In order to investigate the corrosion behavior of N80
steel in
production wellbores of oxygen-reduced air drive, the main corrosion
control factors are analyzed based on gray relational analysis. Taking
reservoir simulation results as indoor simulation parameters, the
corrosion behavior in different production periods is studied by the
dynamic weight loss method combined with metallographic microscopy,
XRD, 3D morphology, and other related characterizations. The results
show that oxygen content is most sensitive to the corrosion of production
wellbores. The corrosion rate increases significantly under oxygen-containing
conditions, and the corrosion rate at an oxygen content of 3% (0.3
MPa) is about 5 times higher than that without oxygen. At the initial
stage of oil displacement, the corrosion is CO2-dominated
localized corrosion, and the corrosion products are mainly compact
FeCO3.With the prolongation of gas injection time, the
wellbore is in a CO2/O2balanced environment,
the corrosion changes into a combined action of the two, and the corrosion
products are FeCO3and loose porous Fe2O3. After continuous gas injection for 3 years, the production
wellbore is in a high O2and low CO2environment,
the dense FeCO3is destroyed, the corrosion pit develops
horizontally, and the corrosion changes to O2-dominated
comprehensive corrosion.