气体钻井用Φ139.7 mm钻杆DS55螺纹接头断裂原因分析

Analysis on DS55 Joint Fracture ofΦ139.7 mm Drill Pipe in Air Drilling

在采用气体钻井技术施工过程中,所使用的Φ139.7 mmDS55双台肩大水眼钻杆发生了外螺纹断裂事故。该钻杆是为深井、超深井降低钻井循环压耗进行水力优化开发的钻杆,钻杆接头外径为184 mm,内径为101.6 mm。在钻井液环境下具有良好的降压耗作用。对断裂外螺纹的断口形貌进行了宏观和微观分析,对该外螺纹接头材料的力学性能和金相组织进行了试验分析。结果表明,钻杆外螺纹接头材料符合API SPEC 5DP标准要求。对钻杆接头结构及承载力分析,水力优化的大水眼钻杆螺纹的抗拉和抗扭强度低于5 1/2 FH规格的API接头。由于该外螺纹接头在气体钻井中承受了较大的交变载荷,因而发生了疲劳断裂。

External thread joint fracture of aΦ139.7 mm DS55 double shoulder large water hole drill pipe occurred in the process of gas drilling.The drill pipe was hydrauliclly optimized for the deep well and ultra deep well to reduce the drilling cycle pressure consumption with outer diameter of 184 mm and inner diameter of 101.6 mm.Through the macro and micro analysis of the fracture morphology of the fractured thread as well as testing of mechanical properties and metallographic structure of the joint material,the drill pipe joint meets the requirements of API SPEC 5DP.Based on the analysis of the structure and bearing capacity of the drill pipe joint,the tensile and torsional strength of the thread of the hydrauliclly optimized large water hole drill pipe are lower than that of the 5 1/2 FH API joint.Large alternating load in gas drilling eventually led to fatigue fracture failure.