[pt] A injeção de soluções poliméricas tem sido utilizada em muitas aplicações para aumentar a viscosidade da fase aquosa e, por conseguinte, reduzir a elevada razão de mobilidade durante o deslocamento de óleo num meio poroso. Evidências experimentais mostraram também que o comportamento viscoelástico de algumas soluções poliméricas pode contribuir para um melhor deslocamento do óleo na escala de poros, reduzindo assim, a saturação de óleo residual. Este comportamento na escala de poros não é claramente compreendido já que a modelagem de um fluxo viscoelástico de uma solução polimérica em meios porosos é extremamente desafiadora. O comportamento do escoamento em escala macroscópica está diretamente associado com o fluxo extensional dominante através das gargantas e poros que formam o meio poroso. Muitos modelos têm sido desenvolvidos com o objetivo de descrever o efeito extensional observados no fluxo de soluções poliméricas de elevado peso molecular. O modelo desenvolvido neste trabalho baseia-se na relação entre a vazão e a queda de pressão do escoamento de soluções poliméricas através de capilares com garganta que servem como um modelo simples da geometria das gargantas de poro. Um modelo de rede de capilares bidimensional foi desenvolvido para obter os parâmetros macroscópicos do escoamento a partir do entendimento do comportamento microscópico. No modelo monofásico, os resultados apresentam efeitos de diferentes parâmetros reológicos no comportamento macroscópico do escoamento. Para estudar o escoamento bifásico, um modelo de rede dinâmico foi desenvolvido. Os resultados obtidos fornecem uma descrição mais detalhada do processo de deslocamento de óleo pela fase aquosa. / [en] Injection of a polymer solution is used in many applications to increase the viscosity of the water phase and therefore reduce the high mobility ratio during oil displacement in porous media. Experimental evidence has shown that the viscoelastic behavior of some polymer solutions may contribute to a better oil displacement at the pore-level, reducing the residual oil saturation. This pore-level behavior is not clearly understood. Modeling viscoelastic flow of polymeric solutions in porous media is extremely challenging. The macroscopic flow behavior is directly associated with the extensional dominant flow through pore throats that form the porous media. Accurate models should be able to describe the extensional thickening effect observed in the flow of dilute high molecular weight polymer solutions. The model developed in this work is based on the flow rate-pressure drop relationship of polymer solution flow through constricted capillaries that serves as a simple model of the geometry of pore throats. A two-dimensional capillary network model is constructed in order to obtain macroscopic parameters from upscaling of the microscopic behavior. In single-phase flow, results show the effect of different rheological parameters on the macroscopic flow behavior. To study a two-phase flow, a dynamic network model was developed. The results obtained provide a more detailed description of the oil displacement by the water phase.

[pt] Após uma jazida de petróleo ser encontrada, a produção de óleo ou gás é feita através de um poço produtor que é perfurado até atingir as camadas de rocha onde os hidrocarbonetos estão alojados. Com a constante produção, a pressão de reservatório decresce até atingir um nível que é insuficiente para o aproveitamento econômico. Geralmente, utiliza-se a injeção de água para manter o nível de pressão do reservatório. Nos estudos de um reservatório de petróleo é fundamental o conhecimento de propriedades básicas da rocha e dos fluidos nela contidos. São essas propriedades que determinam as quantidades de fluidos existentes no meio poroso, a sua distribuição, a capacidade desses fluidos se moverem e, mais importante, a quantidade de fluidos que pode ser extraída. Através do método convencional de injeção de água objetiva-se a manutenção da pressão do reservatório e o deslocamento de óleo em direção aos poços produtores. A água (fluido deslocante) tende a ocupar gradualmente o espaço antes ocupado pelo óleo (fluido deslocado), contudo, por efeitos capilares, uma parcela do óleo não é retirada do meio poroso configurando o que chamamos óleo residual. Em função da razão de mobilidade da água e do óleo, a frente de deslocamento não é uniforme, e um grande volume do reservatório não é atingido pela água de injeção. A adição de polímero à água de injeção visa o aumento da viscosidade da água, e assim, melhorar a razão de mobilidade água-óleo, aumentando a eficiência de varrido uma vez que uniformiza a frente de avanço, reduzindo a formação de caminhos preferenciais no reservatório. Além de diminuir a razão de mobilidade, soluções poliméricas podem contribuir para um melhor deslocamento de óleo em escala de poro, a partir de seu efeito elástico, reduzindo, portanto, a saturação de óleo residual. Contudo, tal mecanismo em micro-escala, ou seja, em escala de poro não é totalmente compreendido. O presente trabalho preocupa-se principalmente em analisar o fator de recuperação do óleo e saturação de óleo residual após processo de deslocamento de óleo por água salgada, solução polimérica de poliacrilamida parcialmente hidrolisada (HPAM) e solução de glicerina em testemunhos de Arenito Bentheimer. Um porta-testemunho especial foi utilizado para a realização dos testes de deslocamento, sendo monitoradas a variação de pressão ao longo da amostra, além dos volumes de injeção e produção de fluidos em função do tempo. / [en] After an oil deposit is found, oil or gas is produced through a production well that is drilled until it reaches the rock layers where the hydrocarbons are housed. With constant oil production, the reservoir pressure decreases until it reaches a level that is insufficient for economic use. Water injection is generally used to maintain the reservoir pressure level. It is essential to know the basic rock and fluid properties to study an oil reservoir. These properties determine the volume of fluids in the porous medium, their distribution, the ability of these fluids to move, and most importantly, the volume of fluids that can be extracted. The conventional water injection method aims to maintain the reservoir pressure and the oil displacement towards the producing wells. Water (displacing fluid) tends to gradually occupy the space previously occupied by oil (displaced fluid), however, due to capillary effects, an oil portion is not removed from the porous medium, configuring what we call residual oil. Because of the water-oil mobility ratio, the displacement front is not uniform and a large volume of the reservoir is not reached by the injection water. Polymer addition in the injection water aims at increasing water viscosity, and thus, improving the water-oil mobility ratio, increasing the sweeping efficiency since it unifies the advance front, reducing the formation of preferential paths in the reservoir. Besides reducing the mobility ratio, polymeric solutions can contribute to a better oil displacement in pore-scale, based on its elastic effect, reducing residual oil saturation. However, this mechanism is not fully understood in the micro-scale. The present work is concerned with analyzing oil recovery factor and residual oil saturation after the oil displacement process by saltwater, polymeric solution of partially hydrolyzed polyacrylamide (HPAM), and glycerin solution in sandstone Bentheimer samples. A special core holder was used to displacement tests, the injection differential pressure on the sample was monitored, in addition to the injection volumes and production volume as a function of time.

[pt] A poliacrilamida parcialmente hidrolisada (HPAM) é amplamente empregada no processo de recuperação avançada de petróleo (EOR). No entanto, sua eficácia é prejudicada pela degradação das moléculas do polímero durante o fluxo através das linhas de injeção, válvulas e reservatório. Essa degradação leva a uma diminuição do peso molecular médio e, consequentemente, reduza viscosidade e as propriedades viscoelásticas da solução, afetando sua eficácia no deslocamento do petróleo. Para abordar essas questões, nossa pesquisa caracterizou o grau de degradação mecânica das soluções de HPAM usando reologia de cisalhamento e extensional. Induzimos a degradação fazendo as soluções fluírem por uma válvula com constrição e diferentes vazões através deum modelo microfluídico de um médio poroso. Os resultados revelam que aadição de nanopartículas de sílica (SiO2) tem um efeito insignificante sobreas viscosidades de cisalhamento e extensional de soluções frescas e minimiza a degradação mecânica das soluções de HPAM. As propriedades reológicas das soluções de HPAM com nanopartículas de SiO2 não são significativamente afetadas pela degradação mecânica, o que sugere que a incorporação de nanopartículas poderia aumentar a eficiência da injeção de polímeros em processosde EOR por meio da estabilização das soluções de HPAM. Além disso, nosso estudo explorou escoamento de deslocamento de óleo usando soluções de polímero HPAM frescas e degradadas em dispositivos microfluídicos usados como modelos de meios porosos. Os resultados sugerem que o HPAM fresco é mais eficiente na produção de óleo do que o HPAM degradado. Além disso, a adição de nanopartículas de sílica em soluções degradadas de NPs-HPAM resultou em um aumento de 9-13 por cento na recuperação de petróleo, destacando o enorme potencial das nanopartículas no aprimoramento dos processos de EOR. / [en] Partially hydrolyzed polyacrylamide (HPAM) is widely employed in enhanced oil recovery (EOR) process. However, its effectiveness is hindered by degradation of polymer molecules during flow through injection lines, valves and reservoir. This degradation leads to a decrease in average molecular weight and subsequently reduces the solution’s viscosity and viscoelastic properties, impacting its effectiveness on displacing oil. Our research characterized the degree of mechanical degradation of HPAM solutions using shear and extensional rheology. We induced degradation by flowing the solutions through a valve with varying constriction and flow rates and through a microfluidic porous medium model. Our findings reveal that the addition of silica (SiO2) nanoparticles has a negligible effect on the shear and extensional viscosities of fresh solutions and minimizes the mechanical degradation of HPAM solutions. The rheological properties of HPAM solutions with SiO2 nanoparticles are not significantly affected by mechanical degradation, suggesting that incorporating nanoparticles could enhance the efficiency of polymer injection in EOR processes by stabilizing HPAM solutions. In addition, our study explored oil displacement flow using both fresh and degraded HPAM polymer solutions in microfluidic devices used as models of porous media. The findings suggest that fresh HPAM is more efficient in displacing oil than degraded HPAM. Furthermore, the addition of silica nanoparticles into degraded NPs-HPAM solutions resulted in a 9-13 percent increase in oil recovery, highlighting the enormous potential of nanoparticles in enhancing EOR processes.

Ce manuscrit présente les résultats d'expériences illustrant différentes manifestations de la présence de polymères dans un écoulement. Pour chacune d'elles, nous étudions l'interaction entre la structure microscopique et l'écoulement.Lorsqu'une goutte se détache d'un capillaire, la colonne de liquide liant la goutte au capillaire doit se rompre. Pour les liquides simples, l'amincissement suit des lois universelles bien établies. La dynamique de détachement d'une goutte de fluide complexe est très différente. Pour les solutions de polymères, après une phase de décroissance rapide du diamètre de cette colonne, il se forme un long filament cylindrique entre la goutte et le capillaire. Afin de mieux comprendre comment les polymères présents en solution donnent naissance à ce filament, nous avons observé leurs conformations au cours du détachement. Ces observations confirment que l'étirement des polymères est à l'origine du ralentissement du processus de détachement. Cependant, lors de l'amincissement du filament, la distribution des longueurs reste inchangée. Ce résultat inattendu, nous a amené à mettre en place une nouvelle méthode pour estimer la viscosité élongationnelle.D'autres expériences sont présentées, l'une porte sur un effet de déplétion qui apparait lors de l'écoulement confiné d'une solution de polymères, alors que l'autre porte sur l'écoulement instable d'une solution concentrée de polymères dans une conduite rectiligne. / This work considers the interaction between a flow field and the microscopic degrees of a freedom of a polymer solution. Different flow configurations were considered.Droplet pinch off, which occurs when a drop of liquid detaches from a capillary, can be strongly modified in the presence of polymers giving rise to long and slender filaments that thin slowly in time. We here study experimentaly the dynamics of necking and the conformations of polymers during the thinning of the neck. Our results show that the slow down of the thinning dynamics is the result of polymer stretching. Moreover, during the filament thinning, the polymer length distribution remains the same. This result is unexpected and led us to introduce a new method to estimate the extensionnal viscosity which represents the polymer solution resistance to stretching.In a second flow configuration, we have observed that depletion of polymer molecules near a surface occurs when a bead approaches a plate in a polymer solution.

In recent years, a compound N-nitrosodimethylamine (NDMA), a probable human carcinogen, has been identified as an emerging disinfection by-product (DBP) since its formation and detection were linked to chlorine-based disinfection processes in several water utilities in the U.S. and Canada. Numerous organic nitrogen compounds present in water may impact the formation of NDMA during disinfection. Amine-based water treatment polymers used as coagulants and flocculants have been suggested as potential NDMA precursors due to the presence of amine functional groups in their structures, as well as the possible presence of dimethylamine (DMA) residues in polymer products. To minimize the potential risk of NDMA associated with water treatment polymers, the mechanisms of how the polymers behave as NDMA precursors and their contribution to the overall NDMA formation under actual water treatment conditions need to be elucidated. This research involved a systematic investigation to determine whether amine-based water treatment polymers contribute to NDMA formation under drinking water and wastewater treatment conditions, to probe the involved reaction mechanisms, and to develop strategies to minimize the polymers NDMA formation potential. The investigation included five research tasks: (1) General screening of NDMA formation potential of commonly used amine-based water treatment polymers, (2) NDMA formation from amine-based water treatment polymers under relevant water treatment conditions, (3) Probing the mechanisms of NDMA formation from polyamine and PolyDADMAC, (4) Effect of water treatment processes on NDMA formation from amine-based water treatment polymers, and (5) Developing strategies to reduce polymers NDMA formation potential. Direct chloramination or chlorination of high doses of polymers in deionized water at longer than typical contact time was used in the general screening of the NDMA formation potential of water treatment polymers and in the studies to identify reaction mechanisms. On the other hand, realistic dosages of chloramines and polymers and contact time were used in simulating representative water treatment conditions to evaluate the contribution of polymers to the overall NDMA formation in real systems. On the basis of the study results, strategies were developed to reduce the NDMA formation potential of amine-based water treatment polymers, which include modification of polymer structures and treatment parameters.

Recently, a new kind of turbulence has been discovered in the flow of concentrated polymer melts and solutions. These flows, known as purely elastic flows, become unstable when the elastic forces are stronger than the viscous forces. This contrasts with Newtonian turbulence, a more familiar regime where the fluid inertia dominates. While there is little understanding of purely elastic turbulence, there is a well-established dynamical systems approach to the transition from laminar flow to Newtonian turbulence. In this project, I apply this approach to purely elastic flows. Laminar flows are characterised by ordered, locally-parallel streamlines of fluid, with only diffusive mixing perpendicular to the flow direction. In contrast, turbulent flows are in a state of continuous instability: tiny differences in the location of fluid elements upstream make a large difference to their later locations downstream. The emerging understanding of the transition from a laminar to turbulent flow is in terms of exact coherent structures (ECS) — patterns of the flow that occur near to the transition to turbulence. The problem I address in this thesis is how to predict when a purely elastic flow will become unstable and when it will transition to turbulence. I consider a variety of flows and examine the purely elastic instabilities that arise. This prepares the ground for the identification of a three-dimensional steady state solution to the equations, corresponding to an exact coherent structure. I have organised my research primarily around obtaining a purely elastic exact coherent structure, however, solving this problem requires a very accurate prediction of the exact solution to the equations of motion. In Chapter 2 I start from a Newtonian ECS (travelling wave solutions in two-dimensional flow) and attempt to connect it to the purely elastic regime. Although I found no such connection, the results corroborate other evidence on the effect of elasticity on travelling waves in Poiseuille flow. The Newtonian plane Couette ECS is sustained by the Kelvin-Helmholtz instability. I discover a purely elastic counterpart of this mechanism in Chapter 3, and explore the non-linear evolution of this instability in Chapter 4. In Chapter 5 I turn to a slightly different problem, a (previously unexplained) instability in a purely elastic oscillatory shear flow. My numerical analysis supports the experimental evidence for instability of this flow, and relates it to the instability described in Chapter 3. In Chapter 6 I discover a self-sustaining flow, and discuss how it may lead to a purely elastic 3D exact coherent structure.

The flow of polymer solutions in the high Elasticity number, El, regime in complex geometries may lead to strong viscoelastic behaviour and eventually become unstable as the Weissenberg number, Wi, is increased beyond a critical level. So far, the success of numerical simulations in predicting the highly non-linear behaviour of polymer solutions in complex flows has been limited. In this thesis, selected constitutive models are evaluated under the high El flow regime in the cross-slot and contraction benchmark flows using a numerical technique based on the finite volume method. The numerical technique is implemented within the OpenFOAM framework and thoroughly validated in the benchmark flow. A modification to the FENE dumbbell model based on the non-affine deformation of polymer solutions is proposed, which enabled the prediction of some non-linear material functions and also enhanced numerical stability, allowing a higher Wi to be attained. Asymmetric flow instability in the cross-slot flow has been studied. Time-dependent stability diagrams were constructed based on Wi and the strain, ε, both of which govern the stretching of a polymer chain. In the contraction flow, elastic instability is simulated for the first time in this geometry. Substantial time-dependent asymmetric flow patterns were predicted as seen in experiments. The effect of the contraction ratio is investigated through a stability diagram. Three-dimensional finite element simulations were also carried out to study the effect of the aspect ratio in the contraction flow of a Phan-Thien-Tanner fluid. The simulations suggest that a lip vortex mechanism is a signature for the onset of strong viscoelastic behaviour.

[pt] Soluções poliméricas diluídas podem ser usadas na indústria de Óleo e Gás para injeção em reservatórios de petróleo como agentes de controle de mobilidade em técnicas de recuperação avançada de óleo, com o objetivo de aumentar o fator de recuperação do campo e postergar a indesejada alta taxa de produção de água. No entanto, o fenômeno macroscópico esperado, aumento da eficiência de varrido, é influenciado diretamente por fatores microscópicos que ocorrem na escala de poro. Devido às suas grandes cadeias moleculares, ao avançar através do meio poroso, soluções poliméricas de alto peso molecular dificultam o avanço da água alterando a razão de mobilidades água/óleo. Porém, o estudo de escoamento de soluções poliméricas ainda é um desafio devido ao comportamento não Newtoniano da relação vazão x diferença de pressão e à sensibilidade a diversos fatores como: tipo de polímero utilizado, concentração, razão de viscosidades, temperatura, salinidade e taxa de cisalhamento. O presente trabalho analisa a implementação de dois modelos constitutivos, Oldroyd-B e FENE-CR, aplicados ao método de solução de elementos finitos, EF, utilizando a formulação dos resíduos ponderados de Galerkin para modelar o escoamento de soluções poliméricas diluídas através de capilares com constrição e entender os fenômenos viscosos e elásticos envolvidos. Os resultados obtidos fornecem uma descrição mais detalhada da aplicação dos modelos testados e do escoamento de soluções poliméricas diluídas em gargantas de poros. / [en] Diluted polymeric solutions can be used in Oil & Gas industry for reservoir injection as mobility control agents in enhanced oil recovery technics, which goal is to increase the oil field recovery factor and postpone the high water production rates. However, the macroscopic expected phenomena, increase of the areal sweep, is directly influenced by microscopic factors that occurs at the pore scale. Due to their huge molecular chains, by advancing through the porous media, high molecular weight polymer solutions hinder the water flow changing the water/oil mobility ratio. Nevertheless, the comprehension of polymeric solutions flow is still a great challenge due to the Non-Newtonian behavior of the flow rate x pressure gradient relation and the sensibility to several variables such as: type of polymer used, concentration, viscosity ratio, temperature, salinity and shear rate. The present work analyzes the implementation of two constitutive models, Oldroyd-B and FENE-CR, coupled with the Finite Element method using the Galerkin weighted residual formulation to model the flow of diluted polymeric solutions through constricted capillaries and understand the viscous and elastic phenomena involved. The obtained results provide a more detailed portrait of the constitutive models and the flow of diluted polymeric solutions through pore throats.