Reason Analysis on Fracture of the Internal-threaded Drill Collar Joint of One Oil Field

In order to find out the fracture reasons of the internal-threaded drill collar joint in the drilling process and prevent such fracture accident happening again, chemical composition analysis, mechanical properties testing, fracture analysis and metallographic analysis were done to the drill collar joint. The results show that: the larger borehole curvature and the ratchet behavior led to the fatigue fracture of the drill collar in the process of drilling.