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Previous issue date: 2009-12-22 === Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior === The production of heavy oil fields, typical in the Northeastern region, is commonly stimulated by steam injection. High bottom hole temperatures are responsible not only for the development of deleterious stresses of the cement sheath but also for cement strength retrogression. To overcome this unfavorable scenario, polymeric admixtures can be added to cement slurries to improve its fracture energy and silica flour to prevent strength retrogression. Therefore, the objective of the present study was to investigate the effect of the addition of different concentrations of polyurethane (5-25%) to cement slurries containing 40% BWOC silica flour. The resulting slurries were characterized using standard API (American Petroleum Institute) laboratory tests. In addition to them, the mechanical properties of the slurries, including elastic modulus and microhardness were also evaluated. The results revealed that density, free water and stability of the composite cement/silica/polyurethane slurries were within acceptable limits. The rheological behavior of the slurries, including plastic viscosity, yield strength and gel strength increased with the addition of 10% BWOC polyurethane. The presence of polyurethane reduced the fluid loss of the slurries as well as their elastic modulus. Composite slurries also depicted longer setting times due to the presence of the polymer. As expected, both the mechanical strength and microhardness of the slurries decreased with the addition of polyurethane. However, at high bottom hole temperatures, the strength of the slurries containing silica and polyurethane was far superior than that of plain cement slurries. In summary, the use of polyurethane combined with silica is an interesting solution to better adequate the mechanical behavior of cement slurries to heavy oil fields subjected to steam injection === Em campos que possuem ?leos pesados ? necess?rio um meio para estimular o ?leo a fluir pela forma??o, tais reservas s?o caracter?sticas da Regi?o Nordeste do Brasil e necessitam da inje??o de vapor para sua recupera??o. Temperatura elevada no fundo do po?o proporciona tens?es induzidas na bainha de cimento, al?m de favorecer a retrogress?o de resist?ncia do cimento, comprometendo a qualidade da cimenta??o. Sendo assim, adiciona-se em pastas cimentantes, o pol?mero, afim de se promover maior plasticidade e s?lica a para evitar o efeito da perda de resist?ncia mec?nica (retrogress?o). Diante disso, o presente trabalho teve como objetivo estudar o comportamento de pastas de cimento contendo poliuretana em diferentes concentra??es (5% a 25%) e 40% BWOC de s?lica flour. Foram realizados ensaios padronizados pelo API (American Petroleum Institute) e ensaios para obten??o do m?dulo de elasticidade e microdureza, al?m da caracteriza??o das pastas formuladas. Os resultados mostraram que as pastas comp?sitas cimento/s?lica/poliuretana apresentaram valores de peso espec?fico, ?gua livre e estabilidade dentro dos estabelecidos por norma. As propriedades reol?gicas foram modificadas, a viscosidade pl?stica, o limite de escoamento e os g?is aumentaram com a adi??o a partir de 10% BWOC de poliuretana. A poliuretana favoreceu melhor controle de filtrado e diminuiu o m?dulo de elasticidade das pastas. A mesma tamb?m promoveu retardamento da pega do cimento. As propriedades mec?nicas de resist?ncia e microdureza diminu?ram com a adi??o de s?lica e/ou s?lica/poliuretana, entretanto, em alta temperatura a resist?ncia mec?nica das pastas com s?lica e poliuretana tiveram um valor bem superior quando comparado com a pasta de cimento padr?o. A caracteriza??o das pastas mostrou que a adi??o de s?lica e pol?mero diminui o teor de c?lcio do cimento e que h? a forma??o do filme polim?rico. Pol?mero combinado com cimento e s?lica pode ser usado como aditivo para diminuir o m?dulo de elasticidade e, desta forma, fornecer maior plasticidade e resist?ncia ?s ciclagens t?rmicas ocasionadas pelo processo de inje??o de vapor
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