LATERAL VIBRATION ANALYSIS OF DRILLSTRING USING FINITE ELEMENT METHOD

This project investigates lateral vibration of a drillstring under the action of weight on bit and drillstring rotation. The dominant cause of drillstring and bottom hole assembly’s failures, shocks and severe damages to borehole wall is recognized to be the lateral vibration. Thus, lateral vibration is chosen to be the only factor of interest and focused in this project. Lateral vibration manifests itself from the increased speed of rotary drilling. This study presents a finite element model using ANSYS software to investigate the lateral vibration of drillstring in a vertical well. The analysis proceeds in two stages. Firstly, modal analysis is performed to determine the natural frequencies of the drillstring and the second stage is to carry out harmonic analysis to obtain the frequency response at a varying length of drill pipe. Simulation is first carried out by simulating benchmark problem before proceeding to deal with the actual case studies by carrying out parametric study (drillstring length, weight on bit, rotational speed). The results show that increase in weight on bit increases the natural frequencies and hence changing the location of maximum amplitude in the harmonic analysis.