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Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains xiii, 132 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 98).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xii, 99 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 53-54).

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. "December 1998." Document formatted into pages; contains x, 78 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 57-58).

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Donald Ralph Petersen. / M.S.

This work addresses the poroelastic effect on the processes involved in hydraulic fracturing and post-fracture production using a finite element based fully coupled poroelastic model which includes a triple system of wellbore-fracture-reservoir. A novel numerical procedure for modeling hydraulic fracture propagation in a poroelastic medium is introduced. The model directly takes into account the interaction of wellbore, hydraulic fracture and reservoir in a fully coupled manner. This allows realistic simulation of near fracture phenomena such as back stress and leak-off. In addition, fluid leak-off is numerically modeled based on the concept of fluid flow in porous media using a new technique for evaluating local pressure gradient. Besides, the model is capable of accommodating the zone of reduced pressure (including intermediate and fluid lag zones) at the fracture front so as to capture the behavior of fracture tip region more realistically. A fully coupled poroelastic model for gas reservoirs has been also developed using an innovative numerical technique. From the results of this study it has been found that fracture propagation pressure is higher in poroelastic media compared to that of elastic media. Also high formation permeability (in the direction normal to the hydraulic fracture) and large difference between minimum horizontal stress (in case of it being the smallest principal stress) and reservoir pressure reduce the rate of fracture growth. Besides, high pumping rate is more beneficial in elongating a hydraulic fracture whereas high viscous fracturing fluid is advantageous in widening a hydraulic fracture. It has been also shown that rock deformation, permeability anisotropy and modulus of elasticity can have a significant effect on fluid flow in a hydraulically fractured reservoir. Furthermore, it has been shown that long stress reversal time window and large size of stress reversal region can be caused by high initial pressure differential (i.e. the difference between flowing bottomhole pressure and reservoir pressure), low initial differential stress (i.e. the difference between maximum and minimum horizontal stresses) and low formation permeability in tight gas reservoirs. By taking advantage of production induced change in stress state of a reservoir, this study has also shown that a refracture treatment, if carried out in an optimal time window, can lead to higher economic gain. Besides, analysis of stress reversal region has depicted that a small region with high stress concentration in the vicinity of the wellbore could impede refracture from initiating at the desired place. Moreover, re-pressurization of the wellbore can result in further propagation of the initial fracture before initiation or during propagation of the secondary fracture.

This work addresses the poroelastic effect on the processes involved in hydraulic fracturing and post-fracture production using a finite element based fully coupled poroelastic model which includes a triple system of wellbore-fracture-reservoir. A novel numerical procedure for modeling hydraulic fracture propagation in a poroelastic medium is introduced. The model directly takes into account the interaction of wellbore, hydraulic fracture and reservoir in a fully coupled manner. This allows realistic simulation of near fracture phenomena such as back stress and leak-off. In addition, fluid leak-off is numerically modeled based on the concept of fluid flow in porous media using a new technique for evaluating local pressure gradient. Besides, the model is capable of accommodating the zone of reduced pressure (including intermediate and fluid lag zones) at the fracture front so as to capture the behavior of fracture tip region more realistically. A fully coupled poroelastic model for gas reservoirs has been also developed using an innovative numerical technique. From the results of this study it has been found that fracture propagation pressure is higher in poroelastic media compared to that of elastic media. Also high formation permeability (in the direction normal to the hydraulic fracture) and large difference between minimum horizontal stress (in case of it being the smallest principal stress) and reservoir pressure reduce the rate of fracture growth. Besides, high pumping rate is more beneficial in elongating a hydraulic fracture whereas high viscous fracturing fluid is advantageous in widening a hydraulic fracture. It has been also shown that rock deformation, permeability anisotropy and modulus of elasticity can have a significant effect on fluid flow in a hydraulically fractured reservoir. Furthermore, it has been shown that long stress reversal time window and large size of stress reversal region can be caused by high initial pressure differential (i.e. the difference between flowing bottomhole pressure and reservoir pressure), low initial differential stress (i.e. the difference between maximum and minimum horizontal stresses) and low formation permeability in tight gas reservoirs. By taking advantage of production induced change in stress state of a reservoir, this study has also shown that a refracture treatment, if carried out in an optimal time window, can lead to higher economic gain. Besides, analysis of stress reversal region has depicted that a small region with high stress concentration in the vicinity of the wellbore could impede refracture from initiating at the desired place. Moreover, re-pressurization of the wellbore can result in further propagation of the initial fracture before initiation or during propagation of the secondary fracture.

Orientador: Osvaldo Luís Manzoli / Banca: Flavia de Oliveira Lima Falcão / Banca: Leonardo José do Nascimento Guimarães / Resumo: A técnica de fraturamento hidráulico é amplamente utilizada na indústria petrolífera para aumentar a permeabilidade da rocha-reservatório numa região próxima ao poço e permitir a extração, e consequente produção, de hidrocarbonetos armazenados em seus poros. Primeiramente a rocha é perfurada criando-se um poço e então injeta-se fluido a uma pressão suficientemente alta para fraturar a rocha. A injeção contínua de fluido permite que as fraturas se propaguem pelo reservatório, formando assim canais de alta permeabilidade. A modelagem e simulação computacional de fraturamento hidráulico são complexas em função da física envolvida no processo. O presente trabalho objetiva o estudo da formação e propagação de fraturas induzidas hidraulicamente em meios rochosos de baixa permeabilidade e também tem o propósito de verificar se a metodologia adotada é capaz de reproduzir características apresentadas num processo de fraturamento hidráulico, como a pressão necessária para causar a ruptura da rocha. Para tal, apresenta-se a técnica de fragmentação da malha utilizando elementos finitos de elevada razão de aspecto (ou elementos de interface) para representar a fratura, aos quais são atribuídas relações constitutivas baseadas na mecânica do dano. Além disso, os elementos de interface também possuem um acoplamento hidromecânico capaz de representar o canal de alta permeabilidade devido à ocorrência da fratura. Os resultados obtidos mostraram que os elementos de interface asso... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The hydraulic fracturing technique is widely used to increase the permeability of reservoirs in the vicinity of the well and to allow the extraction and subsequent production of hydrocarbons trapped in its pores. Firstly, the rock is drilled, creating a well and then a fluid is injected at a sufficiently high pressure to fracture the rock. The continuous fluid injection allows the fractures to propagate through the reservoir, thereby forming some high permeability paths. The computer modeling and simulation of hydraulic fracturing are complex due to the physics involved in the process. This work aims to study the formation and propagation of hydraulically induced fractures in rocky media with low permeability and also aims to verify if the adopted methodology is able to reproduce the characteristics presented in a hydraulic fracturing process, as for instance, the required pressure to cause the breakdown of the rock. For this purpose, it is presented the mesh fragmentation technique using finite elements with a high aspect ratio (or interface elements) to represent the fracture, which are assigned constitutive relations based on damage mechanics. Besides, the interface elements also have a hydromechanical coupling which is able to represent the high permeability path due to the fracture. The results showed that the interface elements associated with the mesh fragmentation technique were able to represent both the formation and the propagation of hydraulically induc... (Complete abstract click electronic access below) / Mestre

Orientadores: Philippe Remy Bernard Devloo, Sonia Maria Gomes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-14T02:00:38Z (GMT). No. of bitstreams: 1 Damas_RenatoGomes_M.pdf: 3286162 bytes, checksum: 85d0d261382f505e55d4f5544f378238 (MD5) Previous issue date: 2005 / Resumo: Neste trabalho avalia-se três modelos que retratam o processo de fraturamento hidráulico. O primeiro, desenvolvido por Fernandes [1998], trata-se de um modelo semi- nalítico cuja formulação fundamenta-se na taxa constante de injeção de fluido fraturante. Esse modelo apresenta como vantagem a simplicidade dos cálculos e a obtenção imediata dos resultados, por outro lado tem seu campo de atuação limitado a intervalos específicos de eficiência volumétrica para os quais foi elaborado. Os outros dois são modelos numéricos desenvolvidos por Devloo et al. [2001] e Devloo [2001]. Incorporam em seu equacionamento taxa variável de injeção e por efetuarem cálculos iterativos são independentes quanto a eficiência volumétrica do processo. Os resultados dos modelos numéricos foram comparados com os do modelo semi-analítico. Buscando-se, desta forma, validar os modelos numéricos para o uso em simulações de fraturamento hidráulico, principalmente para as condições de injeção de água presentes em poços com alta porosidade. Pretende-se com isso oferecer maior liberdade e flexibilidade durante o planejamento da operação de fraturamento. Oferecendo ao projetista a possibilidade de adoção de taxa injeção variável, períodos sem injeção intercalados com períodos com injeção, liberdade para utilização de diferentes fluidos fraturantes entre outros benefícios. / Abstract: The purpose of this research has been evaluated three models of hidraulic fracturing. The first one, developed byFernandes [1998], is a semi-analytical model whose formulation is based on a constant rate of injection of fracturing fluid. This model presents as advantage the simplicity of the calculations and the immediate attainment of the results, on the other hand its performance is limited at specific intervals of volumetric efficiency for which it was elaborated. The others two are numerical models developed by Devloo et al. [2001] and Devloo [2001]. They incorporate variable injection rate and due to the iterative calculations they are not limited in a range of volumetric efficiency of the process. The results of the numerical models had been compared with the ones of the semianalytical model. Searching, in such a way, to validate the numerical models for the use in simulation of hydraulic fracturing, mainly for the characteristic conditions of water injection present in wells with high porosity. It is intended with this to provide freedom and flexibility during the planning of the operation of fracturing. Offering to the designer the possibility to use variable injection rate, periods without injection intercalated with periods with injection, freedom to choose differents fracturing fluids among others benefits. / Mestrado / Estruturas / Mestre em Engenharia Civil

Durante a perfuração de poços de petróleo, a determinação do perfil de temperaturas no poço é importante para tomada de decisões relativas ao processo de cimentação, para a seleção de revestimento do poço e equipamentos e, sobretudo, na identificação de zonas de influxo e perda de circulação. Neste trabalho é proposto um modelo matemático da transferência de calor em regime transitório do escoamento de fluido de perfuração em poços fraturados com perda de circulação. O poço é representado de maneira simplificada através de um cilindro anular concêntrico, cuja parede externa (interface poço-formação) apresenta uma ou mais fraturas discretas. Para a obtenção do modelo térmico é realizado um balanço de energia com foco nas trocas de calor entre a coluna de perfuração, região anular e formação rochosa. A característica principal do modelo proposto é a possibilidade de detecção da posição e número de fraturas a partir do perfil do gradiente térmico da região anular ao longo poço. Para tanto, com o código numérico, obtido via método dos volumes finitos, investiga-se a influência de parâmetros: da fratura (profundidade relativa, perda de circulação, número e distância entre fraturas), físicos (tempo de circulação) e do regime de escoamento (número de Reynolds e viscosidade dos fluidos de perfuração). As variáveis-resposta principais analisadas são a temperatura da região anular e o gradiente térmico. Como variáveis-resposta secundárias são utilizadas as evoluções térmicas da temperatura no fundo do poço e na saída da região anular. É constatado que o aumento da profundidade relativa ou número de fraturas diminui a temperatura do fundo do poço, sem causar variação significativa na temperatura de saída do anular. Para a variação da perda de circulação, o efeito na temperatura do fundo do poço é similar ao da variação do aumento da profundidade relativa da fratura, no entanto são observadas diferenças na temperatura de saída. Além disso, é verificado que, conforme se aumenta o número de fraturas distribuídas ao longo da profundidade do poço, a temperatura do poço tende ao caso de poço não fraturado. De maneira similar é evidenciada a tendência de que a diminuição na distância entre fraturas se aproxima dos resultados para um poço com uma única fratura. Finalmente, o aumento da perda de circulação facilita a detecção de fraturas devido a respectiva mudança na descontinuidade do perfil do gradiente térmico da região anular. / During oil drilling operations, the wellbore temperature profile is used when selecting well casing materials, making cementation related decisions, and, most importantly, to identify loss zones. In this work, a transient heat transfer mathematical model for a fractured wellbore is proposed. The well has its geometry simplified to a concentric annular cylinder which has one or more discrete fracture in its external wall (wellformation interface). In order to obtain the thermal model an energy balance is used, focusing the heat transfer between the pipe, the annular region and the formation. The key characteristic of the model is the fracture detection through thermal gradient graphical analysis. The thermal gradient is an output of the solution of the discretized energy equation in the domains, obtained through the finite volume method. The following parameters are investigated: fracture depth, fracture number, fracture interference, loss circulation, circulation time, Reynolds number and drilling fluid viscosity. The analysis is done through the analysis of the annular region temperature profile and its gradient, along with the thermal evolution of both the bottomhole and outlet temperatures. It is verified that increasing the fracture relative depth or number decreases the bottomhole temperature, while having no significant impact in the outlet temperature. The same bottomhole temperature effect is noted when increasing loss rate, however outlet temperature changes are observed. In a similar way, when decreasing the distance between fractures, the temperature profile in the annular region trends to a wellbore with a single fracture. Finally, increasing loss rate favors fracture detection, since the discontinuity in the annular region thermal gradient profile is intensified.