Gyroscopic Steering Tool Using Only a Two-Axis Rate Gyroscope and Deriving the Missing Third Axis

• US 20070175055A1
• Filed: 04/12/2007
• Published: 08/02/2007
• 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, Estes, Robert, Epplin, David, Bynum, Jonathan
• Granted Patent: US 7,813,878 B2
• Time in Patent Office: Days
• US Class Current: 33/304
• 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.

5-26. -26. (canceled)

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.