Identification and mitigation of whirl within a drilling system
Whirl in a drilling system may be identified and mitigated by monitoring signals from a plurality of sensors positioned at various axial locations along a drill string of the drilling system, determining a respective frequency component and a respective amplitude component for each of the signals, identifying whirl in the drill string based on at least two of the respective frequency components and their respective amplitude components, and mitigating the whirl by introducing noise into the drilling system to reduce or eliminate the whirl without removing the drill string from a bottom of a borehole and without terminating all rotation of the drill string.
1 . A system, comprising:
a plurality of sensors placed at various axial positions on a drill string and configured to output respective sensor signals indicative of movement of the drill string; and
at least one controller communicatively coupled to the plurality of sensors, wherein the at least one controller is configured to:
a) identify whirl in the drill string by operations that include
i) determining frequency components and corresponding amplitude components for the sensor signals;
ii) comparing a first frequency component of the frequency components of i) to a second frequency component of the frequency components of i), wherein the first and second frequency components are based on the sensor signals produced by the plurality of sensors at different axial positions on the drill string;
iii) determining if a frequency difference between the first frequency component and the second frequency component of ii) exceeds a frequency threshold;
iv) if the frequency difference between the first frequency component and the second frequency component is determined to exceed the frequency threshold in iii), comparing both a first amplitude component of the amplitude components of i) and a second amplitude component of the amplitude components of i) to an amplitude threshold, wherein the first amplitude component corresponds to the first frequency component of ii) and the second amplitude component corresponds to the second frequency component of ii); and
v) identifying whirl in the drill string if both the first and second amplitude components exceed the amplitude threshold of iv); and
b) control a downhole component, a surface component, or a combination thereof, in response to identifying the whirl, to introduce noise into the drill string to mitigate the whirl without removing the drill string from a bottom of a borehole and without terminating all rotation of the drill string.
2 . The system of claim 1 , wherein the plurality of sensors comprise accelerometers, gyroscopes, or a combination thereof.
3 . The system of claim 1 , wherein the at least one controller is configured to not identify whirl in the drill string if the frequency difference between the first frequency component and the second frequency component of ii) indicates that the frequency components are multiples or harmonics of the same fundamental frequency.
4 . The system of claim 1 , wherein the at least one controller comprises a surface control unit positioned above a ground surface and a steering control unit disposed within a bottom hole assembly (BHA).
5 . The system of claim 4 , wherein the BHA comprises a steering pad assembly having steering pad actuators configured to extend and retract steering pads of the BHA, and wherein the control of b) comprises the steering control unit controlling the steering pad actuators to extend the steering pads to induce torque on the drill string to mitigate the whirl.
6 . The system of claim 4 , wherein the control of b) comprises the surface control unit controlling a surface-located drilling fluid pump to perturb a fluid flow rate from the drilling fluid pump to induce noise into the drill string to mitigate the whirl.
7 . The system of claim 6 , wherein the BHA comprises a mud motor communicatively coupled to the drilling fluid pump, and wherein the control of b) controls to the drilling fluid pump to reduce the fluid flow rate to cause a stall in the mud motor to induce noise into the drill string to mitigate the whirl.
8 . The system of claim 4 , wherein the surface component comprises a surface-located motor controlled by the surface control unit and configured to rotate the drill string and the BHA, wherein the control of b) controls the surface-located motor to adjust rotational speed of the drill string and the BHA to induce noise into the drill string to mitigate the whirl.
9 . A method of identifying and mitigating whirl within a drilling system, the method comprising:
a) monitoring sensor signals from a plurality of sensors positioned at various axial locations along a drill string of the drilling system;
b) determining frequency components and corresponding amplitude components for the sensor signals;
c) identifying whirl in the drill string by operations that include
i) comparing a first frequency component of the frequency components of b) to a second frequency component of the frequency components of b), wherein the first and second frequency components are based on the sensor signals produced by the plurality of sensors at different axial positions on the drill string;
ii) determining if a frequency difference between the first frequency component and the second frequency component of i) exceeds a frequency threshold;
iii) if the frequency difference between the first frequency component and the second frequency component is determined to exceed the frequency threshold in ii), comparing both a first amplitude component of the amplitude components of b) and a second amplitude component of the amplitude components of b) to an amplitude threshold, wherein the first amplitude component corresponds to the first frequency component of i) and the second amplitude component corresponds to the second frequency component of i); and
iv) identifying whirl in the drill string if both the first and second amplitude components exceed the amplitude threshold of iii); and
d) mitigating the whirl by introducing noise into the drilling system to reduce or eliminate the whirl without removing the drill string from a bottom of a borehole and without terminating all rotation of the drill string.
10 . The method of claim 9 , wherein the plurality of sensors comprises accelerometers, gyroscopes or any combination thereof.
11 . The method of claim 9 , wherein whirl in the drill string is not identified if the frequency difference between the first frequency component and the second frequency component of i) indicates that the frequency components are multiples or harmonics of the same fundamental frequency.
12 . The method of claim 9 , wherein mitigating the whirl in d) comprises:
controlling a steering pad assembly of a bottom hole assembly (BHA) of the drill string to extend steering pads of the steering pad assembly to induce torque on the drill string to mitigate the whirl.
13 . The method of claim 9 , wherein mitigating the whirl in d) comprises:
controlling a drilling fluid pump communicatively coupled to the drill string to perturb a fluid flow rate from the drilling fluid pump to induce noise into the drill string to mitigate the whirl.
14 . The method of claim 13 , further comprising reducing the fluid flow rate to a mud motor of a bottom hole assembly (BHA) that is communicatively coupled to the drilling fluid pump to cause a stall in the mud motor to induce noise into the drill string to mitigate the whirl.
15 . The method of claim 9 , wherein mitigating the whirl in d) comprises:
adjusting rotational speed of the drill string to induce noise into the drill string to mitigate the whirl.
16 . The method of claim 9 , wherein mitigating the whirl in d) comprises:
adjusting weight on bit (WOB) of a drill bit of the drill string to induce noise into the drill string to mitigate the whirl.
17 . The method of claim 9 , wherein introducing noise into the drilling system comprises a disturbance of the drilling system.
18 . The method of claim 9 , further comprising returning the drilling system to normal operation after mitigating the whirl.