Down-hole damages such as borehole collapse, circulation loss and rock tensile/compressive cracking in the open-hole system are well understood at drilling and well completion stages. However, less effort has been made to understand the instability of cemented sections in High Pressure High Temperature (HPHT) wells. The existing analysis shows that, in the perforation zones, casing/cement is subject to instability, particularly in the presence of cavities. This dissertation focuses on the instability mechanism of casing/cement in the non-perforated zones. We investigate the transient thermal behavior in the casing-cement-formation system resulting from the movement of wellbore fluid using finite element method. The critical value of down-hole stresses is identified in both wellbore heating and cooling effects. Differently with the heating effect, the strong cooling effect in a cased hole can produce significant tension inside casing/cement. The confining formation has an obvious influence on the stability of casing/cement. The proposed results reveal that the casing/cement system in the non-homogeneous formation behaves differently from that in homogeneous formation. With this in mind, a three-dimensional layered finite element model is developed to illustrate the casing/cement mechanical behavior in the non-homogeneous formation. The radial stress of cement sheath is found to be highly variable and affected by the contrast in Young’s moduli in the different formation layers. The maximum stress is predicted to concentrate in the casing-cement system confined by the sandstone. Casing wear in the cased-hole system causes significant casing strength reduction, possibly resulting in the casing-cement tangential collapse. In this study, an approach for calculating the stress concentration in the worn casing with considering temperature change is developed, based on boundary superposition. The numerical results indicate that the casing-cement system after casing wear will suffer from severe tangential instability due to the elevated compressive hoop stress. Gas migration during the cementing process results from the fluid cement’s inability to balance formation pore pressure. Past experience emphasized the application of chemical additives to reduce or control gas migration during the cementing process. This report presents the thermal and mechanical behaviors in a cased hole caused by created gas channels after gas migration. In conclusion, the size and the number of gas channels are two important factors in determining mechanical instability in a casing-cement system.

Made available in DSpace on 2014-12-17T14:08:40Z (GMT). No. of bitstreams: 1 PetruciaDS_DISSERT_partes_autorizadas.pdf: 69844 bytes, checksum: 68dd4f60e7dc4e65dd92f5b166d276e6 (MD5) Previous issue date: 2010-03-22 / Os po?os HPHT atravessam zonas anormalmente pressurizadas e com altos gradientes de temperatura. Esses po?os apresentam elevadas concentra??es de tens?es produzidas pelas opera??es de perfura??o e fraturamento hidr?ulico, flutua??es da press?o e temperatura, for?as din?micas geradas durante a perfura??o, forma??es inconsolidadas, entre outros aspectos, podendo resultar em falhas mec?nicas na bainha de cimento. Tais falhas comprometem a estabilidade mec?nica do po?o e o isolamento das zonas produtoras de ?leos e/ou g?s. Para que opera??es corretivas n?o se fa?am necess?rias, ? preciso adequar as pastas ?s condi??es de cada po?o. Sistemas de pastas de cimento para po?os HPHT requerem um bom controle de suas propriedades termo-mec?nicas. Visto que a temperaturas superiores a 110 oC (230 oF) o cimento, ap?s alcan?ar um valor m?ximo de resist?ncia, inicia um processo de perda de resist?ncia (retrogress?o). Para prevenir esse efeito substitui-se parcialmente o cimento Portland por s?lica com objetivo de incrementar a rea??o pozol?nica. Esta rea??o modifica a trajet?ria do processo natural de hidrata??o do cimento, o gel de silicato de c?lcio hidratado (C-S-H) se converte em v?rias outras fases com maior resist?ncia. Pol?meros tamb?m s?o adicionados para proporcionar maior flexibilidade e agir como barreira ? propaga??o de trincas desenvolvidas sob tens?o. O presente trabalho teve como objetivo estudar o comportamento do sistema cimento/s?lica/pol?mero quando submetido ?s condi??es de alta temperatura e alta press?o. Foram formuladas pastas de cimento puro, pastas contendo 40 % BWOC de s?lica flour e pastas com diferentes concentra??es de poliuretana (5 % a 25 %) e 40 % BWOC de s?lica flour. O peso espec?fico das pastas foi fixado em 1,87 g/cm3 (15,6 lb/gal). Os resultados demonstram que as resist?ncias da pasta contendo 40% de s?lica e das com adi??o de pol?mero foram muito superiores a da pasta de cimento puro, n?o ocorrendo o efeito da retrogress?o. As pastas com pol?mero apresentaram um crescente aumento da tenacidade com o aumento da concentra??o da mesma, sendo assim capaz de suportar as tens?es. Al?m de se manterem est?veis termicamente acima de 180 ?C. O sistema tamb?m apresentou excelentes resultados de filtrado, reologia, ?gua livre, estabilidade e permeabilidade. Sendo assim, o mesmo mostrou ser aplic?vel a po?os HPHT

[pt] O presente estudo busca definir uma relação de mistura estável utilizando aditivos poliméricos à base de álcool polivinílico (PVOH) para controlar a perda de filtrado, antiespumante e dispersante, caracterizando a influência de cada adição na cinética de hidratação, propriedades mecânicas, físicas e reologia da mistura. Além disso, foi caracterizado o comportamento das pastas de cimento em condições de cura que simulam a situação do poço até 6100 m de profundidade, seguindo as recomendações da API, e o comportamento do material nos estados in situ, utilizando pressões confinantes para realizar os ensaios de compressão. Por fim, propôs-se a inclusão de microfibras de álcool polivinílico (PVA) para melhorar o desempenho mecânico das pastas cimentícias, avaliando diferentes tipos de carregamento e definindo os impactos da adição de fibras na viscosidade e tixotropia das misturas. Verificou-se que o uso de PVOH como aditivo de perda de filtrado não influencia na cinética de hidratação para concentrações de até 0,4% em peso de cimento, mas à medida que a quantidade de PVOH é aumentada na mistura, o processo de hidratação da pasta de cimento pode ser modificado por causa do mecanismo de absorção do PVOH. Além disso, novas fases de produtos de hidratação aparecem com o aumento da temperatura e pressão de cura: dellaite, hydroxyellestadite e alpha-C2SH. A última fase (alpha-C2SH) está relacionada à perda de capacidade de resistência das amostras curadas a 149°C, simulando o caso do poço de petróleo de 6100 m de profundidade. Para os ensaios triaxiais, a pressão de confinamento conferiu às amostras um comportamento diferente do caso uniaxial, implicando em uma considerável melhora da plasticidade no comportamento tensão-deformação. Embora se observe algum reforço por atrito devido a tensões de cisalhamento no plano das fissuras, o efeito mais importante do confinamento é suportar a deformação dúctil, mesmo para o caso da pasta de cimento reforçada com fibra de PVA. Finalmente, o estudo mostrou que as fibras de PVA conferem um leve aumento da viscosidade da pasta de cimento, uma fase plástica prolongada aparentemente sem perda de capacidade de carga em testes triaxiais e uma capacidade aprimorada de absorver energia ao avaliar cargas de tração e cisalhamento. / [en] The present study seeks to define a stable mixing ratio using powder Polyvinyl Alcohol (PVOH) based polymeric additives to control the loss of filtrate, defoamer, and dispersant, characterizing the influence of each addition on hydration kinetics, mechanical and physical properties, and rheology of the mix. The behavior of cement pastes under curing conditions that simulate the wellbore situation up to 6100 m depth was also evaluated, following API recommendations. Moreover, the behavior of the material under in situ states, using confining pressures to perform the compression tests, was characterized. Finally, the inclusion of Polyvinyl Alcohol (PVA) microfibers is proposed to improve the mechanical performance of cement pastes, evaluating different types of loading and defining the impacts of the fiber addition on the viscosity and thixotropy of the mixtures. It was found that the use of PVOH as a fluid loss additive does not influence hydration kinetics for concentrations up to 0.4% by weight of cement, but as the amount of PVOH is increased in the mixture, the hydration process of the cement paste may be modified because of the PVOH absorptive mechanism. Moreover, new hydration products phases appear with increasing curing temperature and pressure: dellaite, hydroxyellestadite, and alpha-C2SH. The last phase (alpha-C2SH) is related to the loss of strength capacity of the samples cured at 149°C, simulating a 6100 m depth wellbore. For the triaxial tests, the confining pressure gave the samples a behavior markedly different from the uniaxial case, implying a considerable improvement in the plasticity of the stress-strain behavior. Although some frictional reinforcement is observed due to shear stresses in the cracks surface, the most important effect of confinement is to withstand ductile deformation, even in the case of PVA fiber-reinforced cement paste. Finally, the study has shown that PVA fibers impart a slight viscosifying effect on the cement slurry, a prolonged plastic phase with apparently no loss of load-carrying capacity in triaxial tests, and an improved ability to absorb energy when evaluating tensile and shear loads.

TiAlN and TiAlN-based coatings that are used of relevance as protection of cutting tool inserts used in metal machining have been studied. All coatings were deposited by reactive cathodic arc evaporation using industrial scale deposition systems. The metal content of the coatings was varied by using different combinations of compound cathodes. The as-deposited coatings were temperature annealed at ambient pressure and in some cases also at high pressure. The resulting microstructure was first evaluated through a combination of x-ray diffraction and transmission electron microscopy. In addition, mechanical properties such as hardness by nanoindentation were also reported. TiAlN coatings with two different compositions were deposited on polycrystalline boron nitride substrates and then high pressure high temperature treated in a BELT press at constant 5.35 GPa and at 1050 and 1300 °C for different times. For high pressure high temperature treated TiAlN it has been shown that the decomposition is slower at higher pressure compared to ambeint pressure and that no chemical interaction takes place between TiAlN and polycrystalline cubic boron nitride during the experiments. It is concluded that this film has the potential to protect a polycrystalline cubic boron nitride substrate during metal machining due to a high chemical integrity. TiZrAlN coatings with different predicted driving forces for spinodal decomposition were furthermore annealed at different temperatures. For this material system it has been shown that for Zr-poor compositions the tendency for phase separation between ZrN and AlN is strong at elevated temperatures and that after spinodal decomposition stable TiZrN is formed.