Abstract:

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.

Key words: drill string, stability, helical buckling, critical load, finite element