With the application of more and more complex oil and gas production technologies, the field service environment in oil and gas fields has become harsher. Furthermore, some field operations (water injection, agent injection, annular nitrogen injection, reinjection of CO2, pressure testing, etc.) will lead O2 into the downhole environment. As we all know that O2 is highly corrosive and it may cause some unexpected and severe corrosion risks of the downhole tubing. Particularly for 13Cr and some other stainless steels, O2 interfusing can significantly increase the localized corrosion risk and brings a lot of corrosion problems during oil and gas exploitation. In this study, the corrosion behaviors and localized corrosion mechanisms of plain and super 13Cr stainless steels under high temperature and high pressure in O2-contained bromine completion fluids was investigated by corrosion simulation tests and surface characterizations. The corrosion simulation test was performed by high temperature and high pressure autoclave. The corrosion product film that formed on the steel substrate was analyzed by scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. The results show that both plain and super 13Cr steels exhibit bad corrosion resistance in O2-contained bromine completion fluids with various KBr concentrations. Particularly for localized corrosion rate, the corrosion grades of both plain and super 13Cr steels reach to extremely serious. According to NACE PR-0775 standard, the plain 13Cr steel in the solution of 1.01 g?cm-3 has reached the severe corrosion degree, and with the increase of bromine concentration, the degree of corrosion increased, reaching extremely severe corrosion at 1.10 g?cm-3. With the increase of bromide concentration, the corrosion rate increased evidently. Even if the super 13Cr stainless steel is subjected to a high bromide concentration, it can still experience severe localized corrosion (> 5 mm?a-1). The microscopic morphology analysis show that the pitting initiates at the damaged area of the Cr-rich passive layer on substrate surface. The corrosion products accumulate around the pitting. As a result, a local galvanic effect forms between the pitting and the surrounding area, which further accelerates the propagation of the pitting.
