Analysis of Dynamic Behavior of Non-linear FE Model of Drillstring

In this research, dynamic behavior of non-linear finite element model of a drillstring is investigated. By considering total length of drillstring, a three-dimensional timoshenko beam element is employed. In addition the geometric stiffening effect, the added fluid mass and the contact between different parts of the drillstring and the borehole wall has been considered, with a complete model the effects of these factors have been analyzed separately. The equation of motion obtained and full order equations are used to drive the results. For the first time, a domain of drillstring that contact more possibility to occur in this domain is identified. The natural frequencies of the drillstring are evaluated and compared with the available commercial software results and recorded results for the actual drillstring. Coupling of vibrations of model is tested and the effect of linear and non-linear model in analysis of dynamic behavior and vibration of drillstring, especially in contact with the borehole wall and the effect of weight on bit change on the contact at stabilizers are analyzed and for the first time the contact time in each of stabilizers have been evaluated.