Analytical procedures have been developed for the quantitative analysis of phenols in crude oils and sedimentary rock pyrolysates and extracts. The procedures involve isolation of the phenolic components of the sedimentary organic matter by extraction with alkaline aqueous methanol, followed by the removal of carboxylic acids using a back extraction step. Co-extracted non-polar components are removed from the alkaline extract by liquid chromatography or by extracting it with hexane. The phenol isolates thus obtained were analysed by capillary GC, GC-MS and GC-FTIR. Recoveries of 70-95% were measured for C(subscript)0-C(subscript)3 alkylphenol compounds using these procedures.Crude oil samples (45) representing a range of locations, ages, depositional environments, maturities, source types, and biodegradation levels have been analysed for their phenol contents. A range of C(subscript)0-C(subscript)5 alkylphenols (approximately 40) were identified in crude oils using co-chromatography on up to three different stationary phases and by comparison of their retention times, mass spectral and infrared spectral properties with reference compounds. Isopropylmethylphenols (six) and sec-butylmethylphenols (nine) were synthesised for use in the identification of these compounds. A range of C(subscript)0-C(subscript)4 alkylphenols (24) were quantified using a dimethyl siloxane column (BP 1 or DB 1) and found to occur at concentrations ranging from 190x10(subscript)3 ng/g down to the limit of detection of 10 ng/g (ppb).The crude oil samples were classified into six groups based on their C(subscript)0-C(subscript)5 alkylphenol compositions. Group 1 crude oils have at least one isomer class in which the relative proportions of the alkylphenol isomers reflect their relative thermodynamic stabilities. The vast majority of samples, however, do not contain relative proportions of ++ / phenols which reflect their stabilities, and these differences have been used to group the remaining crude oils. Group 2 crude oils contain predominantly alkylphenols derived from natural product precursors. This group has been further subdivided into Group 2A in which samples have isopropylmethylphenol distributions dominated by carvacrol and thymol; and Group 2B which is comprised of crude oils that contain high relative abundances of methylphenols which can be derived from tocopherols. Group 3 crude oils have C(subscript)2-C(subscript)5 alkylphenol compositions dominated by ortho and para substituted phenols which are proposed to be formed from geosynthetic processes. Group 4 crude oils contain alkylphenol compositions in which the relative abundances of meta substituted compounds in six isomer classes are much greater than those expected from chemical equilibration. Group 5 comprises of samples which are biodegraded and as a consequence contain alkylphenols below the limit of detection. Group 6 crude oils contain very low concentrations of alkylphenols and comprises samples which are derived from source rocks that pre-date the widespread occurrence of land plants or contain negligible land plant input.Some alkylphenols in crude oil are structurally related to natural product precursors and therefore appear to be biomarkers. The monoterpenoid natural products carvacrol and thymol, or its rearrangement product 3-isopropyl-5-methylphenol, which occur in high relative abundances in Group 2A samples are such compounds. Because carvacrol and thymol occur widely in extant conifers and angiosperms, their presence in crude oils derived from source rocks deposited when these plant types were widespread suggests they also originate from these plants. A range of trimethylphenols and tetramethylphenols which occur in high relative abundances in Group 2B samples, are also ++ / reaction products obtained from heating alpha-tocopherol with aluminium smectite. This, together with the reported widespread occurrence of tocopherols in plant photosynthetic tissue and in sedimentary rocks, leads to the conclusion that tocopherols are likely precursors to these petroleum methylphenols.The lignin components of terrestrial plants also appear to be important precursors to petroleum alkylphenols. Strong evidence for this is provided by the observation that crude oils derived from source rocks which contain negligible higher plant input contain very low concentrations of kylphenols (Group 6). In order to determine the likelihood of lignins as precursors of petroleum alkylphenols, the phenol contents of coals of lignitic through to bituminous rank were examined. The unbound phenolic components of the lignite samples were analysed by isolating the phenols from their dichloromethane extracts, and the bound phenolic components were analysed by pyrolysis GC-MS. At lignitic rank the unbound methoxyphenols allowed taxonomical classification of the samples and the bound hydroxyphenols bore structural similarities to lignin moieties. The bound C(subscript)0-C(subscript)4 alkylphenol components of lignitic, subbituminous and bituminous coals in a sedimentary sequence were quantitatively analysed by isolating the phenols from their hydrous pyrolysates. In the coals of subbituminous and bituminous rank, the bound alkylphenol components could not easily be related to lignin precursors because molecular transformations of lignins are very severe at these ranks. The increases in the individual concentrations and relative proportions of alkylphenols with methyl and/or isopropyl substituent(s) in the ortho and para positions in the subbituminous coal pyrolysate were attributed to electrophilic methylation and isopropylation reactions occurring to lignin structures in ++ / coals during coalification. The dominance of ortho and para substituted methylphenols in coaly Group 3A crude oils which were also observed in the hydrous pyrolysates of coals suggests that the altered lignin structures in coals may be precursors of some of these petroleum methylphenols.Methylation, isopropylation and sec-butylation, are proposed as geosynthetic processes to account for the alkylphenol compositions of crude oils with phenol distributions dominated by ortho and para alkyl-substituted compounds (Group 3). Many crude oils show high relative abundances of ortho and para substituted C(subscript)1-C(subscript)5 alkylphenol isomers and some were also enriched in C(subscript)3-C(subscript)5 alkylphenols compared to kerogen pyrolysates. Because the alkylphenol products obtained from the laboratory alkylation of cresols have distributions which closely resemble those in these crude oils, it is proposed that similar alkylation processes occur in source rocks. Alkylation ratios reflecting the degree of methylation, isopropylation and sec-butylation, which were based on the relative abundance of the dominant alkylation products compared to their likely precursor ortho cresol, indicate that high levels of methylation occurred in crude oils over a wide range of maturities. In contrast, high levels of isopropylation and sec-butylation were observed only in mature samples. Selective dissolution of phenol isomers in crude oils by water contact was discounted as an explanation for the observed phenol distributions based on the relative distribution coefficients of phenols between isooctane and water.The alkylphenol compositions of the remaining crude oils appear to be produced from alteration processes occurring in the subsurface; these include oxidation and biodegradation processes. Oxidation of alkylphenols is proposed to account for the alkylphenol compositions of ++ / Group 4 crude oils. Because ortho and para substituted alkylphenols are more susceptible to oxidation than their meta substituted counterparts, the selective removal of these compounds via an oxidation process is suggested as an explanation for the high relative abundances of meta substituted isomers observed in these crude oils. A natural product origin for these compounds appears unlikely due to the lack of known natural products which could give rise to meta substituted alkylphenols with isopropyl substituents, and the diverse range of organisms required to give rise to the meta substituted phenols with n-alkyl substituents observed in Group 4 samples.Crude oils from two Australian basins which have undergone various levels of biodegradation were analysed to assess biodegradation effects on petroleum alkylphenol compositions. Alkylphenols could not be detected in the moderately to severely biodegraded crude oils (Group 5) whereas related non-biodegraded samples contained relatively higher levels of alkylphenols. The very low levels of phenols in the biodegraded samples (< 10 ppb) suggests that phenols are depleted via processes that occur during biodegradation. Because water washing often co-occurs with biodegradation, the very low levels of alkylphenols in these samples may also be due in part to the removal of these polar components via water dissolution.

A major problem faced by the petroleum industry is the deposition of wax during the pumping of waxy crude oils. This precipitation occurs at “normal” temperature, typically 20-30°C in Libya. It could occur during the journey from well to terminal through hundreds of miles of pipelines. This kind of transportation is expensive in terms of pumping costs. The pumping has to be continuous; otherwise wax can build up in the pipeline, reducing the pumping or even stopping it. The property that defines this characteristic is the yield stress which depends on wax concentration and cooling rate. The build-up of paraffin and asphaltenes can lead to serious problems in formation, tanks, and pipelines. Blockages can be expensive and time-consuming to deal with; this is precisely the topic of this research. For this research, model and real waxy crude oils are formulated and their rheology systematically measured under various cooling rates to determine the yield stress. A pipeline loop has been designed to measure the start-up pressure of stagnant oil which has been allowed to precipitate wax. The start-up pressure and the thickness of deposited wax are used in a simple mathematical model to calculate the yield stress. This research thus provides two independent means of predicting the yield stress. This research studied three different waxy crude oils. An MCR-301 Anton Paar rheometer was used to measure the rheology of the oils, and a pipeline rig was used to obtain the start-up pressure to calculate the yield stress of each type of oil after different stoppage times. Also, the thickness of the precipitated wax is measured to calculate the yield stress precisely. The data show that the layer thickness has significant effect on the yield stress and start-up pressures and corresponding yield flow stresses have been found to underpin the crystallisation process of the wax and slow cooling rate produce stronger structures requiring higher stresses to fracture and induce flow. Also, longer shutdown times make these structures even stronger and therefore require even larger stresses for flow to commence.

This thesis describes a study in petroleum geochemistry and specifically of the application of Land-plant derived hydrocarbons to elucidating source matter type, depositional environment and thermal maturity of crude oils. Large volumes of petroleum have been generated from land-plant organic matter in many parts of the world, but especially in the Tertiary deltaic provinces of the USA, Canada, Africa, Southeast Asia, Australia and New Zealand. Compared to oils from other regions, these oils have a relatively complex pattern of biomarkers or molecular fossils, a feature reflecting the diversity of deltaic depositional environments and the advanced state of plant evolution during late Mesozoic and Tertiary time. The molecular and carbon isotopic composition of these oils is useful in identifying the character of their source beds and also in understanding the conditions that give rise to oil-prone sediments generally.Despite their widespread occurrence in oils and sediments, land-plant biomarkers have been used less frequently than compounds of algal origin as markers for source, depositional environment and thermal maturity. The present work sets out to extend the range of land-plant biomarker and isotope tools available to the petroleum geochemist and to provide a firmer foundation for some of the existing tools. A systematic study of the biomarker and n-alkane carbon-isotope composition of a set of late Mesozoic/Tertiary-age oils was carried out as a preamble to more focussed investigations. A comparison of the biomarker and n-alkane isotope data showed that parameters such as the oleanane/hopane ratio overestimate the higher plant contribution to marine deltaic oils. The abundance of bicadinane isomers was found to be much more variable than that of the oleananes, probably because of their close association with the highly resinous, dipterocarp hardwoods of ++ / Southeast Asia. However, small amounts of bicadinanes were found in an oil from outside the paleogeographic range of the dipterocarp family, indicating a more general source. Retention indices based on the regular hopane series were calculated for the main bicadinane and methyl bicadinane isomers and for a group of oleanoid triterpanes.Source rock depositional setting proved to be the primary control on the shape of the n-alkane isotope profile, with negatively sloping curves being characteristic of fluvio-deltaic and marginal lacustrine oils and flat or positively sloping curves typical of marine oils. The difference is probably related to the bacterial reworking of higher plant matter in the fluvio-deltaic environment. A slight isotopic anomaly at n-C(subscript)17 correlates with the abundance of algal-derived steranes and may indicate a minor marine contribution to the source of an fluvio-deltaic oil. A study of sediments from the South Sumatra Basin and New Zealand showed that the n-alkane isotope profile is determined mainly by source matter type and is little influenced by thermal maturity or depositional environment.Based on the results of the work described above, three aspects were chosen for further examination. These were: a) the factors controlling the carbon isotopic composition of n-alkanes and of resin-derived compounds in terrigenous oils; b) the influence of source, maturity and biodegradation on the abundance of bicadinanes, especially the effect of maturity on the isomer distribution, and c) the factors controlling the abundance of oleananes and rearranged oleananes in oils and Ancient sediments, especially the role of depositional environment.A preliminary study using sediments, from the Visayan Basin (Philippines) showed the bicadinane isomeric distribution to be sensitive to maturity. This suggested new maturity parameters which would be ++ / resistant to even severe biodegradation and largely immune to interference from diagenetic effects. A more detailed study of a marine-fluvio-deltaic depositional sequence from the South Sumatra Basin confirmed that the maturity indices based on bicadinanes and aromatic analogs were less subject to non-maturity influences than those based on the steranes and aromatic hydrocarbons. The values obtained for the bicadinane indices were compared with the maturity required for oil generation as estimated by kinetic modelling and with conventional maturity indicators such as sterane epimerisation and the methyl phenanthrene index. Values for several of the indices were also measured for 17 Tertiary-age oils from Southeast Asia, Papua New Guinea, New Zealand and Australia. The main bicadinane maturity indicator (BMI-1) continues to change into the oil window and hence is useful in ranking the relative maturity of oils as well as sediments. Values of BMI-1 for two oils having unusually low sterane maturities were found to be normal and, in the light of this observation, the conventional explanation for low sterane epimerisation of many Tertiary-age oils was critically evaluated.The oleananes, as markers for the angiosperms, provide valuable source and age information when present in an oil. Nevertheless, their abundance is not quantitatively related to the land plant input and indeed their presence results from a small "leak" in diagenetic processes leading primarily to aromatic oleanoids. Evidence is presented that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil. Oleananes are absent or present at very low concentrations in samples from the base of an Eocene coal seam affected by post-depositional seawater intrusion. However, their abundance increases toward the top of the seam in correlation with ++ / % organic sulphur, dibenzothiophene/phenanthrene and the homohopane index. Similarly, in deltaic sediments from the South Sumatra Basin, oleanane/hopane is strongly correlated with indicators of marine influence such as C[subscript 27]/C[subscript 29] steranes and of oxic/anoxic conditions such as the homohopane index. In each case, increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and, for the South Sumatra Basin, the proportion of A-ring contracted oleananes. An angiosperm-derived Miocene coal from the Philippines, deposited under freshwater conditions, shows abundant aromatic oleanoids but no oleananes. These results show that oleananes need to be used with caution as age and source markers in fluvio- deltaic and lacustrine petroleum systems. On the other hand, their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems.Compounds derived from plant resins are major components of some terrigenous oils. Although recent studies have elucidated the molecular structure of resinites, very little information was available on the carbon isotope composition of resinites prior to the present study. No carbon isotope studies of resin-derived compounds in oils had been performed. Hence, carbon stable isotope analyses were carried out on a set of modern and fossil resins of diverse origins and compound specific isotope analysis was used to characterise individual hydrocarbons in resin pyrolysates and oils derived from resinitic source matter. The results showed that "Class V' resinites derived from gymnosperms are enriched in the heavy carbon isotope compared with the angiosperm-derived "Class W' resinites. Furthermore, both the fossil resinites themselves and individual hydrocarbons derived from them are isotopically heavy compared with modern plant resins. The reasons for ++ / these differences and their implications for petroleum geochemical studies are discussed.

The ability to select low-cost, high-performance surfactants for a wide range of crude oils under a wide range of reservoir conditions has improved dramatically in recent years. Surfactant formulations (surfactant, co-surfactant, co-solvent, alkali, polymer, and electrolyte) were developed by using a refined phase behavior approach. Such formulations nearly always result in more than 90% oil recovery in core flood when good surfactants with good mobility control are used. The advances that have improved performance, reduced cost, increased robustness, and extended the range of reservoir conditions for these formulations are described in this work. There are thousands of possible combinations of the chemicals that could be tested for each oil and each chemical combination requires many observations over a long time period at reservoir temperature for proper evaluation. It would take too long, cost too much and in many cases not even be feasible to test all combinations. In practice the scientific understanding is used to match up the surfactant/co-surfactant/co-solvent characteristics with the oil characteristics, temperature, salinity, hardness and so forth. Synthesized and new surfactants with much larger hydrophobes and more branching than previously available were tested. New classes of co-solvents and co-surfactants with superior performance were test to improve aqueous solubility. These new developments resulted in improved ASP formulations for both oils that react with alkali to make soap and oils that do not. Many of these developments are synergistic and taken together represent a breakthrough in reducing the cost of chemical flooding and thus its commercial potential. / text

Les activités de production des hydrocarbures sont fortement dépendantes du comportement thermodynamique des fluides produits. La précipitation d'asphaltènes, entités qui constituent les principaux composants de la fraction la plus lourde et la plus polaire du pétrole, peut conduire à la formation d'un dépôt solide. Nous avons mis en oeuvre et évalué plusieurs méthodologies expérimentales appliquées à la détermination des diagrammes de phase de fluides asphalténiques dans les conditions de haute pression et haute température. Nous avons mis au point une technique utilisant un résonateur à cristal de quartz (RCQ), capable d'identifier les conditions thermodynamiques de changement de phase, sous haute pression, dans des fluides avec une teneur faible en asphaltènes. Les données obtenues avec le RCQ ont été validées par filtration isobare et par microscopie haute pression (MHP). Les effets sur la floculation de l'ajout de gaz, des conditions thermodynamiques imposées au fluide et de la vitesse de dépressurisation ont été étudiés expérimentalement à l'aide des trois techniques susmentionnées. Les résultats obtenus par MHP sur différentes live oils suggèrent l'existence de quatre types de comportement de fluides lors d'une dépressurisation isotherme, avec dans certains cas l'apparition d'un équilibre liquide-liquide dans des conditions de températures et de pressions élevées. Enfin, nous avons établi, avec la caractérisation physico-chimique des asphaltènes obtenus (nC7) à partir des huiles mortes, que la différence d'aromaticité entre cette fraction et celle de son huile d'origine, pouvait être un indicateur utile afin d'anticiper un possible phénomène de précipitation. / Oil production activities are strongly dependent on the phase behavior of produced fluids. The flocculation of asphaltenes, the major components of the heaviest and most polar fraction of crude oil, can lead to solids formation in several steps of oil production. In this thesis, we evaluated several methodologies applied for asphaltenes phase behavior assessment under high-pressure conditions. Among the methodologies, we had developed an apparatus based on the quartz crystal resonator (QCR), able to identify thermodynamic conditions of phase changes in pressurized fluids containing low asphaltenes content. The data obtained with the QCR were validated by isobaric filtration and high pressure microscopy (HPM) tests. Applying the three aforementioned techniques, the influence of gas addition, kinetic factors, thermodynamic conditions and the influence of depressurization rate on the onset of asphaltenes flocculation were studied. Live oils were evaluated by the HPM technique. The results from HPM suggest the existence of four phase behavior patterns for isothermal depressurization experiments, highlighting the existence of a liquid-liquid equilibrium at elevated temperatures and pressures. The physico-chemical characterization of asphaltenes extracted with n-heptane from dead oil suggests that the difference of aromaticity between this fraction and its referred oils could be a parameter to indicate possible problems of asphaltenes flocculation during the oil production.

Cette thèse porte sur l'utilisation de champs électriques pour faciliter l'élimination de l'eau coproduite avec le pétrole brut, sous la forme d'émulsions stables, lors des étapes d'extraction et de dessalement. Ce procédé, connu sous le nom d'électrocoalescence, s'appuie sur la capacité qu'ont les forces électrostatiques à promouvoir l'attraction et la coalescence de gouttelettes d'eau proches afin d'en augmenter la taille et ainsi d'en accélérer la sédimentation par gravité. Bien que les premières observations expérimentales datent déjà d'un siècle, de nombreuses zones d'ombres subsistent, notamment en ce qui concerne l'optimisation de l'efficacité des électrocoalesceurs de dernière génération. Dans ce contexte, une démarche, combinant simulation numérique multi-physique et expérimentation, a été mise en place pour étudier les phénomènes de mouvement, de déformation et d'instabilité d'interfaces eau-huile induit par la présence d'un champ électrique. La contribution la plus marquante concerne la modélisation et l'analyse de l'effet des forces électrostatiques sur le mécanisme d'amincissement du film d'huile séparant les gouttes. Les résultats numériques mettent en évidence la singularité du problème et l'inadaptabilité des modèles théoriques de lubrification classiquement adoptés pour représenter la coalescence dans les écoulements diphasiques. Une nouvelle expression asymptotique pour le calcul du temps de drainage entre les gouttelettes de l'émulsion est proposée et utilisée pour déduire un critère prédisant la probabilité d'électrocoalescence lors d'une collision dans un écoulement cisaillé. En parallèle, un dispositif sophistiqué, permettant de reproduire expérimentalement le phénomène et d'améliorer la représentativité du critère, a été construit. Enfin, en réponse à un point bloquant décelé lors de la phase de conception de ce dernier, une technique innovante d'injection à la demande de gouttes conductrices non chargées dans un liquide visqueux isolant, utilisant des impulsions électrostatiques, a été développé. / The present thesis deals with the electrostatically assisted removal of water coproduced with crude oil in the form of stable emulsions during recovery and desalting operations. This process, referred to as electrocoalescence, exploits the ability of electric forces to promote attraction and merging of adjacent water droplets to increase their size and related natural rate of sedimentation under gravity. Still, even one century after the first experimental observations, a lot of gray areas remain, particularly on the optimization of efficiency in state-of-the-art separators. To address this question, an approach combining multi-physics simulation and experiments has been used to investigate the phenomena of motion, deformation and instability of electrically influenced water-oil (droplets) interfaces. The main contribution concerns the modeling and analysis of the mechanism of oil film thinning between droplets approaching under the effect of electrostatic forces. Results from simulations highlight the strong singularity of the present problem and the inadequacy of existing theoretical lubrication models usually employed to represent coalescence events in two phase flows. For the small emulsified droplets, a new asymptotic expression for the drainage time is obtained and allows to deduce a criterion predicting the probability of electrocoalescence resulting from a shear flow induced collision. In parallel, a sophisticated setup, enabling to experimentally investigate the phenomenon and to improve the criterion relevance with regards to the actual processing conditions, has been assembled. At last and as an answer to an otherwise unfulfilled requirement defined in the design of the latter, an innovative actuation technique for the synchronous on-demand injection of two charge free conductive droplets in an insulating viscous liquid, relying on the application of a high electric field pulse, has been implemented.

[pt] O objetivo desta dissertação é avaliar a influência do teor de água e do fator do medidor na incerteza de malhas fiscais de medição de óleo utilizando medidores ultrassônicos. A motivação deste trabalho advém do fato do Regulamento Técnico de Medição de Petróleo e Gás Natural (RTM) existente limitar quais metodologias podem ser utilizadas para realizar a análise de teor de água e qual a incerteza máxima permitida para a malha de medição na qual esta se insere, porém não define a incerteza desta, havendo o risco de se adotar um dos métodos de análise permitidos e, ainda assim, a incerteza de medição da malha ultrapassar a definida pela legislação. Além disso, o RTM adota um critério de repetibilidade para a validação das calibrações dos medidores ultrassônicos, portanto avalia-se também a influência deste na incerteza da malha. A metodologia utilizada foi o planejamento de experimentos, utilizando superfície de resposta. Os resultados demonstram que é possível simular a influência da incerteza da análise da água e do fator do medidor na incerteza da malha. Por fim, as conclusões demonstram que as médias atualmente encontradas para incerteza do teor de água são adequadas para manter a incerteza da malha dentro da permitida pelo RTM, porém com pouca variação pode-se exceder este limite; a influência da incerteza do fator do medidor foi inferior ou similar à do teor de água e, por fim, sugere-se a adoção de um critério limite de incerteza ao invés de um critério de repetibilidade para os medidores ultrassônicos. / [en] The aim of this dissertation is to evaluate the influence of water content dissolved in crude oil and the meter factor on the uncertainty of the fiscal oil metering using ultrasonic flow meters. The development of this work is motivated by the fact that the Technical Regulation for the Measurement of Oil and Natural Gas (RTM) limits which methodologies can be used for water analysis and what is the maximum permissible uncertainty for the oil flow meter in which it is inserted. However, the RTM doesn t define the uncertainty of the water analysis. There is a risk of adopting one of the permitted methods of analysis and, even so, the measurement uncertainty of the flow meter exceeds the defined by the legislation. In addition, the RTM adopts a repeatability standard when validating the calibration of ultrasonic meters, thus the influence of this on oil uncertainty is also evaluated. The methodology used is the design of experiments and response surface. The results demonstrate that the influence of the water content uncertainty analysis and of the meter factor on the uncertainty of the oil flow meter can be simulated. Finally, the conclusions show that the average currently found for uncertainty of water is adequate to maintain the oil uncertainty within the allowed by the RTM, but small variations may cause this limit to be exceeded. The influence of the meter factor uncertainty was inferior or similar to the water content and, finally, it is suggested the adoption of a standard limit of uncertainty instead of a standard of repeatability for the ultrasonic meters.

[pt] Esta tese é sobre a reologia de óleos parafínicos crus. Um protocolo baseado na literatura relevante é desenvolvido para garantir que históricos térmico e de cisalhamento bem definidos sejam impostos em amostras que serão submetidas à medições reológicas. Com este protocolo, uma caracterização reológica quase completa de um óleo parafínico cru brasileiro é executada . Quatro experimentos reométricos são realizados, a saber, escoamento em estado estacionário, taxa de cisalhamento constante, tensão constante e rampa oscilatória de amplitude de tensão. Propriedades reológicas importantes, tais como, viscosidade, tensão limite de escoamento e módulos elástico e viscoso são medidos com o auxílio de técnicas diferentes em uma ampla faixa de condições. Além disso, uma comparação entre essas técnicas de medição é realizada. O processo de quebra da microestrutura do óleo parafínico brasileiro, assim como os efeitos na reologia do histórico do material e do tempo de repouso isotérmico são estudados. Fenômenos interessantes são observados, incluindo bifurcação da taxa de cisalhamento, dependência da tensão limite com os históricos térmico e de cisalhamento e independência dos resultados de regime permanente com relação à condição inicial após o resfriamento. Por fim, oportunidades para futuros desenvolvimentos e investigações são enfatizadas. / [en] This thesis deals with the rheology of waxy crude oils. A protocol based on the relevant literature is developed to guarantee well defined shear and thermal histories to waxy crude oil samples to be submitted to rheological measurements. With this protocol, a fair complete rheological characterization of a Brazilian waxy crude oil is performed. Four rheometric experiments, namely steady-state flow, constant shear rate, constant shear stress, and dynamic-stress-amplitude sweep are carried out. Important rheological properties, such as, viscosity, yield stress, and storage and loss moduli are measured with di↵erent techniques in a wide range of conditions and a comparison between the techniques is presented. The yielding as well as the history effects and the e↵ects of isothermal holding time on the microstructure and rheology of a Brazilian waxy crude oil are investigated. Interesting phenomena are observed, including bifurcation of shear rate, dependence of the yield stress with thermal and shear histories, and independence of the steady-state results with the post-cooling initial condition of the experiment. At last, opportunities for further developments are highlighted.

Le but de ce travail est de fournir des informations qui peuvent aider à clarifier le mécanisme par lequel se produit la précipitation d’asphaltènes afin d'optimiser les modèles qui prédisent ce phénomène. Premièrement, la composition chimique des fractions aromatiques et saturées est analysée au regard à la stabilité des asphaltènes dans le brut. Plus précisément, la composition SARA de différents bruts vénézuéliens est corrélée au seuil de floculation des asphaltènes. Nos résultats mettent en évidence que les saturées, semblables aux résines, ont un effet significatif sur la stabilité des asphaltènes dans le brut. Deuxièmement, la teneur en Ni et V dans les asphaltènes et leurs sous fractions A1 et A2 a été déterminé par spectroscopie d'émission atomique avec plasma inductif. Les données expérimentales établissent que A1 a une concentration en V et en Ni supérieure à celle de A2, quelque soit la stabilité des bruts. Nous interprétons ces données comme l’illustration d’interactions fortes, telles que des liaisons covalentes entre pétroporphyrines et les molécules d’asphaltènes. Finalement, un dispositif haut pression est utilisé pour détecter visuellement la pression seuil de floculation d'un système modèle correspondant à une solution d’asphaltènes dans un mélange toluène/heptane/CO2. Les résultats confirment, pour ces systèmes gazés, que les augmentations de pression conduisent à une augmentation de la solubilité des asphaltènes et que pour la température il y a deux régimes opposés. Le premier correspond à une diminution de la stabilité du fluide avec l’augmentation de la température et le second, passé une valeur seuil proche de 80°C, conduit au phénomène inverse. / The purpose of this work is to provide information that can help in clarifying the mechanism by which asphaltene precipitation occurs in order to optimize the models that predict the phenomenon. The study is divided into three chapters. In the first one, the constituents of aromatic and saturate fractions of some Venezuelan crude oils were associated with the asphaltenes stability. SARA composition was correlated with asphaltene flocculation onsets and the results showed that saturates, similar to resins, have a significant effect on the flocculation process of the asphaltenes. In the second chapter, the concentration of Ni and V was determined in asphaltenes and their fractions A1 and A2. The samples were analyzed using inductively coupled plasma atomic emission spectrometry and elemental combustion analysis. Results show that A1 presents higher Ni and V concentrations than A2, in both stable and unstable crude oils. These results can be explained by strong interactions, such as covalent bonds between the petroporphyrins and the asphaltene molecules. In the final section, the asphaltenes phase envelopes were obteined for a system consisting of asphaltene in a mixture toluene/heptane/CO2. The temperature ranges 10-150 °C with varying concentrations of CO2 between 10 and 20 wt%. The experimental results confirm that increase of pressure leads to increase of solubility of the asphaltenes in the medium. Also, there are two temperature regimes having opposite trends. First, the solubility of the asphaltenes increases with the temperature, then after a threshold value of 80 °C, the stability is getting worse with the temperature