Modeling of the dynamic phenomena “stick‐slip” and “whirl” of a drill string demonstrator

Abstract

Vibrations of drill strings in oil and gas well bores can reduce drilling performance or lead to damage of drill string components. These vibrations are neither optically observable nor measurable because of the geological formation. Hence usually simulations are used to understand the dynamic behavior. The test stand “OSTrator” adds more insight to this problem. The demonstrator represents a scaled drill rig granting direct access to the complex dynamic behavior of the real drill string. Two phenomena are of special interest: the stick‐slip effect, a torsional oscillation, and the whirl effect, a periodic torsional‐lateral movement with permanent wall contact. Since the OSTrator was built for showcase purposes, it has to be piloted in and out Stick‐Slip and Whirl domains by a control algorithm. Therefore efficient multi‐body‐systems able to represent these two effects in faster than real time are demanded. In this presentation, the modeling of the stick‐slip and the whirl effect are discussed. The models should be able to predict these effects and supply data to avoid or confront them. Key questions are the modeling of the wall contact and the resistance at the drill bit. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)