Systems and methods for torque unwind

A control system for controlling a release of torque from a drill string, the control system comprising:

• a processor connected to one or more control systems of a drilling rig enabled to drill a borehole;
• and
• a memory connected to the processor, wherein the memory comprises instructions for performing operations comprising:
• receiving an indication that torque in a drill string coupled to a top drive is to be released, the top drive coupled to a variable frequency drive (VFD) adapted to operate in at least two modes of operation, wherein a first mode regulates speed of the top drive based on a speed limit and a second mode regulates torque of the top drive;
• responsive to the indication, stopping operation of the top drive;
• determining, by the one or more control systems, a direction for rotating the top drive to release the torque in the drill string;
• determining, by the one or more control systems, the speed limit for rotating the top drive to release the torque in the drill string;
• transition the VFD from the first mode to the second mode;
• determine a torque value for the top drive;
• and
• rotating the top drive in the direction and at the speed limit determined by the one or more control systems until a torque value or speed value falls below a threshold value.

A method of releasing torque from a drill string, the method comprising:

• receiving an indication to initiate release of torque in a drill string coupled to a top drive, the top drive coupled to a variable frequency drive (VFD) adapted to operate in at least two modes of operation, wherein a first mode regulates speed of the top drive based on a velocity limit and a second mode regulates torque of the top drive;
• in response to receiving the indication, transitioning the VFD to the second mode;
• setting, via the VFD, a zero torque setpoint;
• determining a direction for rotating the top drive based at least in part on sign of a torque feedback value, wherein the direction is reverse if the sign is positive, and the direction is forward if the sign is negative;
• setting, via the VFD, the velocity limit of the top drive to a negative value if the direction is reverse or to a positive value if the direction is forward;
• rotating the top drive in the determined direction, the VFD regulating the speed based on the velocity limit;
• determining, when the top drive is rotating in reverse, the torque is released if the torque feedback value of the top drive falls below a torque threshold value and if an absolute value of a velocity feedback value of the top drive is less than a speed threshold value;
• and
• determining, when the top drive is rotating in forward, the torque is released if the torque feedback value rises above a negative of the torque threshold value and if the absolute value of the velocity feedback value is less than the speed threshold value.