Mitigating torsional drill string oscillations

1 . A wellbore operation comprising:

rotating a drill string in a wellbore, the drill string including a rotary steerable system having at least three pads configured to contact the wellbore wall to steer a direction of drilling;

while rotating the drill string measuring at least one of a harmonic stick slip amplitude and a backward whirl amplitude;

comparing the measured harmonic stick slip amplitude with a corresponding harmonic stick slip threshold or comparing the backward whirl amplitude with a backward whirl threshold, wherein the measured harmonic stick slip amplitude exceeds the harmonic stick slip threshold or the backward whirl amplitude exceeds the backward whirl threshold;

in response to the comparing and determining that the measured harmonic stick slip amplitude exceeds the harmonic stick slip threshold or determining that the backward whirl amplitude exceeds the backward whirl threshold, actuating the at least three pads to promote stick slip oscillations that mitigate harmonic stick slip or backward whirl;

wherein the measuring further comprises measuring a fundamental stick slip frequency; and

wherein the actuating simultaneously actuates the at least three pads periodically at the measured fundamental stick slip frequency and out of sync with periodic bursts of drill string rotation rates.

2 . The wellbore operation of claim 1 , wherein the measuring, the comparing, and the actuating is automatically implemented using a processor deployed in the rotary steerable system.

3 . The wellbore operation of claim 1 , wherein the actuating simultaneously actuates the at least three pads using independently controlled electronic valves in the rotary steerable system.

4 . The wellbore operation of claim 1 , wherein:

the rotary steerable system comprises a roll stabilized control unit; and

the actuating comprises rotating the roll stabilized control unit in a direction opposite of a direction of the drill string rotation to achieve a differential rotation rate between a rotation rate of the drill string and a rotation rate of the roll stabilized control unit that exceeds 400 rpm.

5 . A wellbore operation comprising:

rotating a drill string in a wellbore, the drill string including a rotary steerable system having at least three pads configured to contact the wellbore wall to steer a direction of drilling;

while rotating the drill string measuring at least one of a stick slip amplitude;

comparing the measured stick slip amplitude with a corresponding stick slip threshold, wherein the measured stick slip amplitude exceeds the stick slip threshold;

in response to the comparing and determining that the measured stick slip amplitude exceeds the stick slip threshold, actuating the at least three pads to promote stick slip oscillations that mitigate stick slip;

wherein the measuring further comprises measuring a fundamental stick slip frequency; and

wherein the actuating simultaneously actuates the at least three pads periodically at the measured fundamental stick slip frequency and out of sync with periodic bursts of drill string rotation rates.

6 . The wellbore operation of claim 5 , wherein the measuring, the comparing, and the actuating is automatically implemented using a processor deployed in the rotary steerable system.

7 . The wellbore operation of claim 5 , wherein the actuating comprises simultaneously actuating the at least three pads using independently controlled electronic valves in the rotary steerable system.

8 . The wellbore operation of claim 5 , wherein:

the rotary steerable system comprises a roll stabilized control unit; and

the simultaneously actuating comprises rotating the roll stabilized control unit in a direction opposite of a direction of the drill string rotation to achieve a differential rotation rate between a rotation rate of the drill string and a rotation rate of the roll stabilized control unit that exceeds 400 rpm.