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Review ListSimultaneusly Analysis of Torsional and Lateral Vibrations of Drillstrings using Cylindrical Superelement
Ghorbani, Shokrollah | 2013
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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 44975 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Ahmadian, Mohammad Taghi; Firoozbakhsh, Keikhosrow
- Abstract:
- One of the most important parts of oil industry is drilling with rotating drillstrings. In a drillstring because of the contact between bit and formation, contact between drillstring and borehole wall, existence of drilling mud, misalignment in drillstring and stick-slip phenomenon; axial, lateral and torsional vibrations is created. These vibrations may lead to fatigue failures and abrasive wear of tubular, damaging the drill bit and borehole wall. In this thesis the drillsting vibrations is studied using finite element method. To this end, cylindrical superslement with C1 continuity is presented. By using the shape functions of this superelement; kinetic and potential energy of drillstring and work done by external forces on drillstring is calculated. In this modeling the drillstring weight, centrifugal force due to rotation of drillstring, contact between drillstring and borehole wall, the stick-slip phenomenon and frictional, hydrodynamic and inertial forces due to the mud flow is considered. Using Galerkin method, the effect of mud flow is appeared as mass, damping and stiffness matrices. In order to modal analysis and calculating time response of drillstring, a computational finite element code is developed. Obtained results show that the mud flow acts as an added mass as well as a damper, and decreases the natural frequencies¬ and vibration amplitude of drillstring.Also, when the rotational speed of drillstring is increased, the stick-slip phenomenon becomes negligible. Very good agreement is found between findings with implementing superelement and those were reported in the literature. Also it is found that the time consumption by conventional finite element method for the same problem, in comparison with implementing cylindrical superelement is very larger. This indicates by implementing a few cylindrical superelements, the same results in much smaller computer time than the conventional finite element method, can be extracted
- Keywords:
- Drill String ; Torsional Vibration ; Lateral Vibration ; Cylindrical Superelement ; Finite Element Method
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