Dissertations / Theses on the topic 'Effective permeability'

This dissertation develops analytical expressions for the effective hydraulic conductivity Kₑ of a three-dimensional porous medium bounded by two parallel planes of infinite extent separated by a distance 2a. Head varies randomly along each boundary about a uniform mean value. The log hydraulic conductivity Y forms a homogeneous, statistically anisotropic random field having a variance σᵧ² and principal integral scales λ₁, λ₂, λ₃. Flow is uniform in the mean parallel to the principal coordinate χ₁. A solution is first derived for mildly nonuniform media with σᵧ² ≪ 1 via an approximate form of the 1993 residual flux theory by Neuman and Orr. It is then extended to strongly nonuniform media with arbitrarily large σᵧ² by invoking the Landau-Lifshitz conjecture as Kₑ = KG exp {σᵧ² [1/2 — (D + S)]} . Here, K(G) is the geometric mean of hydraulic conductivities and D and S are domain and surface integrals, respectively. Based on a rigorous limiting analysis we show that when the length scale ratio p = a / λ₁ → 0, Kₑ is equal to the arithmetic mean hydraulic conductivity K(A). This supports the theoretical finding of Neuman and Orr and the numerical result by Desbarats. When ρ → ∞ we obtain expressions for Kₑ that have been previously derived in the stochastic literature for infinite flow domains. For strongly anisotropic media with integral scale ratios ε₂ = λ₂ / λ₁ and ε₃ = λ₃ / λ₁ equal to each other and tending to zero or infinity ( ) i 0) we obtain the closed form solution Kₑ = K(G) exp {σᵧ²[exp(—p) — 0 .5]} . The latter reduces to K(A) when ρ → 0 and tends to the harmonic mean K(H) as ρ → ∞. One can think of the case ε₂ = ε₃ = 0 as mean flow along parallel channels having mutually uncorrelated hydraulic conductivities, and of the case ε₂ = ε₃ → ∞ as mean flow normal to layers having uniform hydraulic conductivities. For statistically isotropic media we show numerically that Kₑ equals K(A) when ρ = 0.01; when ρ ≥ 4, Kₑ = K(G) exp(σᵧ²/6) the three-dimensional infinite domain solution. Our results support the analytical finding of Rubin and Dagan, and predict and explain all related bounded domain numerical results. Finally, contrary to Dagan's assertion, we show that for small ρ boundary effects are extremely important; the absolute value of the surface integral S equals the value of the domain integral D.

The problem of homogenization the nanostructured materials placed in DC magnetic field has been discussed. The experimental data are obtained using metallic superlattices, metal-dielectric thin films and 3D-nanostructured materials. All these materials contain ferro- or ferrimagnetic component. The trans-mission and reflection coefficients were measured on the waves of millimeter waveband. It has been shown that the experimental frequency spectra of the coefficients in zero magnetic field can be described by the effective conductivity and dielectric permittivity. The spectra of ferromagnetic resonance, however, cannot be calculated correctly with the averaged magnetization. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35340

The importance of shales and mudstones to applied geosciences and in particular to fluid migration in sedimentary basins has never been more recognized than today. Prominent examples are conventional or unconventional petroleum systems, where shales and mudstones act as source, reservoir or cap rock, but also CO2 and nuclear waste storage or hydrogeology. Despite their importance, shales and mudstones are yet not as far well understood as sandstones or carbonate rocks. In particular, the influence of heterogeneity on fluid migration has been poorly addressed in the past, although many authors have identified and studied heterogeneities in shales and mudstones. Nevertheless, their flow properties are fairly well understood when treated as homogeneous on sample scale (centimetre-scale). Typical flow relevant heterogeneities are grain size and thus petrophysical property (e.g. porosity, permeability, capillary entry pressures) variations due to spatial lithological variation induced by primary and secondary sedimentary structures. In this study we investigate flow relevant heterogeneities of shales and mudstones on submetre scale derived from core and borehole images from an off-shore gas field in the Western Nile Delta, Egypt. Thereby, we combine latest models and published measurements of sample-scale petrophysical properties with interpretation, quantitative analyses, advanced modelling and numerical fluid flow simulation to assess the influence of shale and mudstone heterogeneity on fluid flow and hence, fluid migration, retention and mudstone seal capacity. Additionally, the set of mudstone heterogeneities used in this study has been derived from a combined visual and geostatistical interpretation of more than 500 m of mud-rich core and borehole images. As final results, we deliver stress-dependent effective porosity-permeability relationships for a broad range of shale and mudstone heterogeneities, representative model sizes and resolution as well as measures of uncertainty for each heterogeneity type. Moreover, probability density functions describing where and how these heterogeneities appear in larger scale geological units, such as seismic facies or local depositional environments, are provided. As a key result, heterogeneity and lithological variation have great influences on effective permeability and effective permeability anisotropy (Kh/Kv). Furthermore, our results indicate that mudstone heterogeneity is very common in all investigated larger scale geological units (hemipelagites, levees, channels). Modelling of fluid flow through mud-rich sedimentary basins without inclusion of these sub-metre scale heterogeneities of mudstones can therefore lead to misleading results. Thus, effective porosity-permeability (anisotropy) relationships are provided for different lithological variations and mudstone heterogeneities as a final result.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O trabalho apresenta uma ampla revisão de conceitos básicos associados ao fluxo multifásico (fluxo simultâneo de dois ou mais fluidos) em meios porosos, bem como técnicas de ensaios e equipamentos utilizados na determinação de permeabilidades efetiva e absoluta em solos saturados e não saturados com água. Com base nesta revisão, e visando a medida da permeabilidade de solos não saturados submetidos a fluxo de misturas gasolina-álcool, foi projetados, construído e colocado em operação um sistema de permeâmetros de parede flexível com controle de sucção; foi desenvolvido um software de controle e implementando um sistema automático de monitoramento da instrumentação eletrônica utilizada para medidas de variação de volume, de pressões e de deslocamentos axiais das amostras desolo; foi implementado um sistema de bomba de fluxo para aplicação de vazões constantes nos ensaios de permeabilidade, e forma desenvolvidos sistemas de medição do volume dos líquidos e gases passando pela amostra sob diferentes gradientes de pressão. Todos os desenvolvimentos projetados e implementados são descritos em detalhe. Características de uso dos equipamentos e aspectos de calibração da instrumentação eletrônica e demais acessórios são discutidos, procurando-se definir limites de trabalhabilidade, eventuais deficiências e técnicas alternativas de ensaios envolvendo o uso de misturas álcool gasolina. Visando avaliar o comportamento dos equipamentos e acessórios desenvolvidos, apresenta-se e discute-se resultados de um programa experimental envolvendo a) o uso de amostras de um solo inerte, incompressível dentro dos níveis de tensões efetivas aplicadas, preparadas em laboratório utilizando técnicas especiais de modo a se obter uma estrutura repetitiva, fracamente cimentada, simulando os solos residuais de gnaisse; b) execução de ensaios de vazão constante visando a determinação da permeabilidade absoluta de amostras saturadas utilizando como fluidos permeantes água, ar gasolina e álcool; c) execução de ensaios de vazão constante visando a determinação das permeabilidades efetivas à água e ao ar de amostras não saturadas, submetidas a sucções constantes variando de cerca de 10 a 60 kPa. Os resultados obtidos indicam que o equipamento desenvolvido e as técnicas experimentais implementadas constituem ferramentas versáteis que possibilitam a determinação direta das permeabilidades absolutas e efetivas de forma relativamente simples e confiáveis.
This work presents a wide revision of basic concepts associated to the multiphase flow (simultaneous flow of two or more fluids) in porous media as well as techniques of test and equipment s used in the determination of effective and absolute permeability in saturated and not saturated soils with water.With basis in this revision, and locking for the measure of saturated soils permeability submitted to flow of mixtures gasoline-alcohol, it was projected, built and placed in operation a system of flexible wall permeameters with suction control; a control software was developed and implementing an automatic system of monitoring of the electronic instrumentation used for measures of change volume, pressures and axial displacements of the soil samples; a flow pump system was implemented for application of constant rate in the permeability test, and systems of measurement of the volume of the liquids and gases were developed going by the sample under different pressure gradients.All the projected developments and implemented are described in detail. Characteristics of the used equipment s and calibration aspects of the electronic instrumentation and other accessories are discussed, trying to define workability limits, eventual deficiencies and techniques alternatives of testing involving the use of alcohol gasoline mixtures. Look in for evaluate the performance of equipment s and developed accessories, are presented and it is discussed results of an experimental program involving a) the use of samples of a inert soil, incompressible between levels of applied effective tensions,prepared in labortory using special techniques in way obtaining a repetitive structure, weakly cemented, simulating the residual soils of gnaisse; b) execution of constant rate test looking for the absolute permeability determination of saturated samples using as percolate fluids water, air, gasoline and alcohol; c) execution of constant rate test looking for the determination of the effective permeability to the water and the air of non saturated samples, submitted to constant suctions varying about 10 to 60 kPa.The obtained results indicate that the developed equipment and the implemented experimental techniques constitute versatile tools that make possible the direct determination of the absolute and effective permeabilities in way relatively simple and you trusted.
EL trabajo presenta una amplia revisión de conceptos básicos asociados al flujo multifásico (flujo simultáneo de Dos o más fluidos) en medios porosos, así como técnicas de ensayos y equipamentos utilizados en la determinación de permeabilidades efectiva y absoluta en suelos saturados y no saturados con agua. Con el objetivo de medir la permeabilidad de suelos no saturados sometidos a flujo de mezclas de gasolina y alcohol, fue proyectados, construido y colocado en operación un sistema de permeámetros de pared flexible con control de succión; se desarrolló un software de control y se implementó un sistema automático de monitoramiento de la instrumentación eletrónica utilizada para medidas de variación de volumen, de presiones y de desplazamientos axiales de las muestras de suelo. Se implementó además; un sistema de bomba de flujo para aplicación de desbordamientos constantes en los ensayos de permeabilidad, y se deasarrollaron sistemas de medición del volumen de los líquidos y gases pasando por la muestra bajo diferentes gradientes de presión. Se detallan todos los desarrollos proyectados e implementaciones. Se discute las características de uso de los equipamentos y aspectos de calibración de la instrumentación eletrónica y demás accesorios, con el objetivo de definir límites de trabajabilidad, eventuales deficiencias y técnicas alternativas de ensayos que envuelven el uso de mezclas de alcohol u gasolina. Para evaluar el comportamiento de los equipos y accesorios desarrollados, se presentan y discuten los resultados de un programa experimental que considera a) el uso de muestras de un suelo inerte, incompresible dentro de los níveles de tensiones efectivas que fueron aplicadas, preparadas en laboratorio utilizando técnicas especiales para obtener una extructura repetitiva, debilmente cimentada, simulando suelos residuales de gnaise; b) ejecución de ensayos de desbordamiento constante visando la determinación de la permeabilidad absoluta de muestras saturadas utilizando como fluidos permeantes agua, ar gasolina y álcool; c) ejecución de ensayos de desbordamiento constante con el objetivo de determinar las permeabilidades efectivas a agua y aire de muestras no saturadas, sometidas a succiones constantes variando entre 10 a 60 kPa. Los resultados obtenidos indican que el equipo desarrollado y las técnicas experimentales implementadas constituyen herramientas versátiles que hacen posible la determinación directa de las permeabilidades absolutas y efectivas de forma relativamente simple y confiables.

Measuring transport properties of rock samples under stress is essential to understanding and predicting the migration of fluids within the Earth's crust. Mudrocks play an essential role in petroleum systems as they are often the source rock and may act as a seal due to their low permeability. With increasing production from unconventional reservoirs where the mudrock is source, reservoir and seal, there is now even greater demand to understand the permeability and storativity of mudstones and tight sandstones. When hydraulic fracture treatment is used to enhance production, flow of hydrocarbons into the fractures will be ultimately controlled by the matrix permeability. Knowledge of the fluid transport properties of mudstones is currently hindered by a scarcity of published experimental data. In this thesis, a combination of permeability and ultrasonic velocity measurements allied with image analysis is used to distinguish the primary microstructural controls on effective stress dependent permeability. Permeabilities of cylindrical samples of Whitby Mudstone and Eagle Ford Shale have been measured using the oscillating pore pressure method at confining pressures ranging between 30-95 MPa and pore pressures ranging between 1-80 MPa. The results show that samples must be pressure cycled in order to obtain a reproducible behaviour, after which the relationship between permeability and effective stress can be described by an exponential law. The permeability of the Whitby Mudstone samples ranges between 7 ×10-21 m2 and 2 ×10-19 m2 (7 nd to 188 nd) and decreases by ~1 order of magnitude across the applied effective stress range. The permeability of the Eagle Ford Shale samples is slightly higher ranging between 2 ×10-18 m2 and 42 ×10-18 m2 (2 μd to 42 μd) and decreases by half an order of magnitude across the applied effective stress range. Permeability is shown to be more sensitive to changes in pore pressure than changes in confining pressure yielding values of alpha between 1.1-2.1 for Whitby Mudstone and 1.6-4.6 for Eagle Ford Shale. Gas slippage (Klinkenberg) effects are restricted to pore pressures below 10 MPa in the Whitby Mudstone and therefore do not affect the results presented. The permeability-effective stress relationship is thus empirically described using a modified effective stress law in terms of confining pressure, pore pressure and a Klinkenberg effect. Use of a simple reservoir model demonstrates that if pressure dependent permeability is not taken into account, substantial overestimation of gas flow rate and original gas in place will be made from well tests. Changes in ultrasonic velocity and pore volume were related to the observed loss of permeability with increasing effective stress, providing further insight into the nature of the permeability-controlling pore network. Combining the petrophysical data with pore conductivity modelling and microstructural analysis shows that at low effective stresses, permeability is controlled by a network of long, thin crack-like pores associated with grain boundaries. At high effective stresses, these cracks are closed and fluid is restricted to flowing through a less permeable network of higher aspect ratio, stiffer, nm-scale pores in the clay matrix. Applying the methods developed in the present work to different mudstones with a range of compositions and textures will help to refine understanding of the variability in fluid-conducting pore networks, thereby advancing the interpretation of data from well logs and well tests used for reservoir evaluation.

When the reservoir pressure is decreased below dew point pressure of the gas near the wellbore, gas-condensate wells start to decrease production because condensate is separated from the gas around the wellbore causing a decrease in gas relative permeability. This effect is more dramatic if the permeability of the reservoir is low. The idea proposed for reducing this problem is to eliminate the irreducible water saturation near the wellbore to leave more space for the gas to flow and therefore increase the productivity of the well. In this research a simulation study was performed to determine the range of permeabilities where the cylinder of condensate will seriously affect the well’s productivity, and the distance the removal of water around the wellbore has to be extended in order to have acceleration of production and an increase in the final reserves. A compositional-radial reservoir was simulated with one well in the center of 109 grids. Three gas-condensate fluids with different heptanes plus compositions ( 4, 8 and 11 mole %), and two irreducible water saturations were used. The fitting of the Equation of State (EOS) was performed using the method proposed by Aguilar and McCain. Several simulations were performed with several permeabilities to determine the permeabilities for which the productivity is not affected by the presence of the cylinder of condensate. At constant permeability, various radii of a region of zero initial water saturation around the wellbore were simulated and comparisons of the effects of removal of irreducible water on productivity were made. Reservoirs with permeabilities lower than 100 mD showed a reduction in the ultimate reserves due to the cylinder of condensate. The optimal radius of water removal depends on the fluid composition and the irreducible water saturation of the reservoir. The expected increase in reserves due to water removal varies from 10 to 80 % for gas production and from 4 to 30% for condensate production.

This thesis is aimed to calculate the effective permeability tensor and to simulate the fluid flow in naturally fractured reservoirs. This requires an understanding of the mechanisms of fluid flow in naturally fractured reservoirs and the detailed properties of individual fractures and matrix porous media. This study has been carried out to address the issues and difficulties faced by previous methods; to establish possible answers to minimise the difficulties; and hence, to improve the efficiency of reservoir simulation through the use of properties of individual fractures. The methodology used in this study combines several mathematical and numerical techniques like the boundary element method, periodic boundary conditions, and the control volume mixed finite element method. This study has contributed to knowledge in the calculation of the effective permeability and simulation of fluid flow in naturally fractured reservoirs through the development of two algorithms. The first algorithm calculates the effective permeability tensor by use of properties of arbitrary oriented fractures (location, size and orientation). It includes all multi-scaled fractures and considers the appropriate method of analysis for each type of fracture (short, medium and long). In this study a characterisation module which provides the detail information for individual fractures is incorporated. The effective permeability algorithm accounts for fluid flows in the matrix, between the matrix and the fracture and disconnected fractures on effective permeability. It also accounts for the properties of individual fractures in calculation of the effective permeability tensor. The second algorithm simulates flow of single-phase fluid in naturally fractured reservoirs by use of the effective permeability tensor. This algorithm takes full advantage of the control volume discretisation technique and the mixed finite element method in calculation of pressure and fluid flow velocity in each grid block. It accounts for the continuity of flux between the neighbouring blocks and has the advantage of calculation of fluid velocity and pressure, directly from a system of first order equations (Darcy???s law and conservation of mass???s law). The application of the effective permeability tensor in the second algorithm allows us the simulation of fluid flow in naturally fractured reservoirs with large number of multi-scale fractures. The fluid pressure and velocity distributions obtained from this study are important and can considered for further studies in hydraulic fracturing and production optimization of NFRs.

Spatial variability of porous media often prevents precise physical characterization of the system. In order to model moisture and solute transport through this media, certain sacrifices in precision must be made. Physical characteristics of the system must be averaged over large scales, lumping the small scale variability into the large scale characterization. Although this precludes a precise definition of the small scale flow characteristics, parameterization is much more attainable. This study addresses methods for determining effective hydraulic conductivity of unsaturated porous media. Effective conductivity is used to describe the large scale behavior of the system. Different methods for calculating the effective conductivity are presented and compared. Results indicate that the unit mean gradient method produces good estimates of the effective conductivity and can be applied using limited field data. The zone of correlation of the hydraulic parameters can be used in experimental design to minimize the errors associated with estimation of the mean pressure. An inverse method for evaluating the optimum effective hydraulic parameters is presented. Results indicate the optimization procedure is more sensitive to wetting than to drying conditions. Because of interaction between the hydraulic parameters, concurrent optimization of more than two of the parameters based on soil pressure data alone is not advised. Anisotropy in an unsaturated soil was found to be a function of the profile mean soil pressure. Results indicate the effective conductivity for flow parallel to soil layering can be estimated from the arithmetic mean of the unsaturated conductivity values for each of the layers and is between the harmonic and geometric means of these data for flow perpendicular to the layering. Estimates of the effective unsaturated hydraulic conductivity obtained through stochastic analysis agreed well with simulation results. Deviations between the stochastic predictions and simulation results are larger when the variability of the soil profile is greater and begin to deviate significantly when the variance of ln K(ψ₀) exceeds 5.0 and the variance of a exceeds 0.02 1/cm².

Heterogeneous mixtures have the potential to be used as synthetic substrates for antenna applications giving the antenna designer new degrees of freedom to control the permittivity and/or permeability in three dimensions such as by a smooth variation of the density of the inclusions, the height of the substrate and the manufacture the whole antenna system in one process. Electromagnetic, fabrication, environmental, time and cost advantages are potential especially when combined with nano-fabrication techniques. Readily available and cheap materials such as Polyethylene and Copper can be used in creating these heterogeneous materials. These advantages have been further explained in this thesis. In this thesis, the research presented is on canonical, numerical and measurement analysis on heterogeneous mixtures that can be used as substrates for microwave applications. It is hypothesised that heterogeneous mixtures can be used to design bespoke artificial dielectric substrates for say, patch antennas. The canonical equations from published literature describing the effective permittivity, ε_eff and effective permeability, μ_eff of heterogeneous mixtures have been extensively examined and compared with each other. Several simulations of homogenous and heterogeneous media have been carried out and an extraction/inversion algorithm applied to find their ε_eff and μ_eff. Parametric studies have been presented to show how the different variables of the equations and the simulations affect the accuracy of the results. The extracted results from the inversion process showed very good agreement with the known values of the homogenous media. Numerically and canonically computed values of ε_eff and μ_eff of various heterogeneous media were shown to have good agreement. The fabrication techniques used in creating the samples used in this research were examined, along with the different measurement methods used in characterising their electromagnetic properties via simulations and measurements. The challenges faced with these measurement methods were explained including the possible sources of error. Patch antennas were used to investigate how the performance of an antenna may be affected by heterogeneous media with metallic inclusions. The performance of the patch antenna was not inhibited by the presence of the metallic inclusions in close proximity. The patch measurement was also used as a measurement technique in determining the ε_eff of the samples.

Les mousses à cellules ouvertes ont diverses applications industrielles, par exemple pour des échangeurs de chaleur, des réacteurs structurés, la filtration, la catalyse, récepteurs solaires volumétriques en raison de leurs propriétés uniques telles qu'une importante porosité et une surface spécifique élevée. Pour déterminer théoriquement la surface spécifique géométrique et les relations entre les paramètres géométriques de mousses, une corrélation mathématique généralisée a été développée. A cet effet, la géométrie de la tetrakaidecahedron a été utilisé et différentes formes de sections transversales de brins de structures en mousse ont été pris en compte de façon explicite. La corrélation dérivée pour prédire les propriétés géométriques peut facilement être étendue à des formes différentes. Des simulations numériques 3-D à l'échelle des pores ont été réalisées pour étudier la perte de charge et la conductivité effective thermique. L'écoulement du fluide à travers la mousse à cellule ouverte a été réalisé dans trois régimes différents: les régimes de Darcy, transitoire et inertiel. L'importance des propriétés géométriques sur les caractéristiques d'écoulement de fluide et leurs inclusions dans les corrélations proposées pour prédire la perte de charge est discutée. La question « Les paramètres d'Ergun peuvent-ils avoir des valeurs numériques constantes ou non ? » est discutée. Trois différentes corrélations étaient dérivées pour prédire la conductivité thermique effective à la fois isotrope et anisotrope des mousses. Les paramètres géométriques de la matrice de mousse étaient introduits dans les corrélations pour prédire la conductivité thermique effective
Open cell foams have diverse industrial applications e.g. heat exchangers, structured reactors, filtration due to their unique properties such as high porosity and high specific surface area. In order to theoretically determine the geometric specific surface area and relationships between geometrical parameters of isotropic open cell foams, a generalized mathematical correlation was developed. For this purpose the tetrakaidecahedron geometry was used and different shapes of strut cross-sections of foam structures were taken explicitly into account. The derived correlation to predict geometrical properties can be easily extended to different strut shapes. 3-D numerical simulations at pore scale were performed to study the pressure drop characteristics and effective thermal conductivity. Fluid flow through open cell foam was performed in three different regimes: Darcy regime, transition regime and inertia regime. Importance of geometrical properties on fluid flow characteristics and their inclusion in the proposed correlations for predicting pressure drop is discussed. "Can Ergun parameters have constant numerical values or not" is also extensively discussed. Three different correlations were derived to predict the effective thermal conductivity for both, isotropic and anisotropic open cell foams. Geometrical parameters of foam matrix were introduced in the correlations to predict effective thermal conductivity

Cette thèse s’intéresse à la caractérisation de couches diélectriques et magnétiques de structures multicouches par cavité résonante microonde. Les matériaux multicouches ont des propriétés électromagnétiques spécifiques et sont utilisés dans beaucoup de secteurs industriels, par exemple, dans les radiocommunications. La caractérisation électromagnétique reste une priorité pour la compréhension des caractéristiques de propagation des ondes électromagnétiques dans ces milieux. Dans ce travail de thèse nous proposons une nouvelle approche expérimentale pour déterminer les propriétés diélectriques effectives d’une structure multicouches en fonction des propriétés et de l’épaisseur de chacune des couches. En particulier, nous appliquons les expressions de permittivités issues de la méthode des perturbations utilisée en cavité résonante au cas d’un échantillon rectangulaire bicouche. L’analyse théorique établie a montré qu’une expression de simple proportionnalité reliant les propriétés diélectriques moyennes d’un matériau bicouche avec les propriétés diélectriques relatives et les épaisseurs des couches constituantes peut être obtenue. Cette méthode a été appliquée avec succès sur différents matériaux bicouches. En particulier, elle a permis la caractérisation d’une couche de YIG d’épaisseur très mince (19.6 μm) déposée par pulvérisation cathodique sur un substrat d’alumine en connaissant l’épaisseur et les propriétés diélectriques du substrat. La comparaison avec les résultats expérimentaux a révélé un bon accord entre théorie et mesure. L’analyse de l’incertitude associée au calcul de la permittivité par la méthode a montré une bonne sensibilité. Enfin, nous donnons les courbes de variation de la perméabilité effective mesurée pour un empilement bicouche avec une couche mince de YIG
This thesis aimed at characterizing the dielectric and magnetic layers of multilayer structures by using the technique of microwave resonant cavity. Multilayer structures have specific electromagnetic properties and are becoming increasingly important in many industrial domains, such as in radio-communication systems. The electromagnetic characterization remains a priority for understanding the characteristics of electromagnetic wave propagation in such environments. The thesis proposed a new experimental approach to determine the effective dielectric properties in a bilayer structure as a function of the characteristics and thickness of each specific layer. In particular, we apply the expressions of permittivities derived from the perturbations method which are used in resonant cavities in case of a bilayer rectangular sample. The established theoretical analysis leads us to propose a new expression of simple proportionality describing a relationship between the mean dielectric properties of a bilayer material and the relative dielectric properties and thickness of the constituent layers. The presented method has been successfully applied to different bilayer materials. Particularly, it allowed the characterization of a very thin layer (YIG layer) of thickness 19.6 microns deposited by cathodic sputtering on an alumina substrate by knowing the thickness and dielectric properties of this substrate. The comparison with the experimental results revealed good agreement between theory and measurement. The analysis of the uncertainty associated to the calculation of the permittivity by the presented method showed good sensitivity. Finally, we provide the curves of variation of the effective permeability measured for a bilayer stack

Composite metamaterials are periodic metal-dielectric structures operating at wavelengths larger than the structure period. If properly designed these structures behave as homogeneous media described by effective permittivity and permeability parameters. These effective parameters can be designed to take values in domains that are not available in naturally occurring media; notably it is possible to design composite metamaterials with simultaneously negative permittivity and permeability, or, in other words, with a negative refractive index. However, in many experimental or numerical studies it is far from obvious that the use of a homogeneous model is justified for a given structure at a given wavelength. This issue is often glossed over in the literature.
In this work I take a detailed look at the fundamental assumptions on which effective medium models rely and put forward a method for determining frequency domains where a given structure may or may not be accurately described by homogeneous effective medium parameters. This work opens the door to a more detailed understanding of the transition between homogeneous and inhomogeneous behavior in composite metamaterials, in particular by introducing the novel notions of custom made effective medium model, and of meta-photonic crystal.

The introduction of inverters utilizing wide band-gap semiconductors allow for higher switching frequency and improved machine drive energy efficiency. However, inverter switching results in fast voltage surges which cause overvoltage at the stator terminals and uneven voltage distribution in the stator winding. Therefore, it is important to understand how next generation machine drives, with higher switching frequency, affect the voltage distribution. For this purpose, a lumped-parameter model capable of simulating winding interturn voltages for the wide frequency range of 0-10 MHz is developed for a slotless PMSM. The model includes both capacitive and inductive couplings, extracted from 2D finite element simulations, as well as analytically estimated resistive winding losses. The developed model of a single phase-winding is used to investigate how machine design aspects such as insulation materials and winding conductor distribution affects both voltage distribution and winding impedance spectrum. Validation measurements demonstrate that the model is accurate for the wide frequency range. The sensitivity analysis suggests that the winding conductor distribution affect both impedance spectrum and voltage distribution. For the slotless machine, capacitance between the winding and the stator is several times smaller than capacitance between turns. Therefore, the high-frequency effects are dominated by the capacitance between turns. Insulation materials that affect this coupling does therefore have an impact on the impedance spectrum but does not have any significant impact on the voltage distribution.
Nästa generations inverterare för styrning av elektriska maskiner, baserade på bredbandgaps komponenter, tillåter högre switchfrekvenser vilket skapar en energieffektivare drivlina. Nackdelen är att snabba spänningsflanker från den höga switchfrekvensen skapar överspänning på stators anslutningar och en ojämn spänningsfördelning i statorlindningen. Det är därför betydelsefullt att förstå hur dessa nya drivlinor påverkar lindningens spänningsfördelning. I denna rapport används en modell kapabel att simulera lindningens spänningsfördelning i det breda frekvensspektrumet 0-10 MHZ. Modellen är framtagen för en faslindning av en PMSM, utan statoröppning, som inkluderar både kapacitiva och induktiva kopplingar samt analytiskt beräknade lindningsförluster. Modellen används för att undersöka spänningsfördelningen i lindningen samt inverkan från designparametrar som isolationsmaterial och lindningsdistribution. Känslighetsanalysen visar att lindingsdistributionen har en signifikant påverkan på både impedansspektrumet och spänningsfördelningen. För den studerade maskintypen är det kapacitansen mellan varv som är dominerande för högfrekventa fenomen. Isolationsmaterial som påverkar denna koppling har en påverkan på impedansspektrumet men är liten för spänningsfördelningen.

The gas diffusion layer (GDL) is one of the key components in a polymer electrolyte membrane (PEM) fuel cell. It performs several functions including the transport of reactant gases and product water to and from the catalyst layer, conduction of both electrons and heat produced in the catalyst layer, as well as mechanical support for the membrane. The overarching goal of this work is to thoroughly examine the GDL structure and properties for use in PEM fuel cells, and more specifically, to determine how to characterize the GDL experimentally ex-situ, to understand its performance in-situ, and to relate theory to performance through controlled experimentation. Thus, the impact of readily measured effective water vapor diffusivity on the performance of the GDL is investigated and shown to correlate to the wet limiting current density, as a surrogate of the oxygen diffusivity to which it is more directly related. The influence of microporous layer (MPL) design and construction on the fuel cell performance is studied and recommendations are made for optimal MPL designs for different operating conditions. A method for modifying the PTFE (Teflon) distribution within the GDL is proposed and the impact of distribution of PTFE in the GDL on fuel cell performance is studied. A method for characterizing the surface roughness of the GDL is developed and the impact of surface roughness on various ex-situ GDL properties is investigated. Finally, a detailed analysis of the physical structure and permeability of the GDL is provided and a theoretical model is proposed to predict both dry and wet gas flow within a GDL based on mercury intrusion porosimetry and porometry data. It is hoped that this work will contribute to an improved understanding of the functioning and structure of the GDL and hence advance PEM fuel cell technology.

Cette thèse est consacrée au développement d'une méthode numérique visant à modéliser des écoulements dans des milieux poreux fissurés, ainsi qu'à déterminer leur perméabilité effective à partir des avancements théoriques récents. En parallèle, elle a été aussi l'occasion de continuer sur la voie théorique et d'obtenir de nouveaux résultats sur ce plan.Les équations générales gouvernant l'écoulement dans de tels matériaux sont rappelées, et plus particulièrement, la conservation de la masse à l'intersection entre fissures est établie explicitement [132, 139]. Des solutions générales du potentiel sont proposées sous la forme d'une équation intégrale singulière décrivant l'écoulement dans et autour des fissures entourées par une matrice infinie soumise à un champ lointain [136, 139]. Ces solutions représentent le champ de pression dans le milieu infini en fonction de l'infiltration dans les fissures qui prennent en compte complètement l'interaction et l'intersection entre fissures. En considérant le problème d'une fissure super-conductrice, des solutions analytiques de l'écoulement ont été développées et ces solutions sont utilisées comme cas de référence pour valider la solution numérique. De plus, la solution théorique de ce problème dans le cas 3D permet de comparer le modèle d'écoulement de Poiseuille dans une fissure elliptique d'épaisseur nulle et le modèle d'inclusion ellipsoïdale aplatie soumise à l'écoulement de Darcy [140]. Des outils numériques ont été développés en se basant sur la méthode des équations intégrales singulières afin de résoudre les équations générales du potentiel [132, 180]. Cela permet, d'une part, de modéliser l'écoulement stationnaire dans un domaine poreux contenant un grand nombre de fissures et, d'autre part, de proposer une solution semi-analytique de l'infiltration dans une fissure isolée dépendant de la perméabilité de la matrice, de la conductivité de la fissure et de la variable géométrique de la fissure. Cette dernière est l'élément essentiel pour déterminer de la perméabilité effective d'un milieu poreux fissuré en utilisant des schémas d'homogénéisation. Ce modèle auto-cohérent révèle un seuil de percolation qui est alors applicable pour l'estimation de la perméabilité effective d'un matériau contenant un grand nombre de fissures. L'approche par sous-structuration permet l'extension de la solution générale du potentiel, écrite pour un domaine infini, à celle d'un domaine fini [181]. Une solution analytique de l'écoulement dans et autour d'une fissure partiellement saturée est établie, fondée sur la solution analytique pour la fissure super-conductrice. Celle-ci est alors utilisée pour estimer la perméabilité effective d'un milieu poreux fissuré non-saturé [141]. Le modèle de la perméabilité effective est appliqué dans le contexte du stockage géologique du CO2 en vue d'étudier le comportement d'une zone de faille constituée par un noyau argileux et des zones fissurées. La pression d'injection provoque l'augmentation de la pression interstitielle dans le réservoir. Cette surpression engendrée dans le réservoir peut affecter la perméabilité de zones fissurées ce qui conduit à des phénomènes hydromécaniques couplés. Les résultats de simulations numériques permettent d'évaluer, d'une part, le risque de la remontée de la saumure à l'aquifère supérieur, et d'autre part, le risque de l'initiation d'une rupture sur le plan de la faille
This thesis aims to develop a method for numerical modelling of fluid flow through fractured porous media and for determination of their effective permeability by taking advantage of recent results based on formulation of the problem by Singular Integral Equations. In parallel, it was also an occasion to continue on the theoretical development and to obtain new results in this area. The governing equations for flow in such materials are reviewed first and mass conservation at the fracture intersections is expressed explicitly. Using the theory of potential, the general potential solutions are proposed in the form of a singular integral equation that describes the steady-state flow in and around several fractures embedded in an infinite porous matrix under a far-field pressure condition [136, 139]. These solutions represent the pressure field in the whole body as functions of the infiltration in the fractures, which fully take into account the fracture interaction and intersections. Closed-form solutions for the fundamental problem of fluid flow around a single fracture are derived, which are considered as the benchmark problems to validate the numerical solutions. In particular, the solution obtained for the case of an elliptical disc-shaped crack obeying to the Poiseuille's law has been compared to that obtained for ellipsoidal inclusions with Darcy's law [140].The numerical programs have been developed based on the singular integral equations method to resolve the general potential equations [132, 180]. These allow modeling the fluid flow through a porous medium containing a great number of fractures. Besides, this formulation of the problem also allows obtaining a semi-analytical infiltration solution over a single fracture depending on the matrice permeability, the fracture conductivity and the fracture geometry. This result is the important key to upscalling the effective permeability of a fractured porous medium by using different homogeneisation schemes. The results obtained by the self-consistent scheme have been in particular established. The multi-region approach can be used to extend the general potential solution written for the infinite domain to that for a finite domain [181]. A closed-form solution for flow in and around a single partially saturated fracture, surrounded by an infinite matrix subjected to a far-field condition, is also derived combining the solutions for a superconductive fracture and for an imprevious fracture. This solution is then employed to estimate the effective permeability of unsaturated fractured porous media [141].The effective permeability model is applied to study the hydromechanical behaviour of a fault zone constituted by a clay core surrounded by fractured zones in the context of CO2 geological storage. The pressure injection induces an overpressure in the reservoir that may affect the permeability of the fractured zones leading to complexe coupled hydromechanical phenomena. The simulation results allow evaluating the risk of leakage of the reservoir brine to higher aquifers as well as the risk of fault reactivation

Cette de thèse comporte deux volets : Le premier, plutôt applicatif, concerne le design d'échangeurs à ailettes et à mousses ; le second, plus académique, traite des relations entre la texture des mousses métalliques et leurs propriétés thermophysiques effectives. Sur la première partie consacrée à l'amélioration des performances des échangeurs de chaleur Mota. Nous avons mis en place une méthode de dimensionnement multi-échelle adaptés aux batteries tubes-ailettes et aux échangeurs à mousse ; Nous avons développé et caractériser une architecture optimisée d'échangeur à mousse et à ailettes. Des gains de 50% ont été obtenus en termes d'efficacité énergétique et les solutions proposées sont actuellement en production.La deuxième partie concerne l'analyse des mécanismes de transferts dans les mousses et de la détermination de leurs propriétés effectives. Nous avons développé une approche basée sur la modélisation des transferts et écoulements à l'échelle du pore -confortée par le développement de bancs expérimentaux- pour déterminer ces propriétés. Nous avons réalisé une base de données de 900 mousses obtenues par élongation et cisaillement d'une cellule périodique de référence. Les propriétés effectives –tensorielles- de ces mousses ont été mesurées et leur dépendance à la morphologie et aux propriétés thermophysiques des phases a été étudiée.En conclusion, le dernier chapitre illustre la démarche naturelle de poursuite des travaux : Optimisation des géométries des échangeurs et des mousses selon les conditions applicatives
This work is composed of two parts: the first one deals with the design of fins-and-tubes and metal foam heat exchangers; the second one deals with the relationship between foams morphology and their effective thermophysical properties. The first part is dedicated to Mota heat exchanger performance enhancement. We develop a multi-scale method to optimize both local heat transfer surfaces and global architecture of classical and foam units. We develop, using this method, new heat exchanger and we characterize it numerically and experimentally. An increase of 50% of energetic efficiency is obtained and new geometries are nowadays produced and commercialized. The second part deals with the analysis of transport phenomena in metal foams and the determination of their effectives properties. We develop an approach based on pore scale numerical simulation of conjugate heat transfer – validated by experimental results obtained on set-up developed for this study. We have generated 900 virtual samples obtained by deformation a periodic unit cell (Kelvin cell). Full effective properties tensors are determined. The influence of cell shape and classical geometrical parameters on physical properties is then studied. To conclude, in the last chapter, we present natural perspectives involved by this work: Geometrical optimization of heat exchanger architecture and foams morphology depending on the application; The use of a multi-scale approach to design modern –foam- heat exchangers

Автором запропоновано новий підхід до методики визначення адсорбційної здатності гірських порід за рахунок введення параметра адсорбційної водонасиченості та досліджено його зв'язок з фільтраційно-ємнісними властивостями і з закупоркою порового простору порід-колекторів у присвердловинній зоні пласта. Встановлено, що однією із важливих причин істотного зниження фільтраційно-ємнісних властивостей проникних порід у присвердловинній зоні є низька мінералізація фільтратів промивних рідин та вміст в них таких розповсюджених хімреагентів як карбоксиметилцелюлози (КМЦ) та конденсованої сульфіт-спиртової барди (КССБ). Застосування нової розробленої автором установки для лабораторних петрофізичних досліджень, яка зменшує контактний електричний опір та створює умови, наближені до пластових, а також використання нових методичних прийомів вивчення адсорбційної водонасиченості дозволило провести високоточні вимірювання петрофізичних параметрів на зразках гірських порід-колекторів та розробити алгоритм поділу їх на характерні групи, що відрізняються ступенем впливу на них промивних рідин. За результатами статистичної обробки і аналізу даних фізичного моделювання на зразках керну, петрофізичних і геофізичних досліджень, автор подас нову методику оцінки погіршення фільтраційно-ємнісних властивостей проникних пластів у присвердловинній зоні під дією фільтратів бурових розчинів у процесі буріння свердловин.
В диссертации освещаются разные подходы к проблемам изучения изменения фильтрационно-ёмкостных свойств пород-коллекторов в прискважинной зоне, которые охватывают отдельные разделы петрофизики, геофизики, физики нефтегазового пласта и физической химии. Показано, что проникновение в породу-коллектор фильтрата промывочной жидкости и её твёрдой фазы при бурении скважин определяется рядом факторов, основными из которых являются перепад давления, размер поровых каналов, зёрен скелета породы и частиц твёрдой фазы промывочной жидкости. Автором предложен новый подход к методике определения адсорбционной способности горных пород за счёт введения параметра адсорбционной водоиасыщенности, а также исследована его связь с фильтрационно-ёмкостными свойствами и с закупоркой порового пространства пород-коллекторов в прискважинной части пласта. Применение новой разработанной автором установки для петрофизических исследований в условиях, моделирующих пластовые, а также использование новых методических приёмов изучения адсорбционной водонасыщенности позволило провести высокоточные измерения петрофизических параметров на образцах керна и разработать алгоритм разделения пород-колекторов на характерные группы, различающиеся по степени влияния на них фильтратов промывочных жидкостей. Установлено, что одной из важнейших причин существенного снижения фильтрационно-ёмкостных свойств проницаемых пород в прискважинной зоне является низкая минерализация промывочных жидкостей и наличие в ней таких распространённых химреагентов как карбоксиметилцеллюлозы (КМЦ) и конденсированной сульфит-спиртовой барды (КССБ). На основе статистического анализа результатов физического моделирования на образцах керна и геолого-геофизических данных автор представляет новую методику прогнозирования и оценки закупорки прискважинной зоны пластов-коллекторов под воздействием проникающего фильтрата промывочных жидкостей в процессе бурения скважин. Апробация представленного в Диссертации метода оценки закупорки пород-коллекторов на конкретных нефтегазовых месторождениях показала его высокую еффективность. Результаты обработки геологической, технологической и геофизической информации согласно приведенного алгоритма по продуктивных горизонтах Перекоповского, Коржевского и других нефтегазоконденсатных месторождений показали, что для пластов-коллекторов со значительной зоной проникновения фильтрата бурового раствора, наблюдаются повышенные прогнозированные коэффициенты закупорки. Это подтверждается также результатами опробования нефтегазоносных объектов. Из пластов с позитивной характеристикой об их продуктивности, но с повышенными значениями коэффициентов закупорки эффективного порового пространства (К3 >17 %) промышленного притока углеводородной продукции не получено. Рекомендуется таким пластам уделять особое внимание при эксплуатации месторождения (применять различные физико-химические методы интенсификации притока, учитывать временной фактор восстановления проницаемости прискважинной части пласта при депрессиях).
The author has offered a new approach to methods of defining absorptive capacity of geological material due to use of absorptive water saturation parameter, its connection with filtrational-storage properties and with clogging of porous space of reservoir rocks in well bore zone was researched. It was defined that one of important reasons of considerable degradation of permeable rocks filtrational -storage properties in well bore zone is low mineralization of washing fluids filtrates and content of such widely-spread chemical agents as carboxymethyl cellulose (CMC) and condensed spent sulfite-alcohol liquor (CSAL) in them. Application of new equipment which was developed by the author for laboratory petrophysical research, which reduces contact electrical resistance and creates conditions close to reservoir rock ones, as well as application of new methodological research techniques of absorptive water saturation made it possible to fulfill high-precision measurement of petrophysical parameters on reservoir rocks samples and to develop an algorithm of their division by typical groups characterized with washing fluids influence upon them. According to the results of statistical treatment and analysis of physical modeling data on core samples, petrophysical and geological-geophysical research, the author introduces new methods of estimation of permeable beds filtrational-storage properties worsening in well bore zone under the influence of drilling fluid filtrates during well-drilling procedure.

O objetivo deste trabalho é analisar e comparar o comportamento quanto à resistência à corrosão, permeabilidade de hidrogênio e sua relação com a susceptibilidade ao trincamento induzido por hidrogênio de aços ARBL, em ambientes contendo H2S, enfatizando a influência da microestrutura. Foram realizados tratamentos térmicos de normalização e têmpera (em água) de dois tipos de tubos API 5L X65 para aplicação sour service, obtendo-se três condições com diferentes microestruturas para cada tubo. Assim, as duas amostras tais como recebidas apresentavam microestruturas de: ferrita/perlita e, o outro, ferrita/ferrita acicular; após tratamento de normalização os dois tipos de amostras apresentaram microestrutura de ferrita/perlita; e, por último, os aços que passaram por têmpera constituíram-se de martensita. O eletrólito empregado foi a solução A (ácido acético contendo cloreto de sódio) da norma NACE TM0284-2011, saturado com H2S. Os materiais foram submetidos a: ensaios de polarização linear para determinação da Resistência de Polarização (Rp), ensaios de permeabilidade de hidrogênio - baseado na ASTM G148-2003 - e ensaios de resistência ao trincamento induzido por hidrogênio (HIC) segundo a norma NACE TM0284-2011; exames em microscópio óptico e eletrônico de varredura para caracterização microestrutural, da morfologia da corrosão e do trincamento. Após os ensaios de polarização linear, foi observada uma diferença pequena dos valores de Rp entre as diferentes amostras estudadas, entre 120 ?.cm2 e 210 ?.cm2; dentro desta faixa, as microestruturas de martensita (aços temperados) apresentaram a menor resistência à corrosão. Foi realizado o tratamento dos dados obtidos por polarização linear com a metodologia desenvolvida por Mansfeld (1973) para cálculo da taxa de corrosão, observando mudanças nos declives de Tafel evidenciando a formação de produtos de corrosão. Apesar da formação destes produtos a taxa de corrosão não foi afetada, já que estes produtos são dissolvidos na solução A, oferecendo uma baixa proteção contra à corrosão. Nos ensaios de permeabilidade de hidrogênio foi utilizada uma célula modificada tipo Devanathan-Stachurski, com a solução A, com injeção de H2S no lado de geração de hidrogênio e 0,2M NaOH no lado de detecção. Foi realizado o tratamento dos dados com o método tlag, calculando a difusividade aparente, concentração de hidrogênio no metal e quantidade de sítios de ancoramento de hidrogênio. Também foi utilizado um método de ajuste da curva experimental com a equação obtida a partir da segunda lei de Fick para calcular a difusividade aparente. Foram comparados os valores obtidos com os dois métodos, obtendo-se resultados similares de difusividade aparente. As amostras temperadas foram as que apresentaram menor difusividade aparente, maior concentração de hidrogênio e maior número de sítios de ancoramento. Após o ensaio de resistência ao trincamento induzido por hidrogênio os exames em microscópio óptico mostraram que as amostras de tubos API 5L X65 como recebidas e normalizadas não apresentaram trincamento, já as amostras que passaram por tratamento de têmpera apresentaram trincas. A realização dos ensaios e tratamento dos dados permitiram observar a relação entre a quantidade de interface e a taxa de corrosão: assim a microestrutura martensítica apresenta a maior taxa de corrosão devido a maior quantidade de interfaces. A difusividade de hidrogênio também é afetada por esta mesma microestrutura, por ter maior quantidade de interface e maior número de discordâncias, apresentando menor difusividade aparente, maior concentração de hidrogênio e maior quantidade de sítios de ancoramento, tem-se que a microestrutura de martensita apresenta maior susceptibilidade ao trincamento induzido por hidrogênio. A nucleação e propagação das trincas nesta microestrutura depende de vários mecanismos que atuam simultaneamente: (i) nucleação das microtrincas, (ii) formação de H2 nas microcavidades com aumento da pressão local e (iii) migração de átomos de hidrogênio até a ponta da trinca diminuindo a força coesiva do reticulado facilitando a propagação. No entanto, esta relação entre microestrutura e HIC não pode ser generalizada, pois a susceptibilidade ao trincamento depende tanto da quantidade de sítios de ancoramento, como de sua energia de ligação, localização microestrutural e tamanho destes sítios. Outro fator importante é a presença de regiões de pouca ductilidade onde as trincas nucleadas tenham maior facilidade para sua propagação. Este trabalho contribuiu para o melhor entendimento dos mecanismos que levam à fragilização e danos provocados pelo hidrogênio, mostrando a relação entre microestrutura, corrosão, difusão e trincamento. Permitiu ampliar o conhecimento sobre os testes utilizados para avaliar o desempenho de aços microligados para aplicações em ambientes severos.
Pipelines produced from High Strength Low Alloy steels (HSLA) are a safe and cheap way to transport large quantities of petroleum and gas. HSLA steels offers mechanical and economic advantages. When HSLA steels are exposed to environments containing hydrogen sulphide (H2S), the steel can corrode and generate atomic hydrogen in the surface wich can diffuse and trapped, leading loss of mechanical properties and subsequent failures. The infrastructure to transport oil and gas represent a high cost investment, in adittion, they must be free from degradation processes that can causes severe health and environmental impacts. For this reason, the development of materials with high performance in aggressive environments is required. The aim of this study is to analyze and compare the corrosion behavior, hydrogen permeability and its relation with the susceptibility to Hydrogen Induced Cracking (HIC) of HSLA steels in environments containing H2S, with emphasis on the influence of microstructure. Normalizing and quenching heat treatments were applied in two different API 5L X65 pipelines for sour service. Three conditions were obtained (as received, normalized and quenched). The as received has a microstructure of ferrite / pearlite and ferrite / acicular ferrite, respectively; the microstructure of normalized specimens consist of ferrite / pearlite and finally quenched steels presented a microstructure of martensite. Solution A (acetic acid containing sodium chloride), according to NACE TM0284-2011 standard and saturated with H2S was used. The materials were tested by linear polarization technique, hydrogen permeability and Hydrogen Induced Cracking test (HIC). HIC tests were performed according to NACE TM0284-2011 standard. Optical microscope and scanning electron microscope were used for microstructural, corrosion and cracking characterization. Rp values show a slight difference between the different samples studied (120 ?.cm2 e 210 ?.cm2); the martensite microstructure (quenched) showed the lower corrosion resistance. Mansfeld (1973) method was used to calculate the corrosion rates from polarization curves. The Tafel slopes are differents between samples making evident the formation of corrosion products. Despite the growth of those corrosion products, the corrosion rate was not affected, since these products are dissolved in the solution A, providing a low corrosion protection. A modified Devanathan-Stachurski cell was used for the hydrogen permeability tests. It was used the solution A, with injection of H2S in the charging cell, and 0.1M NaOH solution on the oxidation cell. The hydrogen effective diffusivity, sub-surface concentration of atomic hydrogen at the charging side and number of hydrogen-trap sites were calculate by tlag method. Moreover, the experimental data were fitted using an equation derived from Fick\'s second law, in order to determinate the diffusion coefficient. The diffusion coefficient obtained from both methods were compare showing similar results. The quenching samples showed the lower diffusion coefficient, higher hydrogen concentration and number of trap sites. The steels in the as received and normalized conditins did not show cracks in Hydrogen Induced Cracking test; in the other hand, quenched samples presents cracks. The results shoed the relationship between the amount of interface and the corrosion rate. Being the martensitic microstructure the one with the higher corrosion rate. The diffusion coefficient in the martensitic microstructure, is a result of the high amount of interfaces and high dislocation density, leading to a lower diffusion coefficient, higher hydrogen concentration and number of trap sites. In the Hydrogen induced Cracking test the martensitic microstructure has shown the lower resistance to crack. The nucleation and propagation of the cracks in martensite depend of mechanisms that may act simultaneously: (i) nucleation of micro-cracks in preferential sites, (ii) formation of H2 in micro-cavities, with increase the local pressure, and (iii) hydrogen migration to the tip of the crack, decreasing the cohesive force in the lattice. However, the relationship between microstructure and Hydrogen Induced Cracking can not be generalized, since the susceptibility to cracking depends of several factors, like number of trap sites, binding trap energy, microstructural distribution and trap sizes. In addition, the presence of regions of low ductility can result in easy cracks nucleation and propagation. This thesis contributed to the understanding of the mechanisms that lead to hydrogen embrittlement and hydrogen damage, showing the relationship between microstructure, corrosion rate, diffusion and cracking, I ncreasing the scientific knowledge about the standard tests actually used to evaluate the performance of microalloyed steels in sour environments.

Increasing surface pressure buildup levels and surface venting flow rates on intermediate wellbore casing strings provided an opportunity to analyze wellbore field data to determine a distribution of leakage path permeability values. The gas leakage source in the leaky wellbore originated at depth, and formation gas/fluid traveled along defects in the cement to accumulate at the surface wellhead. The most likely pathway is the cement interface with casing or formation. Due to uncertainty about the location of the leak, and the different methods that were used for calculating leakage parameter values, a range of leakage path permeability values was produced. Most leakage pathway permeability values were greater than intact cement permeability (few microdarcies). This finding supports the practice of using cement filled annuli to provide a safe protective barrier against leakage and to prevent gas flow to surface. Proper cementing techniques are presented in order to identify possible reasons for cracks to form. It is hypothesized that the higher permeability values are a result of cracks in the cement interface with the casing or formation. These types of defects could also be found in wellbores that are in communication with CO2 sequestration reservoirs. The risk of leakage along such existing wellbores associated with CO2 sequestration projects is quantified by the distribution of leakage path permeability. The gas migration path through existing leaky wellbores is an analog for wellbores that are in contact with migrating CO2 plumes. Cracks in the leaky wellbores provide a highly permeable conduit for CO2 to migrate out of the injection zone to the surface. By quantifying leakage path permeability, proper leakage risk assessment can be further developed.
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Fractures are the main flow channels in naturally fractured reservoirs. Therefore the fracture permeability is a critical parameter to production optimization and reservoir management. Fluid pressure reduction caused by production induces an increase in effective stress in naturally fractured reservoirs. The change of effective stress induces fracture deformation and changes fracture aperture and permeability, which in turn influences the production. Coupled interactions exist in the fractured reservoir: (i) fluid pressure change induces matrix deformation and stress change; (ii) matrix deformation induces fluid volume change and fluid pressure change; (iii) fracture deformation induces the change of pore pressure and stress in the whole field (the influence disappears at infinity); (iv) the change of pore pressure and stress at any point has an influence on the fracture and induces fracture deformation. To model accurately the influence of pressure reduction on the fracture permeability change in naturally fractured reservoirs, all of these coupled processes need to be considered. Therefore, in this dissertation a fully coupled approach is developed to model the influence of production on fracture aperture and permeability by combining a finite difference method to solve the fluid flow in fractures, a fully coupled displacement discontinuity method to build the global relation of fracture deformation, and the Barton-Bandis model of fracture deformation to build the local relation of fracture deformation. The fully coupled approach is applied to simulate the fracture permeability change in naturally fracture reservoir under isotropic in situ stress conditions and high anisotropic in situ stress conditions, respectively. Under isotropic stress conditions, the fracture aperture and permeability decrease with pressure reduction caused by production, and the magnitude of the decrease is dependent on the initial effective in situ stress. Under highly anisotropic stress, the fracture permeability can be enhanced by production because of shear dilation. The enhancement of fracture permeability will benefit to the production of oil and gas.

The design, modeling, fabrication, and validation of an optical magnetic response in dielectric-based metamaterials are studied. These metamaterials consist of either periodic or random arrays of dielectric particle inclusions, which may be spheres, coated spheres, or completely randomly shaped. It is demonstrated that because of the simple particle shapes and dielectric materials, these metamaterials are quite easy and feasible to implement in a bulk, three-dimensional sample, and the response is isotropic. This in is contrast to other predominant designs of optical metamaterials, which are planar and anisotropic arrays of complicated metallic fishnet or split-ring resonator structures, which require stringent tolerances and sophisticated assembly. It is shown that SiC is one of many materials from which such infrared magnetic metamaterials can be constructed. A simple SiC powder is used to verify these claims. The milled micropowder of crystalline SiC is comprised of particles of random shapes and sizes. A model of the electromagnetic response of such powders is developed, whereby the induced magnetic dipole response is modeled by equivalently-sized spheres of SiC, whereas the electric dipole response is modeled by a continuous distribution of ellipsoidal particles. Infrared spectroscopic measurements and numerical calculations are performed, verifying both the magnetic and electric response of the powder. A alternate approach is also described, where uniform SiC microspheres are fabricated using more sophisticated nanochemical techniques. In the final portion of the dissertation, the mutual near-field coupling between ideal magnetic dipoles induced in dielectric spheres is studied. This is implemented for microwave frequencies using large permittivity ceramic spheres. An approximate coupled dipole model of the multiple scattering among the spheres is developed, and a transition matrix method is implemented to calculate the exact scattering by the clusters. Experimental measurements are performed, confirming the two models. The results for pairs, chains, and rings of spheres indicates that the magnetic dipole modes hybridize in analogy to atomic bonding. A notable result is that certain hybridized magnetic dipole modes may have a net electric dipole moment. The similarity to atomic and molecular bonding should prove useful in conceptualizing and designing more sophisticated metamaterials.