Automatically detecting and unwinding accumulated drill string torque

1. A method comprising:

initiating operation of a control device to thereby receive measurements indicative of present value torque (TrqPv) currently being applied by a top drive to a drill string extending in a well that penetrates a subterranean formation; and

utilizing the operating control device to release torque accumulated in the drill string by:

determining polarity of the TrqPv; and

in response to a manual or automatic trigger, causing the top drive to perform an unwinding operation in a direction opposite to the determined TrqPv polarity,

wherein the operating control device generates the automatic trigger in response to an absolute value of present acceleration of the top drive not being less than a predetermined ramp rate (a 0 ) for changing present speed of the top drive (ω) while either:

when the TrqPv polarity is positive, present set speed of the top drive (ω 0 ) is greater than zero while an associated speed feedback value (ω 1 ) is less than zero; or

when the TrqPv polarity is negative, the ω 0 is less than zero while the ω 1 is greater than zero.

2. The method of claim 1 wherein determining the TrqPv polarity comprises:

determining the polarity of the TrqPv as being negative when the TrqPv is less than a forward unwinding torque setpoint (TrqUwdFwdSp); and

determining the polarity of the TrqPv as being positive when the TrqPv is greater than a reverse unwinding torque setpoint (TrqUwdRevSp).

3. The method of claim 1 wherein causing the top drive to perform the unwinding operation comprises:

dynamically determining unwind speed setpoint (ω UwdSp ) values utilizing a proportional gain (Kp), an integral gain (Ki), an upper speed limit for the top drive (ω max ), and a lower speed limit for the top drive (ω min ); and

sending the dynamically determined ω UwdSp values to the top drive until either an unwind timer lapses or:

when the TrqPv polarity is negative, the present set speed of the top drive (ω 0 ) is greater than zero while the associated speed feedback value (ω 1 ) is greater than a predetermined unwind shutdown speed (ω s ); or

when the TrqPv polarity is positive, the ω 0 is less than zero while the ω 1 is less than negative ω s (−ω s ).

4. The method of claim 3 wherein:

the initiated operation of the control device also comprises receiving measurements indicative of torque demand during monitored cycles of the unwinding operation; and

the unwind timer lapses when the torque demands of two sequential ones of the cycles varies by more than a predetermined unwind torque change limit (T s ).

5. The method of claim 1 wherein the TrqPv measurements are received from at least one of:

a torque sub connected between the top drive and the drill string; and

a variable-frequency drive (VFD) operably connected with the top drive.

6. The method of claim 1 further comprising, before determining the TrqPv polarity, determining that the torque has accumulated in the drill string by determining that one of the TrqPv measurements is not less than a forward unwinding torque setpoint (TrqUwdFwdSp) and not greater than a reverse unwinding torque setpoint (TrqUwdRevSp).

7. An apparatus comprising:

a torque sensor operable to facilitate torque measurements indicative of present value torque (TrqPv) currently being applied by a top drive to a drill string extending in a well that penetrates a subterranean formation; and

a control device comprising a processor and a memory storing computer program code that, when executed by the processor, causes the control device to receive the TrqPv measurements and release torque accumulated in the drill string by:

determining polarity of the TrqPv; and

in response to a manual or automatic trigger, causing the top drive to perform an unwinding operation in a direction opposite to the determined TrqPv polarity,

wherein the computer program code, when executed by the processor, further causes the control device to generate the automatic trigger in response to an absolute value of present acceleration of the top drive not being less than a predetermined ramp rate (a 0 ) for changing present speed of the top drive (ω) while either:

when the TrqPv polarity is positive, present set speed of the top drive (ω 0 ) is greater than zero while an associated speed feedback value (ω 1 ) is less than zero; or

when the TrqPv polarity is negative, the ω 0 is less than zero while the on is greater than zero.

8. The apparatus of claim 7 wherein determining the TrqPv polarity comprises:

determining the polarity of the TrqPv as being negative when the TrqPv is less than a forward unwinding torque setpoint (TrqUwdFwdSp); and

determining the polarity of the TrqPv as being positive when the TrqPv is greater than a reverse unwinding torque setpoint (TrqUwdRevSp).

9. The apparatus of claim 7 wherein the computer program code, when executed by the processor, causes the control device to control the top drive to perform the unwinding operation by:

dynamically determining unwind speed setpoint (ω UwdSp ) values utilizing a proportional gain (Kp), an integral gain (Ki), an upper speed limit for the top drive (ω max ), and a lower speed limit for the top drive (ω min ); and

sending the dynamically determined ω UwdSp values to the top drive until either an unwind timer lapses or:

when the TrqPv polarity is negative, the present set speed of the top drive (ω 0 ) is greater than zero while the associated speed feedback value (ω 1 ) is greater than a predetermined unwind shutdown speed (ω s ); or

when the TrqPv polarity is positive, the ω 0 is less than zero while the ω 1 is less than negative ω s (−ω s ).

10. The apparatus of claim 9 wherein:

the computer program code, when executed by the processor, also causes the control device to receive measurements indicative of torque demand during monitored cycles of the unwinding operation; and

the unwind timer lapses when the torque demands of two sequential ones of the cycles varies by more than a predetermined unwind torque change limit (T s ).

11. The apparatus of claim 7 wherein the torque sensor is operably associated with at least one of:

a torque sub connected between the top drive and the drill string; and

a variable-frequency drive (VFD) operably connected with the top drive.

12. The apparatus of claim 7 wherein the computer program code, when executed by the processor, further causes the control device to, before determining the TrqPv polarity, determine that the torque has accumulated in the drill string by determining that one of the TrqPv measurements is not less than a forward unwinding torque setpoint (TrqUwdFwdSp) and not greater than a reverse unwinding torque setpoint (TrqUwdRevSp).

13. A computer program product comprising:

a tangible, non transitory, computer-readable medium having instructions stored thereon that, when executed by a processor of a control device, cause the control device to:

receive measurements indicative of present value torque (TrqPv) currently being applied by a top drive to a drill string extending in a well that penetrates a subterranean formation; and

release torque accumulated in the drill string by:

determining polarity of the TrqPv; and

in response to a manual or automatic trigger, causing the top drive to perform an unwinding operation in a direction opposite to the determined TrqPv polarity,

wherein the instructions, when executed by the processor, further cause the control device to generate the automatic trigger in response to an absolute value of present acceleration of the top drive not being less than a predetermined ramp rate (a 0 ) for changing present speed of the top drive (ω) while either:

when the TrqPv polarity is positive, present set speed of the top drive (ω 0 ) is greater than zero while an associated speed feedback value (ω 1 ) is less than zero; or

when the TrqPv polarity is negative, the ω 0 is less than zero while the ω 1 is greater than zero.

14. The computer program product of claim 13 wherein determining the TrqPv polarity comprises:

determining the polarity of the TrqPv as being negative when the TrqPv is less than a forward unwinding torque setpoint (TrqUwdFwdSp); and

determining the polarity of the TrqPv as being positive when the TrqPv is greater than a reverse unwinding torque setpoint (TrqUwdRevSp).

15. The computer program product of claim 13 wherein the instructions, when executed by the processor, cause the control device to cause the top drive to perform the unwinding operation by:

dynamically determining unwind speed setpoint (ω UwdSp ) values utilizing a proportional gain (Kp), an integral gain (Ki), an upper speed limit for the top drive (ω max ), and a lower speed limit for the top drive (ω min ); and

sending the dynamically determined ω UwdSp values to the top drive until either an unwind timer lapses or:

when the TrqPv polarity is negative, the present set speed of the top drive (ω 0 ) is greater than zero while the associated speed feedback value (ω 1 ) is greater than a predetermined unwind shutdown speed (ω s ); or

when the TrqPv polarity is positive, the ω 0 is less than zero while the ω 1 is less than negative ω s (−ω s ).

16. The computer program product of claim 15 wherein:

the instructions, when executed by the processor, further cause the control device to receive measurements indicative of torque demand during monitored cycles of the unwinding operation; and

the unwind timer lapses when the torque demands of two sequential ones of the cycles varies by more than a predetermined unwind torque change limit (T s ).

17. The computer program product of claim 13 wherein the instructions, when executed by the processor, further cause the control device to, before determining the TrqPv polarity, determine that the torque has accumulated in the drill string by determining that one of the TrqPv measurements is not less than a forward unwinding torque setpoint (TrqUwdFwdSp) and not greater than a reverse unwinding torque setpoint (TrqUwdRevSp).