Nonlinear Drillstring-Dynamics Modeling of Induced Vibrations in Unconventional Horizontals

Inducing vibrations while drilling is a relatively new concept that shows promise in directional applications. Instigating motion of the drillstring, particularly in the sections lying on the low-side of the wellbore, can lead to substantial improvements in managing the two limiting factors of the long horizontal wells that are typically associated with current unconventional shale plays: removal of formation cuttings from the borehole and frictional drag between nonrotating drillstrings and the wellbore wall. Minimizing these effects by introducing controlled vibrations increases the overall drilling efficiency and reduces the cost associated with the well. The difficulty in implementing such actions, however, is consistency. Because the behavior of drilling assemblies is inherently nonlinear, it has been difficult in the past to reliably predict their response to dynamic events. This, in turn, creates a challenge when trying to optimize the performance of arbitrary vibration-inducing devices (VIDs). This study presents a detailed analysis of the fully coupled, 3D, nonlinear behavior of drillstrings under the action of induced vibrations. Specific focus is given to the dynamic characteristics of a drillstring, during horizontal-drilling operations, in long unconventional wells and how this behavior affects the success of the well. The response of the drillstring, due to induced axial and lateral oscillatory motions, is examined through linearized dynamic analysis and nonlinear time-domain simulations. Solutions obtained from the study provide a clearer understanding of the dynamics experienced downhole and lead to suggestions for improved practices when drilling with lateral VIDs, particularly with regard to hole cleaning. Further insights into the sliding behavior of the drillstring, during the use of these types of tools, are drawn from animated modeling results. Finally, the future applications of this technology are discussed.