Test rig for analysis of friction damping in torsional excited systems

While drilling a wellbore, several types of vibrations exist that can lead to inefficient drilling. These are commonly subdivided into lateral, torsional, and axial vibrations. Especially in hard and dense formations, high-frequency torsional oscillations (HFTOs) are observed in the bottom-hole assembly (BHA). These HFTOs can lead to premature failure of components [1]. It has been shown that HFTOs are induced by a self-excitation mechanism caused by the bit-rock interaction [2].
Common self-excitation mechanisms are regenerative effects, mode coupling, or a velocity-weakening torque characteristic at the drill bit. One alternative to prevent the occurrence of torsional vibrations are bit design changes that influence the bit-rock interaction and the energy input into the system. This approach requires a very good understanding of the excitation mechanism. Another option is to increase the damping of the system, which affects the energy output during vibration. This is a well-known technique to reduce self-excited vibration amplitudes. This paper describes the investigation of a friction damper by experiment and simulation.