Research progress and prospects in nonlinear dynamics of drillstring with high slenderness ratio

Abstract:

When the slenderness ratio （L/D） of a drillstring exceeds 50000， it exhibits high flexibility and pronounced nonlinear characteristics. The coupled axial， lateral， and torsional vibrations easily induce issues such as stick-slip， whirling， and parametric resonance， severely compromising the drilling safety and efficiency of ultra-deep wells. Focusing on the dynamic challenges induced by the extreme geometric features of high-slenderness-ratio drillstrings， this paper systematically reviews their nonlinear vibration characteristics， dynamic modeling methods， vibration control strategies， and engineering application challenges. The review indicates that geometric， boundary， and friction nonlinear couplings exist among the axial， lateral， and torsional vibrations， inducing complex phenomena such as the coexistence of forward and backward whirling and stick-slip multi-stability； the finite element method and geometrically exact beam theory prioritize high-fidelity characterization but incur high computational costs； model order reduction and data-driven methods improve computational efficiency， yet the simplification of wave propagation effects requires careful handling； experimental validation is key to model verification， but extrapolation from scaled models to full-scale conditions remains challenging. Currently， research still faces three major scientific problems at the theoretical level： multi-modal energy transfer mechanisms， state-dependent time-delay dynamics， and bifurcation theory of non-smooth systems. At the engineering level， it is urgent to overcome core difficulties such as efficient full-wellbore prediction and dynamic evaluation of extended-reach limits. In the future， this field will evolve towards intelligent dynamics integrating multi-physics coupling， stochastic reliability analysis， data-driven approaches， and digital twins， providing solid scientific support for enhancing the safety and economic performance of ultra-deep geological resource development.