开窗侧钻对钻柱螺纹应力与密封性能的影响分析

Effect of Window Sidetrack Drilling on Thread Stressand Sealing Performance of Drill Strings

为分析开窗侧钻过程对钻柱螺纹接头强度与密封性能的影响,考虑螺纹在倒划眼和开窗侧钻时的工作状态,建立了钻柱螺纹接头三维有限元模型,分析了复杂载荷下螺纹接头应力和接触压力的分布规律,研究了不同材料和不同公差配合下螺纹接头的应力和密封性能,并与文献计算结果进行对比,验证了模型的准确性。研究表明:开窗侧钻时,螺纹接头受到的弯矩最大,主副台肩拉伸侧密封性能只有压缩侧的52.0%;倒划眼作业时,井口处钻柱受到的轴向载荷最大,外螺纹前两圈齿根应力超过屈服强度,存在断裂风险,主台肩面脱离、螺纹接头密封失效;随着材料弹性模量降低,螺纹接头在开窗侧钻时承受的弯矩减小,当材料弹性模量降至50.0%时,螺纹最大应力减小了17.0%,最小接触压力减小了19.6%;在极限公差下,螺纹接头主要由副台肩承受接触压力转变为主要由主台肩承受接触压力,副台肩应力得到改善,但密封性能完全失效。根据开窗侧钻过程中螺纹结构应力状态的研究结果,可通过改变螺纹材料和公差配合提高钻柱接头的安全性与密封性。

In order to analyze the influence of the window sidetrack drilling process on the strength and sealing performance of the threaded joints of the drill strings,a three-dimensional finite element model of the threaded joints of the drill strings was established by considering the working state of the threads in the inverted hole redressing and the window sidetrack drilling.The distribution laws for the stresses and contact pressures of the threaded joints under the complex loads were analyzed,and the stress and sealing performance of the threaded joints with different materials and under different tolerance fits were discussed.The accuracy of the model was verified by comparison with the calculation results in a literature.The study shows that during window sidetrack drilling,the threaded joint is subjected to the maximum bending moment,and the sealing performance of the tension side of the main and auxiliary shoulders is only 52%of that of the compression side.The drill string is subjected to the maximum axial load at the wellhead during inverted hole redressing,and the stresses of the root of the teeth of the first two turns of the external threads exceed the yield strength,so there is a risk of fracture.The main shoulder surface is detached,and the sealing of the threaded joint is not effective.As the elasticity modulus of the material decreases,the bending moment of the threaded joint during window sidetrack drilling is smaller.When the elasticity modulus of the material decreases to 50%,the maximum stress of the thread is reduced by 17%,and the minimum contact pressure is reduced by 19.6%.In the limiting tolerance,the threaded joint is changed from the auxiliary shoulder bearing the main contact pressure to the main shoulder bearing themain contact pressure, and the stress on the auxiliary shoulder is improved, but the sealing performance is completelyinvalidated. According to the study on the stress state of thread structure during window sidetrack drilling in this paper,the safety and sealing performance of the drill string joint can be improved by changing the thread material andtolerance fit.