Analysis on Downhole High-Frequency Torsional Oscillation of Bottom Hole Assembly

High-frequency torsional oscillation(HFTO)has seriously affects the safety and reliability of drilling tools.In order to clarify the mechanism of HFTO and formulate a reasonable and reliable vibration reduction strategy,the data collected from the new near-bit gauging nipple in the wellbore were processed and interpreted,and the frequency and amplitude of HFTO in the wellbore as well as the coupling effect of stick slip and HFTO were analyzed.Then,the ANSYS dynamic analysis module was used to build a simplified analysis model of BHA,and modal analysis module was used to solve the natural frequency and oscillation mode of torsional vibration of drilling tools.Finally,on the basis of modal analysis,the harmonic response analysis was carried out; and by means of applying different cyclic active forces to simulate the weight on bit and torque,the torsional vibration response of the drilling tool was obtained.The study results show that the modal analysis results are consistent with the actual drilling situation.The harmonic response analysis shows that HFTO is more sensitive to the torque at the bit,and it can be alleviated by reducing the torque.The study results provide theoretical guidance basis for the design of BHA and the optimization of drilling parameters,so as to reduce the damage of HFTO to drilling tool.