Flow assurance is crucial in the oil industry since it guarantees the success and economic production of hydrocarbon fluid, especially in offshore and deep water oil fields. In fact, the ultimate goal of flow assurance is to maintain flow in the wellbore and pipelines as long as possible. One of the most common challenges in flow assurance is the buildup of solids, such as asphaltene and scale particles. These Solid particles can deposit in the wellbore, flowline, and riser and affect the wellbore performance by reducing the cross section of the pipeline, which eventually results in pipeline blockage. Hence, neglecting the importance of flow assurance problems and failure in thorough understanding of the fluid behavior in the production systems may result in plugged pipeline, production loss, flowline replacement, and early abandonments of the well. As a result, continuous evaluations are needed at the development stage and during the life of reservoirs to predict the potential, the extent, and the severity of the problem to plan for inhibition and remediation jobs. In fact, it is more preferable to prevent flow assurance problems through the designing and operating procedures rather than remediating the problems, which has higher risks of success and higher loss of revenue due to frequent well shut down. As a part of this research, we enhanced the capabilities of our in-house compositional wellbore simulator (UTWELL) to model various production and flow assurance scenarios. Initially, we developed and implemented a robust gas lift model into UTWELL to model artificial lift technique for reservoirs with low pressure. The developed model is able to model both steady state and transient flow along with blackoil and Equation-of-State compositional models. The improved version was successfully validated against a commercial simulator. Then, we applied our dynamic model to track the behavior of asphaltene during gas lift processes and evaluated the risk of asphaltene deposition. Several deposition mechanisms were incorporated to study the transportation, entrainment, and deposition of solid particles in the wellbore. The simulation results illustrated the effect of light gas injection on asphaltene deposition and well performance. Finally, a step by step algorithm is presented for coupling a geochemical package, IPhreeqc, with UTWELL. The developed model is able to model homogenous and heterogeneous, non-isothermal, non-isobaric aqueous phase reactions assuming local equilibrium or kinetic conditions. This tool was then utilized to model scale deposition in the wellbore for various scenarios. In addition, the results showed that integrating IPhreeqc has promise in terms of CPU time compared to the traditional approach of reading and writing the input and output files. / text

Les asphaltènes et autres constituants lourds du pétrole, comme les résines et les alcanes de haut poids moléculaire, posent des défis importants dans tous les segments de la chaîne de production pétrolière. Parmi les nombreux problèmes, la déstabilisation et le dépôt des asphaltènes dans les opérations en amont ont fait perdre beaucoup de temps à la recherche et ne sont pas encore complètement compris. Une partie de la difficulté à saisir la véritable physique derrière de tels phénomènes est l'utilisation répandue des systèmes modèles et des molécules extraites, modifiant considérablement l'organisation fluide complexe des pétroles bruts, et donc en contournant les processus réels. À ce jour, deux extrêmes de la structure organisationnelle asphaltenes peuvent être dessinés, en tant que partie d'un agrégat, avec des attractions pi-pi simples et des chaînes d'alcane répulsion, contrôlant l'agrégation; et dans le cadre d'une structure macromoléculaire, avec une participation significative d'autres composants bruts. La dernière structure étant beaucoup plus difficile à modéliser, elle capture sa physique et est difficilement reproductible à l'aide de systèmes modèles. Un autre aspect important de la recherche des dépôts d'asphaltènes est la manière dont se produit la déstabilisation des asphaltènes. Lorsque l'on utilise des asphaltènes extraits dans des systèmes modèles, l'affirmation précédente n'a pratiquement aucune moyenne, car les nombreuses fractions d'asphaltènes ont été préalablement mélangées. Cependant, lorsqu'il s'agit de tout le pétrole brut, la voie de la déstabilisation est importante et est encore largement dépassée au sein de la communauté scientifique. Pour résumer les sujets exposés, il y a plutôt la non-spécificité de la majorité des techniques expérimentales utilisées sur la recherche de la déstabilisation et du dépôt des asphaltènes en relation avec les dépôts d'échelle des particules.Les techniques de spectroscopie, capables de balayer les paramètres physiques interfaciaux, sont de bons candidats pour améliorer les points exposés délétères. Dans la présente thèse, le résonateur à quartz connecté à un analyseur de réseau vectoriel présente le potentiel de révéler de nombreux aspects sur la déstabilisation et le dépôt des asphaltènes directement à partir de pétrole brut (huiles vivantes, recombinées ou mortes) et de systèmes modèles. L'équilibre du pétrole brut est perturbé par les changements de solubilité dans un processus continu ou en gradin imitant les processus de production. L'interprétation des paramètres de résonance des cristaux de quartz, de la fréquence et de la dissipation d'énergie, est effectuée de manière qualitative et, dans une certaine mesure, quantitative. L'étude innove dans le sens d'étendre l'utilisation du cristal de quartz pour interpréter le processus, non seulement en détectant les changements de phase, comme c'est le cas de la majorité des études précédentes. L'évaluation des produits chimiques de production est effectuée une fois que la méthodologie a fait l'objet d'une discussion approfondie. Le potentiel de l'analyse proposée est crédité par la microscopie à force atomique qui ouvre l'horizon pour plus de recherche et d'applications potentielles de la méthodologie. Parmi les applications possibles figure le développement de capteurs d'assurance de débit capables de détecter les changements de phase et d'évaluer les dépôts in situ. / Asphaltenes and other heavy petroleum constituents, like resins and high molecular weight alkanes, pose significant challenges in all segments from the petroleum production chain. Among the many problems, asphaltenes destabilization and deposition within upstream operations has rendered tons of research time and is still not completely understood. Part of the difficulty in capturing the real physics behind such phenomena is the widespread use of model systems and extracted molecules, greatly altering the complex fluid organization of crude oils, and thus bypassing real processes. To date two extremes of asphaltenes organizational structure can be drawn, as a part of an aggregate, with simple pi-pi attractions and alkane chains repulsion, controlling aggregation; and as a part of a macromolecular structure, with significant participation of other crude components. The last structure being way more difficult to model, and captures its physics and being poorly reproducible with the use of model systems. Another important aspect when researching asphaltene deposition is the way asphaltenes destabilization occurs. When using extracted asphaltenes in model systems, the former affirmation has virtually no mean, as the many asphaltenes fractions were beforehand mixed. However, when dealing with the whole crude oil, the path of destabilization matters and is still greatly bypassed within the scientific community. Summing up to the exposed topics, there is the rather non-specificity from the majority of experimental techniques used on the research of asphaltenes destabilization and deposition in relation to the depositing particles size scales.Spectroscopy techniques, capable of sweeping interfacial physical parameters are good candidates for improving the deleterious exposed points. In the present thesis quartz crystal resonator, connected to a vector network analyzer is used is shown to present the potential of revealing many aspects on asphaltene destabilization and deposition directly from crude oils (live, recombined or dead oils) as well as model systems. Crude oil equilibrium is disturbed by solubility changes in a continuous or step gradient mimicking production processes. The interpretation of the quartz crystal resonance parameters, frequency and energy dissipation, is performed in a qualitative and to some extend quantitative way. The study innovates in the sense of extending the use of the quartz crystal to interpret process, not only detecting phase changes, as it is the case of the majority of the former studies. The evaluation of production chemicals is undergone once the methodology is thoroughly discussed. The potential of the proposed analysis is credited by atomic force microscopy which opens the horizon for more research and potential applications of the methodology. Among the possible application is the development of flow assurance sensors capable of detecting phase changes and evaluate deposition in situ.

Understanding when hydrates will nucleate has notable importance in the area of flow assurance. Attempts to model hydrate formation in subsea pipelines currently requires an arbitrary assignment of a nucleation subcooling. Previous studies showed that sII hydrate containing a model water-soluble former, tetrahydrofuran, would nucleate over a narrow temperature range of a few degrees with constant cooling. It is desirable to know if gas phase hydrate formers, which are typically more hydrophobic and hence have a very low solubility in water, also exhibit this nucleation behavior. In this study, differential scanning calorimetry has been applied to determine the hydrate nucleation point for gas phase hydrate formers. Constant cooling ramps and isothermal approaches were combined to explore the probability of hydrate nucleation. In the temperature ramping experiments, methane and xenon were used at various pressures and cooling rates. In both systems, hydrate nucleation occurred over a narrow temperature range (2-3°C). Using methane at lower pressures, ice nucleated before hydrate; whereas at higher pressures, hydrate formed first. A subcooling driving force of around 30°C was necessary for hydrate nucleation from both guest molecules. The cooling rates (0.5-3°C/min) did not show any statistically significant effect on the nucleation temperature for a given pressure. The isothermal method was used for a methane system with pure water and a water-in-West African crude emulsion. Two isotherms (-5 and -10°C) were used to determine nucleation time. In both systems, the time required for nucleation decreased with increased subcooling.

L’activité scientifique du sujet porte sur l’acquisition de données expérimentales et la modélisation de la composition des clathrates hydrates de gaz. Les domaines d’application concernent la séparation et le stockage de gaz, la purification de l’eau, et le stockage d’énergie par matériaux à changement de phase.L’équipe a mis en évidence il y a quelques années que la composition des hydrates de gaz était sensible aux conditions de cristallisation, et que le phénomène de formation se produisait en dehors de l’équilibre thermodynamique.Le travail de thèse a permis d’explorer plusieurs modes de cristallisation à partir de solutions de même composition initiale pour observer les différences concernant l’état final, compositions notamment, et les relier à la vitesse de cristallisation. Suivant le mode de cristallisation, lent ou rapide, l’acquisition des données expérimentales peut prendre de quelques jours à plusieurs semaines. Les expériences sont réalisées en réacteur pressurisé dans lequel nous mesurons en ligne la composition de la phase gaz et de la phase liquide, pour calculer par bilan de matière la composition de la phase hydrate.Nous avons bien mis en évidence des variations dans la composition de la phase hydrate suivant le mode de cristallisation. Nous avons dû établir un modèle thermodynamique donnant la composition de la phase hydrate à l’équilibre pour des mélanges de gaz qui n’avaient jamais été traité par la littérature, et qui ont donc nécessité des campagnes de mesure extrêmement lentes et donc longues pour être sûr de l’état thermodynamique à l’équilibre.Nous sommes en cours d’établir un modèle cinétique pour modéliser les écarts à cet état d’équilibre de référence pour nos expériences réalisées à vitesse de cristallisation rapide. / The scientific goal of this thesis is based on the acquisition of experimental data and the modeling of the composition of clathrates gas hydrate. The domains of application concern the gas separation and storage, water purification, and energy storage using change phase materials (PCMs).Our research team has recently demonstrated that the composition of gas hydrates was sensitive to the crystallization conditions, and that the phenomenon of formation was out of thermodynamic equilibrium. During this thesis, we have investigated several types of crystallization, which are based on the same initial states. The goal is to point out the differences between the initial solution composition and the final solution composition, and to establish a link between the final state and the crystallization rate.Depending on the rate of crystallization (slow or fast), the acquisition time of experimental data lasted from a few days to several weeks. The experimental tests were performed inside a stirred batch reactor (autoclave, 2.44 or 2.36 L) cooled with a double jacket. Real-time measurements of the composition of the gas and the liquid phases have been performed, in order to calculate the composition of the hydrate phase using mass balance calculations. Depending on the crystallization mode, we have identified several variations of the composition of the hydrate phase and final hydrate volume.We have established a successful thermodynamic model, which indicates the composition of the hydrate phase and hydrate volume in thermodynamic equilibrium state using a gas mixture which had never been used before in the literature. So this thermodynamic model has required an extremely slow experimental test. These tests were also long in order to be sure of the thermodynamic equilibrium state.We are currently establishing a kinetics model in order to model the deviations from the reference point of equilibrium of our experimental tests which were carried out at a high crystallization rate.

The use of Kinetic Hydrate Inhibitors (KHI) is one of the optimum methods employed to control gas hydrate formation issues and provide flow assurance in oil and gas production systems. The application of this technology has several advantages to operators, including significant cost savings and extended life of oil and gas systems. This paper will highlight a specific case where a Major operator in the North Sea (UK sector) significantly reduced the cost of well intervention operations by applying a KHI in a subsea gas lift line. Considerable cost savings were realized by reducing volume of chemical required and this enabled the application to be performed from the FPSO eliminating the need for a dedicated Diving Support Vessel (DSV). Furthermore, the application of KHI also reduced manual handling and chemical logistics usually associated with this particular treatment. In order to prevent mineral scale deposition occurring in downhole tubing and near well bore and in the formation; scale inhibitor squeeze applications are standard practice. For subsea wells the fluids can be pumped down in to the well via gas lift lines. However, upon completion of previous scale squeeze operations at this particular location, hydrate formation was observed when a mixture of MEG and water was used following interventions via the gas lift line. By applying 1% KHI with a mixture of MEG and Water, the well was brought back into production following scale squeeze operations without hydrate formation occurring.

Using a combination of micromechanical force and flowloop measurements, hydrate deposition on a pipe wall surface was investigated for ‘dry’ hydrates formed in the bulk phase and for hydrates growing on the pipe surface. Cyclopentane ‘dry’ hydrates (without a free water phase) were used to predict whether hydrates, formed in a bulk condensate phase, would adhere to a pipe wall. Adhesion forces between cyclopentane hydrates and steel were measured using a micro-mechanical force apparatus. The average force of adhesion was measured to be very small, less than 0.01 N/m. This force was used in a particle force balance, predicting that hydrates formed in the bulk phase would not deposit on the pipe wall. It was hypothesized than in the presence of a water saturated hydrocarbon, hydrates would grow on the pipe wall as the fluid cooled below its equilibrium temperature. This hypothesis was confirmed using a single pass condensate flowloop. Water was continuously dissolved into the flowloop inlet stream as water deposited in the flowloop test section, resulting in both a pressure drop and fluid temperature increase. This work illustrates the need for a hydrate wall growth model.

The use of Kinetic Hydrate Inhibitors (KHI) is one of the optimum methods employed to control gas hydrate formation issues and provide flow assurance in oil and gas production systems. The application of this technology has several advantages to operators, including significant cost savings and extended life of oil and gas systems. This paper will highlight a specific case where a Major operator in the North Sea (UK sector) significantly reduced the cost of well intervention operations by applying a KHI in a subsea gas lift line. Considerable cost savings were realized by reducing volume of chemical required and this enabled the application to be performed from the FPSO eliminating the need for a dedicated Diving Support Vessel (DSV). Furthermore, the application of KHI also reduced manual handling and chemical logistics usually associated with this particular treatment. In order to prevent mineral scale deposition occurring in downhole tubing and near well bore and in the formation; scale inhibitor squeeze applications are standard practice. For subsea wells the fluids can be pumped down in to the well via gas lift lines. However, upon completion of previous scale squeeze operations at this particular location, hydrate formation was observed when a mixture of MEG and water was used following interventions via the gas lift line. By applying 1% KHI with a mixture of MEG and Water, the well was brought back into production following scale squeeze operations without hydrate formation occurring.

[pt] Um dos problemas encontrados na indústria do petróleo no que diz respeito a garantia de escoamento durante produção de óleo cru trata-se da deposição das frações parafínicas no interior dos tubos.Gastos significantes estão associados ao bloqueio parcial ou total das linhas de produção. O procedimento mais aplicado para remoção mecânica destes depósitos é a passagem de pigs. Uma das forças de contato que atua no pig durante o procedimento de remoção deste depósito é exercida pela camada de parafína depositada na parede do tubo. À medida que se processa a remoção mecânica e se estabelece o deslocamento do pig e da parafina removida outras forças de contato se caracterizam. O conhecimento da força necessária para quebra e remoção de um depósito específico é um ponto chave para o planejamento seguro e eficiente de uma operação de passagem de pig. Este trabalho propõe-se a estudar experimentalmente a força de contato deste depósito controlando as variáveis que influenciam esta força, analisando os resultados de acordo com os parâmetros envolvidos e os comparando com os resultados obtidos com modelos disponíveis na literatura. / [en] Wax deposition inside transportation pipelines is a relevant problem for the petroleum industry. Significant capital and operatinal cost are associated with the total or partial blockage of production lines. Pigging is the most widely used technique for removing wax deposits. The knowledge of the forces necessary to break and remove a particular wax deposit are key to the safe and a efficient design of a pigging operation. The present work presents an experimental laboratory study of the forces necessary to remove wax deposits inside a duct. The results obtained with the experiments are used to validate predicting models avaiable in the litErature.

[pt] Pigs ainda são a ferramenta mais utilizada pela indústria para remover depósitos de parafina em linhas submarinas de petróleo. A passagem de Pigs é considerada uma operação de risco, pois existe a possibilidade do gradiente de pressão disponível para deslocar o Pig não ser suficiente para vencer as forças de contato entre o Pig e a parede do tubo e as forças necessárias para remoção do depósito de parafina. Neste trabalho realizou-se um estudo experimental visando o levantamento de dados de laboratório sobre as forças de contato Pig-tubo para alguns tipos de Pigs comumente usados em operações de campo. Além disso, foram também determinadas forças para remoção de depósitos de parafina fabricados no laboratório sob condições controladas. Foi projetada e construída uma seção de testes onde os Pigs ensaiados eram puxados com velocidade constante através de trechos de tubo, sendo a força trativa de puxada monitorada continuamente por células de carga. Os resultados de força de contato Pig-tubo sem depósito de parafina foram comparados com modelos teóricos disponíveis na literatura. Para o caso dos experimentos onde depósitos estavam presentes, as forças necessárias para a quebra dos depósitos foram também comparadas com o único modelo disponível na literatura. Os resultados obtidos mostraram que, para Pigs de disco e de espuma os modelos disponíveis prevêem as forças de contato Pig-tubo com incerteza aceitável. Para o caso de remoção de parafina a comparação com os experimentos desenvolvidos mostrou que o modelo disponível consegue estimar a força inicial para a quebra do depósito dentro de uma faixa de incerteza de ± 30% para os Pigs de disco e de espuma. / [en] Pigging is still the most widely used method to remove wax deposits in subsea pipelines. The passage of a pig is still considered a risky operation, since the pressure gradient available for driving the pig might not be sufficient to overcome the contact forces between the pig and the wall, as well as the forces required to remove the wax deposit. If this is the case, the pig will be stuck, and costly remediation procedures will have to be implemented. In the present work, an experimental study was carried out aimed at collecting reliable data on the contact forces developed between pigs and the pipe wall for some types of pigs commonly used in field operations. Also, as part of the work, the forces required to remove wax deposits prepared under controlled conditions were recorded. To this end, a test section was specially designed and constructed. In the tests, the pigs were pulled through a set of pipes at constant speed by a winch, while the pulling force was continuously recorded by load cells. The results obtained for the contact forces between disc, foam and conical cup pigs and the pipe wall without wax deposits were compared with models available in the literature. Good level of agreement was obtained. Experimental results obtained for the cases where the test pipes had controlled wax deposits where compared with the only model available in the literature for predicting the forces required to break the wax deposits. The comparisons demonstrated that the measured forces required for breaking the wax deposit can be estimated by the available models within an uncertainty of ±30%.

Heavy oil production has drawn more and more attention in petroleum industry. The amount of heavy oil in the world is twice more than the conventional oil (low viscosity), which has been consumed rapidly from the past. The understanding of flow patterns and pressure losses in multiphase flow with high viscosity oil are vital to assist the design of transportation pipeline. This thesis involves experimental investigation of two phase and three phase flows under high oil viscosity conditions (up to 17000cP) in horizontal pipelines. The multiphase (oil/water/solid/gas) facility was designed and constructed at Cranfield University and consists of 6m long horizontal pipeline of 0.026m diameter along with instrumentations. The principal objectives of the work were to study the effect of viscosity, water cut, temperature variance, and flow conditions on flow patterns and pressure drops for (oil/gas and oil/water) two phase flows; to compare the measured flow parameters and phase distribution with those predicted from models found in the literature for two phase flows; and to conduct an experimental study of gas injection effect on pressure gradient in (oil/water/gas) three phase flow. Due to the nature of heavy oil reservoirs, sand is associated with oil/water mixture when extracted; therefore sand concentration effect on pressure drop in (oil/water/sand) three phase flow is also examined. For oil-air flow, a smooth oil coating was observed in the film region of slug flow, while a ripple structure of oil coating film was found at higher superficial air velocity for slug flow regime and annular flow regime. The ripple structure was believed to increase the effective roughness of the pipe wall, which resulted in higher pressure gradients. The pressure drop correlations from Beggs and Brill (1973) and Dukler et al. (1964) were used to compare with experimental pressure gradients for oil/air flow. It was found that these correlations failed to predict the pressure gradients for heavy oil/air flows in this work. Several new heavy oil/water flow patterns were named and categorized based on observations. Though the heavy oil viscosity is an essential parameter for oil continuous phase flow on pressure drop, it had no significant effect beyond Water Assist Flow (WAF) condition, as a threshold was found for water cut with fixed superficial oil velocity. The transition criterion by McKibben et al. (2000b) for WAF was found to be able to predict this threshold reasonably well. Core Annular Flow (CAF) models were found to greatly under predict the pressure gradients mainly due to the coating (oil fouling) effect associated with this study. A new coating coefficient was introduced to models presented by Bannwart (2001) and Rodriguez et al (2009). The addition of solid in the mixed flow led to minor increase in the pressure gradient when the particles were moving with the flow. However, higher sand concentration in the system led to higher pressure gradient values. The addition of gaseous phase to the oil/water flow was more complex. The gaseous injection was beneficial toward reducing the pressure gradient when introduced in oil continuous phase only at very low water cuts.