Failure Analysis of Oil Pipe Fracture in an Old Well Production Converting from Thermal Recovery Production into Fireflood Production

An oil pipe fractured during the workover of a production well in Xinjiang Oilfield. The failed pipe experienced steam thermal recovery production and fireflood production two conditions in turn. The causes of the oil pipe fracture were studied by metallographic analysis, micro-morphology detection, energy dispersive spectrum (EDS) analysis and X-ray diffraction (XRD) analysis. The results show that the corrosion products on the surface of the failed pipe were mainly composed of FeCO₃ and Fe sulfides. CO₂ corrosion and H₂S corrosion occurred on the underground oil pipe, and the residual wall thickness of the pipe was insufficient to bear the weight of oil pipe, resulting in the fracture and collapse of the oil pipe. The corrosion of N80 oil pipe which had experienced two working conditions of steam thermal recovery production and fireflood production was severer than that under single working condition of fireflood. So the service capacity of original pipe should be evaluated objectively when oil well production converts from thermal recovery production into fireflood production.