Effect Of Asphaltenes Research Articles

Effect of Asphaltenes and Asphaltene Dispersants on Wax Precipitation and Treatment

A detailed understanding of the interactions between wax and asphaltenes with other components of crude oils and the effect of treatments with paraffin inhibitors (PIs) and asphaltene dispersants (ADs), with a focus on identifying specific structure-activity relationships, is necessary to develop effective flow assurance strategies. The morphological and rheological consequences of treating wax and asphaltenes in oils of differing composition with a series of ADs having structural features in common with an alpha olefin-maleic anhydride (AO-MA) comb-like copolymer PI were assessed alone and in combination with said PI. Of the four ADs studied, two were identified as being effective dispersants of asphaltenes in heptane-induced instability tests and in a West Texas (WT) crude. The degree to which a low concentration of asphaltenes stabilizes wax in the absence of treatment additives is lessened in oils having greater aromatic fractions. This is because these stabilizing interactions are replaced by more energetically favorable aromatic–asphaltene interactions, increasing oil viscosity. Treatment with AD alone also reduces the extent of wax–asphaltene interactions, increasing oil viscosity. In concert with the PI, treatment with the AD having greater structural similarity with the PI appears to improve wax solubility in both the presence and absence of asphaltenes. However, the viscosity of the treated oils is greater than that of the oil treated with PI alone, while treatment with AD having lesser structural similarity with the PI does not adversely affect oil viscosity. These data suggest that rather than treating both wax and asphaltenes, AD may poison the function of the PI. These data illuminate the pitfalls of designing flow assurance additives to interact with both wax and asphaltenes and developing treatment plans.

Study on the influence mechanism of asphaltenes on the gelation and flow behavior of wax-containing simulated oils

The precipitation of wax crystals will lead to the formation of gelation structures in waxy crude oils, and the presence of asphaltenes will affect the gelation and flow process of waxy crude oils. In this work, five waxy oils with different asphaltene contents were formulated, and the effect of asphaltene on the gelation and flow behavior of wax-containing simulated oils was investigated. The results show that asphaltenes can improve the low-temperature rheology of wax-containing simulated oils to a certain extent. When the asphaltene contents in wax-containing simulated oils increased from 0 wt% to 0.5 wt%, the pour points decreased from 25 °C to below 0 °C, while the gelation temperatures and storage modulus were also decreased from the initial 29.01 °C to 25.64 °C and 33262 Pa to 5.9 Pa, respectively. The results were due to the fact that the increase of asphaltene contents weakened the gelation network structure strength of wax-containing simulated oils and inhibited gelation process. Meanwhile, in the range of low asphaltene contents, the apparent viscosity of wax-containing simulated oils at 10 °C decreased from 531.5 mPa·s to 7.6 mPa·s with the increase of asphaltene contents.

Experimental study on the rheological characteristics and viscosity-enhanced factors of super-viscous heavy oil

To reveal the viscosity-enhanced mechanism of super-viscous heavy oil and improve the recovery rate of super-viscous heavy oil, the four components, elemental composition, rheological properties, and effects of asphaltenes and resin on the viscosity of super-viscous heavy oil from well TH12434 in Tahe Oilfield, China have been analyzed from macro and microscopic perspectives by Anton Paar rotational rheometer, gas chromatography-mass spectrometry and scanning cryo-EM to solve the problems of poor fluidity and high asphaltene content. The experimental results showed that in the temperature range of T= 40-100°C, the viscosity of super-viscous heavy oil decreases sharply from 352000 mPa∙s to 1620 mPa∙s, and the super-viscous heavy oil exhibits clear thermo-sensitivity. With T= 100°C and shear rate ranging from γ= 0-800 s-1, the viscosity of super-viscous heavy oil decreases sharply from 45000 mPa∙s to 956 mPa∙s, and the oil sample shows typical pseudoplasticity. The baseline of super-viscous heavy oil analysis by gas chromatography shows too high, and more than 80 % of super-viscous heavy oil compounds have a matching degree of less than 70 % with standard compounds, indicating that the super-viscous heavy oil had poor heterogeneity and many impurities. It is observed by scanning cryo-EM that the micromorphology of super-viscous heavy oil is large granular, strong continuity, asphaltene micromorphology presents an obvious layered structure, the layer spacing is 637.7 nm, and its asphaltene molecules form an order-like or crystal-like association structure through several unit sheet layers, resulting in high viscosity of super-viscous heavy oil. Based on the analysis results of the influencing factors of the viscosity of super-viscous heavy oil, a theoretical basis for the selection of viscosity reduction technology for super-viscous heavy oil the efficient exploitation in Tahe Oilfield, China could be provided.

Novel insights into the effects of asphaltenes on oil phase properties: Crude oil, oil-water interface, and graphene oxide synergistic demulsification

In this work, quantum chemical calculations and molecular dynamics simulations were employed to investigate the aggregation structure of asphaltene (a key component in heavy oil) and the influence of its molecular structure and content on the viscosity of heavy oil. Research suggests that the C5Pe molecules have a strong potential to bind together through π-π interactions (face-to-face). The angle between the two plane normal vectors was 1.4°. The mechanism of asphaltene-oil phase assembly can be succinctly summarized as the “rebar-cement” mode of action. The viscosity of heavy oil increases with the increase of asphaltenes, which can be attributed to the more complete construction of the three-dimensional network structure of asphaltene with the increase of asphaltene mass fraction (especially exceeding 35 wt%). The steered molecular dynamics simulation confirmed that reducing the concentration of asphaltenes in emulsified heavy oil droplets leads to increased susceptibility to mechanical destruction. This observation implies that asphaltenes negatively impact the demulsification and viscosity reduction of crude oil. The findings in this work can contribute to the development of efficient strategies for viscosity control and enhanced production of heavy oil resources.

Adsorption Behaviors of Different Components of Shale Oil in Quartz Slits Studied by Molecular Simulation.

Understanding the adsorption state and molecular behavior of the diverse components of shale oil in shale slits is of critical importance for exploring novel enhanced shale oil recovery techniques, but it is hard to be achieved by experimental measurements. In this paper, molecular dynamics (MD) simulations are performed to quantitatively describe the microbehavior of shale oil mixtures containing different kinds of hydrocarbon components, including asphaltene, in quartz slits. The spatial distributions of all the presenting components are given, the interaction energy between the components and quartz is analyzed, and the diffusion coefficients of all the components are calculated. It was found that asphaltene molecules play a vitally important role in restricting the detachment and diffusion movement of all hydrocarbon components, which is actually a key problem limiting the recovery efficiency of shale oil. The effects of temperature, slit aperture, and the appearance of CO2 on the adsorption behavior of the different shale oil components are examined; the results suggest that the light and medium components are the fractions with the most potential in thermal exploitation, while injection of CO2 is beneficial for the extraction of all the components, especially the medium components. This work gives insights into the effect of asphaltene on shale oil recovery in quartz slits and might provide guidance on the utilization of thermal and CO2-enhanced enhanced oil recovery (EOR) techniques in shale oil production.

Effect of asphaltene on the rheological properties of bitumen

In this paper, the rheological behavior of bitumen as a function of asphaltene concentration has been studied. Several bitumen samples having distinctly different amounts of asphaltene were prepared and characterized using differential scanning calorimetry and rheological measurements. The glass transition temperature of bitumen increases with an increase of the asphaltene concentration. This correlation can be used to estimate the asphaltene concentration of bitumen samples using DSC measurements. Small-amplitude oscillatory shear data for the bitumen-derived samples were fit by the generalized Maxwell model with good agreement. A constitutive model is proposed, where the zero-shear complex viscosity of the bitumen sample is a strong function of the asphaltene concentration, and it can be used to predict the asphaltene concentration.

Effects of asphaltenes on the photolytic and toxic behavior of bitumen and conventional oil products on saltwater

The effects of asphaltenes on the photolytic and toxic behavior of petroleum oil on seawater was investigated by exposing five original oils and their maltenes to solar irradiation for seven days. Polycyclic aromatic hydrocarbons (PAHs) experienced the fastest photo-oxidation, but negligible photolytic loss was observed for most normal alkanes and all the petroleum biomarkers from tri-cyclic to pentyl-cyclic terpanes in the test total oil and maltenes. The removal of most PAHs from some maltenes was greater than the corresponding total oils. Deasphalting process did not affect the characteristics of naphthenic acid fraction components (NAFCs) in all control samples. In all test oils, solar irradiation formed abundant NAFCs, in particular those only containing oxygen as the heteroatoms (Oo species). The formed Oo species were abundant in congeners having highly saturated congeners, and shifted to a lighter carbon number after exposed. Deasphalting process significantly enhanced the formation of Oo species (o from 2 to 4) for all test oils, in particular for the Cold Lake Blend and Bunker C. The toxicity of exposed maltenes was generally higher than the exposed total oil for most oils, suggesting the aqueous toxicity level was positively related to the formed NAFC intermediates.

Effects of Asphaltenes on the Photolytic and Toxic Behavior of Bitumen and Conventional Oil Products on Saltwater

Effects of Asphaltenes on the Photolytic and Toxic Behavior of Bitumen and Conventional Oil Products on Saltwater

Influence of Asphaltenes on the Low-Sulphur Residual Marine Fuels’ Stability

The effects of asphaltenes from two heavy oil residues on the sedimentation stability of residual marine fuels were assessed and compared. As base components of residual marine fuels, the vacuum residue (VacRes) and visbreaking residue (VisRes) were taken. The heptane-insoluble fractions (HI-fractions), including asphaltenes, isolated from vacuum residue and visbreaking residue, were analyzed to determine the elemental composition (XRF) and cluster parameters (XRD). The results of the analysis of the parameters of the asphaltene cluster (HI-fraction) for vacuum residue and visbreaking residue showed that dγ – 6.1 and 5.9 Å, Lc – 26.72 and 20.78 Å, and La – 7.68 and 7.20 Å. The sedimentation stability of residual marine fuel was determined according to the ISO 10307-1-2009 (TSA) method and described using ternary phase diagrams. The ratio of stable compositions to the total number of possible compositions (with a step of 10 wt%) was 65/66 or 98.5% for residual marine fuel comprising a mixture VacRes/ULSD/LCGO (vacuum residue/ultra-low sulphur diesel/light catalytic gas oil). Meanwhile, the ratio of stable compositions to the total number of possible compositions was 38/66 or 57.6% for residual marine fuel comprising a mixture VisRes/ULSD/LCGO (visbreaking residue/ultra-low sulphur diesel/light catalytic gas oil).

Effect of Asphaltenes on the Kinetics of Methane Hydrate Formation and Dissociation in Oil-in-Water Dispersion Systems Containing Light Saturated and Aromatic Hydrocarbons

Effect of Asphaltenes on the Kinetics of Methane Hydrate Formation and Dissociation in Oil-in-Water Dispersion Systems Containing Light Saturated and Aromatic Hydrocarbons

Laboratory Investigation of Permeability Impairment Caused by Asphaltene Precipitation during Screening for Gas-Injection Enhanced Oil Recovery and Pressure Change in a Major Gulf of Mexico Field

Summary As part of studying miscible gas injection (GI) in a major field within the Green Canyon protraction area in the Gulf of Mexico (GOM), asphaltene-formation risk was identified as a key factor affecting a potential GI project. The industry has not conducted many experiments to quantify the effect of asphaltenes on reservoir and well performance under GI conditions. In this paper we discuss a novel laboratory test for evaluating the asphaltene effect on permeability. The goals of the study were to define the asphaltene-precipitation envelope using blends of reservoir fluid and injection gas, and measure permeability reduction caused by asphaltene precipitation in a core under GI. To properly analyze the effect of GI, a suite of fluid-characterization studies was conducted, including restored-oil samples, compositional analysis, constant composition expansion (CCE), and differential vaporization. Miscibility conditions were defined through slimtube-displacement tests. Gas solubility was determined through swelling tests complemented by asphaltene-onset-pressure (AOP) testing. The unique procedure was developed to estimate the effect of asphaltene deposition on core permeability. The 1-ft-long core was saturated with the live-oil and GI mixture at a pressure greater than the AOP, and then pressure was depleted to a pressure slightly greater than the bubblepoint. Several cycles of charging and depletion were conducted to mimic continuous flow of oil along the path of injected gas and thereby to observe the accumulation of asphaltene on the rock surface. The test results indicated that during this cyclic asphaltene-deposition process, the core permeability to the live mixture decreased in the first few cycles but appeared to stabilize after Cycle 5. The deposited asphaltenes were analyzed further through environmental scanning electron microscopy (ESEM), and their deposition was confirmed by mass balance before and after the tests. Finally, a relationship was established between permeability reduction and asphaltene precipitation. The results from the asphaltene-deposition experiment show that for the sample, fluids, and conditions used, permeability is impaired as asphaltene flocculates and begins to coat the grain surfaces. This impairment reaches a plateau at approximately 40% of the initial permeability. Distribution of asphaltene along the core was measured at the end by segmenting the core and conducting solvent extraction on each segment. Our recommendation is numerical modeling of these test results and using this model to forecast the magnitude of the permeability impairment in a reservoir setting during miscible GI.

Microstructure and dynamic mechanical properties epoxy/asphaltene composites

Asphaltenes tend to aggregate to nanoparticles or clusters in crude oil and solvents over a wide concentration and temperature range. In the present paper, asphaltenes extracted from the base asphalt was used as a filler to introduce into epoxy resin. The microstructure and evolution of asphaltenes aggregation in the epoxy resin were observed using laser scanning confocal microscopy. Furthermore, the effect of asphaltenes on the viscosity, dynamic mechanical behavior, thermostability, mechanical properties of epoxy resin was evaluated by Brookfield rotational viscometer, dynamic mechanical analysis, thermogravimetric analysis and universal testing machine. The presence of asphaltenes increased the viscosity of the neat epoxy during all stages of cure reaction. The viscosity of epoxy/asphaltenes composites increased with the filler concentration. Fractal asphaltenes aggregation formed in the composites with 1 mass% asphaltenes. Network microstructures of asphaltenes aggregation appeared in the epoxy phase with a further increase of asphaltenes content. Moreover, the increase of asphaltenes loading resulted in denser network microstructures in the epoxy matrix. Aggregation evolution revealed that asphaltenes particles redispersed evenly in the epoxy resin in the form of some aggregates at the beginning of curing. During the cure reaction of epoxy, asphaltenes aggregates started to agglomerate and grow to network microstructures. The presence of asphaltenes led to the enhancement of the storage modulus of the neat epoxy at the rubbery stage. The glass transition temperature (Tg) of the epoxy composites slightly increased with the increase of asphaltenes loading. The epoxy composite with 5 mass% asphaltenes had higher Tg than the neat epoxy. The inclusion of asphaltenes had a negligible effect on the damping properties and thermal stability of the neat epoxy. The aggregation and heterogeneous dispersion of asphaltenes resulted in the decrease of the tensile strength and elongation at break of the neat epoxy. However, the inclusion of asphaltenes significantly enhanced Young’s modulus of the neat epoxy. Young’s modulus of the neat epoxy was increased by more than fourfold with the addition of 5 mass% asphaltenes.

Effect of Asphaltene on Threshold Pressure Gradient of Heavy Oil in Porous Media

Many studies have shown that heavy oil with high asphaltene content has a yield stress. Coupled with the solid-liquid interaction between porous media and heavy oil, there is a threshold pressure gradient when heavy oil flows in porous media. Meanwhile, some previous research has indicated that the high viscosity of heavy oil is the decisive factor for its threshold pressure gradient. Hence, this concept needs more clarification, especially because its accuracy is questionable. In this research, different oil samples with the same viscosity and also different asphaltene contents heavy oil samples were prepared. The viscosity of the different heavy oil samples was measured. Threshold pressure gradient experiments under different permeabilities and temperatures were also conducted on heavy oils. The results proved that the viscosity was not directly related to threshold pressure gradient of heavy oil. They also suggested that the heavy oil viscosity increased with the increase of asphaltene content. Moreover, the formula of the factors affecting threshold pressure gradient was regressed, and also its applicability was verified. As the temperature and core permeability increase, the threshold pressure gradient was also proven to decrease significantly. Furthermore, it was found that the threshold pressure gradient increased significantly with the increase of asphaltene content. Therefore, the heavy oil threshold pressure gradient could be characterized as a function of temperature, permeability, and asphaltene content. This study provided some theoretical support for the research attempts on the reduction of threshold pressure gradient and also on the effective development of heavy oil reservoirs.

Research on polar substance characterization and adsorption separation process of heavy oil

The combustibility and fluidity is usually a major issue in heavy oil of power plant, which affects by asphaltene and insoluble matter due to the long-term storage. In this dissertation, the effects of asphaltene and insoluble matter characteristics on the heavy oil properties have been theoretically and experimentally studied using different methods. For the combustibility study, the asphaltene was precipitated and verified by X-ray diffraction energy and dispersive spectrum analysis. Also, the rotating disk electrode atomic emission spectrometry was carried out for fluidity study and then calorific value and ash content are calculated. The combustibility and fluidity of heavy oil were improved with the method of non-polar solvents and strong polar adsorption by removing asphaltene polar and insoluble substances. The experimental shows that calorific value is 9721Kcal/kg and viscosity is 14.7mm2/s.

A mechanistic understanding of the water-in-heavy oil emulsion viscosity variation: effect of asphaltene and wax migration

The role of emulsions as a prevalent phenomenon is broadly investigated in the petroleum industry since forming the emulsion has many severe harmful implications. Heavy components of crude oil such as wax and asphaltene make the water-in-oil (w/o) emulsion more stable, while the role of these components on the emulsion viscosity has not been fully understood. In this regard, to find a proper demulsifier to break these emulsions, it is necessary to know the mechanisms of emulsion formation by heavy oil components. In this study, the effects of waxy-oil and asphaltenic-oil on w/o emulsion were investigated by measuring volume and viscosity of the formed emulsion after an elapsed time, followed by proposing a viscosity model based on experimental data. For this purpose, two types of crude oil were used: asphaltenic oil and waxy oil. Next, the emulsion stability and phase separation in these samples were studied, and viscosity for each segment was measured and modeled in the system. Results showed that phase separation and emulsion formation depend on the presence of asphaltenic-oil and waxy-oil after the passage of a specific time such that the system exhibits a strong function of asphaltene rather than wax. Also, free oil volume decreased with increasing water cut to 70%, where most declines occurred at a stirring rate of 1200 rpm in the presence of asphaltene. Besides, the viscosity of the free oil decreased with increasing water cut to 70% in both waxy-oil and asphaltenic-oil systems such that the free oil viscosity decreased from 11.43 cp to 5.89 cp when the water cut increased from 0% to 70%. Findings also showed that the viscosity of the w/o emulsion phase decreased with increasing the shear rate and temperature, resulting in increased stability in the emulsion. Based on a proposed viscosity model, the model results showed a dispersed oil-in-water (D O/W) flow for the highest water cut of 70% with an average deviation of 7.03% and revealed an accurate estimation to the experimental data. The model approach can be applied in the estimation of the water-in-heavy oil emulsion viscosity in pipelines.

Effects of crude oil characteristics on foaming and defoaming behavior at separator during CO2 flooding

CO2 flooding effectively enhances the recovery of crude oil. However, a large amount of foam is generated in the separator when the produced oil releases gas due to depressurization, which reduces the separator capacity. To address the foaming problem, this paper provides some qualitative and quantitative insights by studying the effects of depressurization, resin, asphaltene, wax crystal and other factors on the foaming and defoaming characteristics of four crude oils. A set of experimental devices is developed to assess foaming during depressurization. The experimental results indicate that a larger pressure drop increases the amount of foam generated and the defoaming rate. The ratio of resin to asphaltene is closely related to the foaming and defoaming characteristics of crude oil, and the effect of asphaltene on foam stabilization is greater than that of resin. There is a threshold wax crystal content for affecting the foaming and defoaming characteristics of crude oil. A small amount of wax crystals accelerates foam bursting, but further increasing the wax crystal content stabilizes the foam. These results provide guidance and a reference for CO2 flooding technology, the improvement of separators and research on the foaming and defoaming mechanisms of crude oil.

Polar asphaltenes facilitate the flow improving performance of polyethylene-vinyl acetate

Herein, four asphaltenes in distinguished polarities were first fractionated from heavy crude oil by the solvent-precipitation method (that is, C5I asphaltenes) and characterized, and the effects of asphaltenes on the polyethylene-vinyl acetate (EVA) PPD's performance for the model waxy oil were evaluated. Results show that the asphaltenes in lower polarities contain a greater number of aliphatic groups and present a higher H/C ratio, hence exhibiting better oily compatibility and the greater synergistic performance with EVA in improving the waxy oil flowability at low temperatures. The competition between the co-crystallization and nucleation effect of additives determines the wax precipitating temperature (WPT). Adding asphaltenes delays the wax precipitation, but increases wax crystal number just below WPT, especially together with EVA. According to the micro-observation and isothermal titration tests, EVA can adsorb onto the asphaltene aggregates to form the composite EVA/asphaltene particles, and the adsorption gradually reaches saturated with the EVA injecting. The composite particles act as the heterogeneous crystallizing templates for wax molecules to precipitate, triggering the formation of wax crystal flocs with large size, spherical-like morphology, and compact structure. Reducing the asphaltenes polarity strengthens the stronger interactions among asphaltenes, EVA and paraffin wax molecules, and hence improves the EVA/asphaltene synergistic performance.

Heavy crude oil asphaltenes as a nanofiller for epoxy resin

AbstractAsphaltenes are harmful components of heavy crude oils and require rational utilization after oil refining or deasphalting. Asphaltenes are macromolecules containing various functional groups that self‐assemble to nanoscale aggregates and can be used as nanofillers for polymers. In this research, mixtures of asphaltenes with the diglycidyl ether of bisphenol A were considered. The solubility of asphaltenes in this epoxy resin, the rheological properties of the mixtures, and the effect of asphaltenes on the curing with 4,4′‐diaminodiphenyl sulfone were studied. In addition, the glass transition temperature, strength, and adhesion characteristics of the asphaltene‐filled cured composites were evaluated. The dual role of asphaltenes in polymer modification was demonstrated: the asphaltenes simultaneously plasticize and reinforce the polymer matrix, and the transition from predominant plasticization to strengthening occurs with an asphaltene content at 20 wt%. The dual reinforcement/plasticization effect occurs because epoxy composites contain both nanosized and microsized particles of asphaltenes due to the partial dissolution of asphaltenes in the epoxy resin and the decrease in their solubility during high‐temperature curing.

Aggregation and pressure effects of asphaltene and resin molecules at oil–water interfaces: a coarse-grained molecular dynamics and free energy study

ABSTRACT Coarse-grained molecular dynamics simulations were used to investigate the aggregation of asphaltene and resin molecules in oils and their deposition to oil–water interfaces. Resin, “interfacially-active” asphaltenes, and “bulk-like” asphaltenes are considered as solutes in organic phases consisting of aromatics or saturates. Resins and asphaltenes formed aggregates with a spacing of 0.46 nm between stacked polycyclic sheets. Whether in the aromatic or saturated solvent, resin molecules did not interact with the interface, but its aggregates remained in the bulk. The degree of surface activity of asphaltenes was found to increase with the polarity of their chemical groups, and decrease with the aromatics content of the solvent. Axial stress profiles were measured to calculate the interfacial tension of each system. The tension of interfaces of crude oil with water was found to depend on aromatics content. The free energy of deposition of asphaltenes and resin molecules to the interface was measured using well-tempered metadynamics, in which it was found that “interfacially-active” asphaltenes possess greater stability at the oil-water interface than “bulk-like” asphaltenes, and the organic solvent influences the favorability of deposition.

A series of methods for investigating the effect of a flow improver on the asphaltene and resin of crude oil

With the increasing of oil demand and the decreasing of conventional crude oil production, unconventional crude oil is gaining interest. A flow improver (FI) was synthesized and designed a series of methods for investigating the effect of the flow improver on the asphaltene and resin of two unconventional crude oil samples. Changes in the morphology of the solid samples, as determined by scanning electron microscopy. n-Heptane and alcohol were selected as poor solvents for asphaltene and resin, respectively, to prepare solution samples of different concentrations. The precipitation tendency was judged according to the color change of the solution. Fluorescence microscopy was used to observe the changes in the aggregation morphology of the solution samples before and after FI addition. Solid samples and solution samples were tested by XRD and UV spectrophotometry, respectively. The results consistently showed that the effect of FI on resin was better than that on asphaltene. The effect of asphaltene and resin on the viscosity of crude oil was investigated through the series of studies.