Vibration Analysis of Drill-String with Downhole Shock Absorption Intensifier

The shock absorption intensifier is a downhole drilling tool, which is utilized to generate high pressure water jet while suppresses the drill string vibration. Field tests have shown the improvement of rate of penetration and the protection of downhole tools after utilizing the intensifier. However, the performance of the downhole intensifier during the drilling operation has not been investigated quantitatively. In this paper, the downhole shock absorption intensifier type JZZY-1 is analyzed. This intensifier is designed to generate high pressure water jet to increase the rate of penetration while reduces the drill string vibration to avoid the premature failure of drilling tools. First, the mathematical model of the intensifier is built after analyzing its hydraulic system, and three working stages of the intensifier are identified. Then, the dynamic response of the intensifier is coupled to the drill string vibration. Specifically, the drill string vibration model is built using lumped mass method, where the intensifier is simplified as two of the lumped masses. Furthermore, the numerical algorithm is implemented using fourth order Runge-Kutta method, in which the intensifier status and bit-rock interaction are identified at each time step. Both the time and the frequency domain results show that the intensifier can reduce the drill string vibration significantly. In other words, this downhole intensifier harvests part of the drill string vibration energy to high-pressure water jet. The generated high-pressure water jet can reach up to 150MPa depending on the bottomhole geometry, the drilling parameters, the intensifier structures, and the size of the high-pressure waterjet nozzle. This research casts light on the design and field application of the downhole intensifier.