Drill rig control systems are often not as well tuned nor as well behaved as expected. There can be substantial interaction between systems that is not recognized and is attributed to ‘difficult drilling’. This may only become obvious when supervisory control automation systems are added on top of the existing controllers.
This lecture shares some of the key findings on detecting, modeling, and correcting these issues, with particular attention on integrating drill string models with auto drillers, top drives, and active torsional damping systems. An unstable auto driller controller may induce stick-slip and lead to inefficient drilling and bottom hole assembly damage.
The torque limits set in the auto driller, top drive, and automation systems can also interact in ways that confound attempts to eliminate control instability. In general this interaction between controllers is not well understood by the industry and may not be recognized as a separate excitation mechanism for stick slip. Current best practices are shared to minimize the interaction of these three systems, but this is still an active area of discovery.
Simulation and rig trials have shown that this dysfunctional behavior can be mitigated by appropriate adjustments to the control system. Multiple systems have been designed that make these adjustments automatically and are now being deployed. In general, all control systems, not just drill rigs, can and should be modeled, monitored, and tuned to get the best performance of the system with unconditionally stable performance.