井筒中钻柱系统非线性螺旋屈曲稳定性分析

NONLINEAR STABILITY ANALYSIS FOR HELICAL BUCKLING OF DRILL STRING IN WELLBORE

针对钻井过程中钻柱工作载荷或钻压超过某一临界值导致钻柱失稳现象,建立了钻柱非线性稳定性问题的分析模型,用数值分析的方法对整个钻柱系统的非线性屈曲过程进行了有限元仿真分析,解释了钻柱的失稳机理以及钻柱自重、钻压、转速、扭矩和井斜角等因素对钻柱屈曲的影响规律,研究了钻柱在井筒中发生屈曲时的位移、受力状况和各种工况下的失稳临界载荷。结果表明,在相同条件下钻柱螺旋屈曲临界载荷随井斜角增大而增大,呈非线性变化;临界载荷随扭矩的增大而减小,井斜角较大时临界载荷减小的幅度较小。对钻柱在井筒中的非线性屈曲行为研究和钻具组合设计的优化具有一定的参考价值。

Aiming at the instability phenomena of drill string in the process of drilling operation,the nonlinear drill string helical bucking model is set up.Also,the finite element analysis is presented with numerical method.The theory and the rule of drill string bucking influenced by dead load,rotating speed,weight on the bit and the well deviation are explained.It is shown that under the same conditions,the helical buckling load increases nonlinearly with the increase of the well deviation and decreases nonlinearly with the increase of torsion and the reduction decreases with the increase of deviation angle.From the analysis,the displacement and stress are objectively reflected when drill string buckling occurs in the well.The critical buckling load of drill string under various conditions is forecasted.For the study on nonlinear buckling of drill string,the optimization of BHA design and the reduction of drilling cost,there are both the theoretical and project practical significance.