基于“S”形井钻具疲劳破坏的钻具设计

Drill Tool Design Based on Fatigue Failure of BHA in S-shaped Well

在"S"形复杂轨迹井眼中,井眼弯曲会对钻具产生疲劳破坏,从而严重影响钻具的寿命。鉴于此,对"S"形井钻具组合进行力学分析,并计算井眼曲率限制下的最大轴向拉力及复合应力下钻具的疲劳系数,分析及计算结果表明:存在较大井眼曲率的上部井段,在钻具设计时既需要尽量减小疲劳系数,还需考虑到井眼曲率下部钻具的拉力对钻具失效的影响。以南堡3-35井为例对钻压、钻具刚性及钻具组合等进行优化和调整后,可以将钻具的疲劳系数控制在合理范围,使现场"S"形井眼钻具失效事故率大幅度降低。研究结果为"S"形井钻具安全提供了理论和技术支持。

Wellbore curvature can cause fatigue damage to BHA in the S-shaped complex trajectory borehole, which could seriously impact the life of drilling tools. In view of this, BHA in the S-shaped wellbore has been mechanically analyzed. The maximum axial tensile force under the borehole curvature and the fatigue coefficient of the drilling tool under the combined stress has been calculated. The analysis and calculation results show that, it is necessary to minimize the fatigue coefficient in the design of the drilling tool in the upper well section of large borehole curvature wellbore, and to take into account the effect of the pulling force of the drilling tool in the lower well section on the drilling tool failure. Taking Well Nanpu 3-35 into as case study, after optimizing and adjusting WOB, drill tool rigidity and BHA, the fatigue coefficient of the drill tool can be controlled within a reasonable range to significantly reduce the failure rate of the drill tool in S-shaped wellbore. The study results could provide theoretical and technical support for the drill tool safety of S-shaped well.