Electrochemical Behavior of Low Carbon Medium Chromium Steel in Simulated CO₂ Enhanced Oil Recovery Environment

The corrosion behavior of low carbon medium chromium steel Cr5 and Cr7 in simulated Changqing Oilfield CO₂ enhanced oil recovery environment was analyzed by simulated dynamic corrosion test and electrochemical test. The corrosion resistance of the two materials was compared by weight loss method, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the corrosion rate of Cr5 steel was 0.734 75 mm/a and that of Cr7 steel was 0.217 32 mm/a. The corrosion product films on the surface of Cr5 steel and Cr7 steel were double-layer structures, and the main composition of the corrosion product films were FeCO₃ and Cr(OH)₃. The corrosion product films on the surface of Cr7 steel were more dense. When the temperature was 30 ℃, the electrochemical behavior of Cr5 steel and Cr7 steel was controlled by electrode activation. When the temperature was 50 ℃ and 70 ℃, the electrochemical behavior of Cr5 steel was controlled by electrode activation and diffusion, while the electrochemical behavior of Cr7 steel was still controlled by electrode activation.