Failure Analysis of Oil Tube Corrosion in an Well Converting from Thermal Recovery Production to Fireflood Production

The macrograph and micro morphology of fracture of an oil tube in the well from thermal recovery production to fireflood production, the microstructure of fractured oil tube, chemical composition and corrosion product film were studied by optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. The reasons for oil tube failure were analyzed in combination with field conditions of fire flooding stage. The results show that the mechanism of the oil tube fracture was tensile overload. Second high temperature tempering of the material caused by local high temperature was the main reason for decline in carrying capacity of the oil tube. The partial pressure of CO₂ was over-high during fire flooding stage in the downhole, resulting carbon dioxide corrosion in inner wall and outer wall of the oil tube. Wall thickness thinning caused by CO₂ corrosion also led to the declination of carrying capacity for the oil tube.