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Title: Oil-Well Drillstring and Bit Failures Due to Torsional and Axial Vibrations
Authors: Sulaiman M. Abdullah 
Supervisor: Prof. Andreas P. Christoforou
Keywords: Axial Vibrations
Issue Date: 2017
Publisher:  Kuwait university - college of graduate studies
Abstract: Drillstring failures during oil drilling operations are costly because rig operations may be shut down and the process delayed. This causes cost increases due to damaged equipment and time spent on fishing operations when damaged equipment is lost in the hole. This study focuses on failures at the drill bit caused by vibrations, namely stick-slip and bit-bounce, as they are the most severe forms of axial and torsional vibrations. Existing mathematical models are expanded with an improved contact model at the bit for a top drive system. The simulation results obtained by numerical solution of the governing equations are compared with limited field data. Time responses from the simulations compare qualitatively very well with the data logs recorded at certain Kuwaiti fields. More importantly, the model results are in very good agreement with field data with respect to severity measures of stick-slip vibrations. In addition, correlations between bit-bounce vibrations and drillstring failures at the bit are established. It is shown that bit-bounce with larger impact forces than the fatigue thresholds cause bit failures. Tables are created that map the severe axial vibrations at a given drilling rotational speed and weight on bit These tables can be used as guidelines to avoid severe axial vibrations while drilling. A semi-empirical model that predicts the effects of bit wear is also developed, and the results are compared to field data. The research shows that the semi-empirical model can predict the wear effects on a bit and the rate of penetration with good accuracy.
Appears in Programs:0630 Mechanical Engineering

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