Using Active Circuits to Model Drillstrings and Analyze the Effect of Phase Shift on Stability Analysis

In recent years, deeper wells are drilled in order to reach untapped reserves. The long drillstrings needed for such wells are more susceptible to vibrations induced by instability. To study these vibrations, test rigs are employed. These rigs must represent the dynamics of the drillstring to be effective at predicting bit vibrations. In this paper, we show that active circuits can be used to simulate drillstring dynamics and study bit vibration characteristics. A circuit representing one such vibration mode was used to study the effect of phase shift on bit stability. It is also shown that such circuits can be incorporated in test rigs to provide real-time input to actuators replicating bit displacement.