Absorbance and fluorescence spectroscopy on the aggregation behavior of asphaltene-toluene solutions

Evidence of crude oil stability and the tendency of asphaltene aggregation in crude oil have been investigated by absorption and fluorescence spectroscopy. Octylated asphaltenes were also used as reference because of their low aggregation tendency. Changes in the absorbance vs. concentrations in toluene solutions show that aggregation starts around 50 mg/l for Furrial asphaltene and approximately at 75 mg/l for Hamaca asphaltenes. Red shift and quenching in the fluorescence peak maximum observed for solutions when asphaltenes concentrations are increased demonstrate that the aggregation process starts at low concentration regime. These experimental results are consistent with the fact that Hamaca asphaltenes have lower tendency to aggregate than asphaltenes from Furrial crude oils. Our results verify that the tendency to form aggregates diminishes in the octylated form.     

沥青质/胶质影响稠油乳状液稳定性的研究

对稠油乳状液的稳定性进行了研究,研究发现,沥青质和胶质作为天然的乳化剂,对稠油乳状液的稳定性有较大的影响,沥青质的分散性是影响乳状液油水界面膜强度的重要因素,胶质是沥青质的良溶剂,和沥青质具有强的协同作用,同时发现在稠油中添加溶解剂对沥青质的分散性有较大的改善,从而增强了稠油乳状液的稳定性。研究认为,胶质含量为4%,沥青质含量为0.5%的情况下,乳状液稳定性较好,并且随着两者的大量增加或者减少,都不利于稠油乳状液的稳定性。     

沥青质和胶质对乳状液稳定性的影响

利用光学显微镜-摄像-录像-计算机图象处理系统研究了大庆原油的沥青质和胶质对乳状液稳定性的影响.结果证实,原油乳状液的稳定性与沥青质和胶质浓度有关,沥青质和胶质的分散状态是决定界面膜强度或刚性进而决定乳状液稳定性的关键.当沥青质浓度在0.3%～0.5%（质量分数）,胶质浓度在1%～2%（质量分数）范围时,乳状液水珠聚并的比例随表面活性物质浓度的增加而降低;当沥青质浓度增大到0.7%（质量分数）,胶质浓度增大到3%（质量分数）后,聚并水珠的比例随表面活性物质浓度的增加而增加,形成的乳状液的液滴数量也减少.     

Permeability reduction by asphaltenes and resins deposition in porous media

The deposition of crude oil polar fractions such as asphaltenes and resins in oil reservoir rocks reduce considerably the rock permeability and the oil production. In the present work, a crude oil and various core samples were extracted from Rhourd–Nouss (RN) reservoir rock. Afterwards, core flow experiments were carried out in the laboratory to investigate permeability reduction that causes formation damage. The core permeability damage was evaluated by flooding Soltrol, through the sample and measuring the solvent permeabilities, K_i and K_f, respectively, before and after injection of a given pore volume number of the crude oil.The data indicate that upon flooding the crude oil through the porous medium, considerable permeability reduction, expressed as the ratio (K_i − K_f)/K_i, and ranging from 72.4% to 98.3% were observed. The permeability reduction is found to result from irreversible retention of asphaltenes and resins in the porous core sample. However, no correlations could be established between the depth of the well, the core porosity, the core mineral compositions determined by X-ray analysis, and the permeability damage factors. In addition, effluents flowing away from RN wells were collected and analysed at various periods, after carrying out aromatic solvents squeezes. The amount of saturates, aromatics, resins, and asphaltenes (SARA analysis), of the crude oil, the deposited crude oil fraction, and the effluent’s residues were measured and compared. The asphaltenes weight percent was found to increase from 1.56% for the crude oil to 11.42% for the deposited oil fraction, and was in the range 1.37–2.36% for the effluent’s residues. Such results indicate that the deposited oil fraction and the effluent’s residues consist mainly of asphaltenes and resins.     

Effect of Resins on Asphaltene Self‐Association and Solubility

In previous studies, asphaltenes and resins have been treated as two distinct fractions of a crude oil. The asphaltenes were assumed to be the only self‐associating fraction. However, there is evidence that resins also participate in this self‐association. In this study, molar masses of mixtures of asphaltenes and resins were measured with vapour pressure osmometry. Precipitation from the same mixtures dispersed in solutions of toluene and pentane were also measured. The data were modelled with previously developed self‐association and precipitation models. Model results with asphaltenes and resins characterized as a single distribution and as individual components are compared. The data and the modelling suggest that asphaltenes and resins are better characterized as a single distribution of self‐associating components.     

BA原油沥青质性质及沉积抑制剂作用机理

原油开发中出现沥青质沉积问题，会导致油井及集输管线堵塞，从而影响原油正常生产和油田的高效开发。本文通过对BA原油中沥青质进行元素、XPS和FTIR分析，可知该沥青质表面官能团以碳氢化合物（C-C，C-H）为主，还含有硫酚和硫醇等脂肪类硫以及羧基等酸性官能团，可为沥青质沉积抑制剂的选择提供理论依据。抑制剂是通过破坏沥青质缔合体的相互作用来达到抑制聚沉的作用，利用激光粒度仪对原油加正庚烷（沉淀剂）后沥青质颗粒的粒度分布进行测定，结果表明：在油样中加入含有胺基碱性基团的抑制剂FAE183，能抑制沥青质的絮凝与沉淀，使沥青质颗粒的粒径显著减小。由抑制剂的作用机理分析可知，FAE183抑制剂与沥青质的主要作用机理为酸碱作用，并辅以氢键作用和偶极作用。     

Influence of water-soluble and water-insoluble natural surface active components on the stability of water-in-toluene-diluted bitumen emulsion

Bitumen, a very heavy crude oil, contains both water-soluble and water-insoluble natural surface active species. This study shows that complete removal of the water-soluble surface active species from bitumen by water extraction resulted in an increased emulsion stability and that the water-insoluble surface active asphaltenes are the key stabilizing agents for water-in-toluene-diluted bitumen emulsions. Separation of the toluene-diluted bitumen continuous phase from the emulsion by centrifuging at 1, 10, 100, 1000 and 10,000g was conducted. Emulsion stability tests for the separated toluene-diluted bitumen and element analysis of the precipitated asphaltenes indicated that the asphaltenes in the separated organic continuous phase are different from those associated with the water droplet interface. The asphaltenes associated with the interface had a lower H/C ratio and a higher O/C ratio.     

Dilational rheological properties of interfacial films containing Branch‐Preformed particle gel and crude oil fractions

Dilational rheology method was used to study the interfacial rheology properties of Branch‐Preformed Particle Gel (PPG) and its interaction with Shengli crude oil fractions at the kerosene/water interface. The results showed that the interfacial dilational modulus increased monotonously with increasing PPG concentration, the high values of the modulus could be due to the formation of multilayer near the interface. Study on the interaction between PPG and crude oil components showed that different crude oil components have different interactions with PPG molecules at the oil/water interface. The acidic components can adsorb onto the interface and form mixed adsorption film by replacing the PPG molecules at the interface because of their smaller molecular size and stronger interfacial activity, which results in a dramatic reduction in dilational modulus, while asphaltenes have little effect on the dilational rheological behavior of PPG solution due to their lager molecular sizes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41337.     

Characterization of the wax precipitation in Mexican crude oils

This paper reports the rheological and thermodynamic characterization of the wax formation phenomenon in three Mexican crude oils where the effect of waxes and asphaltenes content on wax precipitation and rheological behavior of crude oils is evaluated and discussed. Wax appearance temperature is measured by using differential scanning calorimetry, rheometry and densitometry. The wax precipitation curves were obtained by fourier transform infrared spectroscopy. Pour point temperatures were evaluated according to the ASTM-D97 method, whereas gelation temperatures were determined by rheological experiments made with a controlled-stress rheometer. Waxes of the crude oils were separated and characterized by gas chromatography/mass spectrometry and differential scanning calorimetry. The methods used in this work for the wax appearance temperature determination showed to be sensitive to the crude oil composition. Results showed that the presence of asphaltenes impacts significantly the liquid–solid equilibrium and rheological behavior of the crude oils studied whereas the wax melting temperature was a key factor to evaluate the propensity of crude oils to present wax precipitation problems.     

Fullerenic structures derived from oil asphaltenes

The handling and properties of heavy oils are becoming an increasingly important problem. Even though petroleum is the widest used source of fuels and it has been studied for decades, its complex nature is still an enigma in several ways. A reasonable approach to a definition of a crude oil is a colloidal fluid formed by several dispersed phases from gases (light hydrocarbons) to solids (heavy paraffins and asphaltenes). Through all these years of research, applications have been found for almost all classes of components in crude oil except for some of the solid phases such as asphaltenes. Very heavy petroleum is a non-newtonian liquid with a viscosity of ≈10⁶ Poise, and an average molecular weight of 600 amu. The solids that are toluene soluble but heptane insoluble are called asphaltenes and are the most aromatic fraction with the highest molecular weight of unconverted petroleum. In the present work, we applied high resolution transmission electron microscopy (HREM) and energy dispersive spectrometry (EDS) in the study of asphaltenes. It was found that when the asphaltenes are well separated from the resins the sample consists of a carbon structure containing S, V, Si, related to fullerenic carbon. During observation in the microscope it was possible to see the formation of fullerenes such as onions and C₂₄₀ @ C₆₀ structures. The fact that they decomposed under further irradiation suggests that they are metastable structures. Since the heteroatoms are still present they are likely to cause instability to the structure. Not only does our result indicate the possibility of obtaining fullerenes from crude oil but it also suggests the asphaltene molecule, when it is resin free, might be a precursor of fullerenic structures.     

Pyrolysis and Pt(IV)- and Ru(III)-ion catalyzed pyrolysis of asphaltenes in organic geochemical investigation of a biodegraded crude oil (Gaj, Serbia)

This paper is aimed at investigating the origin and geological history of the biodegraded Gaj (Serbia) crude oil, based on comparison of biomarkers, particularly alkylaromatics, in crude oil maltene fraction, with those in the liquid raw asphaltene pyrolysis products. The content of asphaltenes in crude oils being generally very low, expecting a higher yield of pyrolysate, pyrolysis of raw asphaltenes was also carried out in the presence of Pt(IV)- and Ru(III)-ions. The used metal ions demonstrated positive effects on the yields of total liquid pyrolysate and corresponding hydrocarbons. Occluded maltene and asphaltene pyrolysis products showed that metal ions had considerably stronger effect on maturation changes in naphthalene and phenanthrene rings than in polycyclic alkanes. The values of maturity parameters observed in maltenes and pyrolysates suggested this crude oil to have been expelled from the source before the “oil window” maximum. The investigated sample of the Gaj crude oil was shown to be in the 4th stage of biodegradation scale and to have originated from source rocks poor in clays, most probably carbonates, with significant contribution of algae to oil precursor biomass, deposited under a stratified saline water column.     

The zeta potential and surface properties of asphaltenes obtained with different crude oil/n-heptane proportions

We have investigated some surface properties of asphaltenes precipitated from crude oil with different volumes of n-heptane. According to the crude oil/n-heptane proportions used, asphaltenes are identified as 1:5, 1:15 and 1:40. Zeta potential results indicate that the amount of n-heptane determines the electrokintetic behaviour of asphaltenes in aqueous suspensions. Asphaltene 1:5 exhibits an isoelectric point (IEP) at pH 4.5 whereas asphaltenes 1:15 and 1:40 show an IEP at about pH 3. Surface charge on asphaltenes arises from the dissociation of acid functionalities and the protonation of basic functional groups. The presence of resins remaining on the asphaltene molecules may be responsible for the different IEP of asphaltene 1:5. Both sodium dodecyl sulfate (an anionic surfactant) and cetylpyridinium chloride (a cationic surfactant) were found to adsorb specifically onto asphaltenes. They reverse the sign of the zeta potential under certain conditions. These surfactants may be potential candidates to aid in controlling the stability of crude oil dispersions. Critical micelle concentration, interfacial tension measurements, and Langmuir isotherms at the air-water interface confirm the different nature of asphaltene 1:5, which also showed more solubility and a larger molecular size.     

Compositional Dependence of Wetting and Contact Angles in Solid‐Liquid‐Liquid Systems under Realistic Environments

The Dual Drop Dual Crystal (DDDC) contact angle measurement technique has been used in this study with a high‐pressure high‐temperature optical cell apparatus to measure dynamic contact angles in rock‐oil‐brine systems at realistic reservoir conditions of temperature and pressure. The experimental observations with live, stocktank, de‐asphalted and de‐resined crude oils indicate that the stability of oil, which determines the precipitation of asphaltenes for wettability alteration, is controlled by the entire oil composition. The ionic interactions caused by the brine composition and surface charged behaviour of rock substrates have been identified as another main mechanism that can affect wetting and contact angles in solid‐liquid‐liquid systems.     

Functions of Demulsifiers in the Petroleum Industry

There are an increasing number of crude oil fields that are now producing both crude oil and water emulsions; such fields are both onshore and offshore. These emulsions are formed during oil exploitation due to the presence of natural surfactants, such as asphaltenes and resins. These molecules strongly stabilize the water/oil interface and prevent coalescence of water droplets. As water/oil phase separation is necessary before oil transportation and refining, demulsifiers are used to break water-in-oil emulsions. This review presents the crude oil emulsion formation, factors affecting demulsification of crude oil emulsion such as demulsifier chemical structure, water content, partition coefficient (K_P), and demulsifier concentration. This review also covers the kinetics and mechanism of the demulsification process.     

Co-adsorption behaviors of asphaltenes and different flow improvers and their impacts on the interfacial viscoelasticity

Commonly used flow improvers in oilfields, such as ethylene–vinyl acetate copolymer (EVA), poly(octadecyl acrylate) (POA), and polymethylsilsesquioxane (PMSQ) are proven to be effective to enhance the flowability of crude oil. However, the addition of these flow improvers may change the stability of the emulsion and make the crude oil treatment process challenging. In this research, the impacts of different flow improvers on the interfacial properties of the emulsions containing asphaltenes are systematically investigated. The co-adsorption behaviors of the flow improvers and asphaltenes are analyzed through dynamic interfacial tension (DIFT). The rheological properties of the interfacial layer after the adsorption are explored via dilational viscoelasticity. Significant difference is observed in the structural properties of the interface adsorbed by different flow improvers, which is attributed to different interactions between the flow improvers and asphaltenes. To investigate these interactions, conductivity, asphaltenes precipitation, dynamic light scattering (DLS), and contact angle experiments are conducted systematically. Results show that EVA and POA can alter the interfacial properties by changing the asphaltene dispersion state. The interaction between EVA and asphaltenes is stronger than that between POA and asphaltenes due to the difference in molecular structures. Unlike EVA and POA, the change of interfacial property with the addition of PMSQ is attributed to the partial adsorption of asphaltenes on PMSQ.     

Liquid Chromatographic fractionation of oil-sand and crude oil asphaltenes

Asphaltenes extracted from Alberta oil sands (Athabasca, Cold Lake, and Peace River) and crude oils (Taber South and Fenn-Big Valley) were fractionated by sequential elution solvent chromatography (SESC) involving 10 organic solvents on a silica column. Athabasca asphaltenes and SESC fractions were further studied by elemental analysis, i.r., u.v., and n.m.r. spectroscopy. Incomplete extraction of maltenes from the oil-sand bitumens increased the yields of the first two SESC fractions, the saturates and aromatics, of oil-sand asphaltenes relative to the crude oil asphaltenes. About 55 wt% of the asphaltenes elute in fractions 3–5. Two distinct molecular types are present in the asphaltenes; namely, lower functionality species with lower heteroatom content and the higher functionality species with higher heteroatom content. Compounds eluting in fractions 3–10 are predominantly polynuclear aromatics with alkyl substituants and probably bridged by cycloalkanes. The extent of bridging as well as the location, number and type of heteroatoms determines the fraction in which each compound appears. Complexity of compounds eluting increases with time: earlier fractions are composed of smaller-size polynuclear aromatic centers and contain heteroatoms in predominantly ring locations, whereas later fractions contain a larger proportion of complex species and more functional heteroatom groups.     

RELAXATION OF ASPHALTENES AT THE TOLUENE/WATER INTERFACE: DIFFUSION EXCHANGE AND SURFACE REARRANGEMENT

Upon adsorption at the oil/water interface, asphaltenes slowly form a glassy interphase. This robust, asphaltene-rich interphase is likely the reason for prolonged stability of crude oil/water emulsions and for the propensity of asphaltenic crude oils to alter the wettability of reservoirs. Here we adopt interfacial dilatation rheology using the oscillating pendant drop with axisymmetric drop shape analysis (ADSA) to investigate the relaxation mechanisms of asphaltenes adsorbed at the toluene/water interface. We compare classical viscoelastic models with the measured rheologic data and find that the frequency response of the dilatational moduli fits a combination of diffusion-exchange and surface-rearrangement mechanisms. The combined relaxation model is verified by solvent washing the asphaltenes from the interface and measuring the dilatational response of the resulting irreversibly adsorbed species. After washout, the oil-phase diffusion component of the frequency response disappears, and the relaxation time of the adsorbed film increases by an order of magnitude. Since the studied asphaltenes prove insoluble in the synthetic aqueous brine (pH = 8.0), this result suggests that reversibly exchanging species in the oil phase weakens an interconnected asphaltene-gel/glass phase at the interface. Our experiments show, for the first time, that most of the surface-active asphaltenic molecules are irreversibly adsorbed from the oil phase.     

原油乳状液的稳定与破乳机理研究进展

综述了原油乳状液中天然表面活性物质 ,如沥青质、胶质、固体颗粒物以及石蜡对原油乳状液稳定性的影响。讨论了原油破乳机理和破乳剂组成、HLB值等物化性质、破乳剂用量、复配与原油破乳脱水的关系。同时介绍了目前国内使用较多的几个系列破乳剂。     

Evaluation of the influence of polyoxide‐based surfactants on the separation process of model emulsions of asphaltenes using the FTIR‐ATR technique

During extraction of crude oil, water is generally present in the oil. This water‐in‐oil (w/o) mixture undergoes turbulent flow that promotes sheer forces, resulting in the appearance of emulsions. These emulsions can be highly stable due to the presence of compounds with polar characteristics such as asphaltenes, which act as natural emulsifiers and form resistant films at the oil–water interface. Nonionic surfactants based on polyoxides are widely used to prevent the formation or to break down w/o emulsions. To shed more light on the destabilization mechanism of w/o emulsions promoted by these surfactants, in this study the techniques of tensiometry and Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR‐ATR) were applied to study the interface formed by poly(ethylene oxide)‐poly(propylene oxide) (PEO‐PPO) block copolymers and asphaltenic petroleum fractions. Initially, the critical micelle concentration of the copolymers in aqueous solution was determined. The results agreed with those found by tensiometry. The bottle test was used to evaluate the break‐down of the w/o emulsions in the presence of the PEO‐PPO block copolymers, and the results presented good agreement with those obtained by tensiometry and FTIR‐ATR. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of asphaltene content on the heavy oil viscosity at different temperatures

Asphaltene content plays an important role in determining the high viscosity of heavy oil. This paper presents an experimental and theoretical study of the specific effects of asphaltene content on the heavy oil viscosity at different temperatures. In the experiment, a deasphalted heavy oil is obtained by using a standard ASTM method to precipitate asphaltenes from a crude heavy oil. Then eleven reconstituted heavy oil samples are prepared by adding the precipitated asphaltenes into the deasphalted heavy oil at a different asphaltene content each time. The viscosities of such reconstituted heavy oil samples with different asphaltene contents are measured at six different constant temperatures by using a cone-plate viscometer. Theoretically, two viscosity models for a colloidal dispersion system are applied to find the best fit to the experimental data by using non-linear regression. The following four important parameters are thus determined to characterize the reconstituted heavy oil samples: the solvation constant, shape factor, intrinsic viscosity, and maximum packing volume fraction. The detailed non-linear regression results show that the state of asphaltene particles in the heavy oil changes with the asphaltene content and temperature and that this state change strongly affects the heavy oil viscosity.