[pt] Freqüentemente, durante os estágios de produção de um poço de óleo, ocorre a produção simultânea de partículas sólidas que originam da massa rochosa ao redor, um processo chamado de produção de areia. Concentrações de tensões nas vizinhanças do poço podem causar perda de coesão entre os grãos, criando assim uma região de matéria granular solta suscetível a ser arrastada pela força de infiltrações. Este trabalho se baseia no estudo da formação de danos nas vizinhanças do poço. Este programa experimental é conduzido ao simular, do interior de uma célula especialmente construída, as pressões crescentes durante esses estágios de escavação numa amostra de rocha, geralmente arenito, pouco consolidada ou um material montado artificialmente simulando arenito. Este processo é conduzido em tempo real dentro de tomógrafo computadorizado de Raio X. Os ensaios tiveram por objetivo identificar a pressão de início e o modo de propagação da ruptura da parede da cavidade interna da amostra ensaiada. Estes são estágios iniciais dos processos de produção de areia em rochas. As análises das imagens tomográficas adquiridas durante os ensaios permitiram a visualização de breakouts e arrombamentos dos poços. Estudos mais detalhados possibilitaram estimar a quantidade de areia produzida e reconstruir tridimensionalmente o processo de propagação de ruptura. / [en] Frequently, during the production stages of an oil well, simultaneous production of solid particles originating from the surrounding rock mass occur, a process called sand production. Stress concentrations around of the well may cause loss of cohesion between grains, thus creating a region of loose granular matter susceptible for drag bye seepage forces. The present work reports on the study of the formation of breakouts/damage around of the well. This experimental program is carried out by simulating, inside an especially constructed cell, the stresses arising during these excavation stages on a sample of a rock, generally a poorly consolidated sandstone or an artificially assembled material simulating a sandstone. This process is carried out in real time inside an X ray computerized tomography. The tests investigated the initial and the evolution of failure at the cavity wall of samples. These are initial stages of the sand production process. The analysis of the CT-scans obtained during tests allowed the visualization of breakouts and collapses of the wells. From studies more details were possible estimate the sand production and produce 3-D images of the propagation of the failure.

[pt] A produção de areia é um dos mais freqüentes e graves problemas observados durante a produção de um poço de petróleo, completado em arenitos mal consolidados. Este fenômeno pode causar obstrução do poço, abrasão dos equipamentos de elevação e de superfície, colapso do revestimento e problemas ambientais derivados da disposição em superfície das areias contaminadas. Por outro lado, em reservatórios de baixa produtividade que produzem óleo de alta viscosidade, uma limitada produção de areia incrementa a produtividade do poço. Nos estudos para previsão da produção de areia é de fundamental importância definir-se um modelo constitutivo capaz de reproduzir o comportamento tensão-deformação do arenito e os mecanismos de ruptura que provocam instabilidade do poço. Este é o tema central desta tese. Em especial, o trabalho procurou explorar modelos constitutivos baseados em meios contínuos de Cosserat. Uma justificativa para isto está relacionada ao fato de experimentos demonstrarem a influência da microestrutura nos processos de ruptura que ocorrem na vizinhança do poço. O modelo utilizado foi o elastoplástico de Bogdanova-Bontcheva & Lippmann (1975) incorporando as leis de fluxo associada e não associada. Inicialmente são definidos alguns conceitos básicos relevantes ao entendimento do fenômeno de produção de sólidos. Uma revisão da teoria dos meios contínuos generalizados de Cosserat é apresentada e em seguida é discutido o modelo elastoplástico de Bogdanova- Bontcheva e Lippmann com detalhes das implementações computacionais necessárias. Finalmente, são feitas análises de geometrias de poços, procurando-se identificar os mecanismos de ruptura que provocam instabilidade e que são uma potencial fonte de produção de areia. / [en] Sand production is one of the most frequent and serious problems observed during the production of an oil well completed in weak sandstones. This phenomenon can cause wellbore plugging, surface and rise equipment abrasion, casing collapse and environmental problems derived from the disposal in surface of contaminated sands. On the other hand, for reservoirs of low productivity, that produce oil of high viscosity, a limited sand production increase the productivity of the well. In the studies for sand production prediction, it is of basic importance to define a consitutive model capable of reproducing the stress-strain behaviour of the sandstones and the failure mechanisms that causes wellbore instability. This is the central focus of the present work. In order to represent the behaviour of the rock masses, models based in Cosserat continuum were used. Elastoplastic models (associated/not associated) under that theory (Bogdanova-Bontcheva and Lippmann) were implemented. Initially, basic concepts related to the understanding of the phenomenon of solid production are presented. A review of the theory of generalized Cosserat continuum is presented, the elastoplastic model of Bogdanova-Bontcheva and Lippmann is described, together with details of the computational implementations. Finally, analyses of well geometries with the implemented Cosserat based elastoplastic models are shown,identifying the failure mechanisms.

[pt] Durante a fase produtiva de um poço de petróleo ou gás, muitas vezes há a produção simultânea de partículas sólidas arrancadas da matriz da rocha reservatório. Este fenômeno recebe o nome de produção de areia. Neste caso as tensões e as condições de fluxo nas vizinhanças do poço são fatores fundamentais para a deflagração do processo. As tensões que se concentram na parede do poço com a perfuração do mesmo, pode ser de tal magnitude que pode causar a perda da coesão entre os grãos e criando , assim , uma região de material granular susceptível ao arraste pelas forças de percolação derivadas do fluxo. Este trabalho visou a realização de ensaios em amostras de arenito Rio Bonito e arenito sintético utilizando a técnica da Tomografia Computadorizada de Raios-X para acompanhamento em tempo real dos ensaios. Os ensaios tiveram por objetivo identificar a pressão de início e o modo de propagação da ruptura da parede da cavidade interna da amostra ensaiada. Estes são estágios iniciais dos processos de produção de areia em rochas. As análises das imagens tomográficas adquiridas durante os ensaios permitiram a visualização de breakouts e arrombamentos dos poços. Estudos mais detalhados possibilitaram estimar a quantidade de areia produzida e reconstruir tridimensionalmente o processo de propagação da ruptura. / [en] During productive phase of the well, manytimes there is simultaneous production of the solid particles detached from matrix of the reservoir rock. This phenomenon receive the name of the sand production. In this case stress and flow conditions around of the well are fundamental factors for deflagration of the process. Stress concentration in the wall of the well lead to the loss of cohesion between grains arising, consequently, a granular material region susceptible for dragging by seepage forces derived from fluid flow. The objective of this work was to perform sand production tests in Rio Bonito and synthetic sandstone samples using real-time X-Ray Computerized Tomography. The tests investigated the initial and the evolution of failure at the cavity wall of samples. These are initial stages of the sand production process. The analysis of the CT-scans obtained during tests allowed the visualization of breakouts and collapses of the wells. From studies more details were possible estimate the sand production and produce 3-D images of the propagation of the failure.

This work shows that toughness (resistance) to fracture propagation is an inherent characteristic of cohesionless particulate materials, which is significant for understanding hydraulic fracturing in geotechnical, geological, and petroleum applications. We have developed experimental techniques to quantify the initiation and propagation of fluid-driven fractures in saturated particulate materials. The fracturing liquid is injected into particulate materials, where the fluid flow is localized in thin crack-like conduits. By analogy, we call them 'cracks' or 'hydraulic fractures'. Based on the laboratory observations and scale analysis, this work offers physical concepts to explain the observed phenomena. When a fracture propagates in a solid, new surfaces are created by breaking material bonds. Consequently, the material is in tension at the fracture tip. In contrast, all parts of the cohesionless particulate material (including the tip zone of hydraulic fracture) are likely to be in compression. In solid materials, the fluid front lags behind the front of the propagating fracture, while the lag zone is absent for fluid-driven fractures in cohesionless materials. The compressive stress state and the absence of the fluid lag are important characteristics of hydraulic fracturing in particulate materials with low, or no, cohesion. Our experimental results show that the primary factor affecting peak (initiation) pressure is the magnitude of the remote stresses. The morphology of fracture and fluid leak-off zone, however, changes significantly not only with stresses, but also with other parameters such as flow rate, fluid rheology, and permeability. Typical features of the observed fractures are multiple off-shots and the bluntness of the fracture tip. This suggests the importance of inelastic deformation in the process of fracture propagation in cohesionless materials. Similar to solid materials, fractures propagated perpendicular to the least compressive stress. However, peak injection pressures are significantly greater than the maximum principle stresses in the experiments. Further, by incorporating the dominate experimental parameters into dimensionless form; a reasonable power-law fit is achieved between a dimensionless peak injection pressure and dimensionless stress. Scaling indicates that there is a high pressure gradient in the leak-off zone in the direction normal to the fracture. Fluid pressure does not decrease considerably along the fracture, however, due to the relatively wide fracture aperture. This suggests that hydraulic fractures in unconsolidated materials propagate within the toughness-dominated regime. Furthermore, the theoretical model of toughness-dominated hydraulic fracturing can be matched to the experimental pressure-time dependences with only one fitting parameter. Scale analysis shows that large apertures at the fracture tip correspond to relatively large 'effective' fracture (surface) energy, which can be orders of magnitude greater than typical for hard rocks.

A gas hydrate production test using the depressurization method was conducted in early April 2007 as part of the JOGMEC/NRCan/Aurora Mallik production research program. The results of the production test were analyzed using a numerical simulator (MH21-HYDRES) coded especially for gas hydrate reservoirs. This paper evaluates the test results based on analyses of production test data, numerical modeling and a series of history matching simulations. Methane gas and water was produced from a 12 m perforation interval within one of the major methane hydrate (MH) reservoirs at the Mallik MH field, by reducing the bottomhole pressure down to about 7 MPa. The measured gas production rate was far higher than that expected for a comparatively small pressure drawdown. However, irregular (on-off) pumping operations, probably related to excessive sand production, resulted in unstable fluid flow within the wellbore, which made the analysis of test performance extremely complicated. A numerical reservoir model was constructed as a series of grid blocks, including those mimicking the wellbore, to enable rigorous simulation of fluid flow patterns in the vicinity of the wellbore. The model was then tuned through history matching, not by simply adjusting reservoir parameters, but by introducing the concept that sand production might have dramatically increased the near-wellbore permeability. The good agreement between observed and simulated performances suggests the mechanism of MH dissociation/production during the test. The history matched reservoir model was employed to predict the second-year production test performance, in order to examine the gas production potential of the Mallik MH reservoir, and to provide insight into future exploration and development planning for MH reservoirs.

[pt] A produção de areia em poços de petróleo é um problema bem conhecido devido às conqüências catastróficas, que muitas vezes chegam a afetar a vida produtiva de um reservatório inteiro. Estudos sobre o assunto vêm sendo desenvolvidos, e uma importante linha de pesquisa tem se formado. No entanto, estes estudos focam principalmente na predição ou começo da produção de areia, dando uma importância menor à sua quantificação. Há mais de vinte anos, este problema tem sido relatado em um Campo da Bacia de Maracaibo na Venezuela, levando ao fechamento de um grande numero de poços. O problema é ainda maior devido às condições do reservatorio: profundidade (maior a 5000 (m)), alta pressão e temperatura assim como a resistência mecânica da rocha (maior a 50 (Mpa)) fazem que estudos mais avançados sejam precisados para além de determinar que fatores influenciam este fenômeno, observar se os modelos de quantificação utilizados neste trabalho representam o que ocorre no campo. Para isto, utilizo-se o software comercial de elementos finitos Abaqus junto com a sub-rotina de erosão assim como o modelo analitico de Willson, baseada na resistência equivalente da formação obtida a partir dos ensaios de cilindro oco ou TWC (thick Walled Cylinder) desenvolvidos também neste trabalho. Em ambos métodos, foram imposta condições reais do campo: estado de tensão, pressão de fundo do poço, poro-pressão, assim como o comportamento tensão-deformação da rocha, obtidos a partir de ensaios de compressão uniaxial. Para o caso da modelagem numerica, forem analisados dois casos, poço aberto (modelo de duas dimensoes) e tunel canhoneado (modelos de tres dimensoes). No caso do modelo de Willson foi implementado o túnel canhoneado. / [en] Sand production at oil wells is a well-known problem, due to the disastrous consequences that in some cases affect the productivity of the entire reservoir. Studies about the subject have been development and a very important research line has been created. However, those progresses are more focus on sand production onset, giving less importance to the quantification issue. Whit more than twenty years, there is a field located on Maracaibo Basin, Venezuela that has been affected with this problem occasionating the closure of a big amount of wells. The problem is even bigger due to the reservoir conditions: depth (more than 5000 (m)), high pressure and temperature conditions and also rock mechanics strength (more than 50 (Mpa)) make that more advanced studies will be need for seeking the factors that affect in this phenomenon and observe if the quantifications models used in this work represent the field observations. For this, was used the commercial software of finite elements Abaqus whit the erosion sub-routine as well as the analytical Willson model based on the equivalent strength formation obtain from thick walled cylinder test development in this work also. In both methods were used real field conditions: state of stress, bottom hole pressure, pore pressure and the stress-strain rock behavior obtain form uniaxial compression test. For the numerical model were analyzed two cases, open hole (two dimension model) and perforation tunnel (three dimension model). For the analytical Willson model was just implemented the perforation tunnel case.

[pt] Um dos maiores desafios para a produção de hidrocarbonetos em reservatórios de arenitos pouco consolidados é o controle da produção de areia. Os mecanismos envolvidos nesse fenômeno são complexos e isto é resultado de uma grande variedade de fatores, como por exemplo, a magnitude das tensões in situ, a resistência mecânica da formação e as operações de desenvolvimento do poço. Este problema pode ser resolvido ou amenizado até níveis aceitáveis através de estratégias de completação específicas, como instalação de telas ranhuradas ou do gravel pack, desde que haja uma previsão do potencial de produção de areia da formação. Apesar do grande número de modelos numéricos desenvolvidos para prever este comportamento, a consistência dos mesmos pode ser questionada, uma vez que podem ser observadas diferenças entre as predições e os dados de campo. Para validar esses modelos, são necessários dados confiáveis, que podem ser obtidos através de ensaios de laboratório. Os objetivos do trabalho foram determinados considerando esses pontos, além da questão do uso em larga escala do gravel pack como técnica de controle da produção de areia nos campos brasileiros. São eles: (i) investigar o comportamento de um sistema de contenção de areia instalado em uma formação com potencial de produção de areia, (ii) verificar a influência do aumento de tensão efetiva na produção de areia e entender como a carga é transmitida para o sistema e (iii) validar um modelo numérico desenvolvido para o estudo de campo. Para ensaios, realizados em uma célula poliaxial sob condições controladas, utilizaram-se blocos de grandes dimensões. Foram analisados 5 casos representativos, sendo cada um deles simulado 4 vezes. O primeiro caso consiste na verificação da formação de um breakout em poço aberto, sem a utilização de nenhum sistema de contenção de areia. Os outros quatro casos são reproduções do sistema gravel-tela, com diferentes configurações. Os resultados foram satisfatórios e de acordo com eles, é possível identificar uma tendência de comportamento para cada cenário: gravel com distribuição uniforme no anular e diâmetro de partícula utilizada no gravel. A verificação de um modelo numérico, desenvolvido na Petrobrás, foi feita a partir destes resultados e mostrou uma boa aproximação de resultados de laboratório. / [en] A major problem during hydrocarbon production from poorly consolidated sandstone in the influx of sand, or sand production. This problem is complex and can occur as a result of a large variety of reasons, like magnitude of the in situ stresses, formation strength, and wellbore-development operations. If the potential for sand production could be predicted, then the problem may be solved or reduced to an accepteble level by proper completion strategy, such as the use of stand alone screens or gravel pack. Although a large number of numerical models for sand production prediction hava been developes, the consistency of the models could be questioned, due to the differences between the predictions and field observations. To improve and validate these models, reliable data are necessary. This study has been developed based on these concerns, and also, considering the massive use of the gravel-pacck as sand control technique on Brazilian fields. The objective were (i) investigation of the gravel-pack system behavior, (ii) varifacation of the increase on effective stress on sand production and (iii) validation a numerical model developed for field sand production prediction. The large-scale tests were carried out on a poliaxial cell. It was selectes 5 representative cases, and they were developed on an artificial well, under controlled conditions. On the first one, it was observed a breakout formation on an openhole. On the other 4 cases, it was simulated the gravel pack, submitted to different conditions, each of them reproduced 4 times. The numerical model was developed by Petrobras/Roncador field engineers, using a commercial numericak modeling program. Results were satisfactory. According to them, is possible to identify a behavior tendency for each condition: the influence of the gravel uniform distribution on the annulus and the influence of gravel diameter. The numerical model showed a very good approach to the laboratory results.

Improving methods of hydrocarbon production and developing new techniques for the creation of natural gas storage facilities are critically important for the petroleum industry. This dissertation focuses on two key topics: (1) mechanisms of sand production from petroleum reservoirs and (2) mechanical characterization of caverns created in carbonate rock formations for natural gas storage. Sand production is the migration of solid particles together with the hydrocarbons when extracted from petroleum reservoirs. It usually occurs from wells in sandstone formations that fail in response to stress changes caused by hydrocarbon withdrawal. Sand production is generally undesirable since it causes a variety of problems ranging from significant safety risks during high-rate gas production, to the erosion of downhole equipment and surface facilities. It is widely accepted that a better understanding of the mechanics of poorly-consolidated formations is required to manage sand production; which, in turn, enables the cost effective production of gas and oil resources. In this work, a series of large-scale laboratory experiments was conducted in fully saturated, cohesionless sand layers to model the behavior of a petroleum reservoir near a wellbore. We directly observed several key characteristics of the sand production phenomenon including the formations of a stable cavity around the wellbore and a sub-radial flow channel at the upper surface of the tested layer. The flow channel is a first-order feature that appears to be a major part of the sand production mechanism. The channel cross section is orders of magnitude larger than the particle size, and once formed, the channel becomes the dominant conduit for fluid flow and particle transport. The flow channel developed in all of our experiments, and in all experiments, sand production continued from the developing channel after the cavity around the borehole stabilized. Our laboratory results constitute a well constrained data set that can be used to test and calibrate numerical models employed by the petroleum industry for predicting the sand production phenomenon. Although important for practical applications, real field cases are typically much less constrained. We used scaling considerations to develop a simple analytical model, constrained by our experimental results. We also simulated the behavior of a sand layer around a wellbore using two- and three-dimensional discrete element methods. It appears that the main sand production features observed in the laboratory experiments, can indeed be reproduced by means of discrete element modeling. Numerical results indicate that the cavity surface of repose is a key factor in the sand production mechanism. In particular, the sand particles on this surface are not significantly constrained. This lack of confinement reduces the flow velocity required to remove a particle, by many orders of magnitude. Also, the mechanism of channel development in the upper fraction of the sample can be attributed to subsidence of the formation due to lateral extension when an unconstrained cavity slope appears near the wellbore. This is substantiated by the erosion process and continued production of particles from the flow channel. The notion of the existence of this surface channel has the potential to scale up to natural reservoirs and can give insights into real-world sand production issues. It indicates a mechanism explaining why the production of particles does not cease in many petroleum reservoirs. Although the radial character of the fluid flow eventually stops sand production from the cavity near the wellbore, the production of particles still may continue from the propagating surface (interface) flow channel. The second topic of the thesis addresses factors affecting the geometry and, hence, the mechanical stability of caverns excavated in carbonate rock formations for natural gas storage. Storage facilities are required to store gas when supply exceeds demand during the winter months. In many places (such as New England or the Great Lakes region) where no salt domes are available to create gas storage caverns, it is possible to create cavities in limestone employing the acid injection method. In this method, carbonate rock is dissolved, while CO₂ and calcium chloride brine appear as products of the carbonate dissolution reactions. Driven by the density difference, CO₂ rises towards the ceiling whereas the brine sinks to the bottom of the cavern. A zone of mixed CO₂ , acid, and brine forms near the source of acid injection, whereas the brine sinks to the bottom of the cavern. Characterization of the cavern shape is required to understand stress changes during the cavity excavation, which can destabilize the cavern. It is also important to determine the location of the mixture-brine interface to select the place of acid injection. In this work, we propose to characterize the geometry of the cavern and the location of the mixture-brine interface by generating pressure waves in a pipe extending into the cavern, and measuring the reflected waves at various locations in another adjacent pipe. Conventional governing equations describe fluid transients in pipes loaded only by internal pressure (such as in the water hammer effect). To model the pressure wave propagation for realistic geometries, we derived new governing equations for pressure transients in pipes subjected to changes in both internal and external (confining) pressures. This is important because the internal pressure (used in the measurement) is changing in response to the perturbation of the external pressure when the pipe is contained in the cavern filled with fluids. If the pressure in the cavern is perturbed, the perturbation creates an internal pressure wave in the submerged pipe that has a signature of the cavern geometry. We showed that the classic equations are included in our formulation as a particular case, but they have limited validity for some practically important combinations of the controlling parameters. We linearized the governing equations and formulated appropriate boundary and initial conditions. Using a finite element method, we solved the obtained boundary value problem for a system of pipes and a cavern filled with various characteristic fluids such as aqueous acid, calcium chloride brine, and supercritical CO₂ . We found that the pressure waves of moderate amplitudes would create measurable pressure pulses in the submerged pipe. Furthermore, we determined the wavelengths required for resolving the cavern diameter from the pressure history. Our results suggest that the pressure transients technique can indeed be used for characterizing the geometry of gas storage caverns and locations of fluid interfaces in the acid injection method.

[pt] Quando um poço de petróleo é completado em arenito brando e pobremente consolidado é possível que ocorra fluxo de areia para dentro do poço. Problemas derivados da produção de areia incluem a obstrução do poço, abrasão de revestimentos e ferramentas, colapso do revestimento e necessidade de separação e disposição, em superfície, de areias impregnadas por óleo. Contudo, em reservatórios de óleo pesado, a alta viscosidade e abaixa produtividade significam que os problemas mencionados acima são menos críticos. Nestes casos, alguma produção de areia é aceitável para aumentar a produtividade.A produção de areia é notória em arenitos mal consolidados, mas também podem ocorrer em arenitos coesivos e medianamente resistentes como resultado da perturbação imposta à rocha durante as operações de perfuração, completação e produção Provavelmente o principal efeito é a destruição da cimentação mineral que produz uma região com material granular na vizinhança do poço. As forças de percolação criadas pelo fluxo podem então arrastar as partículas sólidas para o interior do poço.Um modelo contitutivo que seja capaz de reproduzir o comportamento tensão-deformaçãoresistência de arenitos é de grande interesse para estudos da previsão da produção de areia. Este tema é o ponto central desta tese.Uma revisão dos artigos relacionados com os mecanismos de produção de areia é apresentado no capítulo 2.Dois arenitos brandos obtidos de afloramentos foram caracterizados. Após a diagnose petrográfica realizou-se o tratamento e processamento de imagens da lâminas para mensuração da distribuição granulométrica, parâmetros texturais e dimensão dos poros. Os argilominerais foram investigados por difração de raios- X, usando quatro tipos distintos de preparação de amostras. A porosidade e a permeabilidade intrínseca foram determinadas usando um porosímetro de Boyle e um permeametro à gás. Empregou-se um algoritmo para análise multivariada dos dados para distinguir entre grupos de arenitos com propriedades físicas semelhantes.Realizou-se um exercício numérico, usando soluções analíticas para a distribuição das tensões na parede de um poço, com o objetivo de se identificar as possíveis trajetórias de tensão que ocorrem, considerando as tensões in situ, a perfuração e a produção de fluidos.Foi desenvolvido um programa experimental de ensaios mecânicos que inclui testes uniaxiais,triaxiais convencionais e hidrostático, além de carregamentos seguindo a trajetória de p constante. Estes ensaios serviram para obtenção dos parâmetros do modelo de Lade, bem como para caracterizar o comportamento geomecânico dos arenitos. Deve-se mencionar que os corpos de prova estavam totalmente saturados com água e com óleo. Usou-se um algoritmo de otimização para identificação dos parâmetros do modelo. Por fim, avaliou-se a capacidade do modelo elastoplástico de Lade & Kim para descrever o comportamento tensão deformação dos arenitos estudados. / [en] When a well completed in a poorly consolidated and weak sandstone is produced, sand inflow from reservoir can occour. Problems arising from sand production include sand bridging and wellbore plugging; tools and casing abrasion requiring frequent workovers; casing collapse and distortion in the production zone; sand separation at surface and disposal of an environmentaly contaminated sand. However in heavy oil reservoirs, high viscosity and low production rates means that the problems mentioned before are far less than in high rate light oil wells. In these cases, some sand production can be accepted in order to increase productivity. Sand production is a conspicuous phenomena in poorly consolidated sandstones, but can also occur in cohesive medium-strong sandstones as a result of rock fabric damage during drilling, completion and production activities. Probably the main disturbance imposed to rock is the breakage of mineral cement, which produces a region of a granular yielded material around the bore. The percolation forces created by fluid flow can drag the solid particles to the well. A constitutive model that can be able to simulate stress-strain behavior is of major interest to sand production prediction. This theme is the central point of this work. A review of published articles related to sand production mechanisms is presented in the second chapter. Two weak sandstones obtained from outcrops were characterized. After a diagnosis under petrographic thin sections, an extensive image treatment and processing were carried out to measure grain size distribution, textural parameters and pore dimensions. Clay mineral were investigated by mean of X-ray diffraction techniques, using four distinct kinds of sample preparation. Porosity and intrinsic permeability were determined using a Boyle s principle porosimeter and a gas permeameter. A multivariate data analysis (cluster analysis) algorithm based on distance measures were applied to distinguish among groups with similar physical properties. A numerical exercise using analytical solution equations for the stress distribution on the wall of the well was done to determine the stress path, considering drilling and production effects. A experimental program of rock mechanic tests including uniaxial, conventional triaxial, hydrostatic and proportional loading, besides tests following a (p) constant path, were run in order to characterize the rock behavior as well as to obtain the constitutive model parameters. It must be mentioned that samples were water and oil saturated. An optimization algorithm for of model parameters identification were used and the Lade & Kim elastoplastic constitutive model was evaluated for describe stress-strain relation of sandstones.

[pt] A produção de petróleo em alta vazão a partir de reservatórios formados por arenitos friáveis requer a instalação de sistemas de contenção de sólidos para preservar equipamentos de superfície e subsuperfície. Os projetos de explotação para campos constituídos por estes reservatórios têm na completação uma etapa fundamental na construção do poço. Dentre as diversas operações de completação, a instalação de sistemas de contenção de sólidos é uma das mais complexas e envolve uma ampla gama de recursos humanos e financeiros. A alteração no estado de tensões atuante sobre a formação é uma das principais fontes de carregamento dos sistemas de contenção mecânica de sólidos instalados em poços horizontais. O objetivo deste trabalho é desenvolver um modelo para avaliação do desempenho de sistemas de contenção de sólidos do tipo gravel pack quando submetidos aos esforços relacionados ao comportamento geomecânico das formações produtoras e a variação de pressões durante a vida produtiva de um poço de petróleo, permitindo a otimização de projetos destes sistemas sob a ótica da resistência ao colapso das telas. O carregamento imposto sobre estes sistemas é avaliado através da implementação do modelo de Mohr Coulomb solucionado numericamente através do método de elementos finitos (MEF). O programa comercial ABAQUS™ é utilizado em função da sua flexibilidade para solução de modelos não-lineares. Foram analisados sistemas de contenção de areia com os conjuntos de telas tipicamente utilizados na indústria de petróleo. Em nenhum cenário analisado foram verificados indícios de colapso dos tubos indicando a possibilidade de redução da sua resistência mecânica. / [en] Global increase in energy demand and the lack of opportunities on shore or in shallow waters are driving production of hydrocarbons towards deep and ultra deepwater basins, where reservoirs are usually formed by weak and unconsolidated sandstones that require sand control methods to prevent damage in surface and subsurface equipments. Guidelines to select sand control systems are primarily based on sand exclusion, seeking to optimize balance between oil rate and fines production. Another aspect, often overlooked, is collapse strength of the system formed by the sand control equipment and the formation itself, subjected to mechanical loadings that change during life of the well. This contribution presents a method to evaluate collapse strength of sand control systems taking into account mechanical interaction between the formation and sand control screens. Elastoplastic models are used to represent granular materials. Three sand control systems were studied: gravel pack with premium screens, stand alone premium screens and pre-packed screens. A model to describe contact between granular materials (gravel and formation) and soil-pipe interaction is proposed. Results demonstrate that perforated base pipes used in premium screens may be oversized for applications under regular operating conditions.