某井φ101.6mm G105钻杆刺穿原因分析

Cause Analysis on Piercing of the φ101.6mm G105 Drill Pipe in a Well

某公司在钻井作业时发生一根φ101.6mm×8.38mm G105钢级钻杆刺穿失效事故。采用直读光谱仪、拉伸试验机、光学显微镜、扫描电镜、能谱仪等设备对刺穿钻杆的化学成分、力学性能、显微组织以及断口等进行了分析,并且结合钻井过程中的实际井况对钻杆进行了刺孔腐蚀机理分析、加厚过渡带有限元分析。结果表明:此次钻杆刺穿为早期腐蚀疲劳失效,疲劳裂纹起源于钻杆加厚过渡带消失区域内壁的腐蚀坑底部;失效钻杆没有内涂层,钻杆钻进过程中,在交变载荷的作用下于应力集中的加厚过渡带消失区域腐蚀坑底部萌生腐蚀疲劳裂纹,裂纹不断扩展最终造成刺穿失效。最后根据此次钻杆产生早期腐蚀疲劳裂纹的原因提出了相应的改进建议。

Piercing failure accident happened to a Ф101.6 mm × 8.38 mm G105 steel grade drill pipe during drilling operation in a company.The chemical compositions,mechanical properties,microstructure and fracture surface of the pierced drill pipe were analyzed by direct reading spectrometer,tensile machine,optical microscope, scanning electron microscope and energy spectrometer.And combined with the actual well condition during the drilling operation,the piercing corrosion mechanism of the drill pipe and the finite element analysis of the thickened transition zone were analyzed.The results show that the piercing of the drill pipe was an early corrosion fatigue failure,and the fatigue cracks originated from the bottom of the corrosion pits at the inner wall of the drill pipe where the thickened transition zone disappeared.The failure drill pipe had no inner coating,and under the action of .the alternating load,corrosion fatigue cracks originated from the bottom of the corrosion pits of the stress concentrated thickened transition zone disappearing position.The cracks continued to expand and eventually caused the piercing failure.Finally,according to the reasons of the early corrosion fatigue of the drill pipe,the corresponding improvement suggestions were put forward.