Method for measuring surface torque oscillation performance index

A method for drilling a wellbore with a drill rig, comprising:

• rotating a drill string and a drill bit with a drill rig drive system;
• and
• measuring surface torque oscillations of the drill string, comprising:
• determining a fundamental oscillation time period;
• selecting a time window based on the fundamental oscillation time period;
• collecting torque present value data of the drill string for the selected time window;
• determining an amplitude of torque oscillation from the collected torque present value data;
• determining a reference torque;
• and
• dividing the determined amplitude of torque oscillation by the determined reference torque to obtain a surface torque oscillation performance index, whereby the measurement of the surface torque oscillations of the drill string is a fractional value to indicate the magnitude and severity of surface torque fluctuations of the drilling string.

A controller of a drill rig system having a drill string and a drill bit, the controller comprising:

• a rotation receptor that receives a signal corresponding to drill string rotation speed at the drill rig;
• a torque receptor that receives a signal corresponding to torque applied to the drill string at the drill rig;
• a non-transitory storage medium that stores a set of computer readable instructions;
• a processor to execute the instructions;
• and
• a controller configured to:
• determine a fundamental oscillation time period;
• select a time window based on the fundamental oscillation time period;
• collect torque present value data of the drill string for the selected time window;
• determine an amplitude of torque oscillation from the collected torque present value data;
• determine a reference torque;
• and
• divide the determined amplitude of torque oscillation by the determined reference torque to obtain a surface torque oscillation performance index, whereby the measurement of the surface torque oscillations of the drill string is a fractional value to indicate the magnitude and severity of surface torque fluctuations of the drilling string.