Gyroscopic Steering Tool Using Only a Two-Axis Rate Gyroscope and Deriving the Missing Third Axis
AssigneeBaker Hughes Incorporated
InventorsRobert Estes, Jonathan Bynum, Randell Riggs, David Epplin
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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.
Claims12
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.
-26. (canceled)
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.
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.
Dependencies are inferred from the claim text.