Influence Of Asphaltenes Research Articles

Effect of asphaltenes on thermally- and shear-driven regimes of wax deposition

Waxes and asphaltenes co-exist in crude oils, yet few studies consider the effects of one component on another. The influence of asphaltenes on wax deposition and its properties is studied using a bespoke cold rotating finger which allows measurements to be made in both static and dynamic (sheared) conditions. For static deposition, adding asphaltenes reduces the rate at which the wax deposit is formed, as well as the overall thickness of the deposit. This change is attributed to changes in the fluid properties, with asphaltenes lowering the wax appearance temperature, meaning a greater degree of subcooling is needed to achieve the same amount of precipitated wax. For dynamic measurements, both the rate of deposition and deposit thickness are unaffected by asphaltenes, demonstrating that hydrodynamics strongly govern the behavior. However, the average molecular weight and the wax content of the deposit increases significantly with asphaltenes present. With the deposit thickness being similar with and without asphaltenes, it suggests that the yield strengths of the two deposits are also similar, since thickness in the hydrodynamic regime is affected by the fluid shear stress. The changes in composition and content of the wax deposit will increase yield strength, yet this is balanced by a reduced wax gel yield strength in the presence of asphaltenes. These two factors effectively cancel one another to result in the same deposit thickness when sheared. The study provides new insights into the mechanisms by which asphaltenes modify wax deposition and deposit properties.

The influence of asphaltene and resin on the stability of crude oil emulsion and its demulsification mechanism

Currently, the effects of natural emulsifiers such as resin and asphaltene in crude oil on the stabilities of the emulsions as well as the demulsification mechanism of oil–water separation are still not well understood. In this study, the changes in oil–water wetting angle and interfacial tension (IFT) of crude oil emulsions were compared by extracting resin and asphaltene from crude oil to expound the effects of resin and asphaltene on the stabilities of crude oil emulsions. Meanwhile, the mechanism of demulsifier was discussed based on the competitive adsorption test of demulsifier and asphaltene. It was found that asphaltene was the main emulsifier in the process of oil–water emulsification. With the increase of asphaltene contents, the oil–water wetting angle decreased from 72.9° to 37°, the IFT decreased from 27.13 mN/m to 11.23 mN/m, and the emulsion droplet decreased from 10.3 mm to 1 mm. Demulsifier mainly reduced the stability of crude oil emulsion and realized oil–water separation by the replacement of the interface film-forming substances, the reduction of the oil–water interface tension, and the neutralization of interface charges. The results provide useful information for the demulsification and oil removal of oil-bearing wastewater emulsion.

Different effects of resins and asphaltenes concentration of crude oil on sandstone wettability

The influence of asphaltenes in crude oil on sandstone wettability is widely acknowledged. Although asphaltenes are recognized for their stronger polarity compared to resins, resins also contain the similar acidic and nitrogen-containing compounds to those found in asphaltenes. Nevertheless, the impact of resin adsorption on altering sandstone wettability, the different effects of vary concentrations of resins and asphaltenes, and their microscopic mechanisms influencing sandstone surfaces remain ambiguous. Thus, in this study, resins and asphaltenes were isolated from crude oil individually to investigate the different effects of their concentrations on sandstone wettability and the specific reasons. The contact angle measurements, atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and Cryo-environmental scanning electron microscopy (ESEM) were used to examine and explain the wettability changes of Berea sandstone slices before and after exposure to varying concentrations kerosene solutions of resins and asphaltenes. The results reveal that sandstone wettability could not be changed from strongly water-wet to oil-wet, even at resin concentrations as high as 50.0 mg/mL kerosene. In contrast, lower concentrations of asphaltenes, equivalent to a 5.0 mg/mL kerosene threshold, can facilitate the wettability transition process. After the adsorption of resins and asphaltenes, the roughness of the clay surface changes much more significantly than that of the quartz surface. Combined with the observation of ESEM and the results of EDS, it is believed that the resins and asphaltenes preferentially adsorb to clay surfaces, especially chlorite, rather than quartz surfaces. Clay could provide favorable sites for the accumulation of oxygen-containing compounds, leading to enduring clay-organic complexes that serve as anchor molecules for the adsorption of other compounds, ultimately causing the sandstone surface to an oil-wet state. These results may provide theoretical support for better core aging process in the laboratory, surfactant development and enhanced oil recovery procedure optimization in the oilfield.

Probing the nucleation and growth mechanism of hydrates in emulsion system under the influence of asphaltenes: A molecular dynamics simulation study

Asphaltenes are important components in crude oil, and hydrates are key elements impairing deep-sea flow assurance. So far, the study on the interaction mechanism between the two in water-in-oil emulsion systems is still limited. In this article, the effects of the molecule number of asphaltenes on the nucleation and growth of hydrates was investigated through 2500 ns molecular dynamics simulation. Moreover, hydrate growth experiments were conducted synchronously to verify the relationship between the effect of an increase in asphaltene concentration on hydrate growth at the macro level and the effect of an increase in asphaltene molecule number on hydrate growth at the micro level. The simulation results indicate that the addition of 5 and 10 asphaltene molecules can inhibit the nucleation of hydrates while 15 asphaltene molecules will shorten the induction period. Besides, hydrate growth is promoted in the presence of 5 asphaltene molecules but inhibited with further increase of asphaltene molecules. Experimentally, all concentrations of asphaltenes show inhibitory effects on the growth of hydrates. Based on the comprehensive analysis of structural parameters, potential energy and molecular transport properties, and by combining the measurement results of dynamic interfacial tension and interfacial dilational modulus, it is concluded that affecting the mass transfer process is the major way of asphaltenes affecting the growth of hydrates.

Influence of two asphaltenes on the formation and development of mesophase in fluid catalytic cracking (FCC) slurry oil

Asphaltene constitutes the heaviest component in fluid catalytic cracking (FCC) slurry oil. Mesophase pitch are prepared from FCC slurry oil by adding two asphaltenes (CL-As/JB-As) with distinct structure, and the influence of asphaltenes on the formation of mesophase is investigated. The findings suggest that an addition of CL-As within the range of 0–20 wt% is advantageous for the development and formation of mesophase. The addition of JB-As less than 1 wt% facilitates the formation and development of mesophase, while the opposite is observed with JB-As greater than 1 wt%. This is due to the light fraction of JB-As (JB-As-L), which is similar to CL-As and possesses appropriate concentrations of reactive sites that promote the formation of mesophase. However, the prevalence of alkane-branched chains is most densely concentrated in the heavy fraction of JB-As (JB-As-H), which leads to an excessive concentration of reactive sites. The predominance of JB-As-H causes an increase of the system's viscosity in the early stage so that the collision of polycyclic aromatic hydrocarbon macromolecules is reduced and the formation of the mesophase is postponed eventually. This provides a profound understanding of the preparation of high-quality mesophase pitch by regulating the properties of raw materials.

Experimental study on the influence of asphaltenes with small dosage on the rheological and gelation behavior of waxy mixtures

Asphaltene, the heaviest and most polar non-hydrocarbon component in crude oil, may interact with waxes and affect the flow and gelation behavior of waxy oils. To further study the effect of asphaltene on the flow and gelation behavior of waxy oils, five wax-containing simulated oils with small dosage asphaltene content were prepared. Through pour point and rheometer test, it is found that asphaltenes can improve the low-temperature rheology of waxy oil. There is no critical turning point above which the low-temperature flowability improved. With an increase in asphaltene content from 0 wt% to 0.1 wt%, notable changes were observed in the properties of the waxy oil. The pour point, which measures the temperature at which the oil becomes too viscous to flow freely, exhibited a decrease from 25 ℃ to 13 ℃. Similarly, the gelation temperature, indicating the temperature at which the oil starts forming a gel-like consistency, also decreased from 29.0 ℃ to 27.1 ℃. These modifications can be attributed to the presence of asphaltene in the oil sample. This outcome can be attributed to the interference caused by the presence of asphaltenes, which disrupts the gel network structure of the waxy oil and consequently hinders its gelation process. Simultaneously, within the low asphaltene content range, an increase in asphaltene content resulted in a considerable decrease in the viscosity of the waxy oil at 10 °C, reducing it from 531.5 mPa s to 14 mPa s.

A molecular dynamics approach to revealing effect mechanism of asphaltene on wax deposition behavior

The complex structure of asphaltene itself leads to obvious precipitation and aggregation characteristics, and it interacts with wax molecules, thereby affecting the wax precipitation characteristics of waxy crude oil. To clarify the effect of asphaltene on wax deposition behavior, molecular dynamics simulations were conducted to analyze the aggregation behavior of wax molecules in waxy crude oil systems and the effect of asphaltene on wax deposition. Subsequently, dynamic wax deposition experiments were used to validate the simulation results, and the influence of asphaltene on wax deposition behavior was further discussed in conjunction with the simulation results. The results show that the lower the temperature of the crude oil system, the lower the cooling rate, and the higher the aggregation degree of wax molecules; As the concentration of asphaltene increases, the existence state of asphaltene will undergo a transition, with a concentration of 0.2 wt% asphaltene as the transition boundary. The aggregation of asphaltene molecules is mainly in the form of F-type stacking, and the presence of asphaltene weakens the structural strength of the wax deposition layer. On the other hand, the aggregated asphaltene hinders the growth of wax crystal clusters due to spatial hindrance; Increase the concentration of asphaltene in the model oil, when the asphaltene concentration is 0.2 wt%, the wax deposition rate reaches its maximum, which means that the asphaltene concentration will affect its existence state in the waxy crude oil system, thereby affecting the wax deposition behavior. And analyzed the effects of temperature and moisture content on wax deposition.

Rheological properties of asphaltene-modified asphalt binder and mastic

Asphaltene is one of the component of asphalt binder. Asphaltene certainly contributes to the elasticity and stiffness of a binder's traditional viscoelastic behaviour. Introducing asphaltene as a separate modifier may improve the qualities of asphalt mastic. The influence of asphaltene on the rheological properties of asphalt binder and mastic is discussed in this paper. Asphalt binder grade 60/70 PEN was modified by adding with 1% asphaltene content. Asphalt mastic was then prepared using asphaltene-modified asphalt binder and aggregates passing 75 μm. A viscosity and a dynamic shear rheometer (DSR) test were performed to evaluate the rheological properties indexes such as rutting factor (G*/sin δ), phase angle δ, complex modulus G* and elasticity modulus of asphaltene-modified asphalt binder and mastic. It is anticipated that adding 1% asphaltene would enhance viscosity, stiffness, and rutting resistance. Based on the data analysis, modified mastic viscosity and stiffness reduced. Increased asphaltene did not improve mastic to be more rut-resistance. Among the three types of asphalt binder, PG76 binder has the best rut-resistance performance, modified asphalt binder takes the second place, and 60/70 PEN has the worst rut-resistance performance. While for the mastics, PG76 mastics have the best rut resistance performance, 60/70 PEN mastics take the second place, and modified mastics have the worst rut-resistance performance. Overall, PG76 mastic had the highest complex shear modulus value (G*), rutting parameter (G*/sin), and phase angle (δ), indicating that it had the best viscosity properties, stiffness, and resistance to rutting. Therefore, it is advised to increase the asphaltene content in order to support future research.

Molecular dynamics simulation of bubble nucleation and growth during CO2 Huff-n-Puff process in a CO2-heavy oil system

Foamy oil is the main production mechanism in the CO2 Huff-n-Puff process in heavy oil reservoir. However, the micro-formation mechanism of foamy oil in heavy oil recovery is not yet clarified. It is crucial to gain in-depth knowledge about the evolution process of bubbles and its influencing factors to improve the stability of foamy oil. In this work, molecular dynamics simulation (MD) was used to study the microscopic mechanisms of bubble nucleation and growth, and the effect of the depressurization rate on gas evolution in the CO2-heavy oil system. The microscopic process of bubble evolution during depressurization is as follows: CO2 molecules assemble inside the cavities formed in the oil phase and develop into bubbles, then the bubbles further grow, merge, or disappear. The bubbles evolution is influenced by the binding degree of the surrounding asphaltenes. The macromolecular asphaltene structure contributes to the emergence of cavities in the oil phase for CO2 aggregation. The transfer rate of dissolved gas to gas phase increases with time before forming a continuous phase. The potential energy barrier of bubbles is further analyzed to illuminate the morphological mechanism of bubbles in the oil phase. In addition, the bulk phase properties indicate that higher depressurization rates increase the effective pressure range for bubble oil performance. This work reveals the bubble evolution process and the influence of asphaltene, providing molecular-level insights into gas transport and foamy oil stability.

Insights into the relation of crude oil components and surfactants to the stability of oily wastewater emulsions: Influence of asphaltenes, colloids, and nonionic surfactants

Large amounts of asphaltenes, colloids, and surfactants in the oily wastewater emulsions produced during the resource utilization of oily sludge make the treatment of oily wastewater emulsions difficult. In this study, the crude oil components were separated by solvent separation method, characterized by SEM, XRD, FT-IR, and EDS for crude oil components, suspended solids, and “oil-particulate aggregates”, and compared the emulsification performance of each crude oil component according to the oil–water wetting angle. In addition, the static stability and coalescence stability of different surfactant emulsions were determined, and the kinetic parameters of emulsion decomposition and oil–water interfacial film strength parameters were calculated based on the stability model of emulsion two-phase separation. The mechanisms of active components such as asphaltenes and colloids in crude oil and surfactants on the emulsion stability of oily wastewater were analyzed. It was found that the polar components in crude oil consisted of asphaltenes and colloids, and with the increase of asphaltenes and colloids, the oil–water wetting angle decreased significantly and the emulsion stability increased, and the emulsion stability of nonionic surfactants was better than that of cationic and anionic surfactants, among which octylphenol polyoxyethylene ether (10) (OP-10) had the best emulsion stability. The results of the study provide a theoretical basis for the demulsification and oil removal of oily wastewater emulsions.

Influence of Asphaltenes on Hydrate Formation and Decomposition in Water-in-Waxy Oil Emulsions

Influence of Asphaltenes on Hydrate Formation and Decomposition in Water-in-Waxy Oil Emulsions

Effect of existence state of asphaltenes on microstructure of wax crystals: Fractal dimension and unit cell structure

The influence of asphaltenes on the wax crystallization has long been studied, yet the quantitative analysis of microstructure of wax crystals are rarely involved. In this research work, paraffin (C20∼C40) and n-heptane asphaltenes were used to prepare model oils containing varying amounts of asphaltenes. By means of the Fourier transform infrared spectroscopy (FTIR), microscopy and X-ray diffraction (XRD), the influence of asphaltenes on the microstructure of wax crystals was systematically analyzed focusing on the fractal dimension (area box dimension, perimeter box dimension and average size) and unit cell. Four main findings were made: (1) The influence of asphaltenes on microstructure of wax crystals mainly depends on its existence state, that is, the dispersed asphaltenes and aggregated asphaltenes. (2) As the asphaltene concentration increases, asphaltenes gradually transform from dispersed to aggregated state, and the area box dimension of waxy crystals increases firstly and then decreases, and the maximum occurs at the transition of asphaltenes state, while asphaltenes have no significant effect on the perimeter box dimension of wax crystals. (3) At lower temperatures, the average size of wax crystals without asphaltenes is significantly larger than that cases with asphaltenes, but it can be ignored as the temperatures increase. (4) Existence state of asphaltenes can affect the structural integrity of wax crystals. When the asphaltenes are well dispersed, XRD shows that the structure of wax crystals is relatively intact, but when the asphaltenes are aggregated state, wax crystals show more defects. This study is expected to provide guidance for the control of flow assurance in the coexistence of wax and asphaltenes from the mechanism level.

Influence of asphaltenes and resins on water/model oil interfacial tension and emulsion behavior: Comparison of extracted fractions from crude oils with different asphaltene stability

Asphaltenes and resins make a major contribution for the formation of stable water-in-oil emulsions during crude production, which could affect process operations and increase costs. The purpose of this investigation is to study the influence of these molecular substances from two different crude oil samples (regarding asphaltene stability) on the water-model oil interfacial tension, along with their effect on the emulsion stability. Asphaltene stability of these crude oils presented a marked difference when studied in our past work, with asphaltene precipitation onset that vary from 56 to 75 n- heptane wt %, despite their similar SARA composition. This difference on asphaltene stability was contrasted in this work with the chemical characterization, interfacial activity, and emulsion behavior of crude oil asphaltenes, resins, and their mixtures using toluene solutions. For each crude oil, resins and asphaltenes were extracted and characterized by XRD, SEM/EDS, FTIR, and elemental analysis, to better understand their molecular structure and surface-active species content. Then, it was prepared different model oil solutions in toluene, varying the content of asphaltenes and resins (500, 1,000, and 2000 mg/L). Additionally, it was prepared 2000 mg/L asphaltene/resin mixtures with different ratios (75:25 wt%, 50:50 wt%, and 25:75 wt%). Dynamic interfacial tension between the model oil and water was measured by intermediate of a Du Noüy ring method. Afterward, each model system was emulsified by adding water (at the same volumetric ratio) in a bottle test and stability was analyzed. For the sample with lower stable asphaltenes, a rapid stabilization of the dynamic interfacial tension (IFT) was observed, together with a decrease of IFT from 26.8 to 24.2 mN/m at the limit of asphaltene content studied. On the contrary, for the high stable asphaltenes sample, a transient dynamic IFT behavior was observed, until reach 12.0 mN/m (the lower operational equipment limit). Similar results were obtained for resins model solutions for both crude oils tested. For asphaltene obtained from the sample with lower asphaltene stability, the emulsions presented high stability (for a 24 h test). Besides for the high asphaltene stability sample and resins model oils, all emulsions prepared were unstable. Useful insights are given by the oil fractions chemical characterization, suggesting that smaller sized molecules from high stable crude oils have a predominant effect on IFT reduction, while larger molecules from less stable oils are responsible for the emulsion stability. • Interfacial activity of asphaltenes or resins extracted from crude oils with different stability was compared in model-oil/water systems. • Asphaltenes from lower stable crude oil present a faster stabilization of the dynamic interfacial tension (IFT). • Contrary, asphaltenes from high stable crude oil presented a wider transient dynamic IFT behavior with maximum decrease of IFT. • Resins presented longer stabilization times and lower IFT values. • Results suggest that smaller sized molecules have a predominant effect on IFT, while larger molecules are responsible for the emulsion stability.

Insights into the Relation of Crude Oil Components and Surfactants to the Stability of Oily Wastewater Emulsions: Influence of Asphaltenes, Colloids, and Nonionic Surfactants

Insights into the Relation of Crude Oil Components and Surfactants to the Stability of Oily Wastewater Emulsions: Influence of Asphaltenes, Colloids, and Nonionic Surfactants

Pressure-sensitive characteristics of high-pour-point live oil and quantitative analysis of composition change

Previous studies on high-pour-point (PPT) oil have focused on the effects of temperature. There has been no systematic investigation of the pressure-sensitivity of crude oil, the deposition composition change of solid phases, and the effects of asphaltene deposition on wax precipitation. In the development of a high-PPT oil field, experiments using dead oil instead of live oil will exaggerate the effect of wax precipitation. In this paper, the wax appearance temperature (WAT), PPT, and asphaltene deposition pressure were obtained by the laser transmittance method. Subsequently, a new set of experimental devices and methods were developed to analyze the solid-phase components in live oil under various conditions. Finally, the viscosity of crude oil at various shear rates was measured with a capillary viscometer, and the wax network structure was evaluated. The experimental results showed that the WAT and PPT decrease with decreased pressure, and their fast decreasing ranges were 12–18 MPa and 15–18 MPa, respectively. The oil pressure-sensitivity not only includes the influence of wax; the appearance of the platform stage and trough pattern phenomenon proves that there is also the influence of asphaltenes. The main component of the deposition is C27+, and the amount of wax precipitated can reach 2.72%. For crude oil with a pressure lower than 15.83 MPa, the amount of asphaltene deposition reaches 0.04% at temperatures above WAT. Asphaltene can inhibit the aggregation and growth of wax crystal molecules, leading to a decrease in WAT and an increase in the viscosity at temperatures above WAT; however, the inhibition may be advanced or delayed with decreased pressure. Asphaltene also enhanced the strength of the wax crystal network structure, leading to an increase in the viscosity of crude oil at the critical shear stress under low pressure. When wax precipitation is dominant, there is a positive correlation between asphaltene deposition and wax, and the growth rate of wax is higher than that of nucleation in the early stage. This study improves the understanding of the effect of pressure on the physical properties of high-PTT live oil, provides reliable parameters for numerical simulations and the adjustment of the injection scheme, and lays the foundation for future evaluation experiments on wax removal chemicals.

Influence of Asphaltenes on Gelation of Tetrameric Acid with Calcium Ion at the Oil/Water Interface under Flow-Model Condition

The first step in calcium naphthenate deposition is supposed to be the formation of an interfacial gel by crosslinking between ARN tetrameric acid and Ca2+. Several aspects of the inhibition of the...

Influence of asphaltene on wax deposition: Deposition inhibition and sloughing

Asphaltenes are the heaviest and most polar constituents of crude oils. The influences of asphaltene on wax deposition were investigated with model oils utilizing a Taylor-Couette device. The composition and rheological properties of the deposits and the chemical properties of the asphaltenes entrained in the deposits were analyzed. Three main observations were obtained: (a) Wax deposition rate decreases in the presence of asphaltenes while the wax content of the deposit increases. The carbon number distribution of the deposit and the critical carbon number of the deposition process were also observed to vary due to the presence of asphaltenes. (b) The asphaltene content of the deposit constantly increases as time elapses and eventually reaches several times higher than that of the original oil. The asphaltenes entrained in the deposits are of higher polarity and molecular weight than the asphaltenes originally present in the oil. (c) When the asphaltene content of the oil is above 0.2 wt%, deposits slough off frequently as asphaltenes alter the microstructure of the deposit and lower its yield strength.

Effect of Asphaltene Polarity on Wax Precipitation and Deposition Characteristics of Waxy Oils

Asphaltenes are natural pour point depressants, and the effect of asphaltene polarity on the low-temperature rheology of waxy oils has been well studied. In this paper, the influence of asphaltene ...

Influence of asphaltenes on the performance of electrical treatment of waxy oils

Electrical treatment is emerging as an efficient approach to improve the cold flowability of crude oils. In this work, waxy model oils under static state were electrically treated by an in-house apparatus. The influence of asphaltenes, the most aromatic of the heaviest components of crude oil, on the performance of electrical treatment was systematically examined for the first time. The presence of asphaltenes was found to significantly undermine the effectiveness of electrical treatment on waxy oils, and this negative influence became more pronounced at higher asphaltene contents. The effect of asphaltenes was largely independent on their aggregation state. Interestingly, although asphaltenes generally have a negative effect on electrical treatment of waxy oils, increasing polarity of asphaltenes alleviates this unfavorable effect. The results from microscopic analysis suggest that the less pronounced change in the size distribution of wax crystals might be one of the reasons for the unfavorable effects of asphaltenes on electrical treatment of waxy oils.

Influence of asphaltenes on wettability of gas and oil saturated reservoir rock

The wettability of terrigenous and carbonate rock cores of oil and gas condensate fields extracted with n-hexane and chloroform by asphaltenes was studied. The obtained values of core wettability with asphaltenes show their contribution to the change of wettability of different rocks.