A contribution to efficient calculation of complex drill string dynamics for deep hole drilling

Abstract

This paper presents a hybrid model to describe drill string dynamics for deep hole drilling. Generally, a typical rotary drill string has a length of several kilometers, but the diameter is less than half a meter. Due to the large ratio of length to diameter, a drill string is a very flexible system. Consequently, an operating drill string is always affected by axial, torsional and lateral vibrations, which potentially induce serious failures. In order to avoid fatal defects, simulations to forecast vibrations are necessary. The simulation should be capable to exhibit the complex dynamical phenomena, e.g. sick‐slip, forward whirl and backward whirl, and interactions between drill string and borehole. Usually, these simulations are very time‐consuming. In this work, a hybrid model consisting of lumped masses connected with weightless beam elements representing the drill string is developed. The interaction between the drill string and the borehole is implemented by unilateral constraints to describe the nonlinear contact behavior. It was shown that accuracy and simulating time were improved by this model with respect to classical finite‐element models. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

On the Wellbore Contact of Drill Strings in a Finite Element Model

“…In the second step, we variate the potential energy of wellbore wall and solve this integration in a third step with Gauss-Legendre-Integration. Later, we can derive the nodal reaction force and the bending moment from equation (2).…”

“…The interaction between the drill string and the wellbore causes impacts and several dynamical phenomena [1] [2]. To understand what happens down hole, Finite Beam Elements were frequently utilized for modeling the drill string and penalty functions were implemented to describe the contact problem between drill string and wellbore.…”

“…This is contrary to the requirements of users in research and industry. Furthermore, it is known that Gaussian points can be utilized in FEM for contact problems [2]. In this paper a process for modeling the contact problem between the drill string and the wellbore with Gaussian points along the elements will be introduced.…”