钻柱腐蚀疲劳寿命评价和影响因素分析

Evaluation and influence factors analysis on corrosion fatigue life of the drill string

摘要:

油气钻井过程中钻柱受力复杂，容易发生断裂情况，根据现场情况评价钻柱腐蚀疲劳寿命可以为钻柱安全使用提供依据。从现场实用角度，通过轴向力、循环应力和疲劳极限的计算，对比了基于疲劳系数、寿命百分数和旋转计数的钻柱疲劳评价方法，并考虑了腐蚀的影响。分析结果表明，当在严重狗腿度的井段钻进时，弯曲应力和屈曲增加将加快钻柱疲劳失效；当对应的机械钻速降低、转速增加时，钻柱的剩余使用寿命将进一步降低；当发生较严重的腐蚀时，钻柱剩余使用寿命将迅速降低。在高抗拉井段和狗腿度变化大的井段的钻柱应定期倒换使用，以保障现场钻具安全规范使用。

Abstract:

It is easy for drill string to be cracked when it is subjected to complex forces. Evaluating the corrosion fatigue life of drill string according to the actual situation on site can provide a basis for the safe use of drill string. By calculating the axial force， cyclic stress and fatigue limit of the drill string in the wellbore， the fatigue evaluation methods of drill string based on fatigue coefficient， drill string tension and rotation counting are determined， and the influence of acidic fluids is considered. The results show that the increase of the bending stress and buckling will lead to the fatigue failure of the drill string when drilled with severe dogleg. The remaining service life of the drill string will be greatly reduced when the corresponding ROP is reduced and the rotating speed is increased significantly. When severe acid corrosion occurs， the remaining service life of the drill string will be rapidly reduced. The drill strings in the well section with high tension and large dogleg should be regularly shifted to ensure the safe and normal use of drilling string on site.