Corrosion Behavior of Carbon Steels 20 and L245NS in Drainage of CO₂ Enhanced Oil Recovery

Corrosion behavior of carbon steel 20 and carbon steel L245NS in drainage of CO₂ enhanced oil recovery (CO₂-EOR) was studied by immersion tests and electrochemical measurements combined with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the corrosion rates increased significantly with the increase of temperature and partial pressure of carbon dioxide. When the temperature was 55℃, or the partial pressure of carbon dioxide was 0.75 MPa, the corrosion rates of both carbon steels all reached a maximum. The competition between corrosion inhibition mechanism and corrosion promotion mechanism of Cl^- made the corrosion rates increased first, and then decreased and increased at last with Cl^- concentration increasing. The corrosion product film mainly consisted of FeCO₃ with a loose structure, and had bad protection to substrate. The results of polarization curves and electrochemical impedance spectroscopy showed after corrosion the corrosion current density decreased and the capacitive loop increased for carbon steel 20 and L245NS in comparison with before corrosion, which indicated that protective effect of corrosion product film was not obvious.