METHOD AND SYSTEM FOR AZIMUTH MEASUREMENTS USING GYRO SENSORS

• US 20090287451A1
• Filed: 09/19/2008
• Published: 11/19/2009
• Est. Priority Date: 05/15/2008
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Sato, Shigeru, Yamate, Tsutomu, Kamiya, Akira, Igarashi, Juei
• Granted Patent: US 7,801,704 B2
• Time in Patent Office: Days
• US Class Current: 702/153
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism
• CPC Class Codes: G01C 19/42 for indicating rate of turn; for integrating rate of turn

Abstract

A method and system for azimuth measurements using one or more gyro sensors is disclosed. The method includes acquiring a first data from each of the gyro sensors with an input axis aligned to a first angular orientation and acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation. An earth rate component at the first angular orientations is determined based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors. The method may include acquiring a third data of the gyro sensor with the input axis aligned to the same angular orientation as the first angular orientation. An average of the first data and the third data may be used instead of the first data for determining the earth rate component.

Claims

1. A method for azimuth measurements using a gyro sensor, comprising:

acquiring a first data from the gyro sensor with an input axis aligned to an first angular orientation parallel to a horizontal plane perpendicular to a gravity direction at a measuring position in downhole;

acquiring a second data from the gyro sensor with the input axis flipped to a second angular orientation opposite to the first angular orientation at the measuring position after acquiring the first data; and

determining an earth rate component at the first angular orientation based on a difference between the first data and the second data to cancel out bias of the gyro sensor.

2. The method according to claim 1, wherein the earth rate component is determined by subtracting the second data from the first data and dividing the difference by two.

3. The method according to claim 2, further comprising:

acquiring a third data of the gyro sensor with the input axis aligned to the same angular orientation as the first angular orientation at the measuring position after acquiring the second data; and

obtaining an average of the first data and the third data,

wherein the average is used instead of the first data for determining the earth rate component.

4. The method according to claim 1, further comprising:

determining an azimuth of a target direction on the horizontal plane based on the earth rate component.

5. The method according to claim 1, wherein the data from the gyro sensor are acquired under a stationary condition.

6. The method according to claim 1, further comprising smoothing the data from the gyro sensor.

7. A method for azimuth measurements using two or three gyro sensors, comprising:

acquiring a first data from each of the gyro sensors with an input axis aligned to an first angular orientation at a measuring position in downhole, the input axes of the gyro sensors being orthogonal to each other;

acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation at the measuring position after acquiring the first data; and

determining an earth rate component at the first angular orientation based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors.

8. The method according to claim 7, wherein the earth rate components are determined by subtracting the second data from the first data and dividing the difference data by two.

9. The method according to claim 8, further comprising:

acquiring a third data from each of the gyro sensors with the input axis aligned to the same angular orientation as the first angular orientation at the measuring position after acquiring the second data; and

obtaining an average of the first data and the third data,

wherein the average is used instead of the first data for determining the earth rate component.

10. The method according to claim 7, further comprising:

determining an earth rate vector with respect to a predetermined orthogonal sensor coordinates based on the earth rate components;

determining a north direction by projecting the earth rate vector onto a horizontal plane perpendicular to a gravity direction; and

determining an azimuth of a target direction on the horizontal plane based on the north direction.

11. The method according to claim 10, wherein the target direction is one of coordinate axes of the orthogonal sensor coordinates.

12. The method according to claim 7, wherein the data from each of the gyro sensors are acquired under a stationary condition.

13. The method according to claim 7, further comprising smoothing the data from each of the gyro sensors.

14. The method according to claim 7, wherein the gyro sensors are located at a measuring position in downhole when acquiring the data from the gyro sensors.

15. A method for azimuth measurements using two or three gyro sensors, comprising:

acquiring a first data from each of the gyro sensors with an input axis aligned to an first angular orientation at a measuring position in downhole, the input axes of the gyro sensors being orthogonal to each other;

acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation at the measuring position after acquiring the first data;

determining an earth rate component at the first angular orientation based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors; and

repeating acquiring the first data, acquiring the second data and determining the earth rate component, after rotating each of the gyro sensors so as to align each input axis of the gyro sensors to another first angular orientation rotated by 90 degrees from the original first angular orientation.

16. The method according to claim 15, wherein the earth rate component is determined by subtracting the second data from the first data and dividing the difference data by two.

17. The method according to claim 15, further comprising:

acquiring a third data from each of the gyro sensors with the input axis aligned to the same angular orientation as the first angular orientation at the measuring position after acquiring the second data;

obtaining an average of the first data and the third data, and

repeating acquiring the third data and obtaining the average, after rotating each of the gyro sensors so as to align each of the input axes of the gyro sensors to another first angular orientation,

wherein the average is used instead of the first data for determining the earth rate component.

18. The method according to claim 15, further comprising:

determining a ratio of sensitivity of a pair of the gyro sensors based on a set of data from the gyro sensors with the input axes aligned to the common first angular orientation;

correcting the earth rate components used for determining the earth rate vector, based on the ratio of sensitivity; and

determining an earth rate vector with respect to a predetermined orthogonal sensor coordinates based on the corrected earth rate components.

19. The method according to claim 18, wherein the earth rate vector Ω

₀ is determined based on a predetermined threshold value and a selection criterion with following three equations;

If Ω

_Cz>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Cx}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}}{{\mathrm{\Omega <br><br>}}_{C<br><br><br><br>z}},{\mathrm{\Omega <br><br>}}_{\mathrm{Ay}},{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}\right),$

If Ω

_Bx>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Cx}},{\mathrm{\Omega <br><br>}}_{\mathrm{By}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{Cx}}}{{\mathrm{\Omega <br><br>}}_{B<br><br><br><br>x}},{\mathrm{\Omega <br><br>}}_{\mathrm{Cz}}\right),$

If Ω

_Ay>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Bx}},{\mathrm{\Omega <br><br>}}_{\mathrm{By}},{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{By}}}{{\mathrm{\Omega <br><br>}}_{\mathrm{Ay}}}\right),$

where Ω

_Ax, Ω

_Ay and Ω

_Az represent earth rate components on orthogonal axes measured by an XY-gyro sensor with an input axis rotatable about a Z-axis, Ω

_Bx, Ω

_By and Ω

_Bz represent earth rate components on the orthogonal axes measured by a YZ-gyro sensor with an input axis rotatable about an X-axis, and Ω

_Cx, Ω

_Cy and Ω

_Cz represent earth rate components on the orthogonal axes measured by a ZX-gyro sensor with an input axis rotatable about a Y-axis.

20. The method according to claim 18, further comprising:

determining a north direction by projecting the earth rate vector onto a horizontal plane perpendicular to a gravity direction; and

determining an azimuth of a target direction on the horizontal plane based on the north direction.

21. The method according to claim 20, wherein the target direction is one of coordinate axes of the orthogonal sensor coordinates.

22. The method according to claim 15, wherein the data from each of the gyro sensors are acquired under a stationary condition.

23. The method according to claim 15, further comprising smoothing the data from each of the gyro sensors.

24. The method according to claim 15, wherein the gyro sensors are located at a measuring position in downhole when acquiring the data from the gyro sensors.

25. A method for azimuth measurements using two or three gyro sensors, comprising:

acquiring a first data from each of the gyro sensors with an input axis aligned to a first angular orientation at a measuring position in downhole, the input axes of the gyro sensors being orthogonal to each other;

acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation at the measuring position after acquiring the first data;

determining an earth rate component at the first angular orientation based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors;

repeating acquiring the first data, acquiring the second data and determining the earth rate component for each of the gyro sensors at a plurality of discrete angular orientations;

fitting a sinusoidal curve to the earth rate components at the plurality of discrete angular orientations; and

determining an earth rate vector with respect to a predetermined orthogonal sensor coordinates based on based on a result of the sinusoidal curve fitting.

26. The method according to claim 25, wherein the sinusoidal curve is expressed as follows:

Ω

_i=A cos θ

_i+B sin θ

_i

where Ω

_i is an earth rate component at an angular orientation θ

_i, and A and B are fitting parameters; and

wherein fitting the sinusoidal curve comprises determining the fitting parameters A and B.

27. The method according to claim 25, wherein the earth rate component is determined by subtracting the second data from the first data and dividing the difference by two.

28. The method according to claim 25, further comprising:

acquiring a third data from each of the gyro sensors with the input axis aligned to the same angular orientation as the first angular orientation at the measuring position after acquiring the second data;

obtaining an average of the first data and the third data; and

repeating acquiring the third data and obtaining the average for each of the gyro sensors at the plurality of discrete angular orientations,

wherein the average is used instead of the first data for determining the earth rate component.

29. The method according to claim 25, further comprising:

determining a ratio of sensitivity of a pair of the gyro sensors based on a set of data from the gyro sensors with the input axes aligned to the common first angular orientation; and

correcting the earth rate components used for determining the earth rate vector, based on the ratio of sensitivity.

30. The method according to claim 29, wherein the earth rate vector Ω

₀ is determined based on a predetermined threshold value and a selection criterion with following three equations;

If Ω

_Cz>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Cx}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}}{{\mathrm{\Omega <br><br>}}_{\mathrm{Cz}}},{\mathrm{\Omega <br><br>}}_{\mathrm{Ay}},{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}\right),$

If Ω

_Bx>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Cx}},{\mathrm{\Omega <br><br>}}_{\mathrm{By}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{Cx}}}{{\mathrm{\Omega <br><br>}}_{B<br><br><br><br>x}},{\mathrm{\Omega <br><br>}}_{\mathrm{Cz}}\right),$

If Ω

_Ay>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Bx}},{\mathrm{\Omega <br><br>}}_{\mathrm{By}},{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{By}}}{{\mathrm{\Omega <br><br>}}_{\mathrm{Ay}}}\right),$

where Ω

_Ax, Ω

_Ay and Ω

_Az represent earth rate components on orthogonal axes measured by an XY-gyro sensor with an input axis rotatable about a Z-axis, Ω

_Bx, Ω

_By and Ω

_Bz represent earth rate components on the orthogonal axes measured by a YZ-gyro sensor with an input axis rotatable about an X-axis, and Ω

_Cx, Ω

_Cy and Ω

_Cz represent earth rate components on the orthogonal axes measured by a ZX-gyro sensor with an input axis rotatable about a Y-axis.

31. The method according to claim 25, further comprising:

determining a north direction by projecting the earth rate vector onto a horizontal plane perpendicular to a gravity direction; and

determining an azimuth of a target direction on the horizontal plane based on the north direction.

32. The method according to claim 31, wherein the target direction is one of the coordinate axes of the orthogonal sensor coordinates.

33. The method according to claim 25, wherein the data from each of the gyro sensors are acquired under a stationary condition.

34. The method according to claim 25, further comprising smoothing the data from each of the gyro sensors.

35. The method according to claim 25, wherein the gyro sensors are located at a measuring position in downhole when acquiring the data from the gyro sensors.

36. A system for azimuth measurements, comprising:

a housing;

two or three gyro sensors having input axes orthogonal to each other;

three orthogonal axis accelerometers;

a driving mechanism for rotating or flipping the gyro sensors;

a controller for controlling the driving mechanism;

a data processing unit; and

a power supply unit,

wherein the data processing unit comprises a computer having a processor and a memory,

wherein the memory stores a program having instructions for;

acquiring a first data from each of the gyro sensors with an input axis aligned to a first angular orientation;

acquiring a second data from each of the gyro sensors with the input axis flipped to a second angular orientation opposite to the first angular orientation after acquiring the first data;

determining an earth rate component at the first angular orientation based on a difference between the first data and the second data to cancel out bias of each of the gyro sensors;

repeating acquiring the first data, acquiring the second data and determining the earth rate component for each of the gyro sensors at a plurality of discrete angular orientations;

fitting a sinusoidal curve to the earth rate components at the plurality of discrete angular orientations;

determining an earth rate vector with respect to a predetermined orthogonal sensor coordinates based on based on a result of the sinusoidal curve fitting;

determining a gravity direction with respect to the orthogonal sensor coordinates based on acceleration data of gravity acquired with the accelerometers;

determining a north direction by projecting the earth rate vector onto a horizontal plane perpendicular to the gravity direction; and

determining an azimuth of a target direction on the horizontal plane based on the north direction.

37. The method according to claim 36, wherein the target direction is one of the coordinate axes of the orthogonal sensor coordinates.

38. The system according to claim 36, wherein the sinusoidal curve is expressed as follows:

Ω

_i=A cos θ

_i+B sin θ

_i

where Ω

_i is an earth rate component at an angular orientation θ

_i, and A and B are fitting parameters, and

wherein fitting the sinusoidal curve comprises determining the fitting parameters A and B.

39. The system according to claim 36, wherein the earth rate component is determined by subtracting the second data from the first data and dividing the difference data by two.

40. The system according to claim 39, the program further having instructions for:

acquiring a third data from each of the gyro sensors with the input axis aligned to the same angular orientation as the first angular orientation after acquiring the second data;

obtaining an average of the first data and the third data; and

repeating acquiring the third data and obtaining the average for each of the gyro sensors at a plurality of discrete angular orientations,

wherein the average is used instead of the first data for determining the earth rate component.

41. The system according to claim 36, the program further having instructions for:

determining a ratio of sensitivity of a pair of the gyro sensors based on a set of data from the gyro sensors with the input axes aligned to the common first angular orientation; and

correcting the earth rate components used for determining the earth rate vector, based on the ratio of sensitivity.

42. The system according to claim 41, wherein the gyro sensors comprise an XY-gyro sensor with an input axis rotatable about a Z-axis, a YZ-gyro sensor with an input axis rotatable about an X-axis, and a ZX-gyro sensor with an input axis rotatable about a Y-axis, and

wherein the earth rate vector Ω

₀ is determined based on a predetermined threshold value and a selection criterion with following three equations;

If Ω

_Cz>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Cx}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}}{{\mathrm{\Omega <br><br>}}_{\mathrm{Cz}}},{\mathrm{\Omega <br><br>}}_{\mathrm{Ay}},{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}\right),$

If Ω

_Bx>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Cx}},{\mathrm{\Omega <br><br>}}_{\mathrm{By}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{Cx}}}{{\mathrm{\Omega <br><br>}}_{\mathrm{Bx}}},{\mathrm{\Omega <br><br>}}_{\mathrm{Cz}}\right),$

If Ω

_Ay>

threshold value, use

${\mathrm{\Omega <br><br>}}_0=\left({\mathrm{\Omega <br><br>}}_{\mathrm{Bx}},{\mathrm{\Omega <br><br>}}_{\mathrm{By}},{\mathrm{\Omega <br><br>}}_{\mathrm{Az}}<br><br>\frac{{\mathrm{\Omega <br><br>}}_{\mathrm{By}}}{{\mathrm{\Omega <br><br>}}_{\mathrm{Ay}}}\right),$

where Ω

_Ax, Ω

_Ay and Ω

_Az represent earth rate components on orthogonal axes measured by the XY-gyro sensor, Ω

_Bx, Ω

_By and Ω

_Bz represent earth rate components on the orthogonal axes measured by the YZ-gyro sensor, and Ω

_Cx, Ω

_Cy and Ω

_Cz represent earth rate components on the orthogonal axes measured by the ZX-gyro sensor.

43. The system according to claim 36, wherein the data from each of the gyro sensors are acquired under a stationary condition.

44. The system according to claim 36, the program further having an instruction for smoothing the data from each of the gyro sensors.

45. The system according to claim 36, wherein the azimuth measurement is performed using the gyro sensors located at the measuring position in downhole.

46. The system according to claim 36, wherein the gyro rotating mechanism is configured to rotate each of the gyro sensors about an axis perpendicular to the input axis.

47. The system according to claim 36, wherein each of the accelerometers is a MEMS type accelerometer.

48. The system according to claim 36, wherein each of the gyro sensors is a MEMS type gyro sensor.

49. The system according to claim 48, wherein the MEMS gyro sensor is a ring oscillating type gyro sensor.

50. The system according to claim 36, wherein the rotating mechanism is configured to rotate a peripheral circuit of the gyro sensor together with the gyro sensor, and wherein the peripheral circuit outputs digital signals.

51. The system according to claim 36, wherein the rotating mechanism includes at least one set of a motor and a gear mechanism transporting rotating force from the motor to the gyro sensor.

52. The system according to claim 36, the rotating mechanism includes at least one step motor to flip or rotate the gyro sensors.

53. The system according to claim 36, wherein each of the gyro sensors includes the rotating mechanism.

54. The system according to claim 36, wherein the gyro rotating mechanism includes at least one angle position sensor for measuring a rotation angle of each of the gyro sensors with respect to a reference direction and monitoring each of the angular orientations.

55. The system according to claim 36, further comprising:

at least one temperature sensor to measure temperature of the gyro sensors and the accelerometers.

56. The system according to claim 55, wherein the measured temperature is used to compensate temperature effect in the gyro sensors and the accelerometers.

57. The system according to claim 36, further comprising at least one gyro sensor for monitoring rotation of a downhole tool having the system,

wherein the rotation of the downhole tool is monitored based on the azimuth measurement performed at predetermined timing in downhole.

58. The system according to claim 36, wherein the data processing unit is a DSP or a FPGA.

59. The system according to claim 36, wherein the power unit is a battery.