This paper describes the methodology used and highlights the experimental results that led to the choice of the completion material for an oilfield expansion with a large variation in the concentration of
aggressive gases (both sweet and sour), chloride content, temperature, pressure and water content. The testing program was formed by corrosion (general, localized and DCB), metallurgical and mechanical tests. Finally, Fracture Mechanics concepts and calculations were used to determine the maximum defect size that could be allowed for a safe operation of the new wells. Keywords: SSCC, High strength steels, Fracture Mechanics, Sour Service, Chrome steels, CO2, H2S