Stick-slip Whirl Interaction in Drillstring Dynamics

TLDR

The study aims to explain the complex behavior of drillstring motion involving torsional stick‑slip and lateral whirl vibration. The authors present a simplified, discontinuous Stick‑Slip Whirl Model comprising separate submodels for whirling and stick‑slip motion of a drillstring confined in a borehole with drilling mud. Experimental data indicate that drilling mud fluid forces drive the observed phenomena, and bifurcation analysis of the model shows discontinuous transitions where stick‑slip vibration vanishes as whirl appears, matching full‑scale rig results.

Abstract

Abstract This paper attempts to explain the complicated behavior of oilwell drillstring motion when both torsional stick-slip and lateral whirl vibration are involved. It is demonstrated that the observed phenomena in experimental drillstring data could be due to the fluid forces of the drilling mud. A Stick-slip Whirl Model is presented which consists of a submodel for the whirling motion and a submodel for the stick-slip motion, both as simple as possible. The Stick-slip Whirl Model is a simplification of a drillstring confined in a borehole wall with drilling mud. The model is as simple as possible to expose only the basic phenomena but is discontinuous. Bifurcation diagrams of this discontinuous model for varying rotation speeds reveal discontinuous bifurcations. The disappearance of stick-slip vibration when whirl vibration appears is explained by bifurcation theory. The numerical results are compared with the experimental data from a full-scale drilling rig.