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Constitutive relationships are developed to describe the water transport characteristics of the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs). Additionally, experimental fixtures and procedures for the determination of the constitutive relationships are presented. The water transport relationships are incorporated into analytical models that assess the impact of the water transport relations and that make PEMFC performance predictions. The predicted performance is then compared to experimental results. The new constitutive relationships are significantly different than the currently popular relationships used in PEMFC modeling because they are derived from experiments on actual PEMFC gas diffusion layer materials. In prior work, properties of the GDL materials such as absolute permeability, liquid water relative permeability, porosity, and capillary behavior are often assumed or used as adjustment parameters in PEMFC models to simplify the model or to achieve good fits with polarization data. In this work, the constitutive relations are not assumed but are determined via newly developed experimental techniques. The experimental fixtures and procedures were used to characterize common GDL materials including carbon papers and carbon cloths, and to investigate common treatments applied to these materials such as the bulk application of a hydrophobic polymer within the porous structure. A one-dimensional model is developed to contrast results based on the new constitutive relations with results based on commonly used relationships from the PEMFC literature. The comparison reveals that water transport relationships can have a substantial impact on predicted GDL saturation, and consequently a significant impact on cell performance. The discrepancy in saturation between cases can be nearly an order of magnitude. A two-dimensional model is also presented that includes the impact of the compressed GDL region under the shoulder of a bipolar plate. Results show that the compression due to the bipolar plate shoulder causes a significant increase in liquid saturation, and a significant reduction in oxygen concentration and current density for the paper GDL. In contrast, compression under the shoulder has a minimal impact on the cloth GDL. Experimental inputs to the 2-D model include: absolute permeability, liquid water relative permeability, the slope of the capillary pressure function with saturation, total porosity, GDL thickness, high frequency resistance, and appropriate Tafel parameters. Computational polarization curve results are compared to experimental polarization behavior and good agreement is achieved. / Ph. D.

Benefited from the efficiency of hydraulic fracturing and horizon drilling, the production of unconventional oil and gas resources, such as shale gas and tight oil, has grown quickly in 21th century and contributed to the North America oil and gas production. Although the new enhancing oil recover (EOR) technologies and strong demand spike the production of unconventional resources, there are still unknowns in recovery mechanisms and phase behavior in tight rock reservoirs. In such environment, the phase behavior is altered by high capillary pressure owing to the nanoscale pore throats of shale rocks and it may also influence minimum miscibility pressure (MMP), which is an important parameter controlling gas floods for CO2 injection EOR. To investigate this influence, flash calculation is modified with considering capillary pressure and this work implements three different method to calculate MMP: method of characteristics (MOC); multiple mixing cell (MMC); and slim-tube simulation. The results show that CO2 minimum miscibility pressure in nanopore size reservoirs are affected by gas-oil capillary pressure owing to the alternation of key tie lines in displacement. The values of CO2-MMP from three different methods match well. Moreover, in tight rock reservoirs, the heterogeneous pore size distribution, such as the ones seen in fractured reservoirs, may affect the recovery mechanisms and MMP. This work also investigates the effect of pore size heterogeneity on multicomponent multiphase hydrocarbon fluid composition distribution and its subsequent influence on mass transfer through shale nanopores. According to the simulation results, compositional gradient forms in heterogeneous nanopores of tight reservoirs because oil and gas phase compositions depend on the pore size. Considering that permeability is small in tight rocks and shales, we expect that mass transfer within heterogeneous pore size porous media to be diffusion-dominated. Our results imply that there can be a selective matrix-fracture component mass transfer during both primary production and gas injection secondary recovery in fractured shale rocks. Therefore, molecular diffusion should not be neglected from mass transfer equations for simulations of gas injection EOR or primary recovery of heterogeneous shale reservoirs with pore size distribution. / Master of Science / The new technologies to recover unconventional resources in oil and gas industry, such as fracturing and horizontal drilling, boosted the production of shale gas and tight oil in 21st century and contributed to the North America oil and gas production. Although the new technologies and strong demand spiked the production of tight oil resources, there are still unknowns of oil and gas flow mechanisms in tight rock reservoirs. As we know, the oil and gas resources are stored in the pores of reservoir formation rock. During production process, the oil and gas are pushed into production wells by formation pressure. However, the pore radius of shale rock is extremely small (around nanometers), which reduces the flow rate of oil and gas and raises capillary pressure in pores. The high capillary pressure will alter the oil and gas phase behavior and it may influence the value of minimum miscibility pressure (MMP), which is an important design parameter for CO2 injection (an important technology to raise production). To investigate this influence, we changed classical model with considering capillary pressure and this modified model is implemented in different methods to calculate MMP. The results show that CO2 -MMP in shale reservoirs are affected by capillary pressure and the results from different methods match well. Moreover, in tight rock reservoirs, the heterogeneous pore size distribution, such as fractures in reservoirs, may affect the flow of oil and gas and MMP value. So, this work also investigates the effect of pore size heterogeneity on oil and gas flow mechanisms. According to the simulation results, compositional gradient forms in heterogeneous nanopores of tight reservoirs and this gradient will cause diffusion which will dominate the other fluid flow mechanisms. Therefore, we always need to consider molecular diffusion in the simulation model for shale reservoirs.

[pt] Este trabalho desenvolve uma metodologia para obter experimentalmente a pressão capilar de diferentes fluidos em contato com folhelhos, comparando-a com valores obtidos analiticamente a partir da caracterização dos fluidos e dos folhelhos individualmente. Foram realizados ensaios numa célula de difusão a qual permite simular as condições de pressão aplicadas no campo, avaliar a interação físico- química entre fluidos e rochas, além de determinar os parâmetros de transporte de massa devido a gradientes químicos e hidráulicos. Verifica-se que os valores de pressão capilar obtidos diretamente na célula de difusão são inferiores aos obtidos a partir da equação de pressão capilar utilizando a tensão interfacial, o ângulo de contato e o raio de poros do folhelho. Desta forma, conclui-se que caso seja realizada uma análise de estabilidade considerando a pressão capilar do fluido, este parâmetro deve ser determinado experimentalmente na célula de difusão. Caso contrário, valores superestimados poderão ser encontrados. / [en] A methodology was developed to experimentally obtain the capillary pressure of different fluids in contact with shales and compare these values with analytical results from individual characterization of fluids and shales. Tests were carried out in a diffusion cell, which allows the simulation of in-situ pressure conditions, the evaluation of physical-chemical interactions between fluids and rocks and the determination of mass transport parameters due to hydraulic and chemical gradients. It is observed that the values of capillary pressure directly obtained in the diffusion cell are inferior to the ones obtained from the capillary pressure equation using the interfacial tension, the contact angle and the pore radius of shales. Thus, it can be concluded that, if a stability analysis considering the capillary pressure of the fluid is carried out, this parameter should be experimentally determined in the diffusion cell. Otherwise, overestimated values can be found.

O objetivo do trabalho é analisar e compreender os efeitos das características do fibrocimento reforçado com fibras sintéticas na retração por secagem deste compósito. A importância social do fibrocimento como material de construção, justifica a realização do presente trabalho, de modo a expor como acontece a retração por secagem neste compósito, e desta forma auxiliar o meio técnico na mitigação das manifestações patológicas relacionadas à retração e contribuindo para a redução do importante problema da indústria produtora de fibrocimento, que é a fissuração de borda nas telhas onduladas. Para tal buscou-se demostrar o efeito da porosidade e distribuição de tamanho de poros na retração por secagem. Além disso, foram realizados experimentos onde se variou o tipo de cimento utilizado, as quantidades de todas as matérias-primas envolvidas, além da aplicação de tratamentos modificadores da movimentação higroscópica, manipulando diretamente a tensão capilar causadora da retração. Concluiu-se que a porosidade elevada do fibrocimento faz com que a retração por secagem deste compósito seja fortemente influenciada pela porosidade total do mesmo, com correlação direta com a quantidade de mesoporos. Além disso, no estudo de caso realizado concluiu-se que a redução da retração devido à redução da tensão superficial da água do poro, se refletiu em menor fissuração de borda nas telhas onduladas. / The objective is to analyze and comprehend the effects of properties of cement based composite reinforced with synthetic fibers, on drying shrinkage of such composite. The social importance of fiber cement as construction material justifies the execution of the present work, in order to expose how drying shrinkage occurs on this composite and by those means to assist the technical community on mitigating pathological manifestations related to shrinkage, thus contributing for the reduction of an important problem on fiber cement industry, the edge cracking on corrugated sheets. In order to achieve this goal, it was sought to demonstrate the effect of porosity and pore size distribution on drying shrinkage. Moreover, experiments were performed, varying the type of cement used and the quantities of all materials involved, in addition to the application of treatments that modify hygroscopic movement, directly manipulating the capillary tension which causes shrinkage. It was concluded that the elevated porosity of the fiber cement causes drying shrinkage of this composite to be strongly influenced by its total porosity, directly correlated to the quantity of mesopores. Furthermore, in the case study performed it was concluded that shrinkage reduction due to the reduction of pore water surface tension was reflected into minor edge cracking on corrugated sheets.

In spite of the large number of research works on carbon capture and sequestration (CCS), the migration and behaviour of CO2 in the subsurface (i. e. strata below the earth's surface) still needs further understanding and investigations with the aim of encouraging the governmental policy makers to adopt CCS technology as one of the most viable means to tackle the global warming threats. In this research work, a series of numerical simulations has been carried out using STOMP-CO2 simulation code to determine the flow behaviour and ultimate fate of the injected supercritical carbon dioxide (scCO2) into saline aquifers in medium terms of storage (i. e. few thousand years). The characteristics of the employed simulator, including the mathematical algorithm, governing equations, equations of states and phase equilibria calculations are explained in details.

Dans une démarche de valorisation des déchets, les granulats recyclés sont introduits dans la formulation des bétons pour donner naissance à de nouveaux bétons recyclés qui représentent l’objet du projet national RECYBETON et du projet ANR ECOREB. Cette thèse se concentre sur l’étude du béton frais et en particulier la maîtrise du retrait plastique et l’effet du degré de saturation initial des gravillons recyclés sur le comportement des bétons recyclés. Deux familles de bétons avec des rapports eau/ciment respectifs de 0,6 et 0,45 ont été testés en conditions endogènes ainsi qu’en dessiccation (Vvent = 8 m/s). Chaque famille de bétons est constituée d’un béton naturel de référence et de deux bétons recyclés différenciés pas le degré initial de saturation des gravillons recyclés (50 et 120 % de l’absorption nominale). Les résultats expérimentaux soulignent la capacité des gravillons recyclés initialement partiellement saturés à capter rapidement l’eau contenue dans la pâte de ciment, modifiant ainsi le rapport E/C, les propriétés rhéologiques du béton frais et les résistances mécaniques du béton durci. Après saturation en eau, si les conditions de séchage conduisent à un manque d’eau dans le béton, les gravillons recyclés peuvent fournir de l’eau à la pâte. Ils constituent donc un potentiel de cure interne. Le retrait plastique sous vent est explicitement lié au ressuage, au développement de la pression capillaire et à la fissuration. Le temps d’initiation de la fissuration dépend de la quantité d’eau totale dans le béton et de sa capacité à ressuer tandis que l’ouverture de fissure varie avec la valeur de retrait plastique mesurée. Dans cette étude, le développement de la pression capillaire est la cause de la fissuration qui apparaît dès l’entrée d’air dans le matériau poreux. Les différences de comportements les plus importantes sont observées entre bétons ayant une quantité d’eau totale différente plutôt qu’entre bétons naturel et recyclé. La compilation des résultats expérimentaux a permis de mettre sur pied des modélisations qui illustrent les comportements observés. Les pores concernés par l’entrée d’air dans les bétons recyclés et naturels au moment de la fissuration sont les plus gros pores de la pâte. Enfin, un couplage hygrothermique séchage-température du béton peut influer sur le démarrage de l’hydratation. / In the context of sustainable development, the reuse of construction and demolition waste is necessary to conserve nonrenewable natural aggregate resources, so recycled aggregates are introduced in concrete mix design. This is the aim of the national projet RECYBETON and the research project ECOREB. This study deals with the fresh concrete and more specifically with shrinkage control and the effects of the initial saturation degrees of recycled coarse aggregates on concrete behavior.Two concrete families, with two different water/cement ratios 0,60 and 0,45, are tested under endogenous and drying (wind speed equal to 8 m/s) conditions. Each concrete family contains a reference natural concrete and two recycled concretes. The initial saturation degree is the difference between them (recycled coarse aggregates saturated or semi saturated).Experimental results underline the capacity of non-saturated aggregates to quickly absorb water from cement paste, modifying the W/C ratio, rheological properties of the fresh concrete and the mechanical strength (at 28 days) of recycled concretes. After saturation in water, recycled aggregates can release water into the cement paste if the undergone drying conditions lead to a lack of water in the cement matrix. The recycled coarse aggregates can be seen as an internal curing potential.Experimental plastic shrinkage studies carried out under drying conditions highlight a link between bleeding, capillary pressure, plastic shrinkage and cracking. It should be pointed out that the initial cracking is dependent on the total quantity of water in the concrete and on its bleeding capacity. The opening cracks vary with the plastic shrinkage values measured during the test. The analysis of the results emphasize that the capillary pressure is the determining parameter and that the air entry value matches the cracks. The major behavior differences are found between concretes with different volumes of water rather than between natural and recycled concretes.Finally, the analysis of all the experimental results have allowed concrete modelling and understanding why concretes do not behave in the same way. When it cracks, the air come in the biggest pores of the concrete paste. Moreover, a hygrothermal coupling exists between the drying and the temperature in concrete. It can affect hydration start up.

O objetivo do trabalho é analisar e compreender os efeitos das características do fibrocimento reforçado com fibras sintéticas na retração por secagem deste compósito. A importância social do fibrocimento como material de construção, justifica a realização do presente trabalho, de modo a expor como acontece a retração por secagem neste compósito, e desta forma auxiliar o meio técnico na mitigação das manifestações patológicas relacionadas à retração e contribuindo para a redução do importante problema da indústria produtora de fibrocimento, que é a fissuração de borda nas telhas onduladas. Para tal buscou-se demostrar o efeito da porosidade e distribuição de tamanho de poros na retração por secagem. Além disso, foram realizados experimentos onde se variou o tipo de cimento utilizado, as quantidades de todas as matérias-primas envolvidas, além da aplicação de tratamentos modificadores da movimentação higroscópica, manipulando diretamente a tensão capilar causadora da retração. Concluiu-se que a porosidade elevada do fibrocimento faz com que a retração por secagem deste compósito seja fortemente influenciada pela porosidade total do mesmo, com correlação direta com a quantidade de mesoporos. Além disso, no estudo de caso realizado concluiu-se que a redução da retração devido à redução da tensão superficial da água do poro, se refletiu em menor fissuração de borda nas telhas onduladas. / The objective is to analyze and comprehend the effects of properties of cement based composite reinforced with synthetic fibers, on drying shrinkage of such composite. The social importance of fiber cement as construction material justifies the execution of the present work, in order to expose how drying shrinkage occurs on this composite and by those means to assist the technical community on mitigating pathological manifestations related to shrinkage, thus contributing for the reduction of an important problem on fiber cement industry, the edge cracking on corrugated sheets. In order to achieve this goal, it was sought to demonstrate the effect of porosity and pore size distribution on drying shrinkage. Moreover, experiments were performed, varying the type of cement used and the quantities of all materials involved, in addition to the application of treatments that modify hygroscopic movement, directly manipulating the capillary tension which causes shrinkage. It was concluded that the elevated porosity of the fiber cement causes drying shrinkage of this composite to be strongly influenced by its total porosity, directly correlated to the quantity of mesopores. Furthermore, in the case study performed it was concluded that shrinkage reduction due to the reduction of pore water surface tension was reflected into minor edge cracking on corrugated sheets.

[pt] A compreensão dos mecanismos e fenômenos de transporte relacionados ao fluxo multifásico em meios porosos é de grande relevância para diversas aplicações práticas como captura e sequestro de dióxido de carbono, transporte em células de combustível e recuperação avançada de reservatórios de hidrocarbonetos. A geometria do espaço poroso e as interações dos fluidos com sua parte sólida determinam propriedades macroscópicas como porosidade, permeabilidades relativas e pressão capilar. Porém, a visão em escala microscópica fornece uma melhor descrição e entendimento dos processos físicos e químicos do escoamento de fluidos no espaço poroso. Neste trabalho desenvolvemos um simulador de rede de poros para análise do escoamento bifásico de fluidos imiscíveis tanto para o processo de drenagem quanto para o de embebição. O modelo de rede 240×40 tem capilares com raios médios na ordem de 52.35 micrometro com constrição. Os padrões de escoamento e eficiências de deslocamento foram obtidos para diferentes razões de viscosidade e números de capilaridade. Os resultados encontrados, considerando deslocamento pistão, foram similares a de experimentos realizados previamente, injetando água no meio saturado de óleo. Na drenagem, a saturação residual de óleo cai com o aumento do número de capilaridade. O padrão de escoamento observado é de fingerings viscosos e, a frente de deslocamento torna-se mais estável com o aumento da razão de viscosidade. Na embebição, para números de capilaridade mais baixos, o escoamento foi dominado por fingers capilares. Para números de capilaridade altos, fingers viscosos foram predominantes e, com o aumento da razão de viscosidade, a frente apresentou maior estabilidade. / [en] Understanding the mechanisms and transport phenomena of multiphase flow in porous media has great relevance in several practical applications, such as capture and sequestration of carbon dioxide, transport in fuel cells and enhancement hydrocarbon recovery. The geometry of pore space and the fluid interactions with the solid determine macroscopic properties such as porosity, relative permeabilities and capillary pressure. However, microscopic analysis provides a better description and comprehension of physical and chemical processes of fluid flow in the pore space. In this work, we developed a pore-network simulator to analyze immiscible two-phase flow for both drainage and imbibition processes. The 240×40 pore-network model has constricted capillary channels with radius on the order of 52.35 micrometer. Flow patterns and displacement efficiencies evaluation were obtained at different viscosity ratios and capillary numbers. The results, considering piston-like displacement, were similar to experiments realized previously, injecting water in an oil saturated medium. In the drainage process, the oil saturation reduces with increasing capillary number. The observed flow pattern is viscous fingerings and the front is stable with the higher viscosity ratio. In imbibition, the flow was dominated by capillary fingers at low capillary numbers. At high capillary numbers, viscous fingers were predominant and, with increasing viscosity ratio, the front presented higher stability.

Dans cette thèse, nous nous sommes intéressés à la mesure et à la modélisation des propriétés d'écoulements diphasiques (perméabilités relatives) dans des milieux poreux carbonatés représentatifs de la zone de transition de réservoirs pétroliers carbonatés. Notre étude expérimentale a porté sur deux roches carbonatées de même minéralogie mais de propriétés pétrophysiques différentes (unimodale et bimodale). Les fluides utilisés sont une saumure, une huile minérale pour les expériences en mouillabilité franche à l'eau et une huile brute pour les expériences en mouillabilité altérée (obtenue par macération). Durant les expériences en « écoulements permanents », la perte de charge est mesurée continûment et le champ de saturation locale est mesuré en fin d'expérience par atténuation gamma. Les principaux résultats expérimentaux de cette étude sont les suivantes :- La mouillabilité dépend de la saturation initiale en huile et donc de la hauteur de la zone de transition. Elle a une influence sur les perméabilités relatives à l'huile ET à l'eau.- L'hystérésis des perméabilités relatives à l'eau est d'autant plus prononcée que la saturation initiale en huile augmente. Une observation similaire est faite sur la courbure des perméabilités relatives à l'huile.- Les évolutions des Sorw en fonction des Soi ne vérifient pas toutes, une loi monotone de type Land. Leur évolution dépend aussi de la structure poreuse.- Les deux types de roches carbonatés présentent une altération de mouillabilité différente, la structure vacuolaire favorisant l'altération de mouillabilité. Nos données expérimentales ont été interprétées en utilisant différents modèles d'hystérésis de la littérature. Il apparait clairement des différences entre les prédictions numériques et nos données expérimentales car ces modèles ne prennent pas en compte l'évolution de la mouillabilité. Nous avons proposé un modèle de calcul des perméabilités relatives qui décrit nos données expérimentales de manière satisfaisante. / In this work, we take an interest in measuring and modeling the multiphase flow properties (relative permeabilities) in different carbonate rock types that are representative of the transition zone of carbonate reservoirs. Our experimental study focused on two different carbonate rock types, with almost the same mineralogy, but different petrophysical properties (bimodal and unimodal). The system of fluids used is composed of brine, a mineral oil (for experiments at water-wet conditions), and a crude oil (for experiments including wettability alteration after an ageing process at high temperature). During the experiments performed by the steady-state core flooding method, the pressure drop is continuously measured along the core, and the saturation profiles are obtained at the end of the flooding, by gamma ray measurements. The main results of this study are as follows:- Wettability depends on the initial oil saturation and hence the heights above the oil-water contact. It affects the oil relative permeabilities AND water relative permeabilities- The hysteresis observed on water relative permeability is even more pronounced that the initial oil saturation increases. A similar observation is made on the curvatures of the oil relative permeability.- The evolution of Sorw as function of Soi does not always follow a classical Land correlation. Their evolution also depends on the pore structure.- The two rock types exhibit different responses to wettability alteration. The vuggy structure might promote oil-wetness.Our experimental data were interpreted using different hysteretic models of the literature. We observed significant differences between the results predicted by the models and our experimental observations which are attributed mainly to the failures to take into account the change in wettability. We proposed an improved hysteresis model, which described our experimental data satisfactorily.