ABSTRACTS ACCEPTED FOR THE CONFERENCE

The paper and poster abstracts appear below and are organized according to their respective sessions. Use the following links to access the sessions:

• Session on Upgrading and Fouling Downstream
• Session on Flow Assurance
• Session on Characterization of Petroleum Macromolecules
• Session on Thermodynamics of Heavy Oils and Asphaltenes
• Session on the Chemistry and Physics of Petroleum-Water Emulsions

Session on Upgrading and Fouling Downstream

Irwin Wiehe - Keynote Presenter

Perspectives on Refinery Fouling Mitigation

At a time when incentives for refinery fouling mitigation are at a peak to increase refinery utilization and energy conservation, recent progress and future needs will be reviewed. The oil compatibility model and tests have provided the basis to avoid asphaltene fouling in crude heat exchangers and distillation furnaces. When combined with the phase-separation kinetic model for coke formation, a method for diagnosis and mitigation of coke formation in resid conversion units has been developed. By checking for the presence of natural hydrogen donors, a hypothesis in the phase-separation kinetic model, new insight about the thermal chemistry of resids and about the structure of asphaltenes has been revealed. Meanwhile, the understanding of the polymerization of conjugated olefins of volatile liquid products of cokers has enabled the mitigation of another class of refinery fouling. As a result, the refinery fouling by organics has been elevated from the least to the best understood and easiest to mitigate. Today, the greatest challenge is to mitigate fouling by inorganics caused by stable emulsions in desalters, by corrosion with hydrogen sulfide and with naphthenic acids, and by minerals, such as clay, dispersed in the crude oil. In addition, there is a great opportunity to reduce the adhesion of foulants on process surfaces and to take advantage of shear stress for removal.

Mietek Boduszynski - Paper

Some Aspects of Heavy Oil Composition and Upgrading

Characterization of heavy and extra heavy oils continues to be a challenge. Conventional crude assays provide only limited information on attainable product yield and property distribution of heavy oils, which have high vacuum residue content. This paper emphasizes the need to better understand the molecular nature of heavy oils for improved assessment of their processibility and value.

I will provide the overview of key aspects of heavy oil composition and their significance to upgrading processes. I will discuss such key heavy oil compositional characteristics as molecular weight distribution and hetero-element (S, N, V, Ni) distributions. I will also discuss the effect of hydrogen deficiency of heavy oil components on gravity and tendency to form coke.

Murray R Gray , Weidong Bi, and William C McCaffrey - Paper

Mechanisms of Liquid Phase Deposition of Coke during Residue Conversion

Fouling phenomena in crude oil processing, such as coke formation and deposition on surfaces, can involve a combination of kinetic, solubility, and colloidal processes. Hydrophobic fine solids in heavy oils can alter the yield of toluene-insoluble coke from thermal cracking at short reaction times. The mechanism of this interaction was investigated in order to understand its implications for liquid phase coking and fouling of process equipment.

Arab Heavy Vacuum Residue (AHVR) was mixed with a model fine solid in 1-methylnaphthalene (1-MN) and reacted in a batch reactor at 430 ° C under a nitrogen environment. Two hydrophobic fine solids, mesophase carbon and spherical graphite, were used as additives to study the coke formation on well-defined surfaces in a controlled geometry in liquid suspension. The mechanism of coke deposition was investigated by changing the ratio of AHVR to model solid in 1-MN, and analyzing the toluene-insoluble solid products by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS).

All results showed evidence that coke formed deposits on the surfaces of the two hydrophobic additives. The pathway of coke deposition depended on the ratio of AHVR to surface area of the fine solids. At very low ratios of AHVR to fine solids, the coke deposited directly on the surface of the fine solids in nanometer scale layers. As the ratio of AHVR to fine solids increased, a coke-like phase appeared to form first in the liquid phase as submicron scale spheres, which then deposited on model solids. These surface deposits of submicron material subsequently underwent further coalescence and fusion.

Simon Ivar Andersen, Veronica Torcal Garcia, Jesper Bartholdy - Paper

Hydrotreating vs Heat Treatement: Efffects on Asphaltene Stability and Chemistry during Resid Upgrading

To evaluate the various changes in the chemistry and thermodynamic stability of resids towards sludge formation during upgrading, the same feed was processed in a hydrotreater unit as well as in a batch coking unit at similar temperatures. In the past we have reported on effects, indicating that sludge formation was more rapid at high reactor temperatures, where cracking may dominate the hydrogenation. Since sludge formation is an unwanted process, it is relevant to design a resid upgrading process where sludge formation is avoided. The sludge chemistry was previously shown to be intimately linked to the asphaltene chemistry, however, with a balance towards the low molecular weight species. In the present work, the stability will be based on both flocculation onset titration and refractive index measurements, and the relation to the regular solution theory and the solubility parameter concept will be used in the evaluation of data. At the same time, the chemical composition of the asphaltenes will be monitored and related to the stability. The various methods to calculate solubility parameters as proposed in the literature will also be compared.

Alex Wu and Keng Chung - Paper

Hydrotreater Feed Filter Fouling and Its Solution

Hydrotreater feed filters remove large particulates (>25 µm) from gas oil streams to protect the hydrotreater reactors. Severe filter fouling occurred after a configuration change in a bitumen upgrading plant. It impeded the normal operations of the filter and the hydrotreater.

Fouling simulation in the lab using a miniature filter element confirmed that the problem was related to blending two compatible oils: coker heavy gas oil (KHGO) and heavy vacuum gas oil (HVGO) as part of the configuration change. Characterization of the foulant indicated that the fouling was caused by oxidative polymerization of certain polar species in KHGO by O 2 leaking into the system. Further study revealed that the role of HVGO was to provide a catalyst or a promoter of the fouling reaction. The likely candidates were naphthenic acid and iron naphthenate in HVGO. The latter was a corrosion product from the vacuum distillation unit (VDU). A thermal stress test on the gas oils was carried out using air, iron naphthenate and naphthenic acid as additives. Heptane-insoluble content was used as a benchmark to compare the fouling propensities of the stressed oils. The test indicated that iron naphthenate was the “culprit”. The fouling problem was finally solved by eliminating corrosion in VDU.

Bryan Fuhr, Branko Banjac, Tim Blackmore and Parviz Rahimi - Poster

Applicability of Total Acid Number Analysis to Heavy Oils and Bitumens

Industry has typically used the total acid number (TAN) analysis of a crude as a measure of its corrosivity in refinery processing, even though a quantitative correlation does not exist. TAN has thus become a crude specification for producers and refiners, whereas methods which measure the naphthenic acids, which are known to be corrosive, may be more relevant. High TAN's typically tend to give crudes a “bad name” and result in discounted prices. Often high TAN crudes are heavy, with densities in the 900 to 1000 kg/m 3 range, which includes most heavy oils and bitumens. The standard method employed for TAN, ASTM D664, was not even developed for crude oils. It covers the determination of acidic components in new and used refined petroleum products and lubricants. Heavy oils and bitumens present an even greater challenge than light crudes when attempting to apply the procedures in D664.

A project operated under the auspices of the Canadian Crude Quality Technical Association (CCQTA), examining the correlation between the TAN of Athabasca bitumens and corrosivity, encountered problems in applying D664. These problems were manifested by poor reproducibilities and resulted in a thorough review of the application of the method to bitumens. Factors considered were asphaltene precipitation, sample size and reagent concentrations, and correlation to a naphthenic acid extraction method. As a result of this study, modifications were suggested which related to initial sample handling, but did not significantly alter the basic test method. Employing these modifications, a small three-laboratory round robin using an Athabasca bitumen with a mean TAN of 3.30 mg KOH/g, yielded a reproducibility of 3% relative standard deviation.

Roberto Carlos da C. Ribeiro, Julio C. G. Correia, Peter R. Seidl, Jorge B. Soares - Poster

Assessment of Interactions Between Asphalts and Minerals

Asphalts are distillation residua from petroleum refineries and consist of different types of compounds, their chemical structures ranging from non-polar aliphatic hydrocarbons to aromatic sheet-like molecules known as asphaltenes.  Many problems encountered in exploration, transport and refining of heavy crudes have been related to the tendency of their constituents to form aggregates through stacking among fused aromatic ring systems.  These aggregates are thought to be dispersed in less-polar constituents (refered to as maltenes), the stability of these mixtures depending on the extent of interactions among aggregates and with foreign materials.  In the case of asphalts used for highway construction, the interactions of their respective constituents with the minerals will be mainly responsible for the mechanical resistance of a pavement.  In order to study asphalt/mineral interactions we have developed a simple procedure based on UV adsorption that reflects their mechanical resistance as determined by methods such as the Lottman test. Our results on two different asphalts and two minerals used in pavements is  consistent with other data, such as contact angle measurements.  The same procedure was also applied the respective asphaltene and maltene fractions of these asphalts and confirms that association depends mainly on the asphaltene constituents and is a function of their chemical structure.

Luis Castro, Luis Gallardo, Juan C. Pereira and Miguel A. Luis - Poster

Upgrading of Properties of Guafita Crude Oil Asphaltenes Employing Hydrotreating

This work has as its general objective to evaluate the insertion of transition metal (Co and Fe) in order to improve the properties of Guafita crude oil asphaltenes employing hydrotreating, to try to generate “in situ” metal sulphides that work as catalyst for HDT for improvement of heavy crudes. This is a preliminary work of a systematical study where diverse variables are proved. This investigation started with precipitate of asphaltenes of crude oil. Later, the metals Co or Fe were inserted homogeneous route or incipient impregnation, these asphaltenes were characterized with nuclear magnetic resonance and total sulfur in order to observe the changes. The asphaltenes with and without metal were proved in hydrotreating, the reaction products were evaluated with gas chromatography and mass spectrometry techniques and the asphaltenes were evaluated with nuclear magnetic resonance and total sulfur. Finally, the results show that methodology more efficient was homogeneous route and the metal with major influence on the macrostructure of the asphaltenes was the cobalt. Also the results of total sulfur indicate the influence of the hydrotreating showing a decrease after the process.

M. Vita Peralta-Martínez, Elvia M. Palacios-Lozano, Miriam E. García-Trujillo, Georgina Blass-Amador - Poster

Effect of SARA Fractions on Viscosity for Five Mexican Vacuum Residues

Five vacuum residues (Vr) from different Mexican refineries have been fractionated into their four principal components, Saturates, Aromatics, Resins and Asphaltenes, commonly known as SARA fractions. The determinations were made by means of the chromatographic separation technique, using a variation of the standard method ASTM D4124-01.

Safieva R.Z., Frolova T.S., Vasiliev A.E., and Syunyaev R.Z.

Effect of Laser Irradiation to Physical and Chemical Parameters of Diesel Fuels

The study of electromagnetic irradiation is a perspective direction of researches for the development of methods of management of the physico-chemical properties of multicomponent systems by reorganization of their microstructure. Volumetric sources of heat appear as a result of absorption of high-frequency electromagnetic radiation in the sample. Comparing that with the usual broadband signal use of monochromatic laser radiation is more effective because of the selectivity of chemical bonds in molecules. Phase transitions, movement of the interphase border, and change of dielectric characteristics of the environment occur as a consequence of this process. Interest in these problems is the result of an intensification of various processes of petroleum-and-gas technologies. In particular, an increase in the production of high viscous and bitumen petroleum; the fight against complications in wells and pipelines; problems associated with heavy organic depositions and the formation of gas hydrates; and the processing of water-petroleum emulsions and optimization of petroleum refining processes.

The synergetic effects of joint application of physical (laser radiation) and chemical (additives) methods of external influences to the microstructure of diesel fuels is explored. The complex influences result in significant decreases of sulfur content, change of physical, chemical and operational properties of fuels for diesel engines; fractional structure, density, and kinematic viscosity, etc. The allowable power range and wavelengths of the laser radiation which effectively influence the parameters of petroleum fractions were determined.

David W. Jennings and Arif Shaikh - Poster

Heat Exchanger Deposition in an Inverted SAGD Operation - Part 1: Inorganic and Organic Analyses of Deposit Samples

Heat exchanger fouling is a severe operational problem in Steam Assisted Gravity Drainage (SAGD) processes. In an effort to better understand which species are prone to deposit and gain insights into means for mitigating SAGD heat exchanger deposition, analyses were performed on a series of heat exchanger deposit samples from an Inverted SAGD operation in Canada. Deposit samples were obtained from each of five heat exchanger banks used in the facility's operation: exchangers heating the produced raw bitumen reverse-emulsion coming from the wells (two exchanger banks in-series) and exchangers cooling separated produced water leaving the high temperature separator (three exchanger banks in-series). The separated produced water (including suspended solids) leaving the facility high temperature separator was also analyzed.

The analyses focused on determining the overall inorganic and organic elemental compositions; as well as, providing general information on the predominate types of chemical species present. The analyses included: (1) Carbon, Hydrogen, and Nitrogen analyses, (2) X-ray Fluoresence, (3) X-Ray Diffraction, (4) Thermogravimetric analyses, (5) Chloroform & Methanol solubility, and (6) Fourier Transform Infrared Spectroscopy. Ion Chromatography and Induced Coupled Plasma analyses were also run on the water sample.

Analyses indicated preferential deposition of certain species and potential causes of deposition in some of the exchangers. For the SAGD operation, at that particular time, periodic slop tank recycle containing warm lime softener sludge was indicated as a source to a significant amount of fouling in the heat exchangers handling the produced bitumen reverse emulsion and the initial exchanger cooling separated produced water leaving the High Temperature Separator. High Mg +2 and Si +4 compositions were detected in these deposits. Additional deposition of other sand/silicates was also indicated. For the organic portion of these deposits, significant concentrations of organic acid and organic acid salts were indicated within the deposit hydrocarbons. Although all deposits contained both inorganic and organic components, the deposits in the last two exchangers cooling the produced water were found to be predominately organic. Significant concentrations of organic acid and organic acid salts were also indicated in these deposits.

The indications of significant organic acid/acid salt content led to collaboration work with the National High Magnetic Field Laboratory to studies these components in-detail. The National High Magnetic Field Laboratory's Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectroscopy work is discussed in the accompanying Part 2 companion paper.

Tanner M. Schaub, David W. Jennings, Ryan P. Rodgers, and Alan G. Marshall - Poster

Heat Exchanger Deposition in an Inverted SAGD Operation - Part 2: Organic Acid Analysis by ESI FT-ICR MS

We have analyzed heat exchanger deposits and produced water from an inverted SAGD bitumen production process with respect to organic acid content. The analyses were performed by ultrahigh-resolution negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry ((-)ESI FT-ICR MS) and reveal distributions of molecular weight, heteroatom content, aromaticity and carbon number for thousands of organic acids present in each deposit. The ultrahigh resolving power and high mass accuracy of FT-ICR MS combined with Kendrick mass defect analysis allow assignment of unique elemental formulae for each species observed in the complex mass spectra.

Classes based on molecular formula assignment fall into two groups. One group consists of reverse emulsion-type deposits and produced bitumen and shows high levels of O 2 , O 2 S and N 1 compounds. The second group originates from the produced water following high temperature separation of the bitumen from the reverse emulsion and deposits from produced water heat exchangers. This second sample group shows high levels of O 4 compounds, SO 4 compounds and other compounds with high heteroatom content.

Session on Flow Assurance

Jianxin Wang, Jill Buckley, and Jeff Creek (Keynote Presenter)

Rapid Screening for Asphaltene Precipitation during Oil Production

We present a rapid screening technique that uses a minimal amount of measured data. Only in cases where asphaltene precipitation is predicted by the screening test would further experimental evidence, such as the measurement of onset pressure, be required. Currently the criteria proposed by de Boer et al. (1995) are widely used for screening purposes. In general, these criteria yield predictions that are somewhat pessimistic, in part because they fail to account for differences in stability between specific oils and their asphaltenes.

In this paper we propose a practical screening method that is easily applied, yet can dramatically improve the accuracy of stability predictions. The method is based on a modification of the ASphaltene InStability Trend (ASIST) technique, presented previously for predicting the onset pressure during depressurization. The information required in the simplified screening method includes routine PVT data, composition analyses, and a single onset titration using stock-tank oil and a light n-alkane precipitant such as n-heptane. The predicted onset solubility parameter at the bubble point is compared with the calculated solubility parameter of crude oil at that pressure to determine whether asphaltene would become unstable and precipitate. Twenty three crude oil samples from varying geologic locations have been used to develop and test this method. Results are in agreement with the more detailed ASIST predictions and with the field experience, where available.

Cláudio M. Ziglio, Fábio R. Notrispe, Jair B. Monteiro, Gaspar González - Paper

Formation Damage Caused by Asphaltene Deposition: Diagnosis, Treatment and Monitoring

When flocculation of asphaltenes occurs, deposits can be formed anywhere in the oil production system reducing the well productivity. The flocculation process has a strong tendency to initiate as the pressure is reduced, especially near the bubble point. However, in some crudes the precipitation comes about even at pressures higher than the bubble point. Depending on the oil characteristics it is believed that deposition can occur in the porous media, near-well bore area, where the asphaltene can damage the formation and reduce the oil production. Asphaltene deposition problems have been observed in a number of light oil wells in Santos basin, Brazil . The deposition phenomenon has been extensively investigated and a chemical inhibition program has been adopted to mitigate the problem. However, some wells have showed a productivity decline suggesting that asphaltene precipitation is causing a near-wellbore formation damage. This paper presents a systematic study to diagnose and remediate the asphaltene problem in the formation.

Øystein Brandal, Ann-Mari D. Hanneseth, Pål V. Hemmingsen and Johan Sjöblom - Paper

Interfacial Behaviour of C80 Tetrameric Naphthenic Acids Responsible for Naphthenate Deposition in Crude Oil Processing

Naphthenic tetraacids have been isolated from a naphthenate deposit and characterized physico-chemically by means of pendant drop technique and Langmuir technique equipped with a Brewster angle microscope. The tetraacids are very oil/water (o/w) interfacially active as compared to monomeric naphthenic acids existing in crude oil; a concentration of only 0.005mM (~8 ppm) tetraacids is sufficient to lower the interfacial tension (IFT) between toluene/n-hexadecane (1:9 v/v) and water pH 9.0 by about 45 mN/m. Naphthenic acids extracted from crude oil, on the other hand, lower the IFT less than 30 units at 2000 times higher concentration. The high affinity towards the o/w interface makes the tetraacid monomers more prone to react with inorganic cations across the interface to form naphthenates. Moreover, due to the four reactive carboxylic groups within each molecule, the tetraacids may crosslink with calcium ions to form extended network layers / polymeric structures. This behaviour is in deep contrast to that of monomeric acids, which are only able to form dimeric complexes. The polymeric networks of the tetraacids tend to adhere to solid surfaces, whereas dimeric complexes of monoacids can be dispersed into the hydrocarbon solution. The significant difference in the way to precipitate combined with the high o/w interfacial activity of the acid monomers, are likely reasons why the tetrameric naphthenic acids are found to dominate in naphthenate deposits despite of their low concentration in the crude oil (ppm level) as compared to monomeric naphthenic acids (wt% level).

D. Merino-Garcia and S. Correra - Paper

Kinetics of Waxy Gel Formation from Batch Experiments

Waxy deposits constitute one of the main Flow Assurance problems in offshore oil production; in spite of its technical and economic importance, the mechanism of wax deposition is still not well understood. Up to eight different mechanisms have been proposed in the literature to contribute to the transport of either solid or liquid waxes towards the cold wall. Several assessments of these mechanisms have concluded that, among the proposed mechanisms, the only one with a significant flux towards the wall is the so-called molecular diffusion. That is to say, liquid waxes are driven towards the cold wall by a concentration gradient.

This does not mean that the problem has been solved. In fact, a reliable model on wax deposition is still to be agreed upon. Other mechanisms that have been so far neglected may count on the kinetics of deposit formation. Up to now, the focus in wax studies has been on the transport of waxes to the cold wall. An analysis of the experimental evidences led to the conclusion that an important role may be played by the oil gelation on the cold surface, i.e. by the bulk liquid-to-gel change driven by the temperature change. Gelation is considerably faster than diffusion and may lead to the formation of a loose solid network that is slowly filled by diffusion (by a phenomenon called aging ).

An experimental apparatus was then employed to measure the gelation kinetics both on a model mixture and on a stock tank oil. Obtained data were modelled by employing a classic solution of the conductive heat transfer problem, and in this way it was possible to estimate the physical parameters involved in gelation. The resulting values are similar to the ones reported by the literature and a coherent picture of the phenomenon is attained.

Doris L. Gonzalez , George J. Hirasaki and Walter G. Chapman - Paper

Prediction of Asphaltene Precipitation using the PC-SAFT EOS - Field Cases

Proper prediction of the potential for asphaltene precipitation in deepwater reservoirs represents a challenge for the flow assurance area due to both, high intervention costs in case of asphaltene problems and extreme conditions of pressure, temperature and composition. The applicability of the recombined oil model using PC-SAFT equation of state to predict asphaltene onset of precipitation in live oils is demonstrated by studying representative examples from field experiences with asphaltene problems during production. These examples not only validate the proposed model but also confirm the theory that asphaltene phase behavior can be explained based only on molecular size and van der Waals interactions. The PC-SAFT equation of state estimates also properties such as densities and bubble points of live oil systems using a minimum number of real components and ‘realistic' pseudo-components. The amount and composition of the asphaltene precipitated phase is determined as part of the equilibrium calculations. From the obtained results, it can be concluded that the recombined live oil model using PC-SAFT equation of state properly predicts the asphaltene phase behavior under pressure reduction, oil based mud contamination and changes in composition due to gas injection and commingle that may result in either asphaltene precipitation or solubilization. The PC-SAFT equation of state model is a commercial available proven tool in Multiflash software from Infochem.

Ingunn Gjermundsen and Marta Duenas Diez - Paper

Wax Deposition; A Comparison Between Measurements and Predictions from a Commercial Model

The paraffin deposition from condensates is expected to be different from the deposition of paraffin's from crude oils, due to the fact that condensates consists of lighter components, and the dissolved gas acts as a solvent for the wax particles. In the current study the purpose was to establish experimental data from a wax rich condensate for comparison with a commercial model. The condensate density at 20 o C was 812 kg/m 3 and the wax appearance temperature was measured to be 40 o C at atmospheric conditions. The wax melting point is 51 o C. The experiments were carried out in a flow loop with a 5 m long test pipe surrounded by a water jacket.

The wax deposition on the pipe wall was measured as a function of time. First, the condensate flow rate was varied to establish the dependency of velocity or shear on the deposition mechanism. Secondly, the cooling water temperature was varied to establish the dependency of the driving force or the heat transfer caused by the temperature difference between the bulk flow and the ambient temperature. Finally, the temperature of the condensate was varied, to establish the dependency of increased concentration of precipitated wax in the bulk flow.

The experimental conditions were simulated using the commercial multiphase tool, OLGA2000. A comparison of wax precipitation between the model predictions and the measurements shows that the deposition model tends to over-predict the deposition thickness by more than 100% for some cases.

E. Ramirez-Jaramillo, C. Lira-Galeana, and O. Manero - Paper

Modeling of Asphaltene Deposition in Production Pipelines

A multiphase (oil/gas/asphaltene/water) -multicomponent hydrodynamic model is proposed to represent the phenomenon of asphaltene deposition in producing wells. The model is based on the assumption that asphaltene particles are thermodynamically formed at a given set of p-T-x conditions during the flow, and both molecular diffusion and shear removal are two competing mechanisms that define the radial diffusion and later deposition of asphaltene particles for either turbulent or laminar flows in a well. Predictions of the model are presented for the case of two problematic (plugged) wells from the southwest producing area of Mexico , where measured pressure-temperature-depth production profiles related to deposits are available.

Nelson Fong and Anil K. Mehrotra - Paper

Deposition from Wax–Solvent Mixtures in a Flow-Loop Apparatus: Extension of Heat-Transfer Analogy to Turbulent Flow

Wax deposition from crude oils is encountered commonly in the petroleum industry. Many theories have been proposed for the mechanism of deposit formation from ‘waxy' crude oils and mixtures. A recently proposed heat-transfer analogy yielded excellent agreement with experimental and modeling results for solids deposition from wax–solvent mixtures under laminar flow. In this work, a flow-loop apparatus was developed for exploring the deposition process under turbulent flow conditions. All of the tests were carried out with wax–solvent mixtures, prepared by mixing 7–15 mass% Parowax™ in Norpar13 (a paraffinic solvent comprising C 9 H 20 to C 16 H 34 ), at Reynolds numbers ranging from about 10,000 to 30,000.

Experiments were performed to investigate the effects of mixture composition and Reynolds number as well as hot and cold stream temperatures. It was observed that the deposit mass decreased with an increase in the Reynolds number, an increase in the hot stream temperature, and/or an increase in the cold stream temperature. Experimental data, analyzed with the heat-transfer model, 1,2 confirmed that the deposit mass is dependent on the relative magnitudes of thermal resistances at steady state. The deposit mass was related to the ratio of the temperature difference across the deposit to the overall temperature difference. The results were also used to predict the average thermal conductivity of the deposit. GC analyses of deposit samples showed interesting changes in the carbon number distribution.

Jack F. Tinsley, Robert K. Prud'homme, Xuhong Guo - Paper

Effect of polymer additives upon waxy deposits

The nature of a deposit in an oil transportation line depends not only on the material coming out of solution (dictated by thermodynamics) but also upon the microscopic structure of the deposit (dictated by aggregation and self-assembly). Paraffin deposits contain large amounts of liquid trapped by solid paraffin crystals that interlock into a spanning network. We report the effects of polymer additives on waxy gels formed from model oils, examining the strength of waxy gel through yield stress tests, the structure through microscopy and small angle neutron scattering, the effects upon deposition in a laboratory flow-loop deposition cell. Model oils were composed of single paraffin or a multi-component paraffin mixture in an alkane solvent; in some cases crude oils were tested. Polymer additives included random poly(ethylene butene), poly(ethylene -b- propylene), ethylene/vinyl acetate co-polymers and copolymers of maleic anhydride, all of which had a known crystalline content or micro-structure.

In gels from single component paraffin solutions, polymers produced yield stress reductions of three to four orders of magnitude with a corresponding alteration of structure. Polymer efficacy in multi-component waxes was one to two orders of magnitude, with the exception of maleic anhydride co-polymers with alkyl segments eighteen carbons long or greater. These latter polymers produced yield stress reductions of three orders of magnitude over a wider range of concentrations. Tests on crude oils showed varying results due to differing compositions. Flow loop deposition tests in a parallel-plate deposition cell demonstrated the effect of polymers upon the deposit growth rate and wax composition.

Tina Johnson, Abdel Kharrat, Moin Muhammad and Shawn Taylor - Paper

An Overview of Gulf of Mexico Asphaltene Risks - Fact or Fiction?

As exploration of the deepwater Gulf of Mexico (GoM) region continues, producers such as BP are finding more reservoir fluids that tend to precipitate asphaltenes due to pressure depletion. In other regions of the world where dry trees are more commonplace, it is easier to routinely access and remediate wells that have sustained asphaltene precipitation and deposition. This luxury is not an option in the deepwater GoM due to the Severe economic impact on high value wells. Instead, a conservative approach of placing chemical injection capabilities in a subsea system is used to avoid potential spending of tens of millions of dollars on remediation activities later. However, would it be better to balance the inevitability of systematic deposition from problematic crude oils if we had the ability to better characterize asphaltenic oils and, in turn, model asphaltene precipitation and deposition? This presentation will report on a project using a combination of high pressure, high temperature experimental techniques and analytical techniques to identify key compositional and behavior differences of asphaltenes. These techniques included deposition testing using Organic Solids Deposition & Control (OSDC) as well as elemental analysis, high-field NMR, and High Resolution Mass Spectrometry (HR-MS) for chemical characterization of the various asphaltenic samples. Testing was completed using a matrix of crude oils sourced from the Gulf of Mexico that have known asphaltene precipitation and deposition behaviors.

Andrew Shepherd, Robin Westacott, Gillian Thomson , Colin Smith, Mike Turner and Ken Sorbie - Poster

Novel Insights into the Characterization of Naphthenic Acid Deposits

Naphthenic acid deposits in the form of calcium and sodium soaps represent an emerging flow assurance problem within oilfield operations. Despite this, there are, to date, no published accounts of characterization studies of soaps from distinct oil producing regions under the same set of conditions. The present work addresses the characterization of naphthenic acid containing deposits. An analysis protocol has been developed which has been applied to six deposits from distinct geographical locations including the North Sea , West Africa and Southeast Asia . The protocol analysis covered a wide range of techniques aimed at correlating bulk, surface and well as key chemical composition properties. The techniques applied include: gel permeation chromatography, differential thermal analysis, thermogravimetric analysis, X-ray diffraction, energy dispersive X-ray, interfacial tension measurements, liquid chromatography mass spectrometry, electrospray mass spectrometry, tandem mass spectrometry as well as a variety of nuclear magnetic resonance methods.

Within this study it was observed that the bulk and surface properties of the soaps were a direct reflection of the precise naphthenic acid content present. In this protocol analysis, particular soap samples (calcium rich) showed up the presence of a surface active group of naphthenic acids, including a species at m/z ~ 1230, Arn naphthenic acids. This group has been linked with the deposition mechanism of soaps. However, at least one calcium rich soap sample did not contain significant amounts of this species. In addition, a new kind of deposit which is particularly rich in Arn, but which fails to contain significant cationic species is also described in detail. This novel information has provided for several insights into both a possible deposition mechanisms for naphthenic deposits, as well as for the properties of their constituent chemical components.

Marta E. R. Dotto, Sérgio Camargo Jr., Cláudio M. Ziglio - Poster

Study of Adhesion of Paraffins by using Atomic Force Microscopy

Precipitation and crystallization of waxes (solid paraffins) during transportation and processing of crude oils, are a major problems in the oil industry. Waxes are crystalline in nature and tend to crystallize/precipitate from crude oils at and bellow their cloud points onto pipelines walls resulting sometimes in clogging of pipeline. For the oil industry it is very important to obtain information about adhesion forces between paraffin and substrates together with the analysis of the adhesion forces during the aging of paraffin. In this work, we measured the force curves using an atomic force microscope (AFM) to investigate the adhesion forces in surfaces coatings with paraffin deposits. AFM can be used to image the topography of solid surfaces at high resolution, and in addition can measure force-versus-distance curves. Such curves, briefly called force curves, provide valuable information on local material properties such as elasticity, hardness, surface charge density and adhesion. The approximation and retraction curves are obtained during acquisition of the force curve; the retraction one gave us information about adhesion forces.

The paraffin deposits were obtained by casting technique in a solution containing heptane. The force-curves preliminary results indicate that the paraffin deposits undergo a permanent deformation, not returning to the original situation. The retraction curves indicate that an interaction of viscous adhesion occurs during jump-out of AFM probe.

Jack Dunlop - Poster

New Low Environmental Impact Asphaltene Inhibitors for the Norwegian Sector

A new range of asphaltene inhibitors for oil production operations was launched in 2003. This product range is characterized by low toxicity products containing inherently biodegradable and highly oil soluble (high log Po/w) polymers, formulated in a high flash point aromatic solvent. Although rated as low environmental impact for the offshore oil industry, in general, these products have been assigned a red category by the Norwegian regulatory authorities. This paper describes a short term project to develop a product alternative with a more acceptable environmental profile for the Norwegian market. In particular, the project considers manufacturing implications for alternative solvents and additional performance, physical property and environmental charcterisation of this new product line extension.

Kriangkrai Kraiwattanawong, Sumaeth Chavadej Chulalongkorn, Samir G. Gharfeh, Probjot Singh, William H. Thomason, H. Scott Fogler - Poster

An Advanced Thermodynamic Solubility Model to Predict Asphaltene Instability in Live Crude Oils

This paper describes an advanced thermodynamic solubility model developed to predict onset of asphaltene instability including live crude oil systems. The model is based on determination of Hildebrand solubility parameter of stock tank oil, dissolved gas composition and detailed PVT data of live oil. Asphaltene precipitation and deposition of crude oils due to changes in pressure, temperature and composition in the downhole production facility have a huge economic impact on the oil industry. A good asphaltene instability prediction helps in mitigating asphaltenes problems and minimizes asphaltene remediation cost.

In the early method development, the Hildebrand solubility parameter concept was used to determine the asphaltene onset point of stock tank oil but did not capture the effect of dissolved gases on the onset solubility parameter. Later, other researchers have developed an empirical correlation between the onset solubility parameter and the molar volume of precipitants. They found this correlation to be useful in estimating the effect of dissolved gas on the onset solubility parameter of live oil. Their extrapolation to higher temperatures and pressures is limited in range. More precise prediction would require a consideration of entropy of the light ends in the live oil. This model was developed to predict the onset solubility parameter at live conditions based on the advance thermodynamic Gibb's free energy rule.

Solubility parameters of several stock tank oils were determined and coupled with the equation of state models based on the PVT data of the live oils. To validate the model, high temperature and high pressure experiments with a laser near infrared (NIR) detection were performed and the onset points of asphaltenes were determined. This advanced model is capable of predicting asphaltene instability at all live conditions. A complete investigation and validation of this advanced thermodynamic solubility model with extensive experimental data will be discussed in this paper.

W. A. Cañas-Marin, J. D. Ortiz-Arango, U. E. Guerrero-Aconcha and C. Lira-Galeana - Poster

Thermodynamics of Wax Precipitation under the Influence of Magnetic Fields

A thermodynamic framework is developed for calculating wax precipitation in multicomponent (non-ferromagnetic) hydrocarbon mixtures under the influence of a static magnetic field. A mathematical expression was derived for calculating the compositional derivatives of the magnetic susceptibilities using an equation of state. These susceptibilities are required for calculating magneto-chemical fugacities. The model was used to predict the effect of a static magnetic field on crystal temperature and amount of precipitated wax for three normal-paraffin mixtures and one synthetic gas-condensate. Calculated results indicate that static magnetic fields increase the probability of formation of paraffin crystals, in accordance to the experimental evidence.

Nitin V. Bhat and Anil K. Mehrotra - Poster

Modeling the Effects of Heat Transfer and Shear on Composition and Growth of Deposit-Layer from ‘Waxy' Mixtures in a Pipeline under Laminar Flow

When a pipeline carrying paraffinic mixture, such as ‘waxy' crude oils, is exposed to temperatures below the wax appearance temperature (WAT), a deposit layer is formed on the pipe-wall. The deposit-layer is comprised of both liquid and solid phases, giving rise to gel-like characteristics. A new 2-D heat-transfer model, based on the moving boundary problem approach, has been developed to predict the growth of deposit-layer from paraffinic or ‘waxy' mixtures. This unsteady-state model was extended to predict the growth of deposit-layer from binary eutectic mixtures of n -C 16 H 34 and n -C 28 H 58 , in both radial and axial directions, in a pipeline under laminar flow conditions.

Calculations were performed to study the deposit-layer growth with changes in the mixture (hot) temperature, pipe-wall (cold) temperature, and the mixture composition, Reynolds number and WAT. The heat-transfer model was extended to include the effect of shear, caused by the flowing liquid, on the composition and growth of the deposit-layer. This was accomplished by assuming the shear stress to cause plastic deformation of the deposit as it forms at the liquid–deposit interface, which leads to “squeezing out” of a fraction of the liquid phase. Consequently, the concentration of paraffinic (‘waxy') constituents in the deposit becomes higher than that in the mixture. Experimental data obtained from a bench-scale apparatus were used to correlate the deposit-layer composition, relative to the mixture composition, as a function of Reynolds number. The model predictions also support the observed higher thermal conductivity of the deposit-layer due to the increased solid phase fraction.

Oliver C. Mullins, Peter Weinheber, Lalitha Venkataramnan, Ryan P. Rodgers, Alan G. Marshall - Poster

Comparment Hunting by Downhole Fluid Analysis Coupled with Asphaltene Fingerprinting

Compartmentalization, which embodies the lack of flow connectivity within subsurface oil reservoirs, is widely regarded as the biggest problem in exploration in the oil business. Errors in assessment of this issue have resulted in billion dollar problems in individual fields. Downhole Fluid Analysis (DFA), launched in 2001, has been used to identify compartmentalization at times by identifying fluid density inversions – higher density fluids higher in the oil column. In a related manner, DFA has also identified compartmentalization by finding heavy end rich fluids higher in the column. Here we present an analysis of the DFA data coupled with laboratory asphaltene fingerprinting to understand in-situ fluid and formation complexities. These topics covered herein provide a new and valuable venue for fluids experts to impact the oil business.

O. Niemeyer - Poster

New Squeeze Applications for Asphaltene Blocked Wells

In recent years production has shifted towards reservoirs and environments which are considered more problematic and technically challenging than in the past. Deepwater applications and heavy oil production are more and more common. This has caused careful consideration of chemical treatment programs for deepwater applications. Conversely mature on-shore wells have been lost due to organic deposits and are often considered commercially unviable to operate even with regular conventional dissolver treatments. Design of squeeze applications and new developments in asphaltene inhibitor/dispersant chemistry gives a possibility to reinvigorate these wells with cost efficient chemical squeeze treatments.

This paper presents successful squeeze applications for asphaltene problematic wells covering a deepwater application squeeze and a squeeze on an asphaltene blocked shut-in on-shore well. Prior laboratory evaluations are carried out using equipment according to ASTM D 7061-04.

James Foster, Bruno Pinguet, Stefan Smuk and John Nighswander - Poster

Optimisation of Multiphase Flow Metrology through Accurate Phase-Behaviour Characterisation

Modern techniques for multiphase flow metering find broad application in well testing, production monitoring and fiscal allocation. Generally, the accurate discrimination of the relative quantities of vapour, hydrocarbon-liquid and aqueous-liquid phases in a metered well-stream requires description of their physical properties at meter conditions. Also, it is normally required that flow data be reported in terms of equivalent flow rates at standard (atmospheric) conditions; thus it is also necessary to describe the phase behaviour of the metered fluid phases in terms of conversion factors from line conditions to standard conditions.

In this work, we examine the sensitivity of the performance of multiphase flow meters to the accuracy of the fluid-behaviour data inputs on which they rely, in terms of the accuracy of reported flow rate data. Two separate approaches are considered. First, the physical properties of each flowing phase within a meter are estimated using traditional correlations based on simple stock-tank phase property measurements (e.g., gravity, viscosity). Second, individual fluid-phase samples of the well-stream are measured directly. To this end, we present a novel sampling device, which has been developed and extensively field-tested for the express purpose of collecting segregated fluid samples from a multiphase stream. Fluid-property data obtained from samples retrieved using the sampling device can be applied directly to metrological data that have been acquired simultaneously with sample collection. Alternatively, the analytical data can be generalised into fluid-behaviour models that are valid over a broader range of operating conditions, using equations of state, artificial neural network systems, or localized correlations. We report results of selected field trials, in which data obtained from analysis of samples are used to process associated meter-acquisition data. The latter are also reprocessed using correlation-based fluid-property inputs, and the two sets of results are compared with independently known flow rates.

Geza Horvath-Szabo and Janet A. W. Elliott - Poster

Prediction of Surfactant Performance in Reservoirs Under High Pressure

In enhanced oil recovery, surfactants are used to modify the interfacial tensions improving the efficiency of oil recovery. The selection of surfactants is based, among other things, on wettability tests performed under atmospheric conditions. However, the reservoir pressure has an effect on the interfacial tension and hence on the wettability of rocks. It is difficult to perform wetting performance tests at high pressure. We could predict the high-pressure performance of a surfactant based on data at atmospheric pressure from the pressure coefficient of interfacial tension. This pressure coefficient tells us whether a pressure-increase enhances or diminishes the performance. This coefficient is connected to the volume change of a system during interface formation through one of the Maxwell relations. Unfortunately this volume change is so small that nobody has attempted to measure it directly. Another problem is that we also want to include in the description the effect of surfactant adsorption. Therefore we reexamined the thermodynamic description of adsorption usually based on the Gibbs convention. We found that, for our purpose, a different convention suggested by Hansen is more convenient. A novel approach based on the adsorption isotherm of the surfactant and density data of a suspension formed from the solid phase is established for the calculation of the pressure coefficient of the shift in the interfacial tension caused by the addition of the surfactant. This coefficient is presented for the silica/water interface where sodium dodecyl sulfate is used as the surfactant.

Frans G.A. van den Berg and Jacco D.M. Woldendorp - Poster

Asphaltene stability test methods compared

Precipitation of asphaltenes continues to be a problem in production, refining and storage of crude oils and heavy oil streams such as fuel oils. A flurry of activity in 2004 and 2005 has resulted in four new asphaltene stability test methods being accepted as ASTM standards: ASTM D7060, D7061, D7112 and D7157. The advantages and the disadvantages of these and related test methods will be discussed. Different methods may serve different goals. However, experimental data on commercial samples illustrate that incipient precipitation methods are to be preferred over other techniques, such as the Turbiscan method, as they generally allow better prediction under practical conditions. This is due to the fact that these methods take into account both the relative solubility of the asphaltenes and the solvent power of the surrounding hydrocarbon matrix. Recommendations for further work on the development of reliable methods will be given.

Andrew Yen, Justin Debord, Sam Asomaning, Brandie M. Craven, Ryan P. Rodgers and Alan G. Marshall - Poster

Comparison of Calcium and Sodium Naphthenate Deposits by Electrospray FT-ICR Mass Spectrometry

Deposition of unwanted material in petroleum production equipment can be classified into one or more of the following: gas hydrates, inorganic scale, organic scale (waxes and asphaltenes) and naphthenate soap deposits. Soap deposits form from the reaction between naphthenic acids in crude and metal ions in formation water. The two common deposits are calcium napthenates and sodium napthenates. The dramatic increase in production of crudes with very high TAN has led to an increase in the problem of naphthenate salt deposition.

Recent advances in FT-ICR mass spectrometry have led to numerous applications in petroleum characterization. The ElectroSpray Ionization (ESI) provides selective ionization of polar N, S, and O containing compounds of interest to the petroleum industry. The inherent high resolution and mass accuracy of FT-ICR MS allow for the resolution and identification (at the level of molecular formula assignment) of thousands of species from a single sample. The selective ionization and subsequent identification by high resolution mass analysis makes FT-ICR MS a powerful tool for the characterization of naphthenic acids.

In this paper we present the compositional comparison of napthenic acid fractions in calcium and sodium naphthenate deposits from different fields using negative ion ESI FT-ICR MS. The two types of deposits show wide variations in their class (heteroatom content), type (aromaticity) and carbon number distributions. Detailed class by class comparisons of the two naphthenic acid fractions are presented.

Mohammed I. Zougari and Kamran Akbarzadeh - Poster

Organic Solids Deposition and Control Validation: OSDC (Taylor-Couette) Flow vs. Pipe Flow Similitude

Asphaltene/wax formation and deposition is one of the major issues in the oil transportation industry and facility design. To investigate asphaltene/wax deposition in laboratory, various flow loops have been built over the past 50 years. Most of these laboratory scale flow loops operate under laminar flow conditions, while the commercial pipelines usually operate at very highly turbulent conditions. Therefore, it is difficult to mimic the actual commercial pipeline conditions (e.g., diameter, flow rate, shear rate, turbulence intensity, and pressure) using the available flow loops and scale up the obtained deposition results to highly turbulent flows.

This work briefly presents the extensive research that has been performed on the organic solid and deposition control device in the past few years to ensure its scalability to pipeline fluid dynamics and heat transfer processes. A computational fluid dynamics package is also used to predict the hydrodynamic and thermal profiles in both Couette-Taylor flow and pipe flow.

Mohammed I. Zougari and Kamran Akbarzadeh - Poster

Wax Deposition Process at High Temperatures

The precipitation and deposition of wax in process equipment in a subsea environment is a well-recognized problem. In one hand, existing technologies are focused on determining Wax Appearance Temperature (WAT) defined as the temperature at which wax particles appear in the measuring device or system whether at constant temperature or at constant cooling rate. On the other hand, using High Temperature Gas Chromatography HTGC technique inputs, some theoretical models can predict the insipient phase or theoretical WAT occurring at relatively higher temperatures. However, does the deposition due to wax precipitation always happen below the WAT? In other words, is it possible to have wax deposition at a temperature above the defined WAT?

Using the OSDC (Organic Solid and Deposition Control) device, developed to produce deposition process similar that occurring in the pipeline, we have been able to generate deposit from different waxy crude oils at much higher temperatures than the measured and calculated WAT. Consequently, from the obtained results, it can be concluded that the existing definition of WAT needs to be reviewed not only from the fluid physical properties point of view but also from the characterization point of view.

Session on Chemistry and Physics of Petroleum - Water Emulsions

Johan Sjöblom (Keynote Presenter), Pål V. Hemmingsen, Andreas Hannisdal and Anne Silset - Paper

Stability Mechanisms of -Crude Oil Emulsions - A Review

A review is given summarizing different types of stability mechanisms of water-in-crude oil emulsions. The main mechanism is in many practical cases a combination of steric stabilization and small particles. The nature of the steric stabilization is the formation of a rigid film where heavy components like asphaltenes/resins and naphthenic acids are accumulated. It is essential that these interfacial layers have correct rheological properties with regard to interfacial elasticity and viscosity. We summarize recent data from laboratories in Canada , USA and Norway .

In addition to the pure steric component, small particles (fines) are also of paramount importance in stabilization of the water-in-crude oil emulsions. It is clearly shown that the coating of the particles with heavy components (asphaltenes and resins) is essential for obtaining correct wetting properties and correct magnitude of the stability. The importance of multilayers at the water/oil interface (the formation of lyotropic liquid crystals) is especially important in acidic crude oils. It is clearly shown that certain ratios between dissociated and undissociated naphthenic acids (together with structures) will substantially promote stability.

A special case of w/o emulsions is the pressurized ones. This is a new and unique area with additional destabilization mechanisms. We will give a first approach to this novel area.

Jan Czarnecki, Alan G. Marshall, Ryan P. Rodgers, Lateefah A. Stanford, Shawn Taylor, and Alex Wu - Paper

High Resolution FT-ICR Mass Spectroscopy of Water in Crude Oil Emulsion Stabilizers

Contrary to well-established beliefs, compounds constituting the majority of polar components of the material collected from water in crude oil emulsion droplets are not asphaltenes. The material stabilizing water in crude oil emulsions was collected using Wu's method utilizing deuterium oxide (or “heavy” water). High resolution MS data were collected by negative ion Electrospray Ionization (ESI) on a homebuilt 9.4 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS) for ten oil samples (and their corresponding interfacial materials) from various geographical locations and of varying composition. Despite the geographical and compositional differences, the material detected at the oil/water interface for all oil samples analyzed was composed of similar low molecular weight (300 – 600 Da) molecules containing mostly carboxylic (O 2 – O 6 classes) and thiophenic groups (SO 2 – SO 5 classes) with double bound equivalents (DBE) ranging from 1 to 18, with the most abundant species having DBE from 1 to 8. Therefore, many of the species are not even aromatic, and most cannot be polyaromatic. As defined by the mass spectral results, they do not fit a conventional description of asphaltenes, being heavy, polar, polyaromatic species.

Thiophenic functionalities were confirmed by MS n experiments on suspected multifunctional classes such as O 3 S and O 4 S.

Vincent J. Verruto and Peter K. Kilpatrick - Paper

Determining Asphaltenic Film Thickness and Solvent Entrainment using SANS

Recent studies have demonstrated the power of small angle neutron scattering in quantifying the shape, solvent entrainment, and molar mass of asphaltenic aggregates dissolved in model solvents. Very recently, we demonstrated the application of SANS as a characterization tool for asphaltene-stabilized water-in-oil emulsions. The method, however, is challenging and requires contrast-matching between the solvent and aqueous phases, and mitigation of both asphaltenic aggregate scattering and droplet settling. With contrast-matched samples and with 1 wt% asphaltenes dissolved in mixtures of toluene and methylnaphthalene, the core/shell form factor model and the Kratzky-Porod analysis enabled recovery of the interfacial film thickness by two independent means. When the concentration of asphaltenes is increased to 4% (w/w), however, the aggregate scattering signal swamps the interfacial film signal, and subtraction yields data with high relative error. Here we describe studies in which the aggregates are removed, leaving only the asphaltene-adsorbed droplets and fresh solvent, thus eliminating aggregate scattering. We found that in toluene-based water-in-model oil emulsions the film thickness was ~100 Å and over 60% of the film was entrained solvent.

In summary, the ability to use SANS to reproducibly determine asphaltenic film physicochemical properties in water-in-model oil emulsion systems is demonstrated. Asphaltene concentration and solvent chemistry dictate these film properties. Future experiments will expand the investigation to probe the structure of mixed films made by asphaltenes doped with model resins and naphthenic acids.

Harvey W. Yarranton and Patricia Urrutia - Paper

Dynamic Surface Pressure Isotherms from Drop Shape Analysis of Water-Oil Interfaces

It has long been speculated that the stability of water-in-crude oil emulsions arises from a visco-elastic film on the water-oil interface. However, it is not yet clear exactly how this film stabilizes emulsions and under what conditions the effectiveness of the film can be minimized. One approach to analyzing these films is through surface pressure isotherms. In this work, a novel method for measuring surface pressure isotherms is applied. A drop of one phase is formed on the end of a capillary immersed in the second phase. The fluid is withdrawn from the droplet in a stepwise manner and the surface area and interfacial tension are determined from drop shape analysis at each step. In this manner, a dynamic surface pressure isotherm can be constructed; that is, a plot of surface pressure versus film ratio where film ratio is the measured surface area over the initial surface area of the droplet. With the use of an environmental chamber, isotherms at different temperatures and pressures can be obtained.

The method was applied to interfaces between water and hydrocarbon phases consisting of asphaltenes, toluene, and heptane or of bitumen diluted with the same solvents, all at 23°C. The shape of the isotherms depended on the contact time between the phases, the solvent, and, to a lesser extent, the time between the step changes. The maximum surface pressure end point of the isotherms coincided with visual observations of film crumpling. In some cases, a change in slope indicative of an interfacial phase change was observed. There appears to be a correlation between the film ratio at which the phase change occurs and the stability of an emulsion prepared at the same conditions.

G. J. Hirasaki, M. Fleury, C.A. Miller, T. Jiang, and K. Moran - Paper

Emulsion Stability and Coalescence by NMR Diffusion and Profile Measurements

The kinetics of emulsion sedimentation and coalescence is monitored by diffusion and profile measurements using low field NMR. Diffusion measurements give an estimate of the water drop size distribution as well as the fraction of bulk oil, free water, and emulsified water. It was not possible to estimate water drop size by relaxation time measurements because of the interference due to the solids. The vertical profile is monitored with the same approach used in MRI in which the water and oil are distinguished by the contrast in relaxation time. The process is made especially challenging due to the presence of fine mineral solids.

Emulsions were made from diluted bitumen with and without fine mineral solids to contrast the difference from ordinary emulsions. Also, the emulsions were prepared with or without a demulsifier or other surfactant. In the absence of chemical additives, the emulsions were stable water in oil emulsions that settled to the bottom without yielding any free water. The rate of growth of the settled emulsion layer and the measured size of the water droplets indicated that the droplets were flocculated but not coalescing. Addition of 200 ppm of a coalescer that is optimum for the diluted bitumen at room temperature showed a very different behavior. In the absence of solids, free water appeared and the dispersed water had about the same mean drop size but with its quantity greatly reduced from that before addition of coalescer. Water content of the emulsion continued to decrease over time. Addition of coalescer to the emulsion with mineral solids caused it to coalesce so rapidly that it was not possible to make diffusion measurements of drop size. However, visual observations show free water and a rag layer. The diffusion measurements indicate that this layer is not water in oil emulsion. Thus this rag layer must be a floc of mineral solids in water with some adhering oil such that the density is less than that of the brine. In some cases, this rag layer split and part of it settled to the bottom of the free water layer. Apparently, drainage of oil from the mineral solids made the floc more dense than water.

D. Arla , A. Sinquin, C. Hurtevent and C. Dicharry - Paper

Acidic crude oil emulsions: influence of pH and water cut on the type and stability of emulsions

Geza Horvath-Szabo, Howie Zhang, Azizul Haque, Jacob H. Masliyah, Hicham Fenniri, Steven M. Kuznicki, and Zhenghe Xu - Paper

Unorthodox Emulsion Breakers

The emulsion breaking properties of the following three unconventional additives were studied in water-in-diluted bitumen emulsions: (i) Nanoparticles, which usually stabilise emulsions by the formation of Pickering emulsions. (ii) Zeolites, which can be applied as water removing agents. (iii) Nanotubes, which can effectively increase the sedimentation rate of water in diluted bitumen.

(i) When silica nanoparticles with either high or low wetting angles were used as additives, the amount of the residual water in the oil phase was increased, as compared to the blank experiments. However, at an intermediate wetting angle, the amount of residual water decreased, indicating emulsion destabilisation. These nanoparticles could be utilised in an environmentally friendly emulsion destabilisation process.

(ii) Heat-treated zeolites effectively adsorb water in diluted bitumen. The water removal efficiency is dependent on the zeolite type, the incubation time, and the grain size of the zeolite particles. The final water content of the oil could be as little as 0.02%(wt).

(iii) Under non-stirred conditions, organic nanotubes increase the sedimentation rate of water in various mixtures of bitumen/heptane/toluene. Under stirred conditions organic nanotubes increase the mean water drop size, in bitumen containing naphtha. Nanotubes are efficient emulsion breakers at concentrations higher than 250 ppm by weight.

Emulsion breaking mechanisms are suggested for the different additives.

Richard W. Cloud, Samuel C. Marsh, Becky L. Ramsey, Robert A. Pultz and Michael K. Poindexter - Paper

Salt Spheres – Artifacts Isolated from Petroleum-Based Emulsions

Characterization of water-in-crude oil emulsions can be more challenging than resolving such emulsions. In production, achieving dry crude oil and clean water are key requirements for uninterrupted operation. However, minimizing the build-up of unresolved emulsion at the interface is another closely related element in the overall process of demulsification. Most field emulsions are never completely resolved. For example, Karl Fisher measurements always show some water to be present in the oil phase.

Investigations were performed to probe select features of unresolved emulsions. Using the ASTM D4807-88 procedure, which involves diluting samples with hot toluene, emulsion solids were isolated and then studied using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Characterization of the solids from several different oilfields revealed interesting structures that might be called “salt spheres” or “salt scaffolds”. In one case study, partly coalesced salt structures were identified. The occurrence of these more complex structures gives the impression that the demulsification process was frozen in time. It is not clear whether these inorganic artifacts contributed to the stability of the original emulsion or resulted from the lab isolation method. Nonetheless, the existence of these intriguing structures appears to provide indirect evidence regarding the importance of solids in stabilizing emulsions.

Jan H. Beetge - Poster

An IPR-CEF Study of the Demulsification Process of Diluted Bitumen Emulsions

The scientific approach to the resolution of oil field emulsions requires qualitative understanding of the mechanism of emulsion stabilization, as well as quantitative measurement of the processes involved. This knowledge is essential for effective research into the mechanism of demulsification and ultimately the development of demulsification technology.

Most crude oil and bitumen emulsions are considered to be macro-emulsions in which stability is determined by the kinetics of flocculation, coalescence and settling or creaming processes. The IPR-CEF technique is a recent development as extension of the existing Critical Electric Field (CEF) method for the evaluation of water-in-oil emulsion stability. Although still in its infancy, the IPR-CEF approach shows significant value in the quantification of flocculation and coalescence behavior of an emulsion system. However, this measurement and interpretation are only valid at a given point in time. Parameters affecting flocculation and coalescence behavior can change during the demulsification process, particularly as the interfacial area decreases during coalescence. Measurements made directly after emulsion formation are indicative of first generation droplet behavior, while subsequent measurements can reveal flocculation and coalescence behavior of later generations of droplets.

This study focuses on flocculation and coalescence behavior during the demulsification process to determine the effect of degree of coalescence on the stability of diluted bitumen emulsion. An attempt is made to evaluate the effect of a chemical demulsifier on an emulsion, during the demulsification process.

Guoxing Gu, Zhenghe Xu and Jacob Masliyah - Poster

Bitumen Froth Treatment Using Water Wash

A typical bitumen froth from bitumen extraction contains 30% water, 10% solids and 60% bitumen. Centrifugation, inclined plate separation (IPS), hydrocyclone and asphaltene precipitation are the four major methods used for bitumen froth treatment. Using a setup constructed in our laboratory, it has been found that a two-step water washing of naphtha-diluted bitumen froth (NDBF) can improve oil/water/solids separation performance significantly. In this approach, the NDBF as 1-5 mm diameter droplets was introduced into an aqueous phase to allow the NDBF droplets rising to the top as an organic phase. The top organic phase was then washed using the bottom aqueous phase by circulating the top organic phase back to the aqueous phase.

The proposed approach was tested at 80 ° C and two different naphtha-to-bitumen weight ratios of 0.7 and 7. For both cases, after the first processing step, water and solids content reduced by more than 91% and 87% of their original levels, respectively. Continuous circulation of the top organic phase back to the aqueous phase further reduced the residue water and solids content. Two factors contribute to the improved separation performance: (1) a significantly shorter distance for the internal water droplets and solids particles traveling out of the NDBF droplets, as compared with them traveling from top organic phase, middle rag layer and then to the bottom aqueous phase in a normal separation process; and (2) larger interfacial area for the internal water droplets and solids particles penetrating the surface of NDBF droplets into the external bulk aqueous phase.

Pål V. Hemmingsen, Irune I. Vega, Vanesa R. Sánchez and Johan Sjöblom - Poster

Studies of Asphaltene Aggregation, Interaction with Resins and Effects on Emulsion Stability

The aggregation of asphaltenes by solvency in model heptane/toluene systems is studied by light scattering in the near-infrared region. For n -heptane asphaltenes from six crude oils, the precipitation onset is between 40 and 50 vol% toluene in heptane. There is a variation of the optical density increase in the aggregation region, indicating differences in structure. It is demonstrated that, in general, water-in-oil emulsion stability is high in the aggregation region; however, the two asphaltene model systems with the smallest increase in optical density also show the lowest emulsion stability. Some emulsions also show a destabilization in the heptane rich region, this behaviour correspond with very high optical density indicating large asphaltene particles incapable of stabilizing small water droplets.

For interaction studies, two types of resins have been used, the whole resin fraction similar to the SARA group type fractionation and an acidic fraction extracted from the crude oils with an ethanol aqueous solution at pH 14. For the whole resin fraction, the optical density decrease in the aggregation region with a corresponding decrease in the emulsion stability. This indicates that the resins destabilize the emulsion by solubilising the asphaltenes. The acidic fraction, however, show only a slight decrease in the optical density, but a higher effect on reducing the emulsion stability. The acidic fraction comprises interfacial active compounds like naphthenic acids and phenols. Such compounds are very interfacial active and will populate the water-oil interface faster than the larger asphaltenes, thereby preventing the formation of strong asphaltenic films.

Kevin Moran and Jan Czarnecki - Poster

Towards Destabilizing Crude Oil Emulsions with Sodium Naphthenates

The interfacial properties of persistent water-crude oil emulsions can be altered by sodium naphthenates ( NaN ), a low molecular weight surfactant, to a state more amenable to oil clarification. The rigid nature of water droplet surfaces, which characterize these emulsions, change to a fluid-like state as the bulk concentration of NaN is increased. Novel micropipette techniques, that maintain specific surface areas characteristic to commercial emulsion systems, were employed to measure interfacial tension, surface compressibility and droplet adhesion. Apparent tension data indicate that the water-oil interface is increasingly dominated by the added surfactant. The NaN limits adsorption of less surface-active, higher molecular weight material. Furthermore, without NaN addition, the apparent tension at an emulsified droplet surface decreases over a period of weeks indicating long term, irreversible adsorption or a slow reorganization of adsorbed macromolecules. Although emulsified water droplets remain stable despite surfactant addition, the nature of the stability changes. In the presence of added surfactant the droplets flocculate – a phenomenon not observed in its absence.

Farshid Mostowfi, Jan Czarnecki, Jacob H. Masliyah and Subir Bhattacharjee - Poster

Thin Film Breakup by Electric Fields: Development of Microfluidic Device for Emulsion Stability Studies

Stability of emulsions, emulsion break-up by coalescing the dispersed phase using chemical additives or external forces, and stability of thin liquid films are of paramount importance in a wide array of industrial applications. Fundamental to all these processes is a clear understanding of the role of different physical and chemical factors in the stability of a thin film formed by two droplets of one fluid phase approaching each other in another phase. Several experimental techniques are currently available to explore the thermodynamic properties and stability of thin emulsion films, such as, micropipettes and thin film cells employing a porous plate; all of which provide a platform for forming a thin emulsion film in a macroscopic sense. Setting up these experimental techniques to quantitatively and reproducibly measure thin emulsion film behavior requires considerable time and dexterity.

A novel microfluidic chip has been developed to study the break-up of oil thin films in aqueous media under the influence of an externally applied electrical field. The basic concept involves two crossing micro channels etched onto the surface of a glass substrate. Carefully designing the intersection of the two perpendicular channels allows to form an emulsion film at the intersection. One channel would be filled with oil and the second channel would deliver two water droplets toward each other in the oil. Once emulsion thin liquid film is created, an electrical potential polarization can be applied across the film. The electrical stresses developed at the interfaces of the two fluids forming the film lead to a rupture of the film above a certain threshold voltage. The break up of the film was induced using a ramped DC potential, and a series of capacitance measurements determined the variation.

Lateefah A. Stanford, Donald F. Smith, Jan Czarnecki, Alex Wu, Ryan P. Rodgers and Alan G. Marshall - Poster

Compositional Analysis of Non-Acidic Water-in-Oil Emulsion Stabilizers in Athabasca Bitumen by ESI FT-ICR MS

Prior detailed negative-ion ElectroSpray Ionization (ESI) FT-ICR mass spectral analysis of the material collected from water in crude oil emulsion droplets resulted in the identification of thousands of acidic species that aid emulsion formation. In this work, we expand the mass spectral analysis to both polar basic and nonpolar species in an attempt to identify those species that, along with the acids, stabilize these emulsion systems. High resolution mass spectral data were collected with a homebuilt 9.4 T FT-ICR mass spectrometer equipped with a MIDAS data station. Basic species were selectively ionized by positive-ion electrospray. Nonpolar species were analyzed with a different 9.4 T FT-ICR mass spectrometer equipped with a Field Desorption (FD) ion source. Material collected from the water-in-oil droplets is enriched in C 30-34 alkanes, alkenes, alkylated benzothiophenes and dibenzothiophenes detected by FD FT-ICR MS. Heteroatom class, type (rings plus double bonds), and carbon number distributions for all identified species are presented.

Syunyaev R.Z., Safieva R.Z., Orinbasarov K.O., Klimova L.Z. - Poster

Increase of Efficiency of Deemulsification Processes for High Paraffinic Petroleum

One of necessary technological stages in petroleum industry is deemulsification. Now the basic efforts of researchers are directed on development of new more effective types of synthetic deemulsifiers which accelerates the processes of division of water and petroleum phases. At the same time there are latent reserves of increase of deemulsification efficiency by selection of optimal mixed compositions both crude petroleum-water emulsions and various deemulsifiers.

Petroleum-water emulsions from three petroleum fields in Kazakhstan were searched. On temperature dependences of viscosity the phase transitions with allocation of paraffines in low temperature range are found out. Simultaneously method of differential thermal analysis ( DTA) shows presence high melting components. The quantitative data of group composition of high paraffinic petroleum are received and its influence on stability of petroleum-water emulsions is established. Also DTA was used for definition of a share of boiled away water drops from emulsions. Dispersity degree of water drops changes the temperatures of boiling of crude petroleum.

Triangular diagrams "structure - property" where used for testing the area of the full phase separation after mixing the initial emulsions that is not observed for individual ones. These mixes collapse more effectively. Efficiency of deemulsification can be increased by selection of an optimal ratio of mixes. Synergetic effect of composite deemulsifier is found, when efficiency of separate components is rather low. The method of increase of deemulsification efficiency is offered by application of deemulsifier mixes. In industrial experiment the time of water removal for deemulsifier mixes was reduced twice.

Lamia Goual, Alejandro Magual, Geza Horvath-Szabo, Jacob Masliyah, and Zhenghe Xu - Poster

The Role of Electrically Charged Species of Bitumen in the Stabilization of Water-in-Oil Emulsions

The electrodeposited amount of cationic and anionic species of diluted bitumen was measured with an electrochemical quartz crystal microbalance (EQCM) by applying a constant electric potential difference between two oscillating crystals. By this approach the lower limit of the potential-window was extended by one order of magnitude. The electrodeposition begins with an electrode polarization step leading to an alteration of the adsorption layer at the solid/liquid interface, which, in turn, results in a secondary adsorption process. Simultaneous presence of positive and negative charge carriers is revealed in toluene solutions of asphaltenes, maltenes and bitumen. A model is suggested to better understand the ionic nature of crudes.

Water-in-oil emulsions of diluted bitumen was also studied using the latest advances of electroacoustic spectroscopy. The electrical surface charge density of the water droplets is obtained from the colloid vibration current. In the case of freshly prepared water-in-oil emulsions the surface charge density decreased with time. The time-dependent relaxation of the surface charge ranges from several hours to three days, and it is likely due to the slow adsorption/desorption kinetics of bituminous components at the water-oil interface.

These findings imply that the charge-charge interactions play a role in the formation of the stabilization adsorption layer of water-in-oil emulsions.

Session on Characterization of Petroleum Macromolecules

Alan G. Marshall (Keynote Presenter), Christopher L. Hendrickson, Geoff C. Klein, Jeremiah M Purcell, Tanner M. Schaub, Donald F. Smith, Lateefah A. Stanford, and Ryan P. Rodgers - Paper

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: The Platform for Petroleomics

First reported in 1974, 1 FT-ICR mass spectrometry now offers the highest mass resolution and mass accuracy. 2 At sub-ppm mass accuracy, it becomes possible to determine a unique elemental composition, C c H h N n O o S s , for each of up to 20,000 resolved peaks in a single mass spectrum. That capability has spawned the field of "petroleomics," namely, correlation (and ultimately prediction) of the properties and behavior of petroleum and its products from detailed chemical composition. 3 Moreover, as a separation technique, FT-ICR offers 200x higher "peak capacity" than any single-stage wet chemical separation method (GC, LC, gels, etc.)--thus, it is often possible to analyze samples directly without prior treatment. The principles, techniques, capabilities, and limits of ultrahigh-resolution mass analysis will be described, along with applications spanning petroleum crude oil, distillates (vacuum gas oil and refined fuels), coal, and asphaltenes.

Érika C.A.N. Chrisman, Peter R. Seidl , Priscila de Oliveira Menechini, Sonia M.C. de Menezes, Ronaldo C. Silva, Alexandre M.N. Carauta - Paper

The Influence of Sample History on Structures of Petroleum Asphalthenes Generated from Analytical Data

Chemical structures of petroleum asphaltenes that fit experimental data are based on analytical information from several sources. In particular, those that reflect aggregation phenomena of asphaltenes are strongly dependent on certain features of their representative components. Modeling studies indicate that the number and arrangement of aromatic rings will be responsible for the stabilization that arises from p - p stacking of the aromatic ring systems while the presence of naphthenic rings will determine the stereochemistry of the association process, limiting the interactions among these systems. The energy that may be gained on forming an aggregate from individual molecules is thus strongly dependent on such molecular properties. NMR is the most reliable source of this data as long as the conditions for processing the corresponding signals are observed. Quantitative 1 H and 13 C NMR spectra of asphaltenes from the same sample, extracted when received and after six months by the same method, were compared to spectra corresponding to those extracted using small variations of the IP 143 method generation. Minimal changes in the conditions that are employed lead to significant differences in the proportions of aromatic carbon types and naphthenic rings. These discrepancies would result in the generation of distinct average structures for the same constituent based on NMR and elementary analyses, and the prediction of quite distinct properties for their respective aggregates.

Yuesheng Cheng and Abdel M. Kharrat - Paper

Asphaltene Aggregation in Chloroform Studied by NMR Relaxation Times and Self-Diffusion Measurements

Asphaltenes play an important role in oil production, transportation and refining. Many advanced techniques have been applied to investigate the colloidal nature of asphaltenes. In this work, we present a preliminary study of asphaltene properties by low field NMR techniques of relaxation and diffusion. The asphaltenes were extracted from crude oils using heptane as titrant. Various asphaltene solutions (0.1 – 10 g/L) in the presence of chloroform as solvent have been studied by 2 MHz 1 H NMR. The experiments lead to the following observations. A linear relationship exists between T1 and T2, and asphaltene concentrations in the range we investigated. The observed self-diffusion coefficients of chloroform in an asphaltene solution are lower than that of pure chloroform because the asphaltene aggregates obstruct the paths of the chloroform molecules. The obstruction factor (D eff, CHCL3 /D 0 ) is about 0.5, which depends on the topology of the asphaltene aggregates.

For the two limited cases, the obstruction factor is 2/3 if the self-diffusion confines to the lamellar region; and the obstruction factor will be 1/3 (Physical Review E, 62, 8182 (2000)) if it confines to the cylindrical region (negligible diameter). Our experimental results fall between 2/3 and 1/3, which indicates the asphaltene aggregates may exist in a cubic liquid-crystalline phases, which consist of bicontinuous regions of chloroform and asphaltenes. Chloroform network is separated by the asphaltenes formed surfaces. In addition, the obstruction factor maintains constant as the asphaltene volume fraction is increased. This is explained as at the investigated asphaltene concentration range the bicontinous meso-phase still maintains. We intend to present further results on aggregation of asphaltenes as impacted by pressure and temperature.

Dettman H.D., Salmon S.L., Rodgers, R.P., Schaub, T.M. and Marshall, A.G. - Paper

Athabasca Asphaltene Structure

Molecular characterization of oil components is important for understanding and modeling petroleum behavior during production and refining processes. For those components with boiling point (bp) <524 ° C, gas chromatography (GC) can be used to separate species before analysis. For asphaltenes (bp>524 ° C) GC cannot be used but gel permeation chromatography (GPC) has proven useful (Dettman et. al. Energy & Fuels, 2005, 19, 1399-1404). Analyses of Athabasca asphaltene GPC fractions reveal that the asphaltenes consist of two types of species: “crunchy” (graphitic in appearance) and “oily”. GPC, high temperature simulated distillation, and vapor pressure osmometry (VPO) results suggest that the “oily” asphaltenes comprise the lowest molecular weight (mw) species while the “crunchy” asphaltenes have the highest mw. Low resolution MS of the oily asphaltenes confirms that these species were separated by size with mw values between 400 and 2000 g/mole. VPO results were similar to the average MS values for the largest of these species (1700 g/mole) while the VPO results for the smallest species suggest that these “oily” asphaltenes are multimeric. For the “crunchy” asphaltenes, a wide range of mw species was also detected by MS (from 200 to 2000 g/mole). However, the average mw was lower than that of the largest oily asphaltenes (700 g/mole compared to 1700 g/mole) and was considerably lower than that measured by VPO (6000 g/mole). The roles of metals and chemical structural differences between “crunchy” and “oily” asphaltenes with respect to their apparent molecular sizes, along with recent high resolution FT-ICR MS results, will be discussed.

J. Murgich, H.J. Franco, P.S. Alejos and O.P. Strausz - Paper

Molecular Modeling of The Aggregation of Resins Aromatics and Archipelago Asphaltenes from the Athabasca Crude Oil

The existence of aromatic regions linked with saturated chains in asphaltenes of the archipelago type allows the formation of complex aggregates with other components of the crude. These asphaltenes may form bridges between different aggregates. Some tangling between the chains is also likely to occur leading to the formation of extremely complex aggregates. These will have empty spaces that increase the energy due to the loss of attractive inter-atomic contacts. Therefore, these spaces are likely to be filled by smaller molecules of appropriate volume and shape to stabilize the aggregates. In order to study these types of aggregates, the energy of interaction between different model asphaltenes, resins and aromatics from Athabasca was calculated using Molecular Mechanics. It was found that the global shape of the aggregates was influenced by the solvent and that the interaction between asphaltenes, resins and aromatics was determined by the extension and number of aromatic regions and the number of H bonds present. Both resins and aromatics produced aggregates with a significant distribution in energies showing that some of them form aggregates with the asphaltenes of longer lifetimes than others.

Keith L. Gawrys, George A. Blankenship, and Peter K. Kilpatrick - Paper

On the Distribution of Chemical Properties and Aggregation of Solubility Fractions in Asphaltenes

Asphaltenes from B6, Canadon Seco (CS), and Hondo (HO) crude oils were separated on a preparatory-scale into 20 - 30 so-called “fine fractions” by sequential precipitation from mixtures of n-heptane and toluene. Chemical analyses were performed to measure the carbon, hydrogen, nitrogen, sulfur, oxygen, and trace metals contents of the fractions. Small angle neutron scattering (SANS) was performed on fractions dissolved or dispersed in mixtures of d-toluene (or d-methylnaphthalene) and d-methanol to determine the average aggregate size. Statistical analyses were performed to calculate the weighted moments of each elemental parameter assuming the data were “normally” distributed. High values of the standard deviation and skewness due to early precipitation of metal oxides and inorganic salts suggested that a Gaussian distribution was inappropriate to describe the behavior of most metals. H/C, N/C, and S/C ratios in B6 and HO asphaltenes appeared to obey a Gaussian distribution with mean values approximating the average values for the whole asphaltenes.

For CS asphaltenes, the initial 10 % of precipitated material were generally less aromatic than the remaining fractions. Coefficients of linear correlation were calculated for the chemical composition, solubility, and aggregate size parameters and provided a statistical means of determining the properties of the asphaltene fractions that promoted aggregation and precipitation. Polar and hydrogen-bonding interactions appeared to be more important than dispersion interactions in the precipitation of B6 and HO asphaltenes. In particular, interactions of metalloporphyrins appeared to play a key role in the asphaltene aggregation mechanism. On the other hand, dispersion interactions likely dominated the solubility of CS asphaltenes.

Yosadara Ruiz-Morales and Oliver C. Mullins - Paper

Characterization of Asphaltene Fused Ring Systems Comparing Molecular Orbital Calculations with Optical Spectroscopy

One of the more important unresolved issues for asphaltenes is the nature of their polycyclic aromatic hydrocarbon (PAH) ring systems. A variety of studies, including chemical stability studies show that the asphaltene PAHs are predominantly pericyclic. The question remains – what is the distribution of the number of fused rings in asphaltene PAHs? There is a plethora of readily obtained optical absorption and fluorescence emission data for asphaltenes, all dependent on this ring distribution. However, interpreting this data quantitatively has never been accomplished. Here, we perform molecular orbital (MO) calculations on ~100 different, predominantly pericyclic PAHs with differing fused ring numbers in order to determine corresponding absorption and fluorescence emission spectral predictions.

The ZINDO methodology was employed here and these results were checked favorably against ab-initio calculations. The optical spectral parameters are shown to depend critically on both ring geometries and ring number; the expected red shift with greater ring number is obtained. By comparing MO spectral predictions with constraints from both optical absorption and fluorescence emission we find that the mean number of fused rings for virgin petroleum asphaltenes is 7, with a range in this number spanning roughly 4 to 10. Comparison of the results with other relevant data is presented.

Martin G. Chodakowski, Bei Zhao and J. M. Shaw - Paper

On Reducing Ambiguity in the Interpretation of Small-Angle X-ray Scattering Data for Asphaltene Shape or Size Distribution Evaluation

Small Angle X-ray Scattering (SAXS) is an important technique for studying the size, shape and nature of supramolecular structures in both solids and fluids. SAXS has been applied successfully to the study of nano-scale tubes produced through self assembly of molecules, nano-scale powders, nano-porous catalysts, supramolecular structures in plastics and polymers, metals, solid-fluid suspensions, to cite but a few examples, and has been applied to the description of asphaltene shape and size distribution as well. The hallmark of successful applications is that independent measurements of the shape, size and structure of the domains of interest be available. This is critical, as scattering emission curves obtained from SAXS are smooth and featureless, with the exception of cases where the domain of interest is mono dispersed and spherical.

We show in this contribution that without exogenous knowledge concerning the size, shape and nature of the domains under investigation, SAXS emission data are readily over-interpreted or misinterpreted and their value for such applications is severely restricted. For example, SAXS emissions for carbon nanotubes are readily described as a narrow distribution of spheres, without fore knowledge. We also report on our first attempts to reconcile independent leading dimensions for asphaltenes with SAXS measurements by contrasting SAXS measurements for as-received and nano-filtered Athabasca Bitumen and Maya Crude samples where aggregates greater than 20 nm in diameter are eliminated. Results obtained to date are mixed.

Donald F. Smith, Ryan P. Rodgers, Parviz Rahimi, and Alan G. Marshall - Paper

Self-Association of Organic Acids in Canadian Athabasca Bitumen Characterized by Negative Ion Electrospray Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Negative electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is a powerful tool for characterizing complex mixtures such as petroleum. Negative-ion electrospray ionization selectively ionizes acidic species without prior sample fractionation. The ultrahigh mass resolving power (m/?m 50% >350,000) and high mass accuracy (better than 1 ppm) of FT-ICR MS enables the assignment of unique elemental compositions for each peak in the mass spectrum. Negative-ion ESI FT-ICR MS allows for the detailed characterization of acidic species in petroleum samples according to the class (heteroatom content), type (number of rings and/or double bonds, or double bond equivalents), and carbon number distributions.

Here, the self association of organic acids in Athabasca bitumen is characterized by negative-ion ESI FT-ICR MS. Three bitumen distillation cuts were analyzed; 375 – 400 °C, 450 – 475 °C and 500 – 525 °C. Concentrations from 0.01 – 5 mg/mL were tested. Surprisingly, the lowest boiling cut displays the highest degree of self-association, with dimerization present at a concentration as low as 0.05 mg/mL. Quadrupole linear ion trap negative-ion ESI mass spectra confirm the earlier onset of self-association in the lower boiling distillation cut. Compositional variations in the acidic species in each distillation cut along with details of their concentration dependent aggregation will be discussed.

A. B. Andrews, R. Guerra, K. Ladavac, O.C. Mullins and P. Sen - Paper

Molecular Diffusivities of Asphaltene Monomers by Fluorescence Correlation Spectroscopy

Many analytical techniques have been applied to elucidate the properties of asphaltenes due to their extraordinary importance in the petroleum industry. Despite significant progress in determining structural and aggregation properties of asphaltenes, many fundamental issues such as the molecular size are still in debate. Fluorescence Correlation Spectroscopy (FCS), a preeminent technique for studying the kinetics of single molecules, is used to measure the translational diffusion coefficient of asphaltene molecules in toluene at extremely low concentrations (< .001g/L). To avoid focal volume artifacts common in FCS we use a scaling procedure to determine asphaltene diffusivities relative to known dye molecules such as porphyrins, perylene and coumarin 30. Estimates of the monomer size using the Stokes-Einstein equation agree favorably with earlier estimates based on rotational diffusion measurements, yielding an unaggregated hydrodynamic diameter somewhat larger than porphyrins, confirming that the molecular weight is less than 1000 amu.

Sonia M.C. de Menezes, Peter R. Seidl, L. Tasic, Alexandre N. M. Carauta, Erika C.A.N. Chrisman - Poster

Structural Information on Petroleum Asphaltenes from NMR Data

Modeling studies on petroleum asphaltenes that fit experimental data are based on structural information from several sources. Aggregation phenomena of asphaltenes isolated from vacuum residues processed in Brazilian refineries, in particular, are strongly dependent on certain features of the molecules that are chosen as their representative components. In a decreasing order of importance these are: the number and arrangement of aromatic rings; the number and position of naphthenic rings; the number and position of side chains; the types and functionality of the heteroatoms that are present; the length of the side chains; and the position of ramifications on side chains. NMR provides the most reliable source for this type of information if the proper precautions are observed in processing quantitative spectra. The 1 H and 13 C spectra of the same sample were obtained and processed using three different procedures reported in the literature. Depending on the method chosen, different proportions of aromatic carbon types and other relevant parameters are observed, generating different structures for respective average molecules. As a consequence different stabilization energies for their respective dimers (used as models for aggregation studies) are also expected.

Peter R. Seidl, Jacques F. Dias, Alexandre M.N. Carauta and Lina C. Navarro Quintero - Poster

What Can Modeling Tell Us About Asphaltene Structure?

Most of the problems in production, transportation and refining heavy petroleum fractions can be traced to the presence of asphaltenes. They are a class of compounds defined essentially by the extent that they dissolve in certain media rather than any chemical property and correspond to such complicated isomeric structures that separation into individual constituents is an almost hopeless task. Modeling can be of considerable value in estimating properties. Computer simulations have reached a point in which many experiments may be run on models that represent classes of compounds. Structures can be generated and their respective properties simulated in a fraction of the time and cost of making measurements or running experiments. Defining asphaltenes as the constituents which are most prone to self-associate, tentative structures that best fit analytical data (especially NMR spectra) can be calculated by molecular mechanics (MM) and molecular dynamics (MD) and used to generate monomers, dimers, trimers and tetramers of a given sample. Respective energies may be used to identify the features that are most relevant for formation of stable aggregates. and verify to what extent their behavior under certain conditions reproduces experimental data. Care must be taken in choosing methods, however, since not all of the commercially available programs are suitable for the required MM/MD simulations.

Alexandre N. M. Carauta, Julio C. G. Correia, Peter R. Seidl - Poster

Computational Simulation of Asphaltenes: A Study of Aggregation and Thermal Stability

Asphaltene aggregation is probably responsible for several problems related to fouling and deposition in the petroleum industry.  It would thus be highly desirable to develop representative models for asphaltene compounds and probe their behaviour under certain conditions.  From data relative to "cleaner" asphaltenes extracted by the IP 143 method, the solubility of model compounds found in vacuum residues from Brazilian refineries could be sucessfully predicted by a combination of molecular mechanics/molecular dynamics (MM/MD) methods.  A similar approach may be employed to compare energy-minimum conformations of respective monomers, dimers and amorphous structures.  Hildebrand solubility parameters were calculated and used to estimate the solubility of aggregates. Their thermal stability at different temperatures was studied by MD and was shown to be stable up to around 573 K. 

Vincent J. Verruto and Peter K. Kilpatrick - Poster

Selective Solvent Entrainment in Asphaltenic Aggregates

Previously we have applied a geometric form factor model to SANS spectra from asphaltenic aggregate with considerable success. This oblate cylinder model, with radial polydispersity, enabled reproducible determination of solvent entrainment in asphaltenic aggregates. Typical values for solvent entrainment were 30-50 vol% of the aggregates, depending on the asphaltene and solvent. Our latest investigation looks to extend the scope of this previous SANS work, with a particular interest in mixed solvent systems.

Oliver C. Mullins - Poster

Asphaltene Molecular Architecture

To be predictive in asphaltene science, it is necessary to understand asphaltene molecular structure; a review of this latter topic is provided herein. All molecular diffusion measurements using four very different techniques, some newly published, are in accord with all mass spectral techniques excepting laser desorption measurements. These results are presented. The size of the fused aromatic ring systems are discussed; results here rely on optics with molecular orbital calculations, as well as on direct molecular imaging. In addition, the ‘like your hand' model of asphaltene structure is compared with the ‘archipelago' model. Both nondestructive and destructive techniques are considered as well as other known constraints. Finally, important new predictions based on the above conclusions are discussed.

Jose Gregorio Delgado-Linares, Carlos Rodriguez-Abreu, Ana Forgiarini, Johnny Bullon, Hironobu Kunieda - Poster

Properties of Venezuelan Asphaltenes in the Bulk and Dispersed State

Asphaltenes are associated with several problems in crude oil production and processing. We present a comprehensive study on the properties of bulk and dispersed Venezuelan asphaltenes using several experimental techniques such as Small Angle X-ray Scattering (SAXS), Rheometry, Differential Scanning Calorimetry (DSC), Spectroscopy, Electrophoretic Measurements, and Interfacial Tensiometry. It was found that asphaltene fractions are complex mixtures with the ability to form microstructures that might play a role in floculation and precipitation behavior. Saponificable (acidic) groups seem to be very important for the interfacial and dispersive properties of asphaltenes, as confirmed by results on the stability of asphaltene-containing water/toluene emulsions.

Do-Gyun Kim, Ryan P. Rodgers and Alan G. Marshall - Poster

Isolation and Characterization of South American, Middle Eastern and North American Crude Oil Asphaltenes and Coprecipitants by Negative-Ion ElectroSpray Ionization FT-ICR Mass Spectrometry

Prior high resolution mass spectrometric applications have focused on the characterization of polar materials in crude oils, bitumens and their SARA isolated fractions by Electrospray Ionization (ESI) FT-ICR mass spectrometry. 1-3 The selectivity of the ESI process effectively ionizes acidic and basic species without interference from the bulk hydrocarbon matrix. However, less polar sulfur containing species are rendered unobservable due to their low ionization efficiency. Furthermore, polar sulfur species are often overwhelmed by the more abundant polar species and therefore, if observable, are present at low signal to noise. In this work, we focus on the compositional characterization of both polar and slightly polar sulfur species in asphaltene and resin isolated fractions to provide insight into their compositional variation in the whole crude.

Desirée Lima, Rafael Muñoz and Henry Labrador - Poster

To Examine the Effect of an Agent Precipitant on the Formation of Films of Asphaltenes on Glass Sheets using the Ellipsometry Technique

Adsortion of asphaltenes on glass surface has been studied by ellipsometry. This technique was used to measure the thickness of the thin films formed by the asphaltenes of Guafita and DML-153 varying the concentration among 0.1 to 3 g/L in toluene measured to room temperature and adding a precipitant agent below its flocculating threshold. It was observed that the agent's precipitant presence induces the increase of the thickness of the films in both asphaltenes, and a multicapas formation is found, the volume of the n-heptane is independent of its quantity, small volumes induce to the instability of the asphaltenes in solution favouring the adsorption on the basis increasing the thickness. This could also be proven using an optic microscope using an increase of 400X, where was found an increase of the presence of aggregates, when you increase the volume of the n-heptane added at the asphaltenes solution, and the necessary time for the formation of the films was enough with 24 hours. The ellipsometry is very useful for the study of the thickness films of asphaltenes.

Juan Pereira , Jose Tovar and Rafael Muñoz - Poster

Effect of Resins in the Thicknesses of Asphaltene Films Adsorbed on Glass

By their interfacial nature asphaltenes are adsorbed on many interfaces. Due to their complex nature, the asphaltenes can form an interfacial film that influences its properties such as adsorption, stability of W/O emulsions, etc. In this work the thicknesses of films of asphaltene appear adsorbed on glass measured by ellipsometry. The interval of thicknesses obtained was of 5-128 nm, for concentrations of asphaltenes in toluene of 200-10,000 mg/L. For all the studied systems the formation of diverse sizes of aggregates is corroborated, that they suggest the existence of several mechanisms of interaction in each case. The extraction of a greater amount of resins of the asphaltenes, as large as allows to a diminution aggregates of asphaltenes adsorbed in the surface of the substrate, that was demonstrated by means of the thickness of films. The refractive index of the films tends to be constant as it increases the concentration.

Jeremiah M. Purcell, Ryan P. Rodgers, Christopher L. Hendrickson and Alan G. Marshall - Poster

Molecular Analysis of Asphaltenes by Negative Ion Atmospheric Pressure Photoionization (APPI) Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Electrospray ionization (ESI) coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) has provided great inroads for the speciation of the polar maltene and asphaltene fractions of petroleum. Because the ESI mechanism involves proton transfer reactions, it selectively ionizes those acids (negative) or bases (positive) that can either lose or gain a proton. However, a limitation of ESI is that it will more efficiently ionize the most acidic/basic species. Atmospheric Pressure Photoionization (APPI) ionizes both polar and non-polar compounds in petroleum thereby expanding the mass spectral coverage to nonpolar species of interest. Since the APPI ionization mechanisms primarily consist of dopant-assisted proton transfer reactions and charge exchange reactions that target aromatic ring systems, polars and non-polars, it should provide speciation of highly aromatic, less polar asphaltenes not observed by ESI. Initial results of negative-ion APPI FT-ICR MS have resulted in the assignment of >12,000 unique molecular formulas across a 400 Dalton mass window with 60+ mass spectral peaks per nominal mass. In this work, we shall employ ESI and APPI coupled to 9.4 Tesla FT-ICR MS and present an extensive comparative molecular speciation of the asphaltenes of a South American crude and an Arabian medium crude.

Ryan P. Rodgers, Do-Gyun Kim, Jeremiah M Purcell and Alan G. Marshall - Poster

Characterization of Sulfur Species in Petroleum Asphaltenes and Resins by FT-ICR Mass Spectrometry

Prior high resolution mass spectrometric applications have focused on the characterization of polar materials in crude oils, bitumens and their SARA isolated fractions by Electrospray Ionization (ESI) FT-ICR mass spectrometry. 1-3 The selectivity of the ESI process effectively ionizes acidic and basic species without interference from the bulk hydrocarbon matrix. However, less polar sulfur containing species are rendered unobservable due to their low ionization efficiency. Furthermore, polar sulfur species are often overwhelmed by the more abundant polar species and therefore, if observable, are present at low signal to noise. In this work, we focus on the compositional characterization of both polar and slightly polar sulfur species in asphaltene and resin isolated fractions to provide insight into their compositional variation in the whole crude.

Juan Pereira, Freddy Silva, Reinardo Salas, Celeste Fernández and Caribay Urbina - Poster

Advances in the Studies of Resin Adsorption on Asphaltene

The main causes of asphaltenes deposition are not completely understood at the present. The strong interactions between asphaltenes and resins have been proposed as the causes of stability in colloids in crude oil. In this work the resin adsorption of the crude Guafita studied, Apure, Venezuela, on different substrates in n-heptane from 25 °C. The isotherm of adsorption on asphaltene showed to a behavior linear or type C, which indicates that the resins can penetrate the structure of the asphaltene. The adsorption of asphaltene was made from solutions in toluene between 200-2000 mg/l on silica, and these solid was used like adsorbent. The behavior observed for each one of the isotherms on asphaltene/silica, was very similar and of type C, Langmuir and in multilayers. From different adsorbent asphaltene/silica from studied, the corresponding one to the concentration of 800 mg/L with an adsorption of 160 mg of resin, turned out to be the best one. This way it is suggested to use this adsorbent one for later studies of the interaction asphaltene-resin from. An increase of the amount of material could be observed adsorbed in the adsorbent ones up to 800 mg/L, in the rest of the samples was not clear the behavior. These results rather suggest it amount of resins that is adsorbed directly does not depend on the amount of asphaltene adsorbed on the silica, but of the chemical nature of the asphaltene aggregate.

Session on Thermodynamics of Heavy Oils and Asphaltenes

Stig E. Friberg - Keynote Presenter

Micellization in Water and in Non-Polar Liquids – Entirely Different Phenomena

Micellization in water and in non-polar liquids are two distinctly different phenomena. The former process is best described as a frustrated phase separation, while the latter is a gradual association process similar to the dimerization of alcohols or carboxylic acids.

The first process is based on two phenomena:

1. The low solubility of surfactant causing phase separation and

2.  The perturbation of the structure of the potentially separated phase by the repulsive forces of the surfactant polar groups.

In short, the structure is characterized by an association structure with weak intermolecular forces and a surrounding liquid with strong intermolecular forces. Hence, the high surface tension of the surrounding medium becomes a useful tool to determine the onset of micellization.

The association in non-polar liquids to inverse micelles, on the other hand, takes place because of strong intermolecular forces between the associating molecules. The molecules in the surrounding medium have weak intermolecular forces and the low surface tension is not a useful tool to obtain information about the process.

The lecture will clarify the difference between phase separation due to low solubility and micellization in aqueous environment and will show a simple proof that the repulsive forces are the vehicle preventing phase separation. It will subsequently clarify the importance of intermolecular forces for inverse micelles and demonstrate different combinations of surface active molecules to achieve the association. For special cases of inverse micellization in non-polar liquids the weak ordering effect of the micellization may specifically expose methyl parts of the surfactant hydrocarbon chain leading to a small reduction of the low surface tension of the non-polar liquids. For these cases the small change of surface tension will provide some information about the association process.

S. Correra and D. Merino-Garcia - Paper

Simplifying the Thermodynamic Modelling of Asphaltene Behaviour

Asphaltene deposition is a significant problem in oil production and transportation. There is a great effort directed into understanding the nature of this phase separation. The hypothesis drawn on the nature of the separation sets the characteristics of the model applied to describe the behaviour of asphaltenes. The literature about asphaltenes is very vast, and so is the number of hypothesis on the nature of the separation: the theories applied include liquid-liquid equilibrium, solid-liquid equilibrium, liophilic colloid formation and even a colloidal-micellar approach.

The approach followed is based on two points: a liquid-liquid separation, and the critical influence of the solvent quality on the stability of asphaltenes. Therefore, the previously developed model (OCCAM) makes use of the concept of solubility parameter. In this work, the Regular Solution model is simplified by assuming the asphaltenes to be in infinite dilution regime. It is further demonstrated that, this simplified Regular Solution model is exactly the same as the previously proposed OCCAM model. In fact, at infinite dilution, the interaction parameter ( c ) of the Regular Solution model becomes constant and equal to 1. After demonstrating that OCCAM Model is related to Regular Solution, it has been applied to describe the Propane De-Asphalting of oil in a column.

P. Peczak, Mark A. Stadtherr, and Youdong Lin - Paper

Reliable Computation of Phase Stability and Equilibrium for Gibbs Energy Model

Numerical modeling of multiphase equilibria at constant temperature and pressure is a challenging computational problem. This is because the standard flash-calculation approach may fail by converging to trivial or nonphysical solutions or to a point that is a local but not a global minimum. A similar problem is also encountered when calculating the phase boundary curves on the phase diagrams. We are reporting here an application of a recently developed interval method, based on an interval Newton/generalized bisection algorithm, to calculate the phase boundary curves of ternary mixtures for an excess Gibbs energy model. The interval method is completely reliable because it is initialization-independent, immune from rounding error, and provides both mathematical and computational guarantee of global optimality.

Though the applied technique is general-purpose, the presented application focuses on recently-developed model for liquid-liquid phase behavior of heavy-hydrocarbon fluids. The phase stability analysis has been used to calculate the coexistence curve for model ternary mixtures of asphaltene, maltene, and solvent. We have demonstrated that the new approach, the tangent-plane method of Baker and Michelsen, combined with the interval analysis, requires no assumptions regarding the number of phases and it leads to unambiguous results. The new technique eliminates the problems of the conventional flash calculations and hence it can be used to determine complete multinary phase diagrams of mixtures.

Wojciech Marczak, Honggang Zhou and Marek Rogalski - Paper

Physical State and Ageing of Flocculated Asphaltenes

The phase transition leading to the petroleum asphaltene flocculation is considered either as a liquid-solid or a liquid-liquid transition. In spite of the fact that asphaltenes obtained by the usual procedure are amorphous solids, numerous arguments support the second hypothesis. In this work we present results of asphaltene flocculation kinetics and we compare the results with kinetics of coalescence of flocculated asphaltenes that were re-dispersed mechanically in the solvent. Re-dispersion of flocculated asphaltenes was realized using a ultrasound bath. Kinetic measurements were performed using dynamic light scattering technique. The Malvern 4800 apparatus used in this study makes it possible to follow the growth of aggregates in the range 2 ­ 5000 nm. It was observed that kinetic curves of re-dispersed asphaltenes are very similar to those corresponding to the initial flocculation induced by an anti-solvent. This finding confirms the liquid-like behaviour of flocculated asphaltenes. Moreover, the energy of cohesion of asphaltene aggregates and consequently the amount of energy needed to re-dispersion was very low.

The ageing of the flocculated sample accelerates the aggregation kinetics that indicates that very slow reorganisation of the asphaltene structure leads to more compact, solid-like flocs.

J. M. Shaw - Paper

Challenges and Misconceptions: Bitumen and Heavy Oil Thermophysical Property Measurement and Prediction

Bitumen and heavy oil pose numerous challenges for thermophysical property measurement and prediction. Chief among them are their opacity to visible light and difficulties associated with their speciation. The apparent irreproducibility of viscosity, density and other physical property measurements, even at room temperature, and the inability to predict even the vapour pressure of these materials comprise but a few examples that point to a fundamental lack of understanding of these materials and their properties. As a consequence, unwarranted assumptions are made that have consequences for the successful development and operation of processes for the production and refining of these increasing important hydrocarbon resources. In this contribution, recent results from our laboratory which show that these materials possess a minimum of two phases at room temperature and that they exhibit classic polymorphic behaviours which account for apparent measurement irreproducibility as well as our inability to predict thermophysical properties, with any degree of certainty, are discussed.

Eric B. Sirota, Pawel Peczak, Min Lin and Hasnain Rangwalla - Paper

Asphaltenes: Phase Behavior and Viscosity

We have previously highlighted the problems which arise when interpreting asphaltene data with the prior assumptions of colloidal or micellar behavior. [Energy & Fuels 2005, 19, 1290-1296] This includes, for example, the small-angle scattering from compositional fluctuations as occur in any one-phase liquid mixture of unlike molecules, which were often interpreted as though the scattering arose from asphaltene colloidal aggregates. Asphaltenes are, in-fact, molecules which can undergo a thermodynamic liquid-liquid phase separation from solution. That said, one cannot use simple versions of solution theory to explain the behavior, because most approximations one might consider, are not likely to be valid. The fractal-like morphology exhibited by asphaltenes has been shown to be related to the asphaltenes high glass transition temperature, and the viscous behavior of asphaltenes has been shown to be a result of the proximity of the mixture to the glass transition. We will elucidate the above, with recent results on phase behavior and viscosity.

Liyan Zhang, Zhenghe Xu and Jacob H. Masliyah - Paper

Adsorbed Bitumen Films at Solvent/Water Interfaces

Stable water-in-bitumen emulsions are detrimental in the commercial operation processes of bitumen extraction processes from oil sands in Alberta . These emulsions are stabilized by the formation of interfacial films due to adsorption of natural surfactants in bitumen to the bitumen/water interface. It is therefore important to study the adsorption phenomenon of nature surfactants in bitumen to the oil/water interface in order to better understand the mechanism of emulsion stabilization.

In this regard, the interfacial characteristics of adsorbed interfacial films from adsorption of natural surfactants in bitumen at a solvent/water interface were studied using a Langmuir interfacial trough. A novel method was used to investigate the adsorption of interfacial active components from bitumen at a solvent/water interface. In this method, a prepared bitumen-in-toluene solution at a given concentration and volume was injected into the bulk solvent topphase. This method is different from the conventional method of preparing an interfacial film by spreading a bitumen-in-toluene solution at the air/water interface first and then covering the interface with a bulk solvent phase. We choose a mixture of heptane and toluene, termed as heptol , as the solvent to simulate commercial naphtha used in commercial froth treatment processes. This approach allowed us to study the effect of solvent aromaticity by varying the ratio of heptane to toluene on adsorption of interfacial active components in bitumen at oil-water interfaces.

In this study, the adsorption kinetics of surface or interfacial active components in bitumen at the solvent/water interface was recorded as a function of time. After 30 minutes, the adsorbed bitumen films at a given solvent/water interface were compressed. Interfacial pressure-area isotherms showed that the highest attainable interfacial pressure increases as a function of heptane concentration in heptol. The adsorbed bitumen film at the heptol-water interface becomes more rigid with increasing heptane concentration in heptol. In general, the interfacial film also becomes more rigid with an increasing concentration of the injected bitumen-in-heptol solutions.

Hussein Alboudwarej, Julian Zuo, Elham Mahmoodaghdam, Abdel M. Kharrat - Poster

Effective Tuning of Wax Thermodynamic Models

Wax thermodynamic models are mainly used to predict the wax appearance temperature (WAT) locus for a particular hydrocarbon fluid. Except for well-defined fluid compositions, wax thermodynamic models are not intrinsically predictive and need to be tuned with some experimental data. Experimental WAT are traditionally used to tune these models. However, measured WAT is known to be lower than the thermodynamic WAT. A more effective approach is to tune the wax thermodynamic models to the composition of precipitated wax under fixed conditions of pressure and temperature.

In this study three live waxy crude oils were used to evaluate this approach. The wax content of the oils varied between 7.9 to 13.8 wt % (n-alkanes) with a corresponding API gravity of 34.5 to 37.3 degree. WAT were measured for live oils using high-pressure cross-polar microscopy (HPCPM) and light scattering techniques. The precipitated waxes were collected at two temperatures below the measured WAT using 0.2 micron filters for selected pressure points. Original oils and the collected waxes were analyzed for composition using high temperature gas chromatography (HTGC) method. A thermodynamic model developed based on modified UNIQUAC activity coefficient model was used to model wax precipitation.

Modeling results indicated that in all cases the predicted thermodynamic WAT locus (with no tuning) is higher than the measured WAT. Model tuned to the composition of the precipitated wax was able to accurately predict the precipitation amount and composition at other conditions. It was also shown that the precipitation of only a very small amount of wax could shift the thermodynamic WAT to match the measured WAT points. The overall results indicated that tuning wax thermodynamic models to precipitated wax compositional data provides more accurate predictions.

William C. McCaffrey, Jeffrey M. Sheremata, Murray R. Gray, Alan E. Nelson, Heather D. Dettman - Paper

Pure component and ensemble property predictions based on quantitative molecular representations

The development of advanced methods to recover and process heavy oils is hindered by the complexity of the feed as well as the lack of detailed models that can be used to predict properties and reactivity. Quantitative molecular representations are evolving into a tool that will have tremendous predictive power in the future. The advantage of quantitative molecular representations is that they can be used to reconcile a large variety of analytical data into a manageable and realistic set of molecules. These models can then be used in combination with group contribution based methods for the estimation of pure component and ensemble properties such as normal boiling point, critical temperature, critical pressure, critical volume, standard enthalpy of formation, standard enthalpy of vaporization, standard Gibbs energy, normal melting point and standard enthalpy of fusion. Molar volumes for the individual molecules can also be predicted using molecular dynamic calculations. Of interest to petroleum phase behaviour, solubility parameter data can also be calculated from the quantitative molecular representations.

Honggang Zhou, Grégoire Porte, Véronique Lazzeri, and Valérie Montel - Paper

A Consistent Interpretation of the Intriguing Solubility Properties of Asphaltenes in Apolar Solvents

Asphaltenes precipitation often has catastrophic impact on oil production and transportation. Yet, their unique solubility properties in apolar solvent remains to date poorly understood. The precipitation threshold appears remarkably insensitive to the degree of dilution. Moreover, resins, which are usually considered as more soluble asphaltene fractions, have strong cosolubilising power on the most insoluble asphaltene fractions. In this work, some controversial topics such as asphaltene molecular weight, critical concentration of nano-aggregation, size of nano aggregates, role of resins are discussed. A modeling method is also proposed. Our purpose here is not to add one more thermodynamic model pretending to predict accurately the asphaltene precipitation, but rather to build up a consistent qualitative explanation of these intriguing facts. In our interpretation asphaltene in good solvents always self-assemble in presumably 2-D aggregates due to strong specific attractive interactions. Precipitation then occurs when shifting down the quality of the oil solvent due to non-specific dispersion forces. Within this picture, the ultra low sensitivity to dilution and the cosolubilising effects are easily understood. We present recent measurements of critical nano-aggregation concentrations (CNAC), the effect of fractionation on the precipitation thresholds as well as neutron scattering data against which the consistency of our general scheme is further checked.

Douglas J. Escalante A., and Vladimir León - Poster

Determination of the Free Energy Adsorption of Crude Heavy Oil Venezuelan on Minerals of Reservoir by Means of the use of the Superficial Tension Components

One of the main problems that present the crude heavy oil is the strong adhesion that this display to the reservoir rock and one of the properties that contribute to this adhesion is viscosity, which very is elevated in this type of crude oil. But in addition to this property there is another one that plays a fundamental role in the adhesion phenomenon, as it is the superficial and interface tension of these crude oils and the form to relate this property to the adhesion it is by means of the use of the superficial tension components. These Parameters were introduced to beginning of the 90, by C. J. van Oss, and constitute a landmark of great importance in the description of condensed phases polar and their interactions.

In the present work the superficial tension components for the different crude heavy oil Venezuelans were determined, by means of the propose methodology by C. J. van Oss, doing use of these parameters were calculates the values of free energy adhesion of Gibbs, for the systems crude-mineral-water and crude-mineral-methane. Of the obtained results it is appraised that the methane presence in means increases the adhesion of the crude oil to rocks. The determinations of theoretical values of free energy adhesion using the values of the superficial tension component are a great contribution to the oil industry, since it can give an idea us, of the type of interactions present in the reservoir of a fast and simple form.

Doris L. Gonzalez , Walter G. Chapman, Jill Buckley, and George J. Hirasaki - Poster

Asphaltene Deposition Model Evaluation of Coating Materials

The Hamaker-Lifshitz theory of van der Waals interaction has been employed to predict the tendency of asphaltene to deposit on coatings and solid surfaces of interest in oil well tubing design. The understanding of the conditions under which asphaltene start precipitating has improved lately; however there is a lack of understanding about asphaltene deposition on solid surfaces. Although asphaltene precipitation appears to be necessary condition for deposition, sometimes asphaltene comes out of solution and it does not adhere to the surfaces. In this case asphaltene can be produced as slurry and without any plugging problems. To predict the conditions under which asphaltene deposits, we have developed a deposition model using Hamaker-Lifshitz theory that facilitates the prediction of the interaction in a three phase system, crude oil / precipitated asphaltene / solid surface.

In this work, Tuboscope supplied samples used in the coating of tubing to mitigate asphaltene precipitation, New Mexico Tech did contact angle measurements to determine the surface energy of the tubing coating materials using the Zismann technique and, Rice University apply the Deposition Model based on Hamaker-Lifshitz theory to predict the tendency for asphaltene to deposit from the system asphaltene/ toluene / sample solid surface at ambient conditions. Results are compared to common polymer and metal materials.

A. Ortega-Rodriguez, F. Alvarez-Ramirez, S.A. Cruz and C. Lira-Galeana - Poster

Interaction Energy and Adhesion Force between Petroleum Asphaltenes and Some Metallic Surfaces

A simple analytical expression is derived for calculating the interaction energy and adhesion force between petroleum asphaltenes and metallic surfaces of Iron, Aluminum and Chromium embedded in a host solvent. These systems are found in typical oil wells and production facilities of the oil industry. The model assumes that the total molecule-surface interaction potential may be constructed through superposition of corresponding interactions with a relevant number of atomic layers forming the substrate and resorting to the Lindhard continuum planar potential (CPP) approximation, which requires only of knowledge of binary molecule-atom interactions.

Molecular Mechanics (MM) calculations are performed to generate the average binary interaction between the asphaltene molecule and an atom in the substrate, which in turn is represented by a parameterized analytical- physically sound- expression. The resulting CPP yields an analytical expression representing the interaction between the asphaltene molecule and each substrate layer. Comparison between the CPP and MM calculations for the asphaltene- single plane (A-P) and asphaltene- substrate (A-S) interactions indicate reasonable agreement pointing to the adequacy of the CPP method to represent molecule-surface interactions.

Finally, the effect of a surrounding (i.e. solvent) medium is addressed with the use of a dielectric constant of the medium, e , incorporated in the molecule-atom potential. Sample calculations are presented for asphaltene-metallic wall interactions embedded in the following host environments: vacuum ( e = 1), n-heptane ( e = 1.92), toluene ( e = 2.38), and pyridine ( e = 12.3).

F. Alvarez-Ramirez, E. Ramirez-Jaramillo, and Y. Ruiz-Morales - Poster

Calculation of the Interaction Potential Curve between Asphaltene-Asphaltene, Asphaltene-Resin, and Resin-Resin Systems Using Density Functional Theory

In this work we present the calculated analytical form of the intermolecular pair interaction potential in vacuum between asphaltene-asphaltene ( U AA ), asphaltene-resin ( U AR ), and resin-resin ( U RR ) systems using two methods: density functional theory (DFT) and compass-classical force field. The binding energy was obtained varying the minimum atomic distance (contact distance) between the interacting species, and their relative angle; that is, by taking into account all the possible ways of interaction between the species (T-shape, face to face, edge to edge, and random configurations). For the case of the asphaltene molecule we used the proposed Groenzin-Mullins structure and for the resin molecule we used 6-methyl-dibenzothiophene.

The binding energy between the interacting species was obtained using compass-classical force field, DFT with the Harris functional (DFT-Harris), and DFT with the self-consistent GGA Perdew-Wang 91 functional (DFT-SC). The potential curves were obtained by fitting an algebraic expression to the energy vs. contact distance data. The DFT calculations allow taking into account the correlation between the electronic clouds in the molecules, which is not possible to account for with classical force field calculations. The DFT intermolecular dimmer interaction potentials between species a and ß , where a and b correspond to asphaltene or resin species, U aß , are compared with the classical force field results. To validate the quantum and classical calculations we applied the same methodology for the case of the benzene-benzene dimmer and coronene-coronene dimmer.

Our results are compared with experimental and theoretical data reported. We found that the DFT-SC method gives a reliable result of the binding energy and a good description of the potential curve shape. For the asphaltene-asphaltene dimmer, asphaltene-resin dimmer and resin-resin dimmer we found that the preferred configuration corresponds to the face to face orientation. We found that the binding energy for the asphaltene-asphaltene, asphaltene-resin, and resin-resin dimmers are between ~12-15 kcal/mol, ~12-14 kcal/mol and ~4-7.5 kcal/mol respectively.

D.R. Molina V., J. R. Martínez, U. Navarro b, J. Murgich - Poster

Influence of Pressure, Temperature and Solvent on the Onset of the Asphaltene Precipitation from the Castilla Heavy Crude Oil ( Colombia )

In order to determine the influence of different parameters on the onset of the precipitation of the asphaltenes from the Castilla heavy crude oil, a 2 3 experimental design was used. The asphaltenes were dissolved in dichloromethane or toluene and were introduced in a Microreactor NIR where the transmitance of the solution was monitored in order to determine the onset. In each experiment of the design matrix the temperature and pressure were set to predeterminated values and then n-C 7 was added. The analysis of the results showed that for this heavy crude oil, the solvent was the most important variable in determingh the onset, in second order was the temperature and in third the pressure. ( R 2 = 99,99% and R 2 adjusted 99.98%).

M.R.Omidkhah, M. Nikookar, G.R. Pazuki - Poster

Prediction of Phase Behavior of Asphaltene Precipitation in Crude Oil Using SAFT Equation of State

Asphaltene precipitation from reservoir fluids during oil production is a serious problem because it can result in plugging of the formation, wellbores and production facilities. Currently, mechanical and chemical cleaning methods of wellbore are being improvised to maintain production, but these methods are time-consuming and expensive. Asphaltene precipitation also occurs frequently during enhanced-oil-recovery by gas injection which impedes seriously the recovery. A model for correlating and predicting asphaltene precipitation is highly desirable because it would allow the design of injection/production schemes such that asphaltene precipitation can be avoided or minimized.

In this study, at first stage, the Soave-Redlich- Kwong equation of state is modified based on perturbation theory. The parameter of the new cubic equation of state considered reduced temperature and acentric factor dependent. The average of absolute deviations of predicted saturated vapor pressure, vapor volume and saturated liquid density of 40 pure hydrocarbon and non-hydrocarbon compounds are 0.99, 1.94 and 4.29 percent, respectively.Also comparison with the new equation of vaporization of pure compounds is given. The equilibrium parameters such as, , and are calculated using modified equation of state and will applied with the Flory-Huggins model to predict asphaltene precipitation during solvent titration in crude oil.

At the second stage, the Statistical Associating Fluid Theory (SAFT) equation of state (EoS) was used to model asphaltene phase behavior in crude oil under reservoir conditions. The underlying hypothesis of our approach is that molecular size and non-polar van der Waals interactions dominate asphaltene phase behavior in crude oil. The estimated amounts of asphaltene precipitation by this model are compared to the Flory-Huggins model and experimental data. This comparison displays that the predicted amount of precipitation by above mentioned model into crude oil is more accurate than Flory-Huggins model.

P. Peczak and E.B. Sirota - Poster

Asphaltene Precipitation and Liquid-Liquid Phase Separation: A Statistical-Thermodynamic Model and Experiment

We present a novel model of asphaltene precipitation based on a fundamental, physical approach. Our goal is to develop a predictive model for the solid-liquid and liquid-liquid phase behavior of asphaltene-containing streams based on the statistical picture of the interactions in mixtures of complex molecules. The enthalpic interaction between molecules is calculated using the solubility theory. We have developed a novel approach to the entropy of mixing. The petroleum molecules are neither rigid objects where a simple "ideal" form for the entropy of mixing is appropriate, nor are the asphaltenes long flexible polymers for which the Flory-Huggins form is appropriate. We have therefore proposed a novel model where the molecules are represented by a system of rigid, super-structural units. In addition, we recognize, based on scattering data, that the molecules are not randomly distributed, but tend to cluster ephemerally. We therefore have modified the entropic and enthalpic terms of the free energy of mixing by using the effective local composition in the vicinity of a given species.

The novel thermodynamic model yielded first successes by being able to calculate and explain the crossover experimentally observed as the composition of the precipitate is varied, from phase separation where the minority phase is composed of solvent-rich light drops to one with asphaltene-rich dark aggregates.

Wojciech Marczak, Honggang Zhou and Marek Rogalski - Poster

New Model of Surface Layers Formed by Asphaltenes on the Water Surface

Asphaltenes are natural surfactants of the crude oils and play a crucial role in formation and stabilisation of oil/water emulsions. Properties of the films formed by asphaltenes at the water-oil interface are often studied with Langmuir balance technique. By analogy to the classical thermodynamic approach, surface monomolecular layers (Langmuir's films) are usualy described in terms of ?-A-T equations of state, where ? is the surface pressure, A is the area per given number of molecules, usually one molecule or one mole, and T is temperature. Numerous 2D equations of state, were proposed to describing monolayer properties but all of them were found unsuitable with films formed by petroleum asphaltenes on the water surface. Indeed, a sphaltenes exhibit high propensity to aggregation and form multilayer rather than mono-layer films. Here, we present a new model, based on a mechanical approach, that takes this phenomenon into consideration. The model seems particularly suitable for surface layers formed by molecules interacting through strong lateral forces that restrict molecules in their movement at the surface. It yields a good description of Langmuir isotherms of asphaltene on the water surface.

Y. Maham, X. Zhang and J. M. Shaw - Poster

Specific Partial Molar Volumes at Infinite Dilution and Volumes of Mixing for Athabasca Bitumen and Bitumen Vacuum Resid + Solvent Mixtures

Partial molar volumes at infinite dilution and volumes of mixing are sensitive measures of molecular interactions in mixtures that have direct application in process development and can also be used to establish or validate parameters in solution or phase behaviour models, or to test the theories which underlie them. For example, solutes undergoing phase change on dissolution are readily discriminated from those which do not. In this contribution, partial molar volumes at infinite dilution for Athabasca bitumen and Athabasca vacuum resid in dodecane, decane, 1 methyl naphthalene, quinolin, and toluene + dodecane mixtures, are reported for the 20 C to 80 C temperature range, along with volume of mixing data for the same solutes in decane. The impact of the thermal history of samples on the results obtained is highlighted. Implications for production, extraction and refining process development and operation are discussed.

Geza Horvath-Szabo and Jacob Masliyah - Poster

The Acoustic Fingerprint of Diluted Bitumen

A novel approach, based on the acoustic properties of fluids, was developed to gain information about the shear and volume viscosity coefficients of bitumen dissolved in heptane/toluene mixtures. These coefficients, which we calculated from the acoustic attenuation spectra within 1-100 MHz range, turned to be frequency dependent quantities. This frequency dependency can be explained by asphaltene precipitation in the presence of heptane. However with toluene we also observed a similar, though smaller effect, showing additional relaxation processes. The acoustic fingerprint i.e. the attenuation as a function of acoustic frequency, bitumen concentration, and aliphatic-to-aromatic ratio of the solvent is a useful tool to characterize asphaltene precipitation at as high as 60-80% bitumen concentration.

For comparison we also measured the shear viscosity of diluted bitumen in heptane/toluene solvents with a capillary viscometer. These viscosity data were irreproducible at high heptane concentration where asphaltene precipitation occurred. In contrast, the acoustic approach provided reliable data in the whole composition range.

We characterized the aliphatic/aromatic nature of an industrial solvent as well by tracking the acoustic response of bitumen as a result of dilution. It also turned out, based on viscosity properties, that the naphtha used in the industry to dilute the bitumen does not correspond to any heptane-to-toluene mixture used often in laboratories to model the dilution process.

About Us | Site Map | Contact Us | ©2005 PetroleumPhase