Gyroscopic steering tool using only a two-axis rate gyroscope and deriving the missing third axis

• US 20050056461A1
• Filed: 08/05/2004
• Published: 03/17/2005
• Est. Priority Date: 08/07/2003
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Riggs, Randell, Bynum, Jonathan R., Epplin, David M., Estes, Robert A.
• Granted Patent: US 7,234,540 B2
• Time in Patent Office: Days
• US Class Current: 175/45
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism
• CPC Class Codes: G01C 19/00 Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects

Abstract

A two-axis gyroscope used on a bottom hole assembly can be used for determining a rate of rotation about the rotational axis of a BHA. The method takes advantage of possible misalignment of at least one axis of the two axis gyroscope from orthogonality with respect to the rotational axis of the BHA, resulting in the misaligned gyro being sensitive to BHA rotation.

Claims

1. A method of using a two-axis gyroscope on a housing for determining a rate of rotation of said housing about a third axis, said two axes of the two-axis gyroscope being substantially orthogonal to each other, wherein said third axis has a small deviation from orthogonality relative to at least one of said two axes.

2. The method of claim 1 further comprising:

(a) measuring an output of said two-axis gyroscope along said at least one of said two axes in response to said rotation about said third axis; and

(b) determining from said output and a misalignment term an estimate of said rate of rotation about said third axis.

3. The method of claim 1 wherein said at least one of said two axes comprises both of said two axes, the method further comprising determining said rate of rotation by averaging measurements made by two components of said two-axis gyroscope in response to said rotation.

4. The method of claim 2 further comprising using a relation of the form:

$R_x=\frac{S_x}{F_x}-B_x-B_{\mathrm{xg}}-M_x<br><br>R_z$

where R_x is a rotation rate about said at least one axis, S_x is an output of said gyroscope corresponding to said at least one axis, F_x is a calibration scale factor for said at least one axis, B_x is a bias for the at least one axis, B_xg is a bias term for said at least one axis that is gravity related, M_x is said misalignment term.

5. A method of drilling a borehole comprising:

(a) conveying a bottomhole assembly (BHA) on a drilling tubular into said borehole, said BHA including a drillbit for drilling said borehole;

(b) making measurements with a gyroscope having at least one sensitive axis with an angle of misalignment from orthogonality relative to an axis of rotation of said drilling tubular;

(c) determining from said measurements a toolface angle of said BHA; and

(d) drilling said borehole based on said determined toolface angle.

6. The method of claim 5 wherein said angle of misalignment is less than 100 milliradians.

7. The method of claim 5 wherein said angle of misalignment is greater than 1 milliradian.

8. The method of claim 5 wherein determining said toolface angle comprises integrating a determined rate of rotation about said axis of rotation of said drilling tubular.

9. The method of claim 8 wherein determining said rate of rotation comprises using a relation of the form:

$R_x=\frac{S_x}{F_x}-B_x-B_{\mathrm{xg}}-M_x<br><br>R_z$

where R_x is a rotation rate about said at least one sensitive axis, S_x is an output of said gyroscope corresponding to said at least one sensitive axis, F_x is a calibration scale factor for said at least one axis, B_x is a bias for the at least one axis, B_xg is a bias term for said at least one axis that is gravity related, M_x is a misalignment term.

10. The method of claim 9 further comprising determining said misalignment term from measurements outside said wellbore.

11. The method of claim 5 further comprising correcting said measurements for a bias.

12. The method of claim 11 further comprising determining said bias by making measurements at a plurality of rotational angles of said gyroscope.

13. The method of claim 12 further comprising correcting said measurements at said plurality of rotational angles for a time dependent drift.

14. The method of claim 5 wherein said at least one axis comprises two axes.

15. An apparatus for drilling a wellbore comprising:

(a) a bottomhole assembly (BHA) conveyed on a drilling tubular into said borehole, said BHA including a drillbit for drilling said borehole;

(b) a gyroscope on said BHA, said gyroscope having at least one sensitive axis with an angle of misalignment from orthogonality with an axis of rotation of said drilling tubular; and

(c) a processor which determines from measurements by said gyroscope a toolface angle of said BHA.

16. The apparatus of claim 15 further comprising a processor which controls a direction of drilling of said borehole based on said determined toolface angle.

17. The apparatus of claim 15 wherein said angle of misalignment is less than 100 milliradians.

18. The method of claim 15 wherein said angle of misalignment is greater than 1 milliradian.

19. The method of claim 15 wherein determining said toolface angle comprises integrating a determined rate of rotation about said axis of rotation of said drilling tubular.

20. The apparatus of claim 18 wherein said processor determines said rate of rotation using a relation of the form:

$R_x=\frac{S_x}{F_x}-B_x-B_{\mathrm{xg}}-M_x<br><br>R_z$

where R_x is a rotation rate about said at least one sensitive axis, S_x is an output of said gyroscope corresponding to said at least one sensitive axis, F_x is a calibration scale factor for said at least one axis, B_x is a bias for the at least one axis, B_xg is a bias term for said at least one axis that is gravity related, M_x is a misalignment term.

21. The apparatus of claim 20 wherein said misalignment term is determined from measurements outside said wellbore.

22. The apparatus of claim 15 wherein said processor corrects said measurements for a bias.

23. The apparatus of claim 22 wherein said processor determines said bias by making measurements at a plurality of rotational angles of said gyroscope.

24. The apparatus of claim 23 wherein said processor further corrects said measurements at said plurality of rotational angles for a drift that is at least one of (i) time-dependent, and, (ii) temperature-dependent.

25. The apparatus of claim 15 wherein said at least one axis comprises two axes,

26. The apparatus of claim 24 further comprising a temperature sensor which provides a plurality of temperature measurements corresponding to said plurality of rotational angles.

27. A method of compensating measurements made by a downhole survey instrument, the method comprising:

(a) making measurements with the downhole survey instrument at a plurality of rotational positions;

(b) applying a first correction to said measurements using a thermal model to give a first set of corrected measurements;

(c) fitting a sinusoidal function of angular position to the first set of corrected measurements;

(d) fitting a polynomial function of temperature to a residual remaining after said sinusoidal fitting; and

(e) determining a corrected bias for said measurements made by the downhole gyroscope using results of said polynomial fitting.

28. The method of claim 27 wherein said survey instrument comprises a gyroscope.

29. The method of claim 27 wherein said survey instrument comprises an accelerometer.

30. A system for making downhole survey measurements, the system comprising:

(a) a downhole survey instrument which makes survey measurements at a plurality of rotational positions, and

(b) a processor which;

(i) applies a first correction to said measurements using a laboratory-derived thermal model to give a first set of corrected measurements,

(ii) fits a sinusoidal function of angular position to the first set of corrected measurements,

(iii) fits a polynomial function of temperature to a residual remaining after said sinusoidal fitting; and

(iv) determines a corrected bias for said measurements made by the downhole gyroscope using results of said polynomial fitting.

31. The system of claim 30 wherein said survey instrument comprises a gyroscope.

32. The system of claim 30 wherein said survey instrument comprises an accelerometer.

33. The system of claim 30 wherein said survey instrument is conveyed downhole on one of (A) a wireline, and, (B) a drilling tubular.