Study of Passive Vibration Assisted Rotary Drilling Tool with the Help of Bold Graphs

—The use of passive-Vibration Assisted Rotary Drilling (p-VARD) tool to improve drilling performance has been experimented and well documented in many occasions. In addition to increasing the Dynamic Downhole Weight on Bit (DDWOB), the use of this tool has also reported in improvement in the drilling rate of penetration. The works until now are limited to experimental studies and lack the explanation as to how it actually works. Theoretically, adding a p-VARD tool increases the compliance of the drill string in an axial direction allowing the drill bit to oscillate axially. In this paper, a mass-spring-damper bond graph model of p-VARD tool is built in 20-Sim. The spring is modelled with the help of Almen-Laszlo’s load-deflection equation for Belleville springs and the damper is modelled as neoprene rubbers with moderate damping ratio. The bit-rock interaction is represented in the form of a source of flow providing sinusoidal displacement to the drill bit and the oscillating portion of the p-VARD tool. A parametric analysis of the drilling system consisting of a pVARD tool shows that the resonating frequency of the system can be lowered to a workable range with the help of this tool thus allowing it to resonate and amplify the impact generated. Similarly, this modeling tool also enables us to study the parameters which may flatten the Belleville springs. A stack of flat springs is as stiff as the rigid drill string and this terminates the impact generated by the resonance. Results show that spring and damper inside the p-VARD tool can be tuned to be operated at different Weight on Bit (WOB) and excitation parameters.