Experimental Study of Asphaltenes Flocculation Onset in Crude Oils Using the Densitometry Measurement Technique

The asphaltenes flocculation proceeds with changes of oil composition and causes significant losses in petroleum industry operations. The main objective of this work is to evaluate the reliability of the densitometry technique in studying experimentally the mechanism of aggregation and flocculation of asphaltenes occurring in crude oils. As asphaltene flocculation threshold in crude oils or mixture can be achieved by addition of n-heptane, various n-heptane concentrations were added to crude oil, and their effects have been investigated trough density measurements. Thereby, measurements were based on mixture of crude oil + toluene and cyclohexane + n-heptane, respectively. While asphaltene aggregates form clusters and flocculate, the mixture volumetric mass change and the reduced density of non-Newtonian fluids under investigation have been pointed out as one of appropriate measures of flocculation process. In particular, the curve representing the reduced density as function of the ratio between n-heptane concentration and concentration of crude oil under study featured a break point that well characterizes the flocculation threshold. Besides the quantity needed to initiate and to aggregate asphaltenes within crude oils, the amount required to completely achieve deposition of asphaltenes has also been identified. A quantity of 4 and 20 g of n-heptane per gram of crude oil was found necessary.     

Effect of Surfactant on the Growth of Onset Aggregation of Some Egyptian Crude Oils

This work pertains to study the asphaltenes aggregates' settling behavior of crude oil in absence and presence of oil‐soluble surfactants including long‐chain fatty acid in the form of amidation and estrification. First, the onset points as a function of light absorbed asphaltenes aggregates were quantified before and after adding asphaltenes dispersants using ultra violet spectroscopy, and the photograph fractal‐like aggregate structures were quantified using Carl Zeiss Trinocular microscope. Second the shear rates against shear stress induced aggregation were also measured in absence and presence of different concentrations of asphaltenes dispersants using Brookfield digital rheometer model LVDV‐III⁺. The results reviled that the asphaltenes aggregates are found to depend on toluene–heptane ratios. In absence of dispersant the accumulated and aggregates clusters of asphaltenes are formed at heptane: toluene ratio of 50∶50. Whereas, in the presence of dispersant the asphaltenes are solvated at heptane: toluene ratio of 60∶40, followed by appearance of stronger and dots aggregates clusters at a ratio of 70∶30, and finally, a larger aggregates growing at heptane: toluene ratio of 80∶20. The dispersant solvates the asphaltenes and maintains them in solution, while their surface activity remains high. This means that the dispersant apparently functioned well in decreasing the degree of flocculation and precipitation beyond the critical micelle concentration (CMC) of asphaltenes at 0.0027 g/L. Also, the reduction in the viscosity in presence of dispersant suggests that the asphaltenes aggregates are highly porous and very fragile.     

A Study of Thin Liquid Films as Related to the Stability of Crude Oil Emulsions

In this paper, we report the influence of surface-active compounds on the stability of crude oil emulsions using the apparatus designed for bilayer lipid membrane studies. The results obtained show that natural surface-active materials in crude oil, such as petroleum acids and asphaltenes, play a pivotal role. The ionized acids formed by the reaction between the petroleum acids and the alkali can decrease the interfacial tension and accelerate the thinning as well as the breakdown of the thin liquid film. The asphaltenes can adsorb onto the interface and improve the stability of the film. The order of the stability of the films between crude oil and alkaline solutions is found to be as follows: crude oil with asphaltenes removed (ii) 相似文献   

Asphaltene flocculation in crude oil systems

Flocculation points of complex systems of the type crude oil+solvent+precipitant were experimentally and theoretically studied. In this work 6 crude oils are combined with the solvents toluene and cyclohexane and the precipitants n-pentane, n-hexane, n-heptane and i-octane. Experimentally, the oil solution was titrated by the precipitant to determine the precipitant volume necessary for flocculation. Detecting the intensity of a light beam which passes the sample, the flocculation point is assumed to correspond to the maximum of the titration curve. The modeling of the flocculation points is based on the simple Scatchard–Hildebrand solubility theory in the framework of continuous thermodynamics. The crude oil is considered to consist of maltenes and asphaltenes. The composition of these two subsets is described by separate continuous distribution functions. The oil species are identified by their solubility parameters reflecting their degree of aromaticity and their content of heteroatoms. Both maltenes and asphaltenes are assumed to obey Gaussian distribution functions with respect to the solubility parameter. In this way only the polydispersity with respect to the solubility parameter is taken into account. The molar mass polydispersity, here, is much less important and, therefore, it will be neglected. To calculate the flocculation points only a single equation has to be numerically solved. The only fit parameter is the number average of the molar mass of the asphaltenes, the experimental values of which are too inaccurate. The comparison of the calculated and the experimental results are surprisingly reasonable considering the simplicity of the model and the inaccuracies of some input data.     

Dewatering of crude oil emulsions 2. Interfacial properties of the asphaltic constituents of crude oil

The importance of the interfacial rheology in determining the stability of water-in-Buchan crude oil emulsions has been demonstrated in part 1 of this series of papers (R.A. Mohammed, A.I. Bailey, P.F. Luckham and S.E. Taylor, Colloids Surfaces A: Physicochem. Eng. Aspects, 80(1993)223). In part 2, interfacial tensions of crude oil, and solutions of asphaltenes and resins in a model oil have been investigated. Surface pressure vs. area (Π—A) curves of monolayers of asphaltenes, resins and their mixtures have been established. In its dependence on the ratio of resins to asphaltenes, the pseudostatic dilatational modulus has high values for low resin-to-asphaltene ratios and low values for high resin-to-asphaltene ratios. This is expected to throw light on the cause of the enhanced stability of water-in-crude oil emulsions.     

Experimental Evaluation of the Inhibitors Performance on the Kinetics of Asphaltene Flocculation

The kinetics of asphaltene flocculation are studied on two types of Iranian crude oil. Kinetic studies are conducted by applying near infrared spectrophotometry. The presence of inhibitors in the sample reduces the amount of light absorption of crude oil sample. The effect of these inhibitors according to the initial changes in the light absorption of crude oil samples is studied. The obtained results indicate that the asphaltenes are the highest stabilized in presence of the vegetable oil types (hazelnut and walnut) and chemical compound (4-dodecylresorcinol).     

Effect of Interfacially Active Fractions of Some Egyptian Crude Oils on Their Emulsion Stability

Four samples from different crude oils were used for this study: light and heavy crude oils from Iran and two crude oils from Egypt, namely, Ras Gharb and Suez mix. The asphaltenes were separated from these crude oils and then the maltene (non‐asphaltenic fraction) was fractionated into waxes, aromatics, and resins. All fractions were characterized using FTIR and UV spectroscopic analyses in addition to gel permeation chromatograph (GPC). These fractions were tested for their emulsion stability. For chemometric analysis different parameters (variables) have been used to study the effect of different fractions (objects) on the emulsion stability. Such variables included the integrated areas under the stretching absorption peaks of CH in the range of 3000–2800 cm^?1, C?O in the range of 1750–1650 cm^?1, and the aromatic C?C in the range of 1650–1550 cm^?1, as well as UV absorption value at 235 nm and average molecular weight (MW). Principal component analysis (PCA) and multiple linear regression (MLR) were conducted for examining the relationship between multiple variables and the stability of water‐in‐crude oil emulsions. The results of PCA explain the interrelationships between the observations and variables in multivariate data. The correlation coefficients between different parameters derived from PCA reveals that the UV absorption value and MW are strongly correlated with emulsion stability. It also reveals that the resins, asphaltenes, and maltene have better emulsion stability than waxes and lower molecular weight aromatics. The linear relationship between the parameters and the stability of water‐in‐crude oil emulsions using MLR was modeled according to the better statistical results. The obtained mathematical model can be used to predict the stability of water‐in‐crude oil emulsions from the chemical groups and functionalities in each crude oil fraction.     

Effect of Asphaltenes and Resins on Asphaltene Aggregation Inhibition,Rheological Behaviour and Waterflood Oil-Recovery

This study presents an investigation about the influence of resins and asphaltenes, extracted from two Mexican crude oils (light and heavy oil samples), on the asphaltene aggregation inhibition, rheological behavior, and waterflood oil-recovery. Resins and asphaltenes were characterized by means of elemental analysis, metals analysis by atomic absorption, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization mass spectrometry (ESI-MS) in order to evaluate the effect of their structural parameters on the phenomena studied. Efficiency of the resins fraction as natural inhibitors of asphaltene aggregation was evaluated trough ultraviolet–visible (UV–vis) spectroscopy. Results showed better efficiencies of resins on asphaltene aggregation inhibition at resin/asphaltene (R/A) ratios close to unity and at high temperature. In addition, efficiencies were influenced by structural characteristics of the asphaltene–resin system. Rheological behavior of the heavy crude oil sample was significantly influenced by the presence of asphaltenes and resins. Finally, asphaltenes and resins played an important role on wettability and waterflood oil-recovery.     

Stability of emulsions of water in mineral oils containing asphaltenes

Emulsions of water in mineral oils are stable if the oil phase contains asphaltenes which are near the condition of incipient flocculation. This condition is determined by the composition of the oil phase and by the nature of the asphaltenes. High aromaticity of the oil phase and the presence of deflocculants prevent flocculation of asphaltenes; the deflocculants may be interfacially active agents or asphaltene-like compounds with better solubility in the oil phase. Conditions of incipient flocculation of asphaltenes correlate very well with a considerable increase of rheological resistance of the interface between the oil phase and distilled water, determined according to the torsion oscillation method. Stabilization of the water-in-oil emulsions is therefore caused by the build-up of a coherent layer of asphaltenes in the water-oil interface in these cases. Deflocculants of asphaltenes in the oil phase destroy their stabilizing effect; however, the deflocculants themselves may stabilize the water-in-oil emulsions by adsorption on the water-oil interface and then the correlation between the condition of asphaltenes and emulsion stability does not hold, nor is the interfacial viscosity perceptibly increased. Under borderline conditions of emulsion stability a few percent of sodium chloride in the water phase counteracts the build-up of a stabilizing layer of asphaltenes in the water-oil interface and so do higher p_H values of a buffered water phase. At low p_H-values emulsion stability does not correlate with interfacial resistance. It can be concluded that asphaltenes stabilize water-in-oil emulsions if they accumulate on the water-oil interface. This interfacial layer may show a coherence, which is an indication of the presence of asphaltenes rather than a condition for stability of the emulsions.     

Biocatalytic removal of nickel and vanadium from petroporphyrins and asphaltenes

Asphaltenes from a crude oil rich in heavy metals (Castilla crude oil) were fractionated and partially characterized. Biocatalytic modifications of these fractionated asphaltenes by three different hemoproteins: chloro-peroxidase (CPO), cytochrome C peroxidase (Cit-C), and lignin peroxi-dase (LPO) were evaluated in both aqueous buffer and organic solvents. The reactions were carried out in aqueous buffers, ternary systems of toluene: isopropanol: water, and aqueous-miscible organic solvent solutions with petroporphyrins as substrate. The petroporphyrins were more soluble in the ternary systems and aqueous miscible-organic solvent systems than in the aqueous buffer systems. However, only the CPO-mediated reactions were effective in eliminating the Soret peak in both aqueous and organic solvent systems. The effects of CPO-mediated reactions on the release of the metals complexed with the porphyrins and asphaltenes were also determined. Chloroperoxidase was able to alter components in the heavy fractions of petroleum and remove 53 and 27% of total heavy metals (Ni and V, respectively) from petroporphyrin-rich fractions and asphaltenes     

Effect of Crude Oil Aging on Asphaltene Inhibitor Product Recommendation

Aging refers to the deterioration of hydrocarbon fluids that manifests as changes in the physicochemical characteristics of the fluid upon exposure to ambient conditions. In order to understand the effect of aging of crude oils on asphaltene inhibitor product recommendation, simulated aging studies were performed on a crude oil from Wyoming with known asphaltene issues. The results clearly show that aging of crude oil affects the stability of the oil with respect to asphaltenes and caution must be exercised when recommending asphaltene inhibitor if the evaluations were performed on fluids after long-term storage. A real case study where ambient storage in the lab adversely affects the stability of the crude oil and renders asphaltene inhibitor ineffective further confirms results from simulated aging.     

Determination of volatile and non-volatile nickel and vanadium compounds in crude oil using electrothermal atomic absorption spectrometry after oil fractionation into saturates, aromatics, resins and asphaltenes

In recent work, it has been shown that electrothermal atomic absorption spectrometry (ET AAS) can be used to differentiate between volatile and non-volatile nickel and vanadium compounds in crude oil. In the present work, the distribution of these two groups of compounds over different fractions of crude oil was investigated. For this purpose two crude oil samples were separated in two steps: firstly, the asphaltenes were precipitated with n-heptane, and secondly, the maltenes were loaded on a silica column and eluted with solvents of increasing polarity. The four fractions of maltenes eluted from silica column were: F1, saturated and light aromatics; F2, polyaromatics; F3, resins; and F4, polar compounds. Fractions F1 and F2 were further investigated using gas chromatography, and all fractions were characterized by CHN analysis, confirming the increase of aromatics in the fractions 2, 3, 4 and asphaltenes. For the determination of Ni and V by ET AAS, oil-in-water emulsions were prepared. The speciation analysis was carried out measuring without chemical modifier (stable compounds) and with 20 μg palladium (total Ni and V) and the volatile fraction was calculated by difference. The limits of detection were 0.02 μg g⁻¹ and 0.06 μg g⁻¹, for Ni and V, respectively, based on an emulsion of 2 g of oil in 10 mL. The volatile species of Ni and V were associated with fractions F3 and F4, while only thermally stable Ni and V was precipitated in part together with the asphaltenes.     

Using of Modified Plastic Waste Based on Poly(ethylene‐co‐acrylic acid) Grafts to Solve Transportation Problem of Petroleum Crude Oil

Polyethylene acrylic acid copolymer (PEAA) was modified with different types of alkanols and hydroxybenzoic acids to produce three types of esterified grafts. The molecular structures of the synthesized dispersants were performed using ¹H NMR analysis. The molecular weights of the synthesized dispersants were determined by GPC technique. The activity of PEAA derivatives as asphaltene stabilizer in the crude oil was evaluated by means of flocculation measurements. The effect of asphaltenes on the rheological behavior of highly asphaltenic crude oils was studied to evaluate the transportation parameters of crude oils. The rheological properties were measured at different temperature ranges of 5°C to 25°C in presence and absence of PEAA additives. It was observed that the PEAA having side chain lengths below C₁₆ show non‐Newtonian pseudoplastic relationships at temperatures from 25°C to 5°C. While, PEAA additives having side chain lengths equal or above C₁₆ show Newtonian relationship even at low temperature (5°C) for all tested crude oils.     

Separation and Chemical Characterization of Wetting Crude Oil Compounds

To improve the understanding of wettability, especially the influence of colloidal stability and composition of crude oil, wetting experiments on quartz sand were performed with an asphaltene-rich oil, a resin-rich oil, and with model oils containing different colloid compositions. A two-step procedure was developed to investigate the wetting behavior. In the first step those crude oil components were extracted, which preferentially wet solid surfaces. The extracted crude oil components were characterized in the second step. The amount of adsorbed oil components correlates with the stability of the crude oil colloids: low colloidal stability of crude oil leads to larger amounts of adsorbed components than does high colloidal stability. The addition of resins and/or low molecular weight asphaltenes to the crude oil stabilizes the crude oil colloids; i.e., a lower amount of wetting components are isolated by extraction in such systems. To find out, which fraction of the adsorbed oil components determines the wetting behavior of a crude oil, the wetting properties of the toluene solutions of these fractions were compared to those of the toluene solutions of the precipitated crude oil colloids. The fractions extracted with the solvent systems chloroform and methanol/chloroform showed nearly the same wetting behavior as the crude oil colloids. These fractions are characterized by the highest molecular weights, higher sulfur compositions, and the lowest H/C ratios. On the other hand, the nitrogen compounds predominate in the acetone fraction.     

Study on the Mechanism of Asphaltenes Reducing Oil-Water Interfacial Tension

As high polar components of crude oil, asphaltenes play a significant role in reducing oil-water interfacial tension(IFT). In this paper, the effects of asphaltenes on reducing IFT in the presence of surfactant were compared, and the mechanism of asphaltenes reducing the IFT was studied by the dynamic interfacial tension(DIFT) equation. Whether asphaltenes were added to the oil or 2,5-dimethyl-4-(4-dodecyl) benzene sodium sulfonate(p-S14-4) was added to the water phase, either of all results in the IFT reducing and the IFT is related to the coverage and the mass of asphaltenes adsorption at the interface. In the presence of asphaltenes, the adsorption of the active substances to the interface is not entirely dependent on diffusion, and the process can be divided into three regions. Region I: the IFT rapidly reducing, this process is controlled by diffusion of surfactant; Region II: the IFT reducing slowly, resulted from the lower diffusion rate that is limited due to the aggregates formed by the interaction of asphaltene-asphaltene; Region III: the interaction of asphaltene-asphaltene is broken by the interaction of surfactant-asphaltene. The asphaltene aggregates are reduced and adsorbed rapidly at the interface. Furthermore, the results reveal that the asphaltenes concentration affects the coverage rate and adsorption at the interface.     

原油组分低温氧化机理和反应活性实验研究

分析了原油和原油组分低温氧化的机理,通过实验进行了不同油品低温氧化反应,考察了氧化反应前后原油族组成的变化,并研究了单组分(正十六烷、蜡、蒽、沥青质)在不同温度下的低温氧化速率和反应活性,得出了不同原油组分的低温氧化反应的活化能。结果表明,稠油较轻质油有更好的氧化反应活性,在较低温度下稠油更容易被氧化,原油中不同组分及含量是影响氧化反应活性和氧化反应速率的重要因素,重组分的沥青质和长链烷烃在低温下(70~90℃)氧化活性较高,正十六烷和蒽反应活性较之重组分低。揭示了原油组分低温氧化反应机理以及不同组分氧化反应活性的区别,为油田注空气工艺方案设计提供基础。     

Multivariate Screening Analysis of Water-in-Oil Emulsions in High External Electric Fields as Studied by Means of Dielectric Time Domain Spectroscopy

The effect of crude oil resins with various polar characters on the stability of w/o model emulsions containing asphaltenes is investigated using a mixture design. The resins were extracted using an adsorption-desorption technique. One asphaltene fraction and four different resin fractions from one European crude oil were used. The stabilities are measured using time-domain dielectric spectroscopy in high external electric field. It is found that resins with different polar character have different effects on the emulsion stability. At asphaltene/resin ratios of 1 and 5 : 3 the resins in some cases lead to an emulsion stability higher than that of a similar emulsion stabilized by asphaltenes only, while at low asphaltene/resin ratios ( approximately 1 : 3) the emulsion stability is reduced by the resins. The effect on emulsion stability of combining two different resin fractions depended on the resin types combined as well as the relative amount of resins and asphaltenes. Also, an increase in the stability of some of the emulsions containing resins and asphaltenes for a period of 50-300 min after the emulsification was observed. This time-dependence of emulsion stability is attributed to the mobility of resins at the oil-water interface and the slow buildup of a stabilizing interfacial film consisting of resins and asphaltenes. Copyright 2000 Academic Press.     

Water-in-Oil Emulsions Stabilized by Asphaltenes Obtained from Venezuelan Crude Oils

W/O emulsions were studied using asphaltenes as surfactants. Asphaltenes were obtained from three Venezuelan crude oils: “Lago Cinco,” “Rosa Mediano,” and “Ayacucho.” They were extracted using n-heptane as a precipitanting agent. The following variables were studied: concentration of asphaltenes in the oleic phase and pH of the aqueous phase. An increase in asphaltene concentration in the oleic phase increases emulsion stability. On the other hand, the most stable emulsions correspond to an alkaline aqueous phase. Likewise, emulsion stability was higher for asphaltenes obtained from “Lago Cinco” crude oil and lowest from Rosa Mediano asphaltenes.     

Characterization of asphaltenes precipitated with three light alkanes under different experimental conditions

Asphaltene precipitation plays an important role in both oil production and refining processes. In this paper, asphaltenes are precipitated from a heavy oil sample under different experimental conditions by using three different light alkanes, i.e., propane, n-pentane, and n-heptane. A variety of analytical techniques are applied to characterize the precipitated asphaltenes and deasphalted heavy oil (i.e., maltenes), such as the density and viscosity measurements, vapour-pressure osmometry, freezing-point osmometry, scanning electron microscope (SEM) imaging, nuclear magnetic resonance (NMR) measurement, and simulated distillation for compositional analysis. It is found that the yields and properties of the precipitated asphaltenes and remaining maltenes strongly depend on the specific precipitant tested and the liquid precipitant-to-oil volume ratio used. The asphaltene yield decreases as the carbon number of an alkane increases, while it increases monotonically and finally reaches a plateau if the liquid precipitant-to-oil volume ratio increases up to 20–40 for n-pentane and n-heptane, respectively. As a result, n-heptane-precipitated asphaltenes (C₇-asphaltenes) have the highest molecular weight and aromaticity among the three kinds of precipitated asphaltenes. C₇-asphaltenes are bright and black particles, whereas n-pentane-precipitated asphaltenes (C₅-asphaltenes) are dull and brown powders. Propane-precipitated asphaltenes (C₃-asphaltenes) together with some amount of co-precipitated resins are found to be highly viscous and semi-solid like immediately after the flashed-off process but become more and more liquid-like afterward. Compositional analysis results of the original heavy crude oil and three different maltenes indicate that the carbon numbers of most precipitated asphaltenes are higher than C₅₀.