含表面双裂纹的钻杆管体断裂性能研究

Study on fracture behavior of drill pipe bodywith surface double cracks

钻杆刺漏是钻杆在服役过程中最常见的失效形式,而钻杆表面裂纹的扩展是钻杆发生刺漏的直接原因。为更有效地评估钻杆表面含有多条裂纹时的安全性能,以某超深直井G105钻杆井口段为研究对象,建立管体外表面双裂纹有限元模型,分析了拉扭载荷下裂纹间距、次裂纹尺寸以及走向对环向主裂纹前缘J积分的影响。结果表明:轴向排列的环向次裂纹是相对最安全的,可大幅消减钻杆主裂纹前缘的J积分;环向排列的环向次裂纹相对最危险,可大幅增大钻杆主裂纹前缘的J积分;轴向次裂纹可增大钻杆主裂纹前缘或部分前缘的J积分,但增幅相对环向排列的环向次裂纹来说要微弱得多。次裂纹对主裂纹前缘J积分的影响强度随两裂纹间距的增大或次裂纹尺寸的减小而减小。因此在对含表面双裂纹的钻杆进行分析时,在次裂纹尺寸较大且距离较近的情况下应考虑次裂纹的影响;在次裂纹尺寸较小或距离较远时则可忽略次裂纹,将模型简化为单裂纹钻杆模型进行分析。

Drilling pipe leakage is the most common failure form of drilling pipe in service,and the expansion of surface crack of drilling pipe is the direct cause of drilling pipe leakage.In order to evaluate the safety performance of drill pipe with multiple cracks on the surface,a finite element model of double cracks on the surface of drill pipe was established by taking the wellhead section of G105 drill pipe of an ultra-deep vertical well as the research object.The effects of crack spacing,crack size and strike on the J-integral at the leading edge of the circular main crack under tensile and torsional loading were analyzed.The results show that the circumferential secondary cracks arranged in the axial direction are relatively the safest,which can greatly reduce the J-integral of the leading edge of the main crack.The circumferential secondary cracks arranged in the circumferential direction are the most dangerous,which can greatly increase the J-integral of the leading edge of the main crack.The axial secondary cracks can increase the J-integral of the leading edge or part of the leading edge of the main crack in the drill pipe,but the increase is much weaker than that of the circumferential secondary cracks.The influence intensity of secondary cracks on the leading edge J-integral of the main crack decreases with the increase of the distance between two cracks and the decrease of the size of secondary cracks.Therefore,the influence of secondary cracks should be considered when the size of secondary cracks is large and the distance between them is relatively close.When the size of the secondary crack is small or the distance is long,the secondary crack can be ignored,and the model is simplified to a single-crack drill pipe model for analysis.