 50% of the VR transition, the solubility was found to be unstable and the amount of deposition increased dramatically. At the same time, microscopic observation directly confirmed asphaltene flocculation. However, when H2 partial pressure was increased, the hydrogenation reaction of asphaltene was promoted so that it could reduce sediment formation and improve both the asphaltene solubility and structure for the stable dispersion. On the other hand, increasing the superficial gas velocity did not give an effect on the asphaltene dispersion stability.

Evaluation of Jatropha gossypiifolia oil as a asphaltenes stabilizer in a petroleum sample at the laboratory level

Asphaltenes are condensed polyaromatic solids that are present in oil forming colloidal suspensions in a thermodynamic system that in some cases tends to be unstable producing flocculation and aggregation. In the oil industry, dispersant chemical compounds are used to minimize the flocculation of asphaltenes to avoid clogging problems in pipes and production equipment, which represent an important investment since they are formulated with synthetic resins and oils, in addition to expensive solvents. This research evaluates the use of Jatropha gossypifolia oil as an active stabilizing component of asphaltenes, mixed with diesel as a solvent in laboratory level tests. Five dilutions of oil in diesel (10 to 50%) were evaluated. The procedure consisted of observing the asphaltene aggregates under an optical microscope when applying n-heptane to a crude oil sample from Monagas State, Venezuela, the volume of n-heptane used being the flocculation onset. Successive volumes of each dilution were then applied until the dispersion of the aggregates was achieved, being this volume the point of dispersion. In addition, xylene was used as a standard dispersant to compare the performance of the dissolutions. The tests were performed at two temperatures of 25 and 40 ºC. A factorial statistical design was used with experimental factors dissolution and temperature and dependent variable instability index, with ANOVA analysis and Tukey HSD test with α = 0.05. With the application of the solutions, a greater dispersion of the aggregates was achieved with efficiencies greater than 94% with respect to the dispersion obtained with xylene, being the solution with 40% oil the most efficient. The statistical results showed that stability is dependent on the solution used and independent of the test temperature with a 95% confidence level.

ORGANIC DEPOSITION IN PETROLEUM STORAGE TANKS AT REFINERIES DUE TO BLENDING OPERATIONS

Petroleum blending is viewed as a critical optimization strategy adopted by several operations of petroleum production in the refineries around the world. A persistent problem called crude oil incompatibility occurs when the mixture of different oils lead to the formation of solid phases due to the precipitation of asphaltenes. The present work investigates the relationship between the occurrence of sludge in petroleum storage tanks and petroleum blending operations. Hildebrand solubility parameters of the oils were determined, revealing that one of the samples of petroleum analyzed is at the threshold of the asphaltene flocculation parameter, with an average of 16.1 Mpa1/2. Thus, it implies that blending operations with dissimilar petroleum feedstocks must be well planned, since they can initiate the precipitation of the asphaltenes and, consequently, the formation of sludge that accumulate and deposit as sediments inside petroleum storage tanks.

Mechanistic study to investigate the effects of different gas injection scenarios on the rate of asphaltene deposition: An experimental approach

Asphaltene deposition during enhanced oil recovery (EOR) processes is one of the most problematic challenges in the petroleum industry, potentially resulting in flow blockage. Our understanding of the deposition mechanism with emphasis on the rate of the asphaltene deposition is still in its infancy and must be developed through a range of experiments and modelling studies. This study aims to investigate the rate of asphaltene deposition through a visual study under different gas injection scenarios. To visualise the asphaltene deposition, a high-pressure setup was designed and constructed, which enables us to record high-quality images of the deposition process over time. Present research compares the effects of nitrogen (N2), carbon dioxide (CO2) and methane (CH4) on the rate of asphaltene deposition at different pressures. The experimental results in the absence of gas injection revealed that the rate of asphaltene deposition increases at higher pressures. The results showed that the rate of asphaltene deposition in the case of CO2 injection is 1.2 times faster than CH4 injection at 100 bar pressure. However, N2 injection has less effect on the deposition rate. Finally, it has been concluded that the injection of CO2 leads to more asphaltene deposition in comparison with CH4 and N2. Moreover, the experimental results confirmed that gas injection affects the mechanism of asphaltene flocculation and leads to the formation of bigger flocculated asphaltene particles. The findings of this study can help for a better understanding of the mechanism of the asphaltene deposition during different gas-EOR processes.

Regular solution model to predict the asphaltenes flocculation and sediments formation during hydrocracking of heavy oil

Experiments of hydrocracking of heavy crude oil were carried out in a 1.8 L batch reactor with a mineral dispersed catalyst. Sediments content was analyzed at different reaction times (2–5 h) and temperatures (360–400 °C). A regular solution model and a kinetic model were applied to predict the flocculation of asphaltenes to form sediments. It was observed that as the temperature increases the solubility parameter of the SARA fractions decreased. Enhanced sediments formation was found when the saturates/asphaltenes ratio increased indicating that the insolubility of asphaltenes in the crude oil depends on saturates fraction. The calculated values obtained with the thermodynamic-kinetic model showed good accuracy with respect to experimental data, particularly at high conversion, which is the most important issue in commercial hydrocracking units.

CO2-induced asphaltene deposition and wettability alteration on a pore interior surface

CO2 enhanced oil recovery has a great potential to improve the rate of oil production and store carbon dioxide emission. However, CO2 injection can destabilize the asphaltene-oil colloidal system and thus favor severe asphaltene particle deposition in porous reservoir formation. These block reservoir pores and change pore wetting condition, finally damage the porous reservoir formation and significantly reduce oil production. A good understanding on CO2-induced asphaltene deposition at a pore scale is of significance for CO2-EOR processes. Few studies have directly investigated the asphaltene deposition behavior and asphaltene-induced pore wetting alteration on a pore interior surface in a confined pore. In this study, we directly measured the CO2-induced asphaltene deposition behavior on the interior surface of a single pore under high pressure and temperature. The particle size and particle size distribution of CO2-induced asphaltene deposition on pore interior surfaces were directly measured and analyzed, by considering the influences of aging time and temperature. The results indicate that long aging period and elevated temperature could favor CO2-induced asphaltene flocculation and deposition on pore interior surfaces. Finally, the pore-scale wetting alteration caused by asphaltene deposition was quantified by direct pore contact angle measurements.