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石油钻柱在钻进过程中,工作环境恶劣,在井位、地质条件及钻进参数等综合因素的影响下,不仅承受着由交变载荷引起的应力突变,还承受着钻具涡动和振动引起的巨大冲击载荷。钻柱在井下既自转又反转,尤其在斜井或大环歇井中时,偏心反转和工作载荷产生的较大交变弯曲应力常造成钻柱疲劳破坏。为此,文章在用动力学观点初步分析了钻柱失效机理的基础上,应用断裂力学等相关知识,对钻柱进行了三轴应力分析,并提出了考虑钻柱进动与反进动的疲劳寿命计算模型。该模型能反映运动状态对寿命的影响,可用于无裂纹钻杆和有裂纹钻杆疲劳寿命预测,计算结果对钻柱的合理使用及预防钻柱失效有较好的指导意义。

PREDICTING FATIGUE LIFE IN CONSIDERATION OF DRILL STEM MOVEMENT BEHAVIOURS

Because drill stem can be not only normally but also reversely rotated at downhole,especially in slant hole or large annular slant hole,a great alternate bending stress produced by eccentric reverse rotating and working load can often make the drill stem′s being damaged owing to fatigue.On the basis of initially analyzing the drill stem failure mechanism from a dynamic point of view,the triaxial stress analysis is carried out for the drill stem and a model of calculating fatigue life in consideration of the precession and reverse precession of the drill stem is set up in the paper.The model may be used for the fatigue lift prediction of both cracked drill pipe and crackfree drill pipe,being able to reflect the influence of movement behaviours on life and its calculation result is of good guiding significance to utilizing reasonably the drill stem and preventing the drill stem from failure.