Method and Apparatus for Detecting Downhole Torsional Vibration Based on Measurement of Surface Torque


A method for detecting stick-slip in a drillstring includes (a) measuring a parameter that is a function of a torque applied to the drillstring by a top drive system over a selected time period, the measuring being performed by at least one surface sensor that produces measurement data including torque values over a frequency range; (b) filtering out measurement data that has a frequency outside a selected frequency band, the selected frequency band including a resonant frequency of the drillstring; (c) identifying a minimum and a maximum torque value in the filtered measurement data and determining a difference of these two values; (d) determining a surface stick-slip index by dividing the difference of the maximum and minimum torque values by an average torque value over the selected time period; and (e) displaying the surface stick-slip index on a display.