On the reduction of self-excited high-frequency torsional oscillations in drilling applications

Due to the slim design of the drill string, unwanted vibrations occur during deep drilling for fossil deposits or geothermal energy. In particular, self-excited high-frequency torsional oscillations can reduce drilling progress and component lifetime. In order to identify ways to reduce these critical vibrations, a method is developed that uses downhole measurement data to determine the energy flow and thus the nonlinear torque characteristic at the bit. This allows quantification of the excitation to identify stable and unstable operating parameters and optimize drilling progress. Using the characterized excitation mechanism, a method is developed to predict the long-term dynamic response of the self-excited drill string by identifying the dominant self-excited mode. The results are used to investigate various damping mechanisms for their applicability in drilling systems. Taking into account drilling-specific effects such as a large number of critical self-excited modes and changing boundary conditions, as well as other constraints such as limited installation space and power supply, damping mechanisms of different complexity are investigated in more detail. Special attention is given to the achievable damping and the associated stability of drill string modes. The simulation results and analytical solutions of the different dampers are validated using a test rig specifically designed to test the effectiveness of the different dampers considering underground conditions. Using these findings, different optimization strategies for the positioning of the dampers within the drill string are discussed. Finally, the damper prototype developed in cooperation with the company Baker Hughes is presented, proving the suitability of the conducted investigations.