Waste-fired boilers suffer severely from corrosion of critical components such as superheater tubes. In this work the high temperature corrosion of candidate superheater alloys have been investigated by detailed laboratory studies and controlled field exposures in full-scale boilers. In a laboratory study the detrimental effect of gaseous hydrochloric acid (HCl) on three  different ground surface and preoxidised austenitic stainless steels was investigated. Exposures were conducted in an environment comprising N2-10O2-5H2O-0.05HCl at both 400 °C and 700 °C. A positive effect of preoxidation is evident when the alloys are exposed at 400 °C. Oxide layers formed during preoxidation effectively suppress chlorine ingress and lower the corrosion rate for all three materials while accelerated corrosion and chlorine accumulation at the metal/oxide interface is detected for ground surface specimens. The positive effect of preoxidation is lost at 700 °C and corrosion resistance is dependent on alloying level. At 700 °C metal chloride evaporation contributes significantly to the material degradation. Based on the results, high temperature corrosion in the presence of gaseous HCl is discussed in general terms.  In two different waste-fired boilers measures for counteracting superheater corrosion were investigated. In a grate-boiler the deposit formation and high temperature corrosion of some candidate superheater materials were studied. Metal loss measurements showed unacceptably high corrosion rates for the lower alloyed ferritic steels 13CrMo44 (Fe-1Cr-0.5Mo) and HCM12A (Fe-11Cr-2W), as well as for the austenitic Super 304 (Fe-18Cr-9Ni-3Cu). The corrosion attack for these alloys was manifested by the formation of mixed metal chloride/metal oxide scales. A different type of behaviour was seen for the higher alloyed austenitic steels and nickel-base alloys, which were able to form a chromium-enriched oxide next to the metal. However, the alloys suffered from localised pitting attack. Since analyses of the deposit revealed appreciable amounts of low melting salt mixtures such as ZnCl2-KCl, PbCl2-KCl, FeCl2-KCl and NaCl-NiCl2, oxide dissolution in these molten salts is the probable reason for pitting attack. In a waste-fired boiler ammonium sulphate solution was added to the flue gas and the effect on flue gas and deposit composition was evaluated. It was evident that the sulphur-rich additive reduced the amount of alkali chlorides in both the flue gas and the deposit. Results also indicated that the initial corrosion rates were lowered with the use of ammonium sulphate. It was concluded that using the additive could be a possible strategy for changing the flue gas chemistry so that superheater corrosion is mitigated. / <p>QC 20110414</p>

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[pt] Diversas operações da indústria petrolífera, como o fechamento e abandono de poços, operações de cimentação e reinício de escoamento em tubos gelificados, utilizam deslocamento de um fluido por outro em tubos anulares. Existem muitas variáveis que podem afetar a eficiência do deslocamento, nomeadamente o comportamento reológico dos fluidos, as relações de viscosidade e densidade e a geometria do poço. A interação desses parâmetros pode levar a instabilidades na interface entre os fluidos, resultando em processos de deslocamento de fluxo ineficientes. Nessas circunstâncias, é necessário um procedimento eficaz para prevenir problemas que possam resultar em perigos e perdas financeiras significativas. Neste trabalho, apresentamos resultados experimentais da eficiência de deslocamento por um tubo anular. A análise é realizada para números de Reynolds baixos, com um fluido newtoniano (água) sendo deslocado por um fluido não newtoniano (solução de goma de xantana), simulando uma operação de fechamento e abandono de poço. O estudo experimental é realizado usando um dispositivo de teste que consiste em um tubo de aço e uma carcaça transparente com diâmetros que refletem um cenário real. Estudamos o processo de deslocamento usando duas inclinações diferentes, geometrias concêntricas e excêntricas, e vibração de tubulação. Para avaliar o impacto desses parâmetros na eficiência de deslocamento, realizamos visualização de fluxo no equipamento experimental e avaliamos a instabilidade da interface. / [en] Several oil industry operations, such as plugging and abandonment wells, cementing operations, and restarting flows of gelled pipes, use the displacement of one fluid by another in annular tubes. There are many variables that can affect the displacement efficiency, namely the rheological behavior of the fluids, the density ratios, and the well geometry. The interaction of these parameters can lead to instabilities at the interface between fluids that will result in inefficient flow displacement processes. In these circumstances, an effective procedure is required to prevent issues that could result in dangers and significant financial losses. In this work we present experimental results of displacement efficiency through an annular tube. The analysis is done for low Reynolds numbers, with a Newtonian (water) fluid being displaced by a non-Newtonian (xanthan gum solution) one, to simulate a plug & abandonment operation. The experimental study is done using a test rig that consists of a steel tubing and a transparent casing with diameters that reflect a real-case scenario. We study the displacement process using two different inclinations, concentric and eccentric geometries, and tubing vibration. To assess the impact of these parameters on displacement efficiency, we perform flow visualization at the experimental rig and evaluate interface instability.

The supply and demand situation is crucial for the oil and gas industry during the first half of the 21st century. For the future, we will see two trends going in opposite directions: a decline in discoveries of conventional oil and gas reservoirs and an increase in world energy demand. Therefore, the need to develop and produce unconventional oil and gas resources, which encompass coal-bed methane, gas-shale, tight sands and heavy oil, will be of utmost importance in the coming decades. In the past, large-scale production from tight gas reservoirs occurred only in the U.S. and was boosted by both price incentives and well stimulation technology. A conservative study from Rogner (1997) has shown that tight gas sandstone reservoirs would represent at least over 7,000 trillion cubic feet (Tcf) of natural gas in place worldwide. However, most of the studies such as the ones by the U.S. Geological Survey (U.S.G.S.) and Kuuskraa have focused on assessing the technically recoverable gas resources in the U.S. with numbers ranging between 177 Tcf and 379 Tcf. During the past few decades, gas production from tight sands field developments have taken place all around the world from South America (Argentina), Australia, Asia (China, Indonesia), the Russian Federation, Northern Europe (Germany, Norway) and the Middle East (Oman). However, the U.S. remains the region where the most extensive exploration and production for unconventional gas resources occur. In fact, unconventional gas formations accounted for 43% of natural gas production and tight gas sandstones represented 66% of the total of unconventional resources produced in the U.S. in 2006. As compared to a conventional gas well, a tight gas well will have a very low productivity index and a small drainage area. Therefore, to extract the same amount of natural gas out of the reservoir, many more wells will have to be drilled and stimulated to efficiently develop and produce these reservoirs. Thus, the risk involved is much higher than the development of conventional gas resources and the economics of developing most tight gas reservoirs borders on the margin of profitability. To develop tight gas reservoirs, engineers face complex problems because there is no typical tight gas field. In reality, a wide range of geological and reservoir differences exist for these formations. For instance, a tight gas sandstone reservoir can be shallow or deep, low or high pressure, low or high temperature, bearing continuous (blanket) or lenticular shaped bodies, being naturally fractured, single or multi-layered, and holding contaminants such as CO2 and H2S which all combined increase considerably the complexity of how to drill a well. Since the first tight gas wells were drilled in the 1940's in the U.S., a considerable amount of information has been collected and documented within the industry literature. The main objective of this research project is to develop a computer program dedicated to applying the drilling technologies and methods selection for drilling tight gas sandstone formations that have been documented as best practices in the petroleum literature.

[pt] Em poços de petróleo, uma boa cimentação é fundamental para garantir o suporte estrutural do revestimento e isolar o poço de águas subterrâneas. A alteração das propriedades e o surgimento de defeitos no cimento podem levar a vazamentos e danos ambientais. Durante a desativação e o abandono do poço em operações conhecidas como P&A (Plug & Abandonment), é necessário avaliar a condição do cimento assim como a identificação de possíveis defeitos. Desde 1950, ferramentas de perfilagem acústica capazes de analisar a condição do cimento vem sendo desenvolvidas e aprimoradas. As ferramentas mais famosas foram a Cement Bond logging Tools (CBT), baseada na técnica de operação CBL (Cement Bond Logging) e VDL (Variable Density Logging), e a Cement Evaluation Tools (CET). Contudo, essas ferramentas foram projetadas para operar somente em configurações com um único revestimento e sem a coluna de produção. Remover a coluna de produção é um processo caro, por isso, um desafio na indústria que permanece até os dias atuais é a criação de uma ferramenta capaz de operar em poços sem a necessidade de se remover a coluna de produção visando a redução dos custos do processo, ou em poços que possuem múltiplos revestimentos. Nos últimos anos muitas patentes e artigos tem sido publicados abordando esse mesmo tema. Este trabalho possui como motivação analisar a eficiência da utilização de ondas ultrassônicas guiadas em poços com multicamadas para detecção de defeitos presentes na camada de cimento. Para isso, primeiramente se realizou uma vasta pesquisa bibliográfica buscando identificar os tipos mais frequentes de defeitos existentes, o princípio de funcionamento das principais ferramentas comerciais existentes e os avanços das pesquisas na fronteira do conhecimento desse assunto. Modelou-se a partir da teoria de ondas e de suas equações analíticas o poço estudado, encontrando as equações de dispersão que regem o problema. Desenvolveu-se um código analítico-numérico capaz de resolver essas equações e de obter as curvas de dispersão. Além disso, analisou-se como os defeitos e suas variações afetam as curvas de dispersão, identificando os comportamentos característicos para cada caso. Posteriormente, a distribuição da energia, obtida a partir do vetor de Poynting no poço, foi usado afim de se investigar os modos que concentram a energia na camada de cimento. Para o caso sem a coluna de produção, concluiu se que os melhores modos de excitação estão em alta frequência, pois a energia se concentra no cimento. Já para o caso com a coluna de produção, encontrou-se que na frequência de 30,13 kHz a uma vagarosidade de 726,5 us/m a energia está praticamente toda concentrada no cimento o que é interessante para se analisar defeitos apenas no cimento e que em 39,17 kHz e 507 us/m a energia está distribuída entre o cimento e a coluna de produção, sendo interessante para analisar defeitos que envolvam ambos. / [en] In oil wells, a good cementation is essential to guarantee the structural support of the casing and isolate the well from groundwater. The variations in the material properties and the presence of defects in the cement can lead to leaks and environmental damage. During the deactivation and abandonment of the well in P&A operations (Plug & Abandonment), it is necessary to evaluate the cement condition as well as investigate possible defects. Since 50 s, cement bond logging tools capable of analyzing the cement condition have been developed and improved. The most famous tools were Cement Bond Logging Tools (CBT), based on CBL (Cement Bond Logging) and VDL (Variable Density Logging) operation technique and the Cement Evaluation Tools (CET). However, these tools were designed to operate only in single-casing set, without the tubing. Remove the tubing is an expensive process, so a challenge in the industry that remains open is the creation of a tool capable of operating in wells with tubing in order to reduce process costs or in wells that have multiple casings. In recent years, many patents and scientific paper have been published on the same topic. This work analyzes the effectiveness of the use of guided ultrasonic waves in multilayer wells to detect defects present in the cement layer. To this end, a vast bibliographic search was first carried out in order to identify the most frequent types of existing defects, the principle of operation of the main commercial tools and the advances in research on this subject. The well studied was modelled from analytical equations of the elastic wave theory, aiming at the dispersion equations that govern the problem. An analytical-numerical code was developed capable of solving these equations and obtaining the dispersion curves. Furthermore, it was analyzed how the defects and their variations affect the dispersion curves, identifying the characteristic behaviours for each case. Subsequently, the energy distribution, obtained by the Poynting vector, in the well was used in order to investigate the modes that concentrate the energy in the cement layer. For the single-casing, it was concluded that the best excitation modes were those with high frequency, because the energy is concentrated in cement. For through-tubing case, it was found that at a frequency of 30.13 kHz and a slowness of 726.5 us/m, the energy is virtually completely concentrated in cement, which is interesting to analyze defects present only in cement layer and that at 39.17 kHz and 507 us/m the energy is distributed between cement and tubing, being interesting to analyze defects that involve both layers.

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[pt] Com o aumento das campanhas de tamponamento e abandono de poços de petróleo maduros pelo mundo, vários centros de pesquisa têm investido em ferramentas de inspeções acústicas e técnicas mais robustas para analisar a integridade do poço de petróleo através do tubo de produção. As análises através do tubo de produção proporcionam uma economia significativa na etapa de abandono, porém as análises são complexas devido à baixa energia recebida e por eventuais excentricidades. O objetivo deste trabalho é analisar as características dos defeitos aplicados na camada de revestimento de cimento de um poço de petróleo com e sem excentricidade do tubo de produção, através de curvas de dispersão e por curvas de coerência de tempo-vagarosidade; e comparar estas curvas com os dados obtidos por simulações pelos métodos de elementos finitos, semi-analíticos e experimentos realizados em escala. Os experimentos realizados incluíram os defeitos mais comuns encontrados, como canalização de fluido na camada de cimento, excentricidade do tubo de produção e baixa impedância de cimento. Os modelos semi-analíticos quando comparados com o método dos elementos finitos apresentaram boa coerência e menor custo computacional. Os experimentos foram realizados em uma bancada experimental dedicada, instrumentada e controlada por um complexo sistema de controle e aquisição de sinais. Para todos os casos com o tubo de produção, notou-se um menor número de modos de onda e menor amplitude de sinal em comparação aos casos sem o tubo de produção. Os resultados do método de tempo e coerência lenta mostraram-se ineficazes na análise de defeitos. Concluiu-se que o método semi-analítico, validado através de diversos modelos analíticos, simulações utilizando o método dos elementos finitos e com diversos experimentos, é uma ferramenta valiosa na análise de defeitos e na verificação da variação dos modos de onda com a excentricidade aplicada. / [en] With the increase in plugging and abandonment campaigns for mature oil wells around the world, several research centers have invested inacoustic inspection tools and more robust techniques to analyze the integrity of the oil well through the production tubing. Analyzes through theproduction tubing provide significant savings in the abandonment stage,however their analysis is complex due to the low energy received and possible eccentricities. The objective of this work is to analyze the characteristicsof defects applied to the cement casing layer of an oil well with and withoutproduction tubing eccentricity, through dispersion curves and slowness-time coherence curves; and compare these curves with data obtained bysimulations using finite element methods, semi-analytical methods and experiments carried out at scale. The experiments carried out included themost common defects found, such as fluid channeling in the cement layer,eccentricity of the production tubing and low cement impedance. The semi-analytical models when compared with the finite element method showedgood coherence. For all cases with the production tubing, a smaller numberof wave modes and lower signal amplitude were noted compared to caseswithout the production tube. The results of the slowness-time coherencemethod proved to be ineffective in defect analysis. It was concluded thatthe semi-analytical method, validated through several analytical models,simulations using the finite element method and with several experiments,is a valuable tool in analyzing defects and verifying the variation of wavemodes with the applied eccentricity.