定向井钻柱稳定性分析

在定向深斜井钻探中,一般采用钻铤和加重钻杆的浮重大于钻压的原理,来保持钻柱的稳定.但钻杆会因此承受过大的扭矩和拉力,加速早期疲劳失效.为此,基于斜井中井眼对钻杆具有弹性支承和约束的理论,通过定向井井眼尺寸及井斜角对钻柱稳定性影响分析,讨论保持钻杆稳定的边界条件和确定其底部钻铤柱的设计原则.结果表明,当井斜角大于45°时,有意让钻杆处于受压且不失稳状态下运行,既可使底部钻铤柱得以优化设计,又可大幅度地减少底部钻铤重量从而减小作用在钻杆上的扭矩和拉力,延长其使用寿命.

Stability Analysis of Drill-String in Directional Drilling

In deviated deep hole directional drilling operation, drill collar and heavy drill pipe are used to provide enough weight on bit in order that penetration of rock can be conducted and drill-string stability can be maintained. However, as a result, this practice usually puts overloaded torque and tension force on the drill-string and hence results in early fatigue failure of drill-string. Based on the elastic deformation and stability analysis of the bottom hole assembly of drill-string, a discussion on the critical condition to keep drill-string in stabilization and the planning criterion to determine bottom hole assembly is presented . Optimized planning of BHA can be achieved by making the drill pipe partially work in compression state, which may considerably reduce the torque and tension force on the drill-string with the weight reduction of drill collar, and therefore reduce the failure possibility of drill-string.