It is widely known in oil industry that changes in fluid flow conditions such as water breakthrough or unsteady flow due to well shut-in can lead to sand destabilization, with a possible consequent sand production. In this research, different flow situations are incorporated into stress and stability analysis for the region around a wellbore producing oil from weak or unconsolidated sands, and the analyses involve strength weakening, stress redistribution, and decrease of rock stiffness. Two main mechanisms, chemical reactions of rock with formation water and variations of rock capillary strength, are identified and analyzed to study strength weakening after water breakthrough, both qualitatively and quantitatively. Using theories from particle mechanics, rock mechanics, and interfacial science, four novel capillarity models are developed and verified to analytically capture the physical behaviors of capillary strength at the grain scale. Based on model calculations, significantly better understanding of strength behavior in two-phase fluid environments is achieved. Based on a simplified model that can conservatively but efficiently quantify capillary strength with only two input parameters (i. e. particle radius and water saturation), a verified new method that physically calculates pore pressure in a multiphase environment, and a coupled poro-inelastic stress model, the redistributions of effective stresses with water saturation around a wellbore are solved. In terms of stress changes and growth of a plastic radius defining shear-failure zone, the effects of different stability factors, including capillarity through water-oil menisci, pore pressure changes due to the variations of fluid relative permeabilities, and loss of strength through chemical reactions of water-sensitive cementation materials, are quantified and compared in order to clarify when and how they contribute to sand production after water breakthrough. The nonlinearities of rock elastic properties in stressed and biphasic fluid environments is analytically addressed, based on an improved nonlinear theory that considers both a failure-based mechanism and a confining-stress-based mechanism, the strength model, and the coupled stress model. The calculations demonstrate the redistributions of stress-dependent rock stiffness around a wellbore and its evolution with increase of water saturation, clarify the relative importance of each mechanism in reducing rock stiffness, and fundamentally explain why current predictive technologies are invalid when water appears in a flowing wellbore. To quantify the effect of well shut-down on rock stability, the redistributions of fluid pressure in reservoir are analytically solved and coupled with the stress model, while the water hammer equations provide a boundary condition for the bottom-hole pressure. This approach allows direct solution of the relationships among fluid properties, rock properties and production parameters, within the context of rock stability. The proposed new approaches and models can be applied to evaluate sand production risk in multiphase and unsteady fluid flow environment. They can also serve as points of departure to develop more sophisticated models, or to develop more useful constitutive laws for numerical solutions.

Highwall mining is a mining method used in surface coal operations that involves driving a series of parallel entries into the exposed coal seam at the highwall face under an unsupported roof leaving behind a series of long, but very slender coal pillars. Highwall mining often occurs simultaneously with production blasting taking place in other areas of the mine. Although no failures of highwall pillars have been attributed to nearby blasting, numerical modelling presents an inexpensive means of investigating the possible effects of strong ground motion on the stability of these pillars. This thesis documents the development of a discrete element rock mass model and its application to the simulation of both static and fully dynamic highwall pillar simulations. The approach is geared toward parameter analysis and mechanism identification rather than exact prediction. Some conclusions are made regarding the potential effects of blast vibration on highwall coal pillars and general excavations in rock. The limitations of the modelling approach are discussed and suggestions for future research are proposed.

A growing demand for more detailed modeling of subsurface physics as ever more challenging reservoirs - often unconventional, with significant geomechanical particularities - become production targets has moti-vated research in coupled flow and geomechanics. Reservoir rock deforms to given stress conditions, so the simplified approach of using a scalar value of the rock compressibility factor in the fluid mass balance equation to describe the geomechanical system response cannot correctly estimate multi-dimensional rock deformation. A coupled flow and geomechanics model considers flow physics and rock physics simultaneously by cou-pling different types of partial differential equations through primary variables. A number of coupled flow and geomechanics simulators have been developed and applied to describe fluid flow in deformable po-rous media but the majority of these coupled flow and geomechanics simulators have limited capabilities in modeling multiphase flow and geomechanical deformation in a heterogeneous and fractured reservoir. In addition, most simulators do not have the capability to simulate both coarse and fine scale multiphysics. In this study I developed a new, fully implicit multiphysics simulator (TAM-CFGM: Texas A&M Coupled Flow and Geomechanics simulator) that can be applied to simulate a 2D or 3D multiphase flow and rock deformation in a heterogeneous and/or fractured reservoir system. I derived a mixed finite element formu-lation that satisfies local mass conservation and provides a more accurate estimation of the velocity solu-tion in the fluid flow equations. I used a continuous Galerkin formulation to solve the geomechanics equa-tion. These formulations allowed me to use unstructured meshes, a full-tensor permeability, and elastic stiffness. I proposed a numerical upscaling of the permeability and of the elastic stiffness tensors to gener-ate a coarse-scale description of the fine-scale grid in the model, and I implemented the methodology in the simulator. I applied the code I developed to the simulation of the problem of multiphase flow in a fractured tight gas system. As a result, I observed unique phenomena (not reported before) that could not have been deter-mined without coupling. I demonstrated the importance and advantages of using unstructured meshes to effectively and realistically model a reservoir. In particular, high resolution discrete fracture models al-lowed me to obtain more detailed physics that could not be resolved with a structured grid. I performed numerical upscaling of a very heterogeneous geologic model and observed that the coarse-scale numerical solution matched the fine scale reference solution well. As a result, I believed I developed a method that can capture important physics of the fine-scale model with a reasonable computation cost.

As the depth of mining increases, so does the risk of fault slip related rockbursts. Currently, there is no way to evaluate this risk, however the need for such a system is clear. Fault behaviour in mining environments is the result of a complex interaction between the mining system and the geological system. Although numerous models exist, the wide spectrum of fault behaviour cannot be fully explained. Additionally, these models are phenomenological, resulting in a disconnect between observable parameters and the models of faults. Fault behaviour is dependent upon the strength of the fault, the stresses acting along the fault, the boundary conditions and fault-system stiffness. Significant work exists in the field of earth science attempting to relate properties of the geological system to fault behaviour. In mining environments, these relationships become increasingly difficult to determine due to the time variable nature of mining activities. In order of importance, the following factors influence fault behaviour: excavations, tectonic history and in situ stress, fault system, fault zone geometry, pore pressure, fault zone slip surface and core, blasting, fault zone damage zone and wall rock and temperature. Numerical stress analysis models were created to evaluate the influence of excavations, tectonic history and in situ stress and the fault system on fault behaviour. Excavations were placed in various locations in a fault system. Results showed that there was no clear relationship between excavation location and fault behaviour; small perturbations in the initial state caused significantly different outcomes. The architectures of many classification and decision support systems were evaluated for purposes of a fault slip classification system. Due to the chaotic nature of fault behaviour and the time variable nature of the factors that influence fault slip, a typical classification system is not an appropriate architecture. Instead, it is recommended that a fault slip risk identification system be created, allowing for the incorporation of historical and live data to create a real time response. Artificial neural networks, numerical stress analysis, data from the identified important factors, and seismic data is recommended to form the basis of the fault slip risk identification system. / Thesis (Master, Mining Engineering) -- Queen's University, 2012-06-01 13:17:08.453

No description available.

[pt] A exploração crescente de campos de petróleo desafiadores é acompanhada por uma também crescente preocupação pública e de companhias petrolíferas em relação a questões ambientais e de segurança. Estudos dos principais acidentes recentes relacionados a exploração de hidrocarbonetos indicam que análises geomecânicas aprofundadas podem ser a chave para prevenir tais ocorrências. Efeitos geomecânicos podem ser muito relevantes durante análises de reservatórios. Há diversas possibilidades para considerar esses efeitos, mas a análise acoplada iterativa tem mostrado ser uma das melhores soluções, pois apresenta resultados precisos em um período de tempo computacional viável. O grupo de pesquisa PUC-Rio/GTEP tem desenvolvido um programa de acoplamento que gerencia o simulador de fluxo (IMEX ou Eclipse) e o programa de elementos finitos (Abaqus ou uma solução em GPU mais rápida chamada Chronos), de uma forma interativa. O referido programa fornece uma solução abrangente para geomecânica de reservatórios. No entanto, a geração de malha, a preparação de dados e a avaliações de resultados são barreiras para a sua aplicação na rotina de trabalho da indústria. Esta dissertação apresenta a elaboração de um fluxo de trabalho desenvolvido em um modelador geológico para aplicar a simulação acoplada de fluxo-tensão para reservatórios reais de hidrocarbonetos. Este fluxo de trabalho permite de forma simples e direta a geração de malha de elementos finitos, a definição de parâmetros mecânicos, supervisão da execução da solução acoplada e, por fim, a avaliação dos resultados de fluxo e tensão em um mesmo ambiente de visualização. / [en] The growing exploration of challenging oil fields is followed by an increasing concern by members of the public and oil companies about environmental and safety issues. Studies of recent major accidents indicate that geomechanics analyses can be the key to prevent future incidents. Geomechanical effects can be very relevant during reservoirs analyses. Actually, there are many possibilities available to consider such effects, but iterative-coupled analysis has shown to be one of the best solutions because it presents accurate results in a feasible computational timeframe. The GTEP/PUC-Rio research group has developed a coupling program that manages both the flow simulator (IMEX or Eclipse) and the finite element solver (Abaqus or a faster in-house GPU solution called Chronos) in an interactive way. The mentioned program provides a wide-ranging solution for reservoir geomechanics. However, mesh generation, data preparation and results evaluations are bottlenecks for its application in the industry s work routine. This dissertation presents the development of a workflow included in a geological modeler to apply the coupled flow-stress for real hydrocarbon reservoir simulation. This workflow allows in a simple and direct manner the generation of a finite element mesh, the definition of mechanical parameters, the supervision of coupled solution execution and the evaluation of results (flow and stress) in a single viewing environment.

[pt] A produção de um reservatório de petróleo é um processo acoplado entre fenômenos geomecânicos e de fluxo, os quais impactam o próprio reservatório e suas rochas adjacentes. Ensaios laboratoriais mostraram que amostras de um reservatório carbonático do Campo B, um campo de petróleo localizado na Bacia de Campos, são muito sensíveis às deformações causadas pela depleção. Desta forma, o objetivo deste trabalho é avaliar aspectos geomecânicos e de produção do desenvolvimento do Campo B, utilizando diferentes esquemas de acoplamento hidromecânico. Foram realizadas simulações hidromecânicas parcialmente acopladas entre o simulador de fluxo IMEX e o programa de análises geomecânicas CHRONOS (um código de elementos finitos executado em GPU) através de uma metodologia que permite análises tanto em uma, quanto em duas vias. Foi construído um Mechanical Earth Model 3D do Campo B no modelador geológico GOCAD através de um workflow específico para esta tarefa. Então, foram confrontadas respostas de respostas de fluxo e geomecânicas entre simulações feitas em uma via e em duas vias. Primeiramente, a permeabilidade não foi considerada como parâmetro de acoplamento. Neste caso, não foram encontradas diferenças significativas entre os resultados dos dois tipos de acoplamento. Posteriormente foram realizadas novas simulações em duas vias, porém considerando variações das permeabilidades decorrentes da depleção do reservatório. Os resultados destas novas análises divergiram da simulação acoplada em duas vias na qual esta propriedade foi mantida constante ao longo do tempo. Logo, neste caso, negligenciar o acoplamento da permeabilidade pode gerar erros significativos. Também foram feitas análises quanto à performance computacional das simulações hidromecânicas realizadas ao longo desta Dissertação. / [en] The production of a petroleum reservoir is a coupled process between geomechanical and flow phenomena, which affect the reservoir and its surrounding rocks. Laboratory tests have shown that samples of a carbonate reservoir from Field B, an oil field located in the Campos Basin, are very sensitive to deformations caused by depletion. Thus, this study aims to assess production and geomechanical aspects of Field B development by different hydromechanical coupling schemes. Therefore, partially coupled hydromechanical simulations between the flow simulator IMEX and the geomechanical analysis software CHRONOS (a finite element code running on GPU) were performed using a methodology which allows either one-way or two-way coupling. A 3D Mechanical Earth Model of Field B was built in GOCAD, a geological modelling software, through a specific workflow for this task. Then, flow and geomechanical results were compared between one-way and two-way coupling simulations. Initially, permeability was not considered as a coupling parameter. In this case, there were no significant differences between the results. Afterwards, more two-way coupling simulations were performed, but at this time, considering variations of permeabilities due to depletion. The results of these new simulations diverged from the two-way coupling case in which permeabilities were kept constant throughout the simulation. Therefore, in this case, neglecting permeability coupling can lead to significant errors. Computational performance of the hydromechanical simulations performed along this Dissertation were also evaluated.

This dissertation presents contributions to the understanding of the dynamic nature of permeability of Indonesian coal. It is the first-of-its-kind study, first presenting a comparison of experimental results with those obtained using existing analytical permeability models, and then modifying the existing anisotropic model for application to the unique physical structure of Indonesian coal. The first problem addressed in this dissertation was establishing the pressure-dependentpermeability of coal in a laboratory environment replicating in situ conditions for two coal types from the Sanga Sanga basin of Kalimantan, Indonesia. The change in permeability with depletion and the corresponding volumetric strain of coal were measured in the laboratory under uniaxial strain condition (zero lateral strain). Two gases, helium and methane, were used as the flowing fluids during experimental work. The results showed that, decreasing pore pressure resulted in significant decrease in horizontal stress and increased permeability. The permeability increase at low reservoir pressure was significant, a positive finding for Indonesian coals. Using the measured volumetric changes with variations in pressure, the cleat compressibility for the two coal types was estimated. In a separate effort, volumetric strain as a result of desorption of gases was measured using sister samples under unconstrained condition, in absence of the stress effect. Sorptioninduced strain processes were modeled using the Langmuir-type model to acquire the two important shrinkage parameters. All parameters calculated using the experimental data were used for the modeling exercise. The second component of this dissertation is the permeability variation modeling to enable projecting long-term gas production in the Sanga Sanga basin. For this, two commonly used isotropic permeability models were selected. These models, developed primarily for the San Juan coal, were unable to match the measured permeability data. This was believed to be due to the inappropriate geometry used to represent Indonesian coal, where butt cleats are believed to be absent. This was followed by application of the most recent model, incorporating partial anisotropy in coal. This consideration improved the modeling results although there clearly was room for improvement. The final challenge addressed in this dissertation was to consider the coal geometry appropriate for Indonesian coal, stack of sheets as opposed to a bundle of matchsticks. In order to incorporate the structural anisotropy for the stack of sheets geometry, two input parameters were modified, based on geo-mechanical anisotropy. After applying these to the modified model, the permeability modeling results were compared with the experimental data. The matches improved significantly. Finally, the effect of maximum horizontal stress on permeability of coal was estimated by using high and low maximum horizontal stress values and constant vertical and minimum horizontal stresses. The effect of maximum horizontal stress on permeability was found to be significant under uniaxial strain condition for both coals.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-04T11:22:15Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TeseLeoCabral_vrsFinal.pdf: 37484380 bytes, checksum: b61e5bb415f505345e69623ffd098b9e (MD5) / Made available in DSpace on 2016-07-04T11:22:15Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TeseLeoCabral_vrsFinal.pdf: 37484380 bytes, checksum: b61e5bb415f505345e69623ffd098b9e (MD5) Previous issue date: 2015-07-08 / A disciplina de geomecânica de reservatórios engloba aspectos relacionados não somente à mecânica de rochas, mas também à geologia estrutural e engenharia de petróleo e deve ser entendida no intuito de melhor explicar aspectos críticos presentes nas fases de exploração e produção de reservatórios de petróleo, tais como: predição de poro pressões, estimativa de potenciais selantes de falhas geológicas, determinação de trajetórias de poços, cálculo da pressão de fratura, reativação de falhas, compactação de reservatórios, injeção de CO2, entre outros. Uma representação adequada da quantificação de incertezas é parte essencial de qualquer projeto. Especificamente, uma análise que se destina a fornecer informações sobre o comportamento de um sistema deve prover uma avaliação da incerteza associada aos resultados. Sem tal estimativa, perspectivas traçadas a partir da análise e decisões tomadas com base nos resultados são questionáveis. O processo de quantificação de incertezas para modelos multifísicos de grande escala, como os modelos relacionados à geomecânica de reservatórios, requer uma atenção especial, principalmente, devido ao fato de comumente se deparar com cenários em que a disponibilidade de dados é nula ou escassa. Esta tese se propôs a avaliar e integrar estes dois temas: quantificação de incertezas e geomecânica de reservatórios. Para isso, foi realizada uma extensa revisão bibliográfica sobre os principais problemas relacionados à geomecânica de reservatórios, tais como: injeção acima da pressão de fratura, reativação de falhas geológicas, compactação de reservatórios e injeção de CO2. Esta revisão contou com a dedução e implementação de soluções analíticas disponíveis na literatura relatas aos fenômenos descritos acima. Desta forma, a primeira contribuição desta tese foi agrupar diferentes soluções analíticas relacionadas à geomecânica de reservatórios em um único documento. O processo de quantificação de incertezas foi amplamente discutido. Desde a definição de tipos de incertezas - aleatórias ou epistêmicas, até a apresentação de diferentes metodologias para quantificação de incertezas. A teoria da evidência, também conhecida como Dempster-Shafer theory, foi detalhada e apresentada como uma generalização da teoria da probabilidade. Apesar de vastamente utilizada em diversas áreas da engenharia, pela primeira vez a teoria da evidência foi utilizada na engenharia de reservatórios, o que torna tal fato uma contribuição fundamental desta tese. O conceito de decisões sob incerteza foi introduzido e catapultou a integração desses dois temas extremamente relevantes na engenharia de reservatórios. Diferentes cenários inerentes à tomada de decisão foram descritos e discutidos, entre eles: a ausência de dados de entrada disponíveis, a situação em que os parâmetros de entrada são conhecidos, a inferência de novos dados ao longo do projeto e, por fim, uma modelagem híbrida. Como resultado desta integração foram submetidos 3 artigos a revistas indexadas. Por fim, foi deduzida a equação de fluxo em meios porosos deformáveis e proposta uma metodologia explícita para incorporação dos efeitos geomecânicos na simulação de reservatórios tradicional. Esta metodologia apresentou resultados bastante efetivos quando comparada a métodos totalmente acoplados ou iterativos presentes na literatura. / Reservoir geomechanics encompasses aspects related to rock mechanics, structural geology and petroleum engineering. The geomechanics of reservoirs must be understood in order to better explain critical aspects present in petroleum reservoirs exploration and production phases, such as: pore pressure prediction, geological fault seal potential, well design, fracture propagation, fault reactivation, reservoir compaction, CO2 injection, among others. An adequate representation of the uncertainties is an essential part of any project. Specifically, an analysis that is intended to provide information about the behavior of a system should provide an assessment of the uncertainty associated with the results. Without such estimate, perspectives drawn from the analysis and decisions made based on the results are questionable. The process of uncertainty quantification for large scale multiphysics models, such as reservoir geomechanics models, requires special attention, due to the fact that scenarios where data availability is nil or scarce commonly come across. This thesis aimed to evaluate and integrate these two themes: uncertainty quantification and reservoir geomechanics. For this, an extensive literature review on key issues related to reservoir geomechanics was carried out, such as: injection above the fracture pressure, fault reactivation, reservoir compaction and CO2 injection. This review included the deduction and implementation of analytical solutions available in the literature. Thus, the first contribution of this thesis was to group different analytical solutions related to reservoir geomechanics into a single document. The process of uncertainty quantification has been widely discussed. The definition of types of uncertainty - aleatory or epistemic and different methods for uncertainty quantification were presented. Evidence theory, also known as Dempster- Shafer theory, was detailed and presented as a probability theory generalization. Although widely used in different fields of engineering, for the first time the evidence theory was used in reservoir engineering, which makes this fact a fundamental contribution of this thesis. The concept of decisions under uncertainty was introduced and catapulted the integration of these two extremely important issues in reservoir engineering. Different scenarios inherent in the decision-making have been described and discussed, among them: the lack of available input data, the situation in which the input parameters are known, the inference of new data along the design time, and finally a hybrid modeling. As a result of this integration three articles were submitted to peer review journals. Finally, the flow equation in deformable porous media was presented and an explicit methodology was proposed to incorporate geomechanical effects in the reservoir simulation. This methodology presented quite effective results when compared to fully coupled or iterative methods in the literature.

[pt] Simuladores de escoamento em reservatórios são ferramentas importantes na otimização do desenvolvimento de um campo de petróleo. Estes simuladores modelam o escoamento multifásico através de meios porosos compressíveis, levando em conta as equações de equilíbrio de fases, as leis de fluxo e a variação volumétrica do meio poroso associada à variação da pressão de poros do sistema. As tensões in situ são consideradas através da aplicação de tensões constantes no contorno do reservatório. Este trabalho descreve a utilização de um simulador convencional de reservatório, baseado em diferenças finitas com e sem um módulo geomecânico, e a utilização de um simulador acoplado, que resolve as equações de escoamento e de tensão num mesmo código de elementos finitos. Nesta dissertação são feitas comparações entre os modelos geomecânicos aproximado e rigoroso oferecidos pelos simuladores comerciais, além de ser apresentada uma análise de situações em que esta última forma deve ser realmente considerada. O objetivo deste trabalho é analisar a influência das tensões in situ em reservatórios de petróleo com base na comparação entre os campos de poropressões obtidos a partir da modelagem de um mesmo sistema com os dois simuladores geomecânicos. São apresentadas as formas de acoplamento e a formulação utilizada em cada um dos modelos. Os modelos geomecânicos utilizados em cada um dos simuladores são comparados. É feita uma comparação entre os resultados obtidos pelos dois simuladores a partir de um modelo bidimensional. / [en] Numerical simulators for reservoir flow analysis are important tools for the optimization of oil field development. These simulators model the multiphase flow through compressible porous medium taking into account the phase equilibrium equations, flow laws and the rock volumetric change associated to the pore pressure change during production. Some simulators have been associated with stress analysis modules in order to use the pore pressure field obtained by the flow simulator and update the stress field within the reservoir. This dissertation describes the use of a conventional reservoir simulator based on finite differences that models multiphase flow in porous media, with and without a geomechanical module, and the use of a fully-coupled simulator that solves both the flow and stress equations in a single finite element code. This dissertation compares the two geomechanical modules, the approximated and the precise, offered by commercial simulators, and analyses the situations in which the rigorous form should be considered, or not. The aim of this dissertation is to investigate the influence of in situ stresses in petroleum reservoirs based on the comparison of the pore pressure fields obtained from the modeling of the same system with both geomechanical simulators. The coupling and formulation used in each model are presented. The geomechanical models of both simulators are described. A comparison of the simulators is made using a bidimensional model.