Effect of CO₂ Partial Pressure on Corrosion Behavior of N80 Steel in Auxiliary Steam Drive Oil Environment

The high temperature and high pressure autoclave was used to simulate the working conditions of CO₂ auxiliary steam drive oil gas injection well. The coupon corrosion test was conducted on N80 steel at 160℃ and CO₂ partial pressures of 1-4 MPa, and the effect of CO₂ partial pressure on corrosion behavior of N80 steel was studied. The results show that with CO₂ partial pressure increasing, the corrosion rate increased first and then decreased; when the CO₂ partial pressure was 2 MPa, the corrosion rate reached the maximum value of 0.073 7 mm·a^-1. The main composition of corrosion products of N80 steel was FeCO₃ and a small amount of Fe₂O₃. With the increase of CO₂ partial pressure, the size of FeCO₃ crystals decreased, and FeCO₃ crystals mixed together when CO₂ partial pressure was 3-4 MPa. Under the test condition, the corrosion rate of N80 steel was 0.034 7-0.073 7 mm·a^-1 which was lower than the corrosion rate control line of oil field (0.076 mm·a^-1) and met the property requirement of CO₂ auxiliary steam drive oil well casing.