Rotational oscillation control using

Abstract

A method and autodriller for drilling a wellbore with a drill rig by rotating a drillstring and a drill bit with a drill rig drive system; applying an initial weight of the drillstring on the drill rig WOB; measuring drill rig properties to derive an anticipated drill bit rotation speed; and changing the weight of the drillstring on the drill rig WOB so that a corresponding change to the downhole weight on the drill bit occurs approximately simultaneously with a change in the anticipated drill bit rotation speed.

1 . A method for drilling a wellbore with a drill rig, the method comprising:
 rotating a drillstring and a drill bit with a drill rig drive system;   applying an initial weight of the drillstring on the drill rig WOB;   measuring drill rig properties to derive an anticipated drill bit rotation speed; and   changing the weight of the drillstring on the drill rig WOB so that a corresponding change to the downhole weight on the drill bit occurs approximately simultaneously with a change in the anticipated drill bit rotation speed.   
     
     
         2 . A method for drilling a wellbore as claimed in  claim 1 , wherein the applying an initial weight of the drillstring on the drill rig WOB comprises lowering a drill rig traveling block from which the drillstring is suspended. 
     
     
         3 . A method for drilling a wellbore as claimed in  claim 1 , wherein the measuring drill rig properties comprises measuring at least one drill rig property selected from:
 drillstring rotation speed at the drill rig; drillstring torque at the drill rig; and rotational impedance of the drillstring at the surface.   
     
     
         4 . A method for drilling a wellbore as claimed in  claim 1 , wherein the changing the weight of the drillstring on the drill rig WOB comprises lowering a drill rig traveling block from which the drillstring is suspended. 
     
     
         5 . A method for drilling a wellbore as claimed in  claim 1 , wherein the changing the weight of the drillstring on the drill rig WOB comprises raising a drill rig traveling block from which the drillstring is suspended. 
     
     
         6 . A method for drilling a wellbore as claimed in  claim 1 , further comprising repeating the steps of: measuring drill rig properties and changing the weight of the drillstring on the drill rig WOB, wherein the weight is changed by a different amount compared to a prior changing step that is repeated. 
     
     
         7 . A method for drilling a wellbore as claimed in  claim 1 , further comprising:
 determining for the drill bit the slope of a data curve defined by a torque in the drillstring at the drill rig versus the weight of the drillstring on the drill rig WOB via at least one method selected from: tests on the drill bit, data acquired during drilling with the drill bit, and modelling the drill bit during a modelled drilling operation; and   determining a size of fluctuations in the torque in the drillstring at the drill rig.   
     
     
         8 - 9 . (canceled) 
     
     
         10 . A method for drilling a wellbore as claimed in  claim 1 , wherein the steps of  claim 1  comprise a first stick-slip mitigation method, and the method for drilling a wellbore further comprises using the first stick-slip mitigation method in combination with a second mitigation stick-slip method. 
     
     
         11 . A method for drilling a wellbore as claimed in  claim 10 , wherein the second mitigation stick-slip method comprises:
 setting a desired drillstring rotation speed at the drill rig;   determining an upgoing rotation speed for rotational energy traveling up the rotating drillstring;   determining a downgoing rotation speed for energy traveling down the rotating drillstring;   deriving an optimal rotation speed for the drillstring that constrains the downgoing rotational energy; and   controlling the drive system to rotate the drillstring at the optimal rotation speed.   
     
     
         12 - 17 . (canceled) 
     
     
         18 . A method for drilling a wellbore as claimed in  claim 1 , further comprising:
 monitoring rotational oscillation of the drill bit via a downhole measurement of rotation speed, during changing the weight of the drillstring on the drill rig WOB.   
     
     
         19 . An autodriller for controlling a drill rig system having a drillstring and a drill bit, the autodriller comprising:
 a rotation receptor that receives a signal corresponding to drillstring rotation speed at the drill rig;   a processor;   a non-transitory storage medium; and   a set of computer readable instructions stored in the non-transitory storage medium, wherein when the instructions are executed by the processor allow the autodriller to:
 apply an initial weight of the drillstring on the drill rig WOB; 
 measure drill rig properties to derive an anticipated drill bit rotation speed; and 
 change the weight of the drillstring on the drill rig WOB so that a corresponding change to the downhole weight on the drill bit occurs approximately simultaneously with a change in the anticipated drill bit rotation speed. 
   
     
     
         20 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions further comprises instructions when executed by the processor to allow the autodriller to: apply an initial weight of the drillstring on the drill rig WOB by lowering a drill rig traveling block from which the drillstring is suspended. 
     
     
         21 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions further comprises instructions when executed by the processor to allow the autodriller to: measure drill rig properties by measuring at least one drill rig property selected from: drillstring rotation speed at the drill rig; drillstring torque at the drill rig; and rotational impedance of the drillstring at the surface. 
     
     
         22 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions further comprises instructions when executed by the processor to allow the autodriller to: change the weight of the drillstring on the drill rig WOB by lowering a drill rig traveling block from which the drillstring is suspended. 
     
     
         23 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions further comprises instructions when executed by the processor to allow the autodriller to: change the weight of the drillstring on the drill rig WOB by raising a drill rig traveling block from which the drillstring is suspended. 
     
     
         24 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions further comprises instructions when executed by the processor to allow the autodriller to: repeat the steps of: measuring drill rig properties and changing the weight of the drillstring on the drill rig WOB, wherein the weight is changed by a different amount compared to a prior changing step that is repeated. 
     
     
         25 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions further comprises instructions when executed by the processor to allow the autodriller to:
 determine for the drill bit the slope of a data curve defined by a torque in the drillstring at the drill rig versus the weight of the drillstring on the drill rig WOB via at least one method selected from: tests on the drill bit, data acquired during drilling with the drill bit, and modelling the drill bit during a modelled drilling operation; and determine a size of fluctuations in the torque in the drillstring at the drill rig.   
     
     
         26 - 27 . (canceled) 
     
     
         28 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions of  claim 19  comprise a first stick-slip mitigation method, and the autodriller further comprises an additional set of computer readable instructions comprising a second mitigation stick-slip method. 
     
     
         29 . An autodriller for controlling a drill rig system as claimed in  claim 28 , wherein the second set of computer readable instructions comprises instructions when executed by the processor to allow the autodriller to:
 set a desired drillstring rotation speed at the drill rig;   determine an upgoing energy component for rotational energy traveling up the rotating drillstring;   determine a downgoing energy component for energy traveling down the rotating drillstring;   derive an optimal rotation speed for the drillstring that constrains the downgoing rotational energy; and   control the drive system to rotate the drillstring at the optimal rotation speed.   
     
     
         30 - 35 . (canceled) 
     
     
         36 . An autodriller for controlling a drill rig system as claimed in  claim 19 , wherein the set of computer readable instructions stored in the non-transitory storage medium, when executed by the processor, further allow the autodriller to:
 monitor rotational oscillation of the drill bit via a downhole measurement of rotation speed, during changing the weight of the drillstring on the drill rig WOB.