超深水平井钻柱动力学研究及强度校核

超深井钻井过程中钻具失效事故频繁发生，钻柱动力学特性研究对增加钻具安全性具有重要作用。考虑真实井眼轨迹、钻头与地层相互作用、钻柱与井壁接触及钻井液黏滞作用等因素的影响，建立了全井钻柱动力学特性仿真模型，模拟了不同钻压及转速下钻柱不同截面轴向力、扭矩、位移及等效应力等随时间的变化，采用第四强度理论计算了井口钻具的安全系数，校核了超深水平井钻具强度。分析结果表明，井口轴向力和等效应力表现为低频变化，MWD处等效应力和加速度表现为高频振动且其横向振动比轴向振动更加剧烈；在钻压和转速较小的情况下，钻压和转速对井口轴向载荷、井口扭矩、井口等效应力及井口安全系数影响不大；MWD处等效应力随钻压的增加而增大，其横向加速度随转速的增加幅值显著增大；对于井深超过8 000 m、井眼尺寸φ120.65 mm及φ114.3 mm的G105钻杆，动力学分析得到的井口安全系数大部分时间内在1.2附近波动，钻具总体是安全的。

The Dynamics Characteristics and Strength Check of Drilling String in Ultra-deep Horizontal Well

Drilling tools failure of occurs frequently in the process of ultra-deep well drilling. Therefore, the research on the dynamic characteristics of drilling string plays an important role in the safety of drilling tools. Considering the influence of the real well trajectory, the interaction between bit and formation, the contact between drilling string and borehole wall and the viscous effect of drilling fluid, a simulation model of the whole well drilling string with dynamic characteristics is established. Under different WOB and rotation speed, the changes of axial force, torque, displacement and equivalent stress over time are simulated. The fourth strength theory is used to calculate the assurance coefficient of the wellhead drilling tools and check the strength of the drilling tools in ultra-deep horizontal wells. The results show that the wellhead axial force and equivalent stress display a characteristics of low-frequency change, while the equivalent stress and acceleration at MWD are high-frequency vibration, and the lateral vibration is more severe than the axial vibration; when WOB and rotation speed are small, WOB and rotation speed have little influence on the wellhead axial load, torque, equivalent stress and assurance coefficient; the equivalent stress at MWD increases with the increase of WOB, and the amplitude of lateral acceleration increases significantly with the increase of rotation speed. When the well depth is more than 8 000 m, the hole size is φ120.65mm, and G105 φ114.3 mm drill pipe is used at the wellhead, the wellhead assurance coefficient obtained from dynamic analysis will fluctuate around 1.2, so generally the drilling tool is safe.