Influences of CO₂ Partial Pressure and Salinity on Corrosion of J55 Steel Tubing

The high temperature autoclave was used to simulate the CO₂ flooding condition, and the corrosion rate of J55 tubular steel in the CO₂ flooding oil injection and production environment was measured by the weight loss method. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), and EDS energy spectrum were used to analyze the morphology and composition of corrosion products, and the effects of CO₂ partial pressure and salinity on the corrosion of J55 pipes were investigated. The results showed that under the simulated CO₂ flooding condition, when the CO₂ partial pressure of J55 steel was 0-25 MPa, the corrosion rates of the gas and liquid phases both exceed the standard requirement of 0.076 mm/a. When the partial pressure of CO₂ was 10 MPa, the corrosion rate was high as 7.047 mm/a, and the corrosion products were composed of FeCO₃ and FeS. The increase of Cl^- concentration would increase the salinity of the solution, and led to the increase of the conductivity of the corrosion medium and the acceleration of the charge transfer rate, thereby intensifying the corrosion, the corrosion and scaling products showed an increasing trend, the average corrosion degree gradually decreased, but the pitting increased.