Analysis on Fracture Cause of S135 Drill Pipe in Horizontal Well

The rupture accident of one S135 drill pipe happened during mud circulating in horizontal well. In order to find out the fracture cause, an investigation was conducted and failure analysis was performed based on fracture analysis, chemical composition analysis, mechanical property testing, metallographic examination and so on. The results showed that the overall angle change rate of the accident well section was large, and the failure drill pipe was severe wear and scratched where fatigue cracks were formed, then under the torque and tensile loads, the drill pipe ruptured from fatigue cracks.