Cause analysis and precautions of drilling tools failure during gas drilling in Puguang gas field

The drilling speed of the upper terrestrial formation in Puguang gas field has been increased remarkably, however, drilling tools failure occurs frequently. As a result, the drilling speed is influenced, and the downhole safety can not be guaranteed. At first, the failure rules are found out through statistical analysis. It is referred that the drilling pipe failure belongs to fatigue and corrosive fatigue fracture, while the drill collar failure is fatigue fracture. Then some preventive measures including using an air hammer, strengthening drilling tools flaw detection, optimizing bottomhole assembly and drilling parameters, preventing drilling tools corrosion, and strengthening the detection of the vibration of drill pipes are proposed, based on analyzing the causes of drilling tools failure, such as the self-factors of gas drilling, the movement of drill pipes（including rotation and vertical covibration）, the corrosion of drilling tools, the drilling way, and the insufficient flexural strength of drill collars. It is pointed out at last that the research and application of the micromechanism of drilling tools failure, the movement of drill pipes and kinematics, the erosion of drilling tools caused by cuttings, the corrosion of drilling tools, and the prevention of drill pipes rotation should be strengthened. As well overall analysis and prevention of drilling tools failure should be intensified.