Dynamic Analysis of Drillstring with Downhole Vibration Absorption Intensifier

Summary

Drilling vibration contributes largely to the premature failure of drillstring. The vibration absorption intensifier is a downhole drilling tool that suppresses the drillstring vibration while generating a high-pressure water jet. Previous studies have demonstrated its vibration suppression effect through experiments and its high-pressure water jet generation through computational fluid dynamics. Those field tests further demonstrated a longer service life of bottomhole assemblies (BHAs) and an improvement in the rate of penetration (ROP). However, the performance of the intensifier and its influence on the drillstring dynamics have not been investigated quantitatively. In this paper, we first derive a mathematical model for the intensifier and identify three working stages. We then couple the intensifier model with the drillstring lumped mass model and implement a numerical integration based on the fourth-order Runge-Kutta method, in which we check the intensifier status and bit/rock interactions at each integration timestep. The undertaken analyses in the time and frequency domains confirm that the intensifier can suppress the drillstring vibration and stabilize the weight on bit (WOB), while the generated high-pressure water jet can reach up to 132 MPa depending on the bottomhole geometry, the drilling parameters, the intensifier structures, and the size of the high-pressure waterjet nozzle. As such, this paper casts light on the vibration suppression of the drillstring and provides theoretical support to the field application of the intensifier.