The Effect of Solvent Nature and Dispersant Performance on Asphaltene Precipitation from Diluted Solutions of Instable Crude Oil

Abstract

The asphaltene precipitation experiments were studied on El Furrial crude oil from western Venezuela, which is known to exhibit serious instability problems. A Turbiscan backscattering apparatus was used to evaluate the precipitation of asphaltenes with different solvents. The transmittance variation with time was studied as the crude was diluted with heptane, pentane, and cyclohexane. Linear alkanes-containing systems exhibit a two-stage behavior, whereas only one is found when diluting with cyclohexane. Dispersing agents were tested by using the precipitate height as a criterion of effectiveness. Results are reported for ethoxylated nonylphenols and a commercial dispersant.     

Effects of Catalyst Properties on Asphaltenes Composition During Hydrotreating of Heavy Oils

Three NiMo commercial catalysts were used for carrying out hydrotreating (HDT) experiments in a high-pressure pilot plant. Maya crude oil was employed as HDT feed. All hydrotreated products and their corresponding precipitated asphaltenes fractions were characterized by elemental analysis and metals contents. Extraction of asphaltenes was carried out according to the method described in ASTM D-3279. It was observed from our characterization results that while nitrogen and metals content in asphaltenes increase sulfur decrease as the reaction temperature is increased. This different behavior was attributed to the localization of each heteroatom in the asphaltene molecule. Pore size of catalysts showed the major influence on hydrotreated product asphaltenes composition.     

Changes in Asphaltenes Properties Modified with Fe in Hydrotreating Reactions

Abstract

The properties of the Hamaca of asphaltenes extra-heavy crude oil (AsfH) of Petroliferous Orinoco Belt can be modified for evaluating the changes produced with hydrotreating (HDT). One characterized the solid modified by means of UV-visible spectroscopy and nuclear magnetic proton resonance (NMR ¹H). The samples were put under hydrotreating to 200°C to avoid thermal cracking, atmospheric pressure, and a flow of feeding of 10.5 mL/hr in a fixed-bed reactor in the presence of H₂S generated in situ. The reactivity was followed by gas chromatography (GC). All the samples were evaluated before and after being hydrotreated by ¹H NMR, total sulfur analysis, and determination of molecular weight average by vapor pressure osmometry (VPO). The obtained results suggest the iron possibly is inserted in the structure of the asphaltene forming a new active phase catalytically, presumably a mixed sulfide (pyrrotite type) of iron-metal of transition (V and Ni) present in the asphaltene.     

Study of Asphaltene Precipitation Using Refractive Index Measurement

Abstract

The measurements of the refractive index of crude oils were utilized in this work to enhance the understanding of the behavior of asphaltenes in crude oil, specifically, their tendency to precipitate from crude oil. The onset of asphaltene precipitation was measured in eight crude oil samples, which were titrated with either heptane or pentane in order to induce precipitation of the asphaltenes. The refractive index of each sample was measured to find its relationship to asphaltene precipitation. The assumption that refractive index of a mixture is a linear combination of the refractive indexes of the individual components was verified. It was also found that mixtures of heptane or pentane and crude oil also followed this same behavior. However, as asphaltenes began to precipitate from the solution, the refractive index no longer followed this linear mixing rule. Careful analysis of the refractive index data for each of the crude oil samples revealed many interesting relationships between the refractive index data and the content of the different polar asphaltene fractions present. The refractive index of asphaltenes was predicted from the refractive index data of crude oils. The results suggest the possibility predicting the properties and characteristics of the asphaltenes contained in a crude oil simply by measuring the refractive index.     

Asphaltene Deposition under CO2 Injection: An Experimental Study of the Bangestan Reservoir of Ahwaz Oilfield,SW Iran

Abstract

It is essential that precipitation of asphaltenes is recognized early in the planning stage of any CO₂ enhanced oil recovery (EOR) project so that appropriate testing can be performed to evaluate whether there will be a negative impact on reservoir performance. This article presents detailed evaluations of slim tube data that were obtained during CO₂ injection using a medium-gravity Iranian crude oil.

A crude oil from Bangestan reservoir of Ahwaz oilfield containing 18.2% asphaltenes with ~31.5 °API gravity was flooded by purified CO₂ (>96% CO₂) in a slim tube apparatus under 2,700 psi at 110°C. We were going to determine the minimum miscibility pressure (MMP) of the sample oil under injection of CO₂ flood, but when a CO₂ slim tube test was performed for this oil at 2,700 psi, less than half of the saturated oil in the tube was recovered, which implied that the displacement process was immiscible. At this pressure, the asphaltene deposition in the slim tube apparatus was so severe that even a pressure gradient of 6,200 lb/in² was not able to displace any fluid through the capillary tube. Therefore, we abandoned MMP determination with this sample and investigated the problem.

Due to the high percentage of asphaltenes in the sample, using the slim tube MMP as an apparatus for determining minimum miscibility pressure of CO₂ and sample oil can be misleading.     

Effect of pressure,temperature, and mass fraction of CO2 on the stability of the asphaltene constituents in crude oil

This paper focus on the main influence factors (temperature, pressure, and mass fraction of CO₂) on the state of asphaltene in the crude oil during CO₂ flooding by using high temperature and high pressure microanalysis system of solid precipitation. For the simulated oil sample – CO₂ system, the state of asphaltene is not affected by temperature within this range of 50°C to 100°C, the particle size of the asphaltene has an increase with the increase of the pressure from 8MPa to 40 MPa. When the mass fraction of CO₂ is less than 35%, the state of the asphaltene has not changed and the asphaltene particles are in a suspension state. When the mass fraction of CO₂ increases to 40%, the aggregation of the asphaltenes occurs and then form precipitation. With the further increase of the mass fraction of CO₂, the particle of the asphaltene aggregates has a significant increase. For the field development project design of CO₂ flooding, the influence of the temperature can be ignored, the appropriate mass fraction of CO₂ is below 35% and the gas injection pressure should maintain a relatively low value. The results can provide a theoretical basis to avoid the asphaltene precipitation during CO₂ flooding.     

NEW TECHNIQUES AND METHODS FOR THE STUDY OF AGGREGATION, ADSORPTION, AND SOLUBILITY OF ASPHALTENES. IMPACT OF THESE PROPERTIES ON COLLOIDAL STRUCTURE AND FLOCCULATION

The solubility of Furrial asphaltene in toluene was 57g L^-1. However, using a new technique, based on the precipitation of this sample by the phenol PNP, we found that a fraction [2], comprising 47% of the asphaltene, is of low solubility. This suggested that this material constitutes the colloidal phase, and the rest acts as the dispersing fraction. This technique allowed the fractionation of asphaltenes in fractions A₁, A₂, and A₃ according to solubility, going from practically insoluble (A₁) to low (A₂, 1 g L^-1) to high (A₃, around 57 g L^-1). The adsorption isotherms of asphaltenes on glass and silica in toluene consist of a sequence of steps or step-wise adsorption. The first layer or first step is formed by the adsorption of free asphaltene molecules and by small aggregates (aggregation number between 3 and 6) which saturate the glass or silica surface in the usual manner (L-type or H-type isotherms). However, we suggest that the second, third, and other asphaltene layers adsorb sequentially according to the above differences in solubility. The very slow changes with time and the negligible desorption from the surface measured for the above isotherms were interpreted as the effect of packing or the building up of a well packed layer. This would be achieved by the slow formation and rupture of bonds between neighboring molecules at the surface. Thus, molecules with difficulties to pack, adsorbed by a kinetically controlled process, are either rejected or relocated in a thermodynamic controlled process. The above results and ideas were used to improve the models for asphaltene and petroleum colloids and to underscore the importance of surfaces and colloid dispersants in asphaltene precipitation during the production of crude oils. For instance, the results described below suggest that colloids are constituted by a well packed and insoluble asphaltene core, impervious to the solvent, and by a loose packed periphery which, by allowing solvent penetration, keep the colloid in solution. According to this model, desorption of compounds in the above loosely packed periphery, such as the one promoted by a surface, would be the main cause of asphaltene precipitation from crude oils. In this case, solubility reductions caused by pressure drops during oil production would have a minor effect. Also, preliminary number average molecular weights M_n for four asphaltenes, obtained using a new procedure, are presented here. The M_n values obtained ranged from 780 to 1150 g/mol.     

PEPTIZATION AND COAGULATION OF ASPHALTENES IN APOLAR MEDIA USING OIL-SOLUBLE POLYMERS

ABSTRACT

The asphaltene fraction of crude oil contains a variety of acidic and basic functional groups. During oil production and transportation, changes in temperature, pressure or oil composition can cause asphaltenes to precipitate out crude oil through the flocculation among these polar functional groups. In this study, two types of oil-soluble polymers, dodecylphenolic resin and poly (octadecene maleic anhydride), were synthesized and used to prevent asphaltenes from flocculating in heptane media through the acid-base interactions with asphaltenes. The experimental results indicate that these polymers can associate with asphaltenes to either inhibit or delay the growth of asphaltene aggregates in alkane media. However, multiple polar groups on a polymer molecule make it possible to associate with more than one asphaltene molecule, resulting in the hetero-coagulation between asphaltenes and polymers. It was found that the size of the asphaltene-polymer aggregates was strongly affected by the polymer-to-asphaltene weight (or number) ratio. At low polymer-to-asphaltene weight ratios, asphaltenes keep flocculating with themselves and with polymers until the floes precipitate out of solution. On the other hand, at high polymer-to-asphaltene weight ratios, asphaltene-polymer aggregates peptized by the extra polymer molecules can remain fairly stable in the solution.     

SEPARATION OF ASPHALTENES BY POLARITY USING LIQUID-LIQUID EXTRACTION

ABSTRACT

In order to investigate the nature of petroleum asphaltenes in terms of polarity a process was developed using initial liquid-liquid extraction of the oil phase followed by precipitation of the asphaltenes using n-heptane. The liquid-liquid extraction was performed using toluene-methanol mixtures with increasing content of toluene. Although large fractions of the crude oil (Alaska '93) was extracted in the higher polarity solvents (high concentration of methanol), the asphaltene content of the dissolved material was low As the toluene content increased more asphaltenes were transferred to the solvent phase. The asphaltenes were analysed using FTir, Elemental analysis, and HPLC-SEC with a diode array detector. With increasing content of toluene in the methanol the molecular weight distribution of the asphaltenes significantly move to higher molecular weights. The content of nitrogen and sulfur of the mallene phase also increase while H/C decreases. The content of heteroatoms in the asphaltenes are relatively higher and apparently increase with the polarity of the solvent. It is concluded that these asphaltenes are indeed dominated by high molecular weight substances that cannot be extracted in the high polarity solvents     

含油气系统Re⁃Os定年及Re⁃Os元素和同位素体系研究新进展

近年来,铼—锇（Re?Os）同位素体系在含油气系统的生油—成藏、热裂解和热化学硫酸盐还原反应等事件的定年,以及油源示踪过程中取得了一系列的成果。Re和Os在原油的沥青质组分中含量较高,同时也在沥青质较早沉淀出来的次组分中含量较高,沥青质与可溶质以及沥青质的次组分之间的Re?Os同位素组成关系复杂。实验表明水中的Re和Os能快速、大量地转移到原油中去。Re?Os同位素体系在油气成藏年代学中具有很好的应用前景。不过,多个原油样品的Re?Os定年法得到的年龄一般不确定度较大,而利用单个原油次组分Re?Os定年法获得的年龄的地质意义有待探讨。Os同位素组成的均一机制、 Re?Os体系的封闭性以及在原油中Re和Os以何种形式存在等问题仍需要进一步研究。     

Determination of the functional groups and the melting point of iraqi asphaltenes

A qualitative analysis study of n-C5 asphaltene of Iraqi crude oil from (Al-Dura, Kirkuk and Basra) oil fields was done using Fourier transform infrared spectroscopy (FT-IR). The melting points of the three oil derived asphaltenes were determined using Hot stage polarizing microscope at 180?°C for Al-Dura, 125?°C for Kirkuk and 140?°C for Basra asphaltenes. The FTIR spectrum shows an aromatic behavior of the asphaltene samples at a wavelength of 3049?cm^?1 and aliphatic chains were found at wavelengths 2924?cm^?1.     

Effect of Different Aromatic Fractions on Colloidal Property of Tahe Atmospheric Residue

Different amounts of FCC slurry oil and HVGO were added to Tahe atmospheric residue respectively.The colloidal stability and asphaltene agglomeration of atmospheric residue and mixed oils were characterized by means of the mass fraction normalized conductivity and the small-angle X-ray scattering technology(SAXS).The results indicated that the stability of Tahe atmospheric residue decreased with an increasing amount of these oil fractions.It was found that the decline of the colloidal stability was attributed to the component polarity difference between oil fractions and the atmospheric residue.Though the aromaticity of FCC slurry oil was higher than that of HVGO,the polarity of aromatics and resins of FCC slurry oil was lower than those of HVGO.So the degree of the colloidal stability was more seriously destroyed by FCC slurry oil.The dispersion of asphaltenes in Tahe atmospheric residue was changed by adding FCC slurry oil and HVGO.The particle size of asphaltenes increased along with the decline of the colloidal stability.     

Spectroscopic Characterization of Asphaltene Fraction of Nigerian Bitumen

This research article offers data on the spectroscopic elucidation of the asphaltene fraction of Nigerian bitumen in order to establish its features that might aid the developmental processes of the fossil fuel. Bitumen was extracted from the oil sands obtained from six locations where there were oil sand out-crops in Southwestern Nigeria using toluene via Soxhlet extraction and then deasphalted using n-pentane. The organic components of the precipitated asphaltenes were investigated using Fourier transform infrared spectrometry, while the elemental contents were determined using Inductively coupled plasma atomic emission spectroscopy and carbon/nitrogen analyzer. The results revealed that the average content (29.15 wt%) of Nigerian bitumen asphaltenes was less than that of Athabasca (40.10 wt%) but slightly higher than that of Cold Lake bitumen (24.40 wt%). The IR spectra of the asphaltenes indicated the presence of various organics and heteroatoms corroborating that asphaltenes composed of high molecular weight polycyclic constituents comprising of nitrogen, sulfur, and oxygen heteroatoms. The results indicated that the values of Cr, Cu, Fe, Mn, Ni, S, V, and Zn were comparatively higher in the asphaltenes than the parent bitumen due to the presence of comparatively high levels of porphyrins in the asphaltenes than the bitumen, while the concentrations of all the elements were higher in the Nigerian bitumen asphaltene than Nigerian crude oil asphaltene (except S and C). Cross plot analysis result between the asphaltenes and bitumen using their elemental mean concentrations as variables indicates that significant and positive correlation (R² = 0.975) exists between them, indicating very strong interelement and geochemical relationships between them. The elements showed close clustering, indicating similar sources because the elements were known to associate with petroleum hydrocarbon formation. Also, apart from N, S, and C, other elements are transition metals with similar chemical affinity.     

PHYSICAL AND CHEMICAL CHARACTERIZATIONS OF ASPHALTENES FROM DIFFERENT SOURCES

ABSTRACT

Asphaltenes and resins are two of the several, but important, heavy organics present in petroleum fluids. Asphaltenes are operationally defined as the non-colatile and polar fraction of petroleum that is insoluble in n-alkanes (i.e., n-pentane). Conversely resins are defined as the non-colatile and polar fraction of petroleum that is soluble in n-alkanes (i.e., n-pentane), and aromatic solvents (i.e., toluene), and insoluble in ethyl acetate. A commonly accepted view in the petroleum chemistry is that crude oil asphaltenes form micelles which are stabilized by adsorbed resins kept in solution by aromatics. Two key parameters that control the stability of asphaltene micelles in a crude oil are the ratio of aromatics to saturates and that of resins to asphaltenes. When these ratios decrease, asphaltene micelles will coalesce and form larger aggregates. The precipitation of asphaltene aggregates can cause problems such as reservoir plugging and wettability reversal.     

Study of Asphaltene Precipitation Using Refractive Index Measurement

The measurements of the refractive index of crude oils were utilized in this work to enhance the understanding of the behavior of asphaltenes in crude oil, specifically, their tendency to precipitate from crude oil. The onset of asphaltene precipitation was measured in eight crude oil samples, which were titrated with either heptane or pentane in order to induce precipitation of the asphaltenes. The refractive index of each sample was measured to find its relationship to asphaltene precipitation. The assumption that refractive index of a mixture is a linear combination of the refractive indexes of the individual components was verified. It was also found that mixtures of heptane or pentane and crude oil also followed this same behavior. However, as asphaltenes began to precipitate from the solution, the refractive index no longer followed this linear mixing rule. Careful analysis of the refractive index data for each of the crude oil samples revealed many interesting relationships between the refractive index data and the content of the different polar asphaltene fractions present. The refractive index of asphaltenes was predicted from the refractive index data of crude oils. The results suggest the possibility predicting the properties and characteristics of the asphaltenes contained in a crude oil simply by measuring the refractive index.     

AGGREGATION OF ASPHALTENES OBTAINED FROM A BRAZILIAN CRUDE OIL IN AROMATIC SOLVENTS

Abstract

Surface and interfacial tensions in model systems formed by a Brazilian crude oil n-pentane insolubles (C5I) and n-heptane insolubles (C7I) in three different aromatic solvents: toluene, pyridine and nitrobenzene, were measured at room temperature, employing an automatic tensiometer and using the ring method. The results obtained indicated possible asphaltene aggregation and allowed the determination of critical micelle concentrations (c.m.c) for both C5I and C7I fractions in each of the three solvents considered. In toluene and pyridine solutions, the C5I fraction consistently presented higher c.m.c. values indicating a lower tendency of association for the organic fraction contained in the C5I, and absent in the C7I. In nitrobenzene solutions, this extra organic fraction appears to facilitate asphaltene association, possibly due to the formation of mixed aggregates. Average molecular areas for asphaltenes adsorbed at different interfaces were estimated using measured tensions and found to be in agreement with literature values and suggest a the flatwise surface adsorption of asphaltene molecules. This is consistent with the currently accepted stacking aggregation mechanism of asphaltenes.     

Fractionation of resins and asphaltenes and investigation of their composition and structure using heavy oil from the Usa field as an example

Asphaltenes and resins of crude oil from the Usa oil field have been subjected to fractionation. The asphaltenes have been separated into fractions by fractional precipitation with chloroform/hexane solvent blends in the ratios of 30/70, 30/75, and 30/120. The resins have been fractionated by liquid adsorption chromatography on silica gel with hexane/benzene and hexane/ethanol mixed solvents taken in the ratios of 3/1, 1/1, and 10/1, 3/1, respectively. The obtained fractions have been analyzed by ¹H and ¹³C nuclear magnetic resonance spectroscopy and infrared spectroscopy, their molecular masses have been measured, and the elemental composition has been investigated. On the basis of structuralgroup analysis data, the structures of the resin and asphaltene molecules have been hypothesized.     

CATALYTIC HYDROTREATMENT OF PETROLEUM RESIDUE

ABSTRACT

Iraqi reduced crude (350°C+) with a sulfur content of 4.3 wt% and a total metal content (Ni+V) of 141 WPPM was n-heptane deasphalted at specified conditions. The deasphalted oil (97.2 wt% of original residue) contains 4.1 wt% of sulfur and 103 ppm of metal. The original reduced crude and deasphalted oil were hydrotreated on a commercial Ni-Mo-alumina catalyst presulfided at specified conditions in a laboratory trickle-bed reactor. The reaction temperatures varied from 300 to 420°C with the liquid hourly space velocity (LHSV) ranging from 0.37 to 2.6 h^?1. Hydrogen pressure was kept constant throughout the experiments at 6.1 MPa, with a hydrogen/oil ratio of about 300 NLL^?1 (normal liters of hydrogen per liter of feedstock). Analysis for sulfur, nickel, vanadium and n-pentane asphaltenes were carried out for hydrotreated products from both the original residue and the deasphalted oil. The comparison of the results obtained for the hydrotreatment of deasphalted oil and original reduced crude indicates that the removal of sulfur, nickel and vanadium was higher for the deasphalted oil than those obtained for the non-deasphalted residue over the entire range of conversion. The exclusion of extremely high molecular weight asphaltenes by n-heptane deasphalting seems to improve the access of oil into catalyst pores resulting in higher desulfurization and conversion of the lower molecular weight asphaltenes. The sulfur content of n-pentane precipitated asphaltenes remained unchaneed with LHSV for various temperature for hydrotreated products produced from both deasphalted oil and original reduced crude.     

Test Methods for Determining Asphaltene Stability in Crude Oils

Abstract

The high cost of remediating asphaltene deposition in crude oil production and processing has necessitated the development of test methods for determining the stability of asphaltenes in crude oils. In the current work, the stability of asphaltenes in crude oils of varying API gravity is predicted using the Oliensis Spot Test, the Colloidal Instability Index, the Asphaltene–Resin ratio, and a solvent titration method with NIR solids detection. The test methods are described in detail and experimental data from them presented. The experimental stability data were validated via correlation with field deposition data. The effectiveness of the various tests as predictors of the stability of asphaltenes in oils is discussed. The Colloidal Instability Index and the solvent titration method were found to predict a crude oil's propensity towards asphaltene precipitation better than both the Asphaltene–Resin ratio and the Oliensis Spot Test. For oils with low asphaltene content where most stability tests fail, live oil depressurization is proposed as the test for predicting the stability of asphaltenes.