Annular Fracture Reason of Super 13Cr Oil Tubing Used in High Pressure and High Temperature Gas Well

The aging reasons for annulus fracture failure of super 13Cr tubing used in a high temperature and high pressure gas wells were analyzed by means of chemical composition analysis, mechanical performance analysis and microstructure observation. The results showed that there were a large number of dendritic cracks on the outer surface of the failed tubing, and the surface had a multi-layer corrosion product structure. The fracture belonged to stress corrosion cracking. Phosphate annulus protection fluid contaminated by drilling fluid was the main environmental factor leading to failure. The leakage of annulus protection fluid led to the formation of high casing pressure difference and thus caused high hoop tensile stress on the outer surface of the tubing, which was the main force factor leading to failure.