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dc.contributor.authorSulaiman M. Abdullahen_US
dc.description.abstractDrillstring 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.en_US
dc.publisher Kuwait university - college of graduate studiesen_US
dc.subjectAxial Vibrationsen_US
dc.titleOil-Well Drillstring and Bit Failures Due to Torsional and Axial Vibrationsen_US
dc.contributor.supervisorProf. Andreas P. Christoforouen_US
dc.description.conclusionsBit failures due to severe axial and torsional vibrations were studied in this research. A dynamic model for representing the coupled axial and torsional vibrations of a drillstring equipped with a PDC bit driven by a top drive system was developed. The model is an extension and modification of an existing model for a drilling rig with a kelly system. The contact model used for the bit-formation interaction was modified to include rock breakage as a form of plastic deformation. The governing nonlinear differential equations were solved numerically, and the results were compared with previously published results and with limited field data. The results show that the elastic-plastic model predicts lower maximum WOB than the elastic model. Consequently, the bit-bounce can be more accurately predicted with the elastic-plastic contact model.en_US
dc.contributor.cosupervisorProf. Ahmet S. Yigiten_US
Appears in Programs:0630 Mechanical Engineering
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