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US 10,415,364 B2Granted
Method and apparatus for reducing stick-slip
AssigneeNational Oilwell Varco, L.P.
InventorAge Kyllingstad
Life of this patent
Estimating the term…
Abstract
A method and apparatus for damping stick-slip oscillations in a drill string. In one embodiment a method includes damping the stick-slip oscillations using a drilling mechanism at the top of said drill string. The speed of rotation of the drilling mechanism is controlled using a PI controller. The control is characterized by tuning the PI controller so that the drilling mechanism absorbs most torsional energy from the drill string at a frequency that is at or near a frequency of the stick-slip oscillations.
Claims18
A method of damping stick-slip oscillations in a drill string, the method comprising:
- damping said stick-slip oscillations using a drilling mechanism at a top of said drill string, wherein said stick-slip oscillations comprise torsional waves propagating along said drill string, the drill string being a transmission line for the torsional waves;
- tuning a PI controller so that said drilling mechanism absorbs torsional energy from said drill string at a frequency that is at a frequency of said stick-slip oscillations;
- wherein the tuning comprises calculating an I-term of said PI controller which uses a value of an estimated frequency of said stick slip oscillations and a value of an effective inertia of said drilling mechanism, and which step of calculating the I-term does not use a value of the length of said drill string and a value of a speed of the torsional waves, whereby said drilling mechanism has a frequency dependent reflection coefficient of said torsional waves, which reflection coefficient is at a minimum at or near said frequency of stick-slip oscillations, the minimum having a value between 0.5 (50%) and 0.9 (90%);
- and
- controlling speed of rotation of said drilling mechanism using the PI controller based upon said tuning,
- wherein the value of the estimated frequency of said stick-slip oscillations is determined by automatic measurement.
3 more elements
A method of drilling a borehole, the method comprising:
- rotating a drill string with a drilling mechanism so as to rotate a drill bit at a lower end of said drill string, the drill string being a transmission line for torsional waves;
- and
- in response to detection of stick-slip oscillations of said drill string, wherein said stick-slip oscillations comprise torsional waves propagating along said drill string, damping said stick-slip oscillations using a PI controller to control said drilling mechanism, the PI controller having been tuned so that said drilling mechanism absorbs torsional energy from said drill string at a frequency that is at a frequency of said stick-slip oscillations;
- and
- tuning the PI controller by calculating an I-term of said PI controller using a value of estimated frequency of said stick slip oscillations and on a value of effective inertia of said drilling mechanism, wherein the calculating the I-term does not use a value of the length of said drill string and a value of a speed of the torsional waves, whereby said drilling mechanism has a frequency dependent reflection coefficient of said torsional waves, wherein the reflection coefficient is at a minimum at or near said frequency of stick-slip oscillations, the minimum having a value between 0.5 (50%) and 0.9 (90%),
- wherein said damping includes using the PI controller to rotate the drill string based on said tuning,
- wherein the value of the estimated frequency of said stick-slip oscillations is determined by automatic measurement.
4 more elements
A drilling mechanism for use in drilling a borehole using a drill string, the drilling mechanism comprising:
- an electronic controller having:
- a PI controller;
- and
- memory storing computer executable instructions that when executed cause said electronic controller to:
- damp stick-slip oscillations using said drilling mechanism at a top of the drill string, wherein said stick-slip oscillations comprise torsional waves propagating along said drill string that is a transmission line for the torsional waves;
- control speed of rotation of said drilling mechanism using said PI controller and to:
- tune said PI controller so that said drilling mechanism absorbs torsional energy from said drill string at a frequency that is at a frequency of said stick-slip oscillations;
- and
- to tune said PI controller, calculate an I-term of said PI controller using a value of an estimated frequency of said stick slip oscillations and a value of an effective inertia of said drilling mechanism, and not using a value of the length of said drill string and a value of a speed of the torsional waves in the calculation of the I-term, whereby said drilling mechanism has a frequency dependent reflection coefficient of said torsional waves, which reflection coefficient is at a minimum at or near said frequency of stick-slip oscillations, the minimum having a value between 0.5 (50%) and 0.9 (90%);
- and
- determine the value of the estimated frequency of said stick-slip oscillations by automatic measurement,
- wherein the computer executable instructions, when executed, cause the electronic controller to control the speed of rotation of the drilling mechanism based on said tuning of the PI controller.
9 more elements
An electronic controller for use with a drilling mechanism for drilling a borehole using a drill string, the electronic controller comprising:
- a PI controller;
- and
- memory storing computer executable instructions that when executed cause said electronic controller to:
- damp stick-slip oscillations using said drilling mechanism at a top of the drill string, wherein said stick-slip oscillations comprise torsional waves propagating along said drill string that is a transmission line for the torsional waves;
- control speed of rotation of said drilling mechanism using said PI controller and to:
- tune said PI controller so that said drilling mechanism absorbs torsional energy from said drill string at a frequency that is at a frequency of said stick-slip oscillations;
- and
- to tune said PI controller, calculate an I-term of said PI controller using a value of an estimated frequency of said stick slip oscillations and a value of an effective inertia of said drilling mechanism, and not using a value of the length of said drill string and a value of a speed of the torsional waves in the calculation of the I-term, whereby said drilling mechanism has a frequency dependent reflection coefficient of said torsional waves, which reflection coefficient is at a minimum at or near said frequency of stick-slip oscillations, the minimum having a value between 0.5 (50%) and 0.9 (90%);
- and
- determine the value of the estimated frequency of said stick-slip oscillations by automatic measurement,
- wherein the computer executable instructions, when executed, cause the electronic controller to control the speed of rotation of the drilling mechanism based on said tuning of the PI controller.
8 more elements
A method of upgrading a drilling mechanism, the method comprising:
- uploading computer executable instructions to an electronic controller to be used on a drilling rig, wherein the electronic controller is for controlling operation of said drilling mechanism;
- wherein said computer executable instructions comprise instructions for:
- damping stick-slip oscillations using said drilling mechanism at a top of a drill string that is a transmission line for the torsional wave;
- tuning a PI controller so that said drilling mechanism absorbs torsional energy from said drill string at a frequency that is a frequency of said stick-slip oscillations,
- wherein said stick-slip oscillations comprise torsional waves propagating along said drill string, and wherein the tuning comprises calculating an I-term of said PI controller using a value of an estimated frequency of said stick slip oscillations and a value of an effective inertia of said drilling mechanism, and wherein calculating the I-term does not use a value of the length of said drill string and a value of a speed of the torsional waves, whereby said drilling mechanism has a frequency dependent reflection coefficient of said torsional waves, which reflection coefficient is at a minimum at or near said frequency of stick-slip oscillations, the minimum having a value between 0.5 (50%) and 0.9 (90%);
- determining the value of the estimated frequency of said stick-slip oscillations by automatic measurement;
- and
- controlling speed of rotation of said drilling mechanism using the PI controller based upon said tuning.
5 more elements
Dependencies are inferred from the claim text.