Method and system for damping vibrations in a tool string system

Patent metadata

Field	Value
Publication number	US-9920612-B2
Application number	US-201414778458-A
Country	US
Kind code	B2
Filing date	Mar 19, 2014
Priority date	Mar 21, 2013
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

The invention provides a control system and method for limiting vibrations in a tool string system, comprising a relatively heavy rotatable device, such as a pump system or a bottom hole assembly, connected to a long rotatable tool string driven by a drive system. The control system comprises feedback of both torque and rotational speed signals to correct the set rotational speed. An objective is to maintain the drive speed over torque ratio equal to the connected tool string impedance. A secondary objective, for lower frequencies, is to approach and maintain a setpoint speed as drive rotation speed. The system may include a rotational speed sensor and a torque sensor, with the latter optionally replaced by a motor torque signal already available from a variable frequency drive (VFD) for an AC motor and the current safeguarding signal for a DC motor.

First claim

The invention claimed is:

1. A method of damping vibrations in a tool string, said vibrations comprising torsional waves propagating along said tool string, the method comprising the steps of:
instructing a drive system to rotate the tool string at a set rotational speed (Ω r );
determining a rotational speed (ω r ) of the tool string;
determining a torque (T d ) proximate an interface between the tool string and the drive system;
determining a tool string impedance (ζ) of a section of the tool string adjacent said interface;
calculating a rotation correction signal using the determined torque (T d ) multiplied by the determined tool string impedance (ζ);
correcting the set rotational speed (Ω r ) using the rotation correction signal to provide a corrected set rotational speed (Ω r,cor ) signal;
subtracting the determined rotational speed (ω r ) from the corrected set rotational speed signal to provide a twice corrected set rotational speed (Ω r,2cor ) signal to the drive system, whereby torsional waves propagating along the tool string are absorbed by the drive system at all frequencies within a selected frequency band comprising a plurality of reflection modes.

2. The method of claim 1 , wherein the step of correcting the set rotational speed includes:
multiplying the set rotational speed by a predetermined factor; and
subtracting the rotation correction signal from the multiplied set rotational speed (Ω r ) to provide the corrected set rotational speed (Ω r,cor ) signal.

3. The method of claim 2 , wherein the predetermined factor is 2.

4. The method of claim 1 , wherein the step of calculating a rotation correction signal comprises:
calculating a torque correction signal using the determined rotational speed (ω r ) of the tool string and the inertia J of the drive system; and
subtracting said torque correction signal from the motor supplied torque (Tm), providing a corrected torque signal (T cor ); and
using the corrected torque signal (T cor ) instead of the determined torque (T d ).

5. The method of claim 4 , wherein the step of calculating a torque correction signal includes:
determining a time differential signal of the rotational speed (ω r ) of the tool string to provide a tool string rotational acceleration signal;
amplifying the tool string rotational acceleration signal by a gain factor G, wherein the gain factor G is substantially equal to the inertia J of the drive system.

6. The method of claim 5 , comprising the steps of:
calculating the gain factor G using the tool string rotational acceleration signal and a torque signal (T).

7. The method of claim 6 , wherein the torque signal is selected from: determined torque (Td), motor torque (Tm), and corrected torque signal (T cor ).

8. The method of claim 1 , including the step of equally low-pass filtering the torque signal (T) and speed signal.

9. The method of claim 1 , comprising the steps of:
periodically adding a step pulse to the set rotational speed (Ω r );
determining a ratio of an amplitude of said step pulse and an amplitude of a resulting step in determined rotational speed (ω r );
automatically adjusting the impedance gain value (z′) accordingly, so that said ratio approaches the value of 1.

10. The method of claim 1 , comprising the steps of:
adding a white noise signal to the set rotational speed (Ω r );
calculating a tool string spatial image via a cross-correlation function using the white noise signal and a sum of the observed rotational speed (ω r ) and the rotation correction signal;
observing from said cross correlation function a discrepancy remaining between an estimated tool string impedance and an implemented drive impedance;
adjusting the impedance gain value (z′) in accordance with the observed discrepancy; and
using said adjusted impedance gain value (z′) as updated impedance gain factor (z′) in the step of calculating the rotation correction signal.

11. The method of claim 10 , wherein the cross-correlation function is periodically calculated at set time intervals.

12. The method of claim 11 , wherein the cross-correlation function is calculated as background process while idling or during steady-state operation of the tool string.

13. The method of claim 11 , wherein the set time interval is in the range of 10 to 30 seconds.

14. The method of claim 1 , comprising the step of:
providing the twice corrected set rotational speed (Ω r,2cor ) signal to a speed controller of the drive system, the speed controller having a gain of at least 10,000 Nms/rad.

15. A control system for damping vibrations in a tool string, said vibrations comprising torsional waves propagating along said tool string, the system comprising:
a user control module for instructing a drive system to rotate the tool string at a set rotational speed (Ω r );
a sensor for determining a rotational speed (ω r ) of the tool string;
a torque sensor for determining a torque (T d ) proximate an interface between the tool string and the drive system;
a calculator for determining a tool string impedance (ζ) of a section of the tool string adjacent said interface;
a first feedback loop comprising an amplifier for multiplying said torque (T) by the determined tool string impedance (ζ), for providing a rotation correction signal, and for correcting the set rotational speed (Ω r ) using the rotation correction signal to provide a corrected set rotational speed (Ω r,cor ) signal;
a second feedback loop for subtracting the determined rotational speed (ω r ) from the corrected set rotational speed (Ω r,cor ) to provide a twice corrected set rotational speed (Ω r,2cor ) signal to the drive system;

wherein a reflection coefficient, of torsional waves propagating along the tool string, at the interface between tool string and drive system is frequency independent for frequencies within a selected frequency band comprising a plurality of reflection modes.

16. The system of claim 15 , comprising a third corrective loop to adjust the tool string rotational speed (ω r ) to the set rotational speed (Ω r ).

17. The system of claim 15 , comprising a speed controller for controlling the speed of the drive system, the speed controller having a gain of 10,000 Nms/rad or more.

18. The system of claim 15 , a downhole end of the tool string being provided with a bottom hole assembly for drilling a wellbore.

19. The system of claim 15 , a downhole end of the tool string being provided with a pump device drivable by the tool string.

Assignees

• Shell Oil Co

Inventors

• Dwars Sicco
• Stulemeijer Ivo Petrus Jozef Maria

Classifications

• E21B44/04

  in response to the torque of the drive {; Measuring drilling torque (E21B44/06 takes precedence; measuring stresses in a well bore pipe E21B47/007)} · CPC title

• E21B44/00 Primary

  Automatic control systems specially adapted for drilling operations, i.e. self-operating systems which function to carry out or modify a drilling operation without intervention of a human operator, e.g. computer-controlled drilling systems; Systems specially adapted for monitoring a plurality of drilling variables or conditions · CPC title

• G05B19/402

  characterised by control arrangements for positioning, e.g. centring a tool relative to a hole in the workpiece, additional detection means to correct position (G05B19/19 takes precedence) · CPC title

• G01L3/00

  Measuring torque, work, mechanical power, or mechanical efficiency, in general · CPC title

• G01P3/44

  for measuring angular speed (G01P3/56 takes precedence) · CPC title