典型载荷下钻具接头螺纹强度分析

Analysis on Thread Strength of Tool Joint Under Typical Loads

钻具接头在使用中存在连接强度不够和抗扭性能不足等问题,进而易发生黏扣、胀扣、滑脱以及断裂等故障。采用ABAQUS有限元模拟方法对不同钻具螺纹形式,在上扣扭矩载荷或复合载荷(拉伸、扭转、弯曲)作用下进行强度分析;同时对某井失效钻铤样品进行宏观形貌、理化性能、微观形貌及弯曲强度比等分析。分析结果表明:钻具接头螺纹在上扣扭矩(25.79 kN·m)或复合载荷作用下,靠近台肩处螺牙应力水平较高,长期井下使用易对接头造成破坏;螺纹锥度、长度的变化将对接头连接强度产生较大不利影响,而应力减轻结构对于提高接头强度、延长钻具使用寿命具有显著意义。失效钻铤分析结果同样表明,在使用过程中钻铤螺纹选用不合理,导致螺纹型式不匹配,从而产生应力集中,造成钻铤接头螺纹断裂。研究结果可为钻具螺纹的合理使用提供理论依据。

There are some problems such as insufficient connection strength and torsional resistance when the tool joint is in service,thus leading to troubles like thread sticking,expanding,slipping and breaking.In the paper,the ABAQUS finite element simulation method was used to analyze the strength of different tool thread forms under the action of make-up torque load or composite load(tension,torsion,bending),and investigate the macroscopic morphology,physicochemical properties,microscopic morphology and bending strength ratio of a failed drill collar sample of a well.The results show that under the action of make-up torque(25.79 kN·m)or composite load,the stress level of the thread near the shoulder of the tool joint is relatively high,and long-term downhole service easily damage the joint.The changes in thread taper and length have great adverse effects on the connection strength of the joint,while the stress relieving structure has obvious significance in improving joint strength and prolonging the service life of drilling tools.The analysis results of failed drill collar also show that the irrational selection of drill collar thread leads to mismatched thread type,thus resulting in stress concentration and then the breaking of drill collar joint thread.The research findings provide theoretical basis for the rational use of tool thread.