Analyzing Toolface Velocity to Detect Detrimental Vibration During Drilling

Abstract

A downhole drilling vibration analysis involves measuring orientation data in at least two orthogonal axes downhole while drilling with a drilling assembly. For example, two orthogonal magnetometers can be used. A toolface of the drilling assembly is determined using the measured sensor data, and velocity (RPM) values for the toolface for a plurality of revolutions of the drilling assembly are determined. From these determined values, a coefficient of variation for the toolface velocity (RPM) values for the revolutions of the drilling assembly is calculated. When a pattern in found in the toolface velocity (RPM) and/or the calculated coefficient of variations exceed one or more thresholds, the processing device determines that detrimental vibrations are occurring in the drilling assembly.

What is claimed is: 
     
         1 . A downhole drilling vibration analysis method, comprising:
 measuring orientation data of a drilling assembly downhole while drilling with one or more drilling parameters;   determining toolface orientations of the drilling assembly using the measured orientation data;   determining toolface velocity values for the toolface orientations for a plurality of revolutions of the drilling assembly;   calculating variation of the toolface velocity values for the revolutions of the drilling assembly;   determining detrimental vibration in the drilling assembly based on—
 determining that the calculated variation for at least some of the revolutions exceeds at least one threshold, and 
 finding one or more patterns in at least one of the calculated variation and the toolface velocity values; and 
   modifying, in response to the determined detrimental vibration, at least one of the one or more drilling parameters used while drilling with the drilling assembly.   
     
     
         2 . The method of  claim 1 , wherein measuring the orientation data comprises measuring one or more of an axis of a magnetometer, an axis of an accelerometer, and a position of an encoder. 
     
     
         3 . The method of  claim 1 , wherein determining the toolface orientations comprises determining orientation of a tool axis relative to at least one of magnetic north, gravitational direction, and encoder position. 
     
     
         4 . The method of  claim 1 , wherein determining the toolface velocity values comprises:
 dividing each of the revolutions into a plurality of equal bins for the toolface orientations;   counting a number of detected sensor samples occurring in each of the bins for each of the revolutions; and   correlating the counted number of samples to the toolface velocity values.   
     
     
         5 . The method of  claim 1 , wherein calculating the variation for the toolface velocity values for the revolutions of the drilling assembly comprises calculating a coefficient of variation of the toolface velocity values for the revolutions. 
     
     
         6 . The method of  claim 5 , wherein the coefficient of variation is a ratio of a standard deviation of the toolface velocity values relative to an arithmetic average of the toolface velocity values. 
     
     
         7 . The method of  claim 1 , wherein determining the detrimental vibration in the drilling assembly comprises determining that the drilling assembly exhibits at least one of stick/slip and bit whirl during one or more of the revolutions. 
     
     
         8 . The method of  claim 1 , wherein determining that the calculated variation exceeds the at least one threshold and finding the one or more patterns in the calculated variation comprises determining that the calculated variation exceeds the at least one threshold at periodic intervals between the revolutions. 
     
     
         9 . The method of  claim 8 , wherein determining the detrimental vibration in the drilling assembly comprises determining detrimental vibration indicative of stick/slip in response to the exceeded at least one threshold at the periodic intervals. 
     
     
         10 . The method of  claim 8 , further comprising:
 finding at least one of the toolface orientations in which a lowest or a highest of the toolface velocity values for one or more of the revolutions occur when the at least one threshold is exceeded; and   determining that a lowest or a highest of the toolface velocity values occurs at the at least one found toolface orientation when the at least one threshold is exceeded for a subsequent one of the revolutions.   
     
     
         11 . The method of  claim 1 , wherein determining that the calculated variation for at least some of the revolutions exceeds the at least one threshold comprises determining that the calculated variation exceeds the at least one threshold for an extent of the revolutions. 
     
     
         12 . The method of  claim 11 , wherein finding the one or more patterns in the toolface velocity values comprises finding one or more of the toolface orientations in which a lowest of the toolface velocity values occurs across the extent of the revolutions. 
     
     
         13 . The method of  claim 12 , wherein determining the detrimental vibration in the drilling assembly comprises determining the detrimental vibration indicative of bit whirl in response to the exceeded at least one threshold and in response to the one or more patterns having more than one of the found toolface orientations in which the lowest of the toolface velocity values occur across the extent of the revolutions. 
     
     
         14 . The method of  claim 13 , wherein the one or more found toolface orientations in which the lowest of the toolface velocity values occurs corresponds to the one or more lobes of the bit whirl. 
     
     
         15 . The method of  claim 1 , further comprising telemetering information uphole indicative of the determined detrimental vibration. 
     
     
         16 . The method of  claim 15 , wherein the information comprises one or more of: data indicative of vibration, an indication of a type of detrimental vibration, an alarm condition, an interval between spikes in the variation exceeding the threshold, a number of lobes in a bit whirl, and the determined toolface velocity values. 
     
     
         17 . The method of  claim 1 , wherein modifying the at least one of the one or more drilling parameters in response to the determined detrimental vibration comprises modifying at least one of a weight on bit (WOB), drilling collar revolutions, a rotary speed, a rotational speed, a rotary speed applied to a drilling string, an energy provided by a rotary drive, a torque, and a pump rate. 
     
     
         18 . A downhole drilling vibration analysis method, comprising:
 measuring orientation data of a drilling assembly downhole while drilling with one or more operating parameters;   determining, from the measured orientation data, orientations of the drilling assembly;   determining velocity values at the orientations for a plurality of revolutions of the drilling assembly;   determining that variation of the velocity values for at least some of the revolutions exceeds at least one threshold;   determining detrimental vibration in the drilling assembly by finding one or more patterns in the velocity values at one or more of the orientations at least in the revolutions exceeding the at least one threshold; and   modifying, in response to the determined detrimental vibration, at least one of the one or more operating parameters of the drilling assembly.   
     
     
         19 . The method of  claim 18 , wherein modifying the at least one operating parameter comprise modifying at least one of a weight on bit (WOB), drilling collar revolutions, a rotary speed, a rotational speed, a rotary speed applied to a drilling string, an energy provided by a rotary drive, a torque, and a pump rate. 
     
     
         20 . The system of  claim 18 , wherein the drilling assembly comprises one or more of a drill bit, a motor, a drill collar, a stabilizer, a rotary steerable system, a bent sub, a drill string component, a bottom hole assembly component, a rotary rig component, and a drilling fluid system component. 
     
     
         21 . The system of  claim 18 , wherein determining the detrimental vibration in the drilling assembly comprises determining that the drilling assembly exhibits at least one of stick/slip and bit whirl.