Axial Vibration Analysis on Drillstring

The problem of drill string vibration occurs in drilling operations and it will affect the usage life of drill pipe and drill bits. Three types of vibration, which are axial, lateral and torsional vibrations exist in the drill string. In order to being able to guide a drillstring in any direction, came the significant task of modelling the whole process mathematically and physically. This paper will study on the axial vibration in drill string by using finite element modelling analysis to observe the dynamic behavior of drill string under several conditions. The structure of drill string mainly consists of drill pipe, which is 80% of the total drill string length, drill collars which are used to provide additional weight and stabilize the drill string, and drill bit which are used for drilling operation. Due to vibrations, are costly. Sometimes these parts can break unpredictably, or the bits may be dull while drilling. When this situation occurs, the whole assembly of drillstring has to be pulled out of the well, to replace the damaged parts in order to continue the drilling process. Axial vibration will increase the risk of early fatigue of components such as bit life reduction, pipe fatigue and failure in drill string. In this project, finite element analysis method is used to find the modal and harmonic frequencies of drill string. Using real field data, a drill string model is designed using ANSYS simulation software. The case studies on drill string model include surface drilling, intermediate drilling, and slim hole drilling. Parametric studies of this project consists of three parts, which are the effect of drill pipe length on frequency of drill string, the effect of rotary speed on frequency of drill string, and the effect of Weight On Bit (WOB) on harmonic response of drill string. The simulation is expected to generate natural frequency of drill string under different depth and harmonic frequency of the drill string when subjected to axial force. Drill string dynamic behavior under influence of length, speed and force will be observed