Cause Analysis of Tubing Fracture in Ultra-deep Well

Based on fracture morphology，physical and chemical properties，microstructure and energy spectrum analysis of the corrosion by product，the causes of cracking for tubing in a oil well were analyzed.The results show that the chemical composition and physical and chemical properties of the tubing meet the entrusted technical agreement. The fracture of the tubing is mainly caused by excessive tensile load.The deformation load caused by changes in temperature，pressure，and other factors of the downhole fluid causes the downhole tubing to bear higher tensile loads.When the ultimate tensile strength of the tubing is exceeded，the tubing ultimately undergoes yield fracture.In order to prevent the reoccurrence of the accident in the future，it is suggested to optimize the design of the selection of the tubing wall thickness，the depth of the packer，and the material and specification selection of the upper casing.