Corrosion behavior of N80 steel in CO2-saturated formation water

Purpose This paper aims to explore the influence of CO2 partial pressure, flow rate and water cut on N80 steel corrosion behaviors in the displacement process of oil in glutenite reservoir by CO2 injection. Design/methodology/approach A self-made 3 L high-temperature and high-pressure autoclave was used to conduct corrosion simulation experiments of N80 steel in different CO2 partial pressures, flow rates and water cut (the independently developed oil and water mixing approach can ensure the uniform mixing of oil and water in experiments). Techniques like weight loss and surface analysis were used to analyze the corrosion behaviors of N80 steel under different conditions. Findings Results showed that the average corrosion rate of N80 steel accelerated at varying degrees with the increase of CO2 partial pressure, flow rate and water cut. Excluding that the samples showed uniform corrosion under the two conditions of 0.5MPa CO2 partial pressure and static corrosion, they displayed mesa attack corrosion under other conditions. Besides, with the increase of CO2 partial pressure, the pH value of solution dropped and the matrix corrosion speed rose, hence leading to the increased Fe2+ and CO32− concentration. Meanwhile, a lowered pH value improved the FeCO3 critical supersaturation, thereby leading to an increased nucleation rate/growth rate and ultimately causing the decrease of the dimension of FeCO3 crystallites formed on the surface of the samples. Originality/value The results can be helpful in targeted anti-corrosion measures for CO2/oil/water corrosive environment.