Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-02-13T15:32:26Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TeseDoutorado_MarcelaSeixas.pdf: 6064842 bytes, checksum: 5d148170b369d14be988b9c57683862a (MD5) / Made available in DSpace on 2017-02-13T15:32:26Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TeseDoutorado_MarcelaSeixas.pdf: 6064842 bytes, checksum: 5d148170b369d14be988b9c57683862a (MD5) Previous issue date: 2015-08-31 / CNPq / O interesse em estudos relacionados ao processo de fraturamento hidráulico vem aumentando, principalmente devido à exploração de reservatórios não convencionais, que se torna cada vez mais importante para a demanda de energia atual, com estimativas de grandes reservas distribuídas por vários países. A modelagem numérica de tal processo é um desafio, devido à complexidade da física envolvida. A interação entre propriedades mecânicas da rocha, tensões in situ, e heterogeneidades como fraturas naturais e planos de fraqueza é determinante na geometria da fratura induzida. Para resolver este tipo de problema acoplado, o método dos elementos finitos é amplamente utilizado e um dos mais versáteis. O presente estudo propõe uma técnica numérica denominada Fragmentação de Malha, que usa elementos finitos com elevada razão de aspecto (ou elementos especiais de interface), combinados com um modelo constitutivo baseado na mecânica do dano para reproduzir os efeitos do processo de formação de fraturas. Esta metodologia, com base na Aproximação Contínua de Descontinuidades Fortes, consiste em introduzir estes elementos de interface entre elementos regulares de uma malha de elementos finitos. Dentre as vantagens dessa técnica estão a sua facilidade de adaptação a programas convencionais de elementos finitos e o fato de não ser necessário o uso de algoritmos de construção de trajetória da descontinuidade. As aplicações apresentados neste trabalho mostram a capacidade da técnica proposta na modelagem do fraturamento hidráulico em reservatórios não convencionais. / The interest in studies related to the hydraulic fracturing process has increased over the last decade, mainly due to the exploitation of unconventional reservoirs, which is growing and becoming more important to the current energy demand, with the estimation of the existence of large reserves spread over several countries. Numerical modelling of such processes is a challenging task because of the complexity of the physics involved, and because of the structurally complicated geometry of the reservoir. The interaction between rock’s mechanical properties, insitu stresses, and heterogeneities such as natural fractures and weak bedding planes is determinant of the induced fracture geometry. To solve this kind of coupled hydromechanical problem, the Finite Elements Method is one of the most versatile and widely used. The present study propose a numerical technique called mesh fragmentation, that uses solid finite elements with high aspect ratio combining with a proper strain softening constitutive model to reproduce the effects of fractures formation process. This methodology, based on the Continuous Strong Discontinuous Approach, consists in introducing these high aspect ratio elements between regular elements of a finite element mesh. Some advantages of this technique are that it can be easily adapted to standard finite elements programs and no tracking algorithms are necessary to follow the evolution of the fracture. The case studies presented in this paper show the ability of the proposed technique to model hydraulic fracturing propagation in unconventional reservoirs.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A demanda das populaÃÃes por mais Ãgua tem forÃado o desenvolvimento de tÃcnicas para melhorar o aproveitamento de todas as formas de recursos hÃdricos. Em algumas partes dos Estados Unidos da AmÃrica, o fraturamento hidrÃulico tem sido utilizado para estimular poÃos perfurados no embasamento cristalino a aumentarem suas vazÃes. Na regiÃo Nordeste do Brasil, os poÃos perfurados neste tipo de formaÃÃo geolÃgica frequentemente exibem baixas vazÃes, o que os leva à posterior desativaÃÃo ou ao simples abandono. O objetivo principal desta pesquisa à estudar, analisar e quantificar os efeitos que o fraturamento hidrÃulico imprime sobre a transmissividade, a conectividade e as vazÃes de um aqÃÃfero fissural. Para tanto se desenvolveu um modelo de propagaÃÃo de fraturas em formaÃÃes rasas e de matriz impermeÃvel. AlÃm disso, fez-se uso de modelos de hidrÃulica de poÃos para a determinaÃÃo dos parÃmetros hidrodinÃmicos do aqÃÃfero. Para testar a metodologia, dados coletados em dois poÃos de bombeamento perfurados na Fazenda de Horticultura da University of New Hampshire, Durham, NH, foram utilizados. Estes dados incluem testes de bombeamento prÃ-fraturamento e pÃs-fraturamento, ensaio geofÃsicos, alÃm dos registros da operaÃÃo de fraturamento. Uma anÃlise conjunta dos resultados dos testes de bombeamento e do modelo de propagaÃÃo de fratura permitiu concluir que, o fraturamento hidrÃulico aumentou a transmissividade das fraturas em 46 vezes em um poÃo e 285 vezes em outro. A conectividade do sistema de fraturas experimentou acrÃscimos entre 11 e 20 vezes. O dado prÃtico foi que um poÃo passou a fornecer vazÃes 10 vezes maiores e no outro este aumento foi de 18 vezes. Estes melhoramentos foram possÃveis porque o fraturamento hidrÃulico alargou a abertura das fraturas e fez seu raio propagar por dezenas de metros. A distÃncia que a fratura propagou a partir do poÃo juntamente com o aumento na interconexÃo das fraturas conectou o poÃo a regiÃes mais favorÃveis à recarga.

Understanding economic success of unconventional production from shales requires an explanation of the relationship between induced seismicity and hydraulic fracturing. This thesis deals with observing and analyzing synthetic and real microseismic monitoring data acquired during hydraulic fracturing. The thesis is based on observation and analyses of source mechanisms of induced microseismic events that have recently become regularly inverted and interpreted in the oil and gas industry. The results of analyses are interpreted with the geomechanical model of the relationship between hydraulic fracturing and induced seismicity. The study of source mechanisms starts with detailed analyses of spatial distribution of full moment tensor inversion stability. It was mapped based on synthetically computed condition numbers in the vicinity of different monitoring arrays including dense arrays at the surface and sparse arrays with sensors in the boreholes. Stability of inversion was tested under several conditions, mainly dependency on size and geometry of monitoring array and level of noise in the data. In this part of the thesis it is shown that dense surface arrays may provide very stable inversion of source mechanisms which may be interpreted. The study shows that an increasing percentage of non-shear...

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[pt] Esta pesquisa aborda o processo de fraturamento hidráulico ou processo de propagação de fraturas em rocha através da injeção de um fluido sob pressão, o que gera fissuras no material que se propagam de acordo com a quantidade de fluido injetado. Esta técnica leva a um incremento da transmissividade hidráulica da rocha e, como consequência, ocorre um incremento da produção de óleo. Diversos trabalhos analíticos e numéricos têm sido propostos para estudar o mecanismo de fratura, geralmente baseados em meios contínuos ou através da utilização de elementos de interface em uma trajetória de propagação conhecida. Neste trabalho, a propagação de uma fratura é simulada utilizando o modelo potencial PPR[72] através da sua implementação extrínseca. Assim, os elementos coesivos de interface são inseridos na malha de elementos finitos de forma adapativa para capturar o processo de fraturamento. A pressão do fluido é simulada utilizando o modelo de lattice-Boltzmann[84]. Através de um processo interativo, os contornos da fratura, computados utilizando o método dos elementos finitos, são transferidos para o modelo de lattice-Boltzmann como uma condição de contorno. Assim, a força que o fluido exerce nestes contornos, gerada pela injeção do fluido, pode ser calculada. Estas forças são utilizadas no modelo de elementos finitos como uma força externa aplicada nas faces da fratura. A nova posição das faces da fratura é calculada e transferida novamente para o modelo de lattice-Boltzmann como condição de contorno. Este processo interativo fluido-estrutura permite modelar o processo de fraturamento hidráulico em trajetórias de propagação irregulares. / [en] This research addresses hydraulic fracturing or hydro-fracking, i.e. fracture propagation process in rocks through the injection of a fluid under pressure, which generates cracks in the rock that propagate according to the amount of fluid injected. This technique leads to an increase of the hydraulic transmissivity of the rock mass and, consequently, improves oil production. Several analytical and numerical models have been proposed to study this fracture mechanism, generally based in continuum mechanics or using interface elements through a known propagation path. In this work, the crack propagation is simulated using the PPR potential-based cohesive zone model[72] by means of an extrinsic implementation. Thus, interface cohesive elements are adaptively inserted in the mesh to capture the softening fracture process. The fluid pressure is simulated using the lattice Boltzmann model[84] through an iterative procedure. The boundaries of the crack, computed using the finite element method, are transferred to the lattice Bolztmann model as boundary conditions, where the fluid pressure (or fluid forces) applied on these boundaries, caused by the fluid injected, can be calculated. These forces are then used in the finite element model as external forces applied on the faces of the crack. The new position of the crack faces is then calculated and transferred to the lattice-Boltzmann model to update the boundary conditions. This feedback-loop for fluid-structure interaction allows modeling of hydraulic fracturing processes for irregular path propagation.

This Ph.D. dissertation focuses on a comprehensive study of seismic waveform similarity aiming at two themes: (1) reliable identification of repeating earthquakes (repeaters) and (2) investigation of the detailed source process of induced seismicity through the three-dimensional spatiotemporal evolution of mainly neighbouring earthquakes. Theme 1: Reliable identification of repeaters. Repeaters, occurring repeatedly on the same fault patch with nearly identical waveforms, are usually identified with the match-filtering (MF) method which essentially measures the degree of waveform similarity between an earthquake pair through the corresponding cross-correlation coefficient (CC). However, the performance of the MF method can be severely affected by the length of the cross‐correlation window, the frequency band of the applied digital filter, and the presence of a large‐amplitude wave train. To optimize the performance of MF, I first examine the effects of different operational parameters and determine generic rules for selecting the window length and the optimal frequency passband. To minimize the impact of a large‐amplitude wave train, I then develop a new method, named the match-filtering with multisegment cross-correlation (MFMC) method. By equally incorporating the contributions from various segments of the waveforms, the new method is much more effective in capturing the minor waveform discrepancy between an event pair due to location difference and hence is more reliable in detecting potential repeaters and discriminating non-repeaters with large inter-event separation. With both synthetic and borehole array waveform data, I further reveal that waveform similarity is controlled by not only the inter-event separation but also many other factors, including station azimuth, epicentral distance, velocity structure, etc. Therefore, in contrast to the traditional view, the results indicate that waveform similarity alone is insufficient to unambiguously identify true repeaters. For reliable repeater identification, we should rely on a physics-based approach considering both the overlapped source area and magnitude difference. Specifically, I define an event pair to be true repeaters if their inter-event separation is smaller than the rupture radius of the larger event and their magnitude difference is no more than 1. For the precise estimation of inter-event distance in cases of limited data, I develop the differential traveltime double-difference (DTDD) method which relies on the relative S-P differential traveltime. The findings of this study imply that previously identified repeaters and their interpretations/hypotheses potentially can be biased and hence may need a systematic reexamination. Theme 2: Investigation of the detailed source process of induced seismicity. Earthquakes induced by hydraulic fracturing (HF), especially those with large magnitudes, are often observed to have occurred near/after well completion. The delayed triggering of induced seismicity with respect to injection commencement poses serious challenges for risk mitigation and hazard assessment. By performing waveform cross-correlation and hierarchical clustering analysis, I reveal a high-resolution three-dimensional source migration process with mainshock delayed triggering that is probably controlled by local hydrogeological conditions. The results suggest that poroelastic effects might contribute to induced seismicity but are likely insufficient to activate a non-critically stressed fault of sufficient size. My analysis shows that the rapid pore-pressure build-up from HF can be very localized and capable of producing large, felt earthquakes on non-critically stressed fault segments. I further infer that the number of critically stressed, large intraplate faults should be very limited, and that reactivation of such faults may require sufficient pore-pressure accumulation. The findings of this study may also explain why so few fluid injections are seismogenic. / Graduate

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20338号 / 工博第4275号 / 新制||工||1662(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 石田 毅, 教授 林 為人, 准教授 奈良 禎太 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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[pt] Os reservatórios não convencionais de folhelho possuem permeabilidades muito baixas sendo necessário fraturar hidraulicamente a formação para aumentar a permeabilidade e conseguir um melhor desempenho do poço. O fraturamento hidráulico em vários estágios criado a partir de um poço horizontal gera uma complexa rede de fraturas, com variadas condutividades dentro do volume de reservatório estimulado. Neste trabalho realizamos análises paramétricas para avaliar os efeitos no desempenho do poço produtor causadas pela variação dos diferentes parâmetros dentro da complexa rede de fraturas criada. Estes parâmetros foram principalmente: os espaçamentos na rede de fraturas (sem propante), a condutividade na rede de fraturas (sem propante), a condutividade das fraturas primárias (preenchidas com propante), os espaçamentos das fraturas primárias (preenchidas com propante), a variação da permeabilidade ao longo das fraturas primárias e finalmente a variação das pressões do fundo do poço. Entender as relações entre o tamanho da rede de fraturas, os espaçamentos, a distribuição do propante e a condutividade das fraturas são parâmetros chaves para definir estratégias de estimulação e completação. Finalmente se fez uma simulação com injeção de água avaliando o impacto que causa na recuperação total de óleo e gás, e analisamos a possibilidade de aplicar este método de recuperação num reservatório fraturado hidraulicamente. / [en] The shale reservoirs have ultralow permeability requiring hydraulically fracturing the formation to improve permeability and get a better well performance. The multistage hydraulic fractures system created from a horizontal well generates a complex fracture network with different conductivities within the stimulated reservoir volume. In this work we made parametric analyzes to assess the effects on producer well performance caused by the variation of different parameters within the complex network fractures created. These parameters were mainly: spacing in the un-propped fracture network, the conductivity in the unpropped fracture network, primary fracture conductivity, primary fracture spacing, the variation of permeability along the primary fractures and finally the variation of downhole pressures. Understanding the relationship between fracture network size, fracture spacing, proppant distribution, and fracture conductivity is critical to stimulation and completion design. Finally a simulation with water injection evaluating its impact on recovering oil and gas was carried out, and the possibility of applying this method of recovery in a fractured reservoir was evaluated.The shale reservoirs have ultralow permeability requiring hydraulically fracturing the formation to improve permeability and get a better well performance. The multistage hydraulic fractures system created from a horizontal well generates a complex fracture network with different conductivities within the stimulated reservoir volume. In this work we made parametric analyzes to assess the effects on producer well performance caused by the variation of different parameters within the complex network fractures created. These parameters were mainly: spacing in the un-propped fracture network, the conductivity in the unpropped fracture network, primary fracture conductivity, primary fracture spacing, the variation of permeability along the primary fractures and finally the variation of downhole pressures. Understanding the relationship between fracture network size, fracture spacing, proppant distribution, and fracture conductivity is critical to stimulation and completion design. Finally a simulation with water injection evaluating its impact on recovering oil and gas was carried out, and the possibility of applying this method of recovery in a fractured reservoir was evaluated.

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