Drilling Dynamics Model to Mitigate High Frequency Torsional Oscillation

Abstract

Abstract In recent years, the phenomenon of drill string torsional oscillation at frequencies over 50 Hz has been well documented. This high frequency torsional oscillation (HFTO) creates cyclic fatigue loading on bits and drilling tools within the bottom hole assembly (BHA) and thus limits tool life and drilling performance. However, few models exist which can predict occurrence of HFTO and its severity. To our knowledge; none of these models consider the entire drilling system including the bit-rock interaction, downhole drive(s), BHA design, and surface drilling parameters, and hence there is a need to develop a system model for HFTO mitigation. A 3D transient drilling dynamics model has been extended to study the severity of HFTO and cyclical loading to drilling tools. The accuracy of the model was validated by theoretical calculation, and high frequency downhole data. An example analysis was conducted to evaluate drilling system design performance in terms of HFTO risks. Good correlation was found between the analysis and field data collected from the Permian Basin. Advanced models were developed for mud motors and rotary steerable system (RSS) tools. After conducting a full drilling simulation, the drilling system behavior under HFTO can be fully described. Cyclical torque loading of differing magnitudes and frequencies were observed for different BHA components depending on HFTO vibration mode, HFTO severity and BHA design. PDC cutters were subjected to different cyclical loading depending on bit design, formation and HFTO conditions. The mud motor power section was found to undergo high frequency cyclical loading which could accelerate its rubber degradation. Since the failure of PDC cutters and the degradation of mud motor power sections have a critical effect on drilling performance, the importance of mitigating HFTO cannot be underestimated. By evaluating the loading conditions, an optimized drilling system can be selected. Field data has proved the validity of this approach. The methodology presented in this paper offers a new way for the industry to systematically mitigate HFTO by considering the rock drilled, bit design, mud motor utilized, the mechanics of RSS and other tools in the BHA, as well as drilling parameters. The usage of this approach can reduce premature drilling component failure and improve drilling performance, especially in the high energy drilling applications found in North America Land and other areas.