Azimuth determination for vector sensor tools

• US 4,559,713 A
• Filed: 12/06/1983
• Issued: 12/24/1985
• Est. Priority Date: 02/24/1982
• Status: Expired due to Term

• Current Assignee: Applied Technologies Associates, Inc.
• Original Assignee: Applied Technologies Associates, Inc.
• Inventors: Engebretson, Harold J., Van Steenwyk, Brett H., LaHue, Philip M., Ott, Paul W.
• Primary Examiner(s): Little, Willis
• Application Number:
  US06/558,598
• Time in Patent Office: 749 Days
• Field of Search: 33/302, 33/304, 33/312, 33/313, 33/324
• US Class Current: 33/302
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

Abstract

This invention relates to mapping or survey apparatus and methods, and more particularly concerns derivation of the azimuth output indications for such apparatus in a borehole from the outputs or output indications of either an inertial angular rate vector sensor (or sensors) and an acceleration vector sensor (or sensors), or a magnetic field vector sensor (or sensors), and from the outputs of an acceleration vector sensor (or sensors). At least one of such sensors in any instrument may be canted relative to the borehole axis. Borehole tilt is also derived.

Claims

1. In mapping or survey apparatus using a single inertial angular rate sensor and a single acceleration sensor, one or both with input axes of sensitivity nominally canted relative to a well or borehole axis, rotated about the borehole axis and both sensors having outputs, the combination comprising

(a) means responsive to the accleration sensor output together with the inertial angular rate sensor output to compute from the rate sensor output the components thereof in the horizontal plane and the vertical plane, and

(b) means to derive azimuth as the Arcsin of the component of sensed inertial angular rate in the horizontal plane normal to the plane containing the borehole axis and the gravity vector divided by the horizontal plane component of the earth'"'"'s angular velocity vector.

2. The apparatus of claim 1 including

(c) means responsive to the acceleration sensor output to compute the component of the earth'"'"'s rotation rate in the horizontal plane at its intersection with the vertical plane containing the gravity vector and the borehole axis from the sensed angular rate, and

(d) means to derive azimuth as the Arcos of the component computed in (c) divided by the horizontal plane component of the earth'"'"'s angular velocity vector.

3. The apparatus of claim 2 including

(e) means to compute azimuth as the Arctan of the argument computed in (b) divided by the argument computed in (c).

7. The combination of claim 1 where the inertial angular rate sensor is replaced by a magnetic field vector sensor, the earth'"'"'s angular velocity vector is replaced by the earth'"'"'s magnetic field vector, and magnetic azimuth is computed.

8. The combination of claim 1 wherein the inertial angular rate sensors are replaced by magnetic field vector sensors, the earth'"'"'s angular velocity vector is replaced by the earth'"'"'s magnetic field vector, and magnetic azimuth is computed.

9. The apparatus of claim 2 in which one of the sensors has its input axis of sensitivity canted so as to provide sensing of a component along the borehole axis, and employing a canted accelerometer output component along the borehole axis to increase the accuracy of tilt or inclination angle for near horizontal boreholes.

10. The apparatus of claim 9 includes means to compute tilt or inclination as the Arccos of the gravity component along the borehole axis, divided by the known magnitude of the earth'"'"'s gravity vector.

11. The apparatus of claim 9 including means to compute tilt or azimuth as the Arctan of the gravity component normal to the borehole axis in the vertical plane divided by the component along the borehole axis.

12. The apparatus of claim 9 including means responsive to the acceleration sensor output together with the canted inertial angular rate sensor output component along the borehole axis to compute a second estimate of the component of the earth'"'"'s rotation rate in the horizontal plane at its intersection with the vertical plane containing the gravity vector and the borehole axis.

13. The apparatus of claim 9 including means to compute azimuth as the Arccos of the component computed in (d) divided by the horizontal plane component of the earth'"'"'s angular velocity vector.

14. The apparatus of claim 9 including means to compute azimuth as the Arctan of the argument computed in (b) of claim 1 above divided by the argument computed in (d) above.

41. Apparatus as defined in claim 9 wherein the inertial angular rate sensor is replaced by a magnetic field sensor, the earth'"'"'s angular velocity vector is replaced by the earth'"'"'s magnetic field vector and magnetic azimuth is computed.

4. In mapping or survey apparatus using two axis inertial angular rate sensor means and two-axis acceleration sensor means both with their two input axes of sensitivity nominally normal to a well or borehole axis, both sensors having outputs,

(a) means responsive to acceleration sensor outputs together with the inertial angular rate sensor outputs to compute from the rate sensor outputs the components thereof in the horizontal and vertical plane, and

(b) means to derive azimuth as the Arcsin of the component of sensed inertial angular rate in the horizontal plane normal to the plane containing the borehole axis and the gravity vector divided by the horizontal plane component of the earth'"'"'s angular velocity vector.

5. The apparatus of claim 4 including

(c) means responsive to the acceleration sensor output to compute the component of the earth'"'"'s rotation rate in the horizontal plane at its intersection with the vertical plane containing the gravity vector and the borehole axis from the sensed angular rate, and

(d) means to compute azimuth as the Arccos of the component computed in (c) divided by the horizontal plane component at the earth'"'"'s angular velocity vector.

6. The apparatus of claim 5 including

(e) means to compute azimuth as the Arctan of the argument computed in (b) divided by the argument computed in (c).

15. In borehole survey apparatus wherein angular rate sensor means and acceleration sensor means are suspended and effectively rotated in a borehole, at least one of said sensors canted at an angle γ

relative to the borehole axis, the angular rate sensor means having amplitude output GA, and rotation related phase output GP, and the acceleration sensor means having amplitude output AA and rotation related phase output AP, there also being means supplying a signal value Ω

_v proportional to earth'"'"'s angular rate of rotation, and means supplying a value derived from γ

, the improvement which comprises

(a) first means for combining AA, AP, GA, GP, said value derived from γ

, and Ω

_v, to derive a value ψ

for borehole azimuth at the level of said sensor means in the borehole.

16. The apparatus of claim 15 including

(b) second means operatively connected with said first means for employing AA modified by said value derived from γ

to derive a value φ

for borehole tilt from vertical at the level of said sensor means in the borehole.

17. The apparatus of claim 15 wherein said first means includes (c) means responsive to GA modified by said value derived from γ

, GP and AP to derive

(i) a first component Ω

_x of the angular rate sensor output, and

(ii) a second component Ω

_y of the angular rate sensor output.

18. The apparatus of claim 17 wherein said (c) means to derive Ω

_x and Ω

_y includes (d) means responsive to GP and AP to produce a phase angle value α

representative of the difference in phase of said GP and AP outputs, (e) means responsive to α

to produce sin α and

cos α

values, (f) means to multiply modified GA and said sin α

value to produce Ω

_y, and (g) means to multiply modified GA and said cos α

value to produce Ω

_x.

19. The apparatus of claim 17 wherein said first means includes (h) means responsive to Ω

_x, AA modified by said value derived from γ and

Ω

_v to derive a value Ω

_B '"'"', and (j) means responsive to Ω

_y and Ω

'"'"'_B to derive said value ψ

for borehole azimuth.

20. The apparatus of claim 19 wherein said (h) means includes:

(h₁) an arc sin generator responsive to modified AA to generate an output,

(h₂) sin and cos generator means responsive to said output of the arc sin generator to generate an output sin φ and

an output cos φ

,

(h₃) multiplier means responsive to sin φ and

Ω

_v to produce a product thereof,

(h₄) substractor means responsive to said product and Ω

_x to obtain a difference value,

(h₅) divider means to divide said difference value by said output cos φ

to obtain said value Ω

'"'"'_B.

21. The apparatus of either one of claims 19 and 20 wherein said (i) means includes an arc tangent generator responsive to Ω

_y and Ω

_B to produce an output proportional to arc tan -Ω

_y /Ω

'"'"'_B which is representative of azimuth ψ

.

22. The apparatus of claim 20 wherein said elements (h₁)-(h₅) are operatively interconnected.

25. The apparatus of either one of claims 15 and 23 including means suspending said rate sensor means and accelerometer sensor means in the borehole at an elevation at which said derivation of ψ

is carried out.

32. The apparatus of one of claims 15, 23 and 26 wherein said value derived from γ

is a value for cos γ and

said first means (a) includes means for dividing GA by said cos γ

value to derive a modified value of GA, and for dividing AA by said cos γ

value to derive a modified vlaue of AA.

33. The apparatus of claim 16 wherein said angular rate sensor has a steady output component GAV and said acceleration sensor means has a steady output component AAV, and said first means receives said steady outputs for combination with AA, AP, GA, GP, values derived from γ

, and Ω

_v to derive said value ψ

.

34. The apparatus of claim 33 wherein said values derived from γ

correspond to cos γ and

sin γ

, and said first means includes (c) means responsive to GA divided by cos γ

to produce a value GA'"'"', GP and AP to derive

(i) a primary component Ω

_y of the angular rate sensor output.

35. The apparatus of claim 34 wherein said (c) means to derive Ω

_y includes (d) means responsive to GP and AP to produce a phase angle value α

representative of the difference in phase of said GP and AP outputs, (e) means responsive to α

to produce sin α and

cos α

values, and (f) means to multiply GA'"'"' and said sin α

value to produce Ω

_y.

36. The apparatus of claim 35 wherein said first means includes (g) means responsive to GAV divided by sin γ

to produce a value Ω

_z, and including (h) means responsive to said values AA and AAV, and said cos α and

sin α

values and _v to produce a value Ω

_y cos φ

for addition to Ω

_z and subsequent division by sin φ

to produce a value Ω

'"'"'_B.

37. The apparatus of claim 36 including (i) means responsive to Ω

_y and Ω

'"'"'_B to produce said value ψ

.

38. The apparatus of claim 36 wherein φ

is the borehole tilt angle, and said (h) means includes (j) means responsive to AA, AAV, cos α and

sin α

to generate φ

.

39. The apparatus of claim 15 wherein the angular rate sensor is canted at said angle γ

.

40. The apparatus of claim 15 wherein the acceleration sensor means is canted at said angle γ

.

23. In well bore survey apparatus wherein angular rate sensor means and accelerometer means are located in a borehole and at a cant angle γ

relative to the borehole axis, the angular rate sensor means having amplitude output GA and phase output GP, and the accelerometer means having amplitude output AA and phase output AP, there being means providing a value Ω

_v proportional to earth'"'"'s angular velocity vector, and means supplying the combination comprising values derived from γ

,

(a) means operatively connection to said sensors to be responsive to GA, GP and AP and a value derived from γ

to derive a first component Ω

_x of the angular rate sensor output,

(b) means operatively connected to said sensors to be responsive to GA, GP and AP and a value derived from γ

to derive a second component Ω

_y of the angular rate sensor output,

(c) means operatively connected to said (a) means to be responsive to Ω

_x, AA and Ω

_v to derive a value Ω

'"'"'_B, and

(d) means operatively connected to said (b) and (c) means to derive ψ

from Ω

_y and Ω

'"'"'_B

wherein ψ

is an azimuth value indicative of the azimuth angle of the borehole relative to the true North at the location of said sensor means.

24. The combination of claim 23 including

(a) means responsive to AA to derive a value φ

for borehole tilt at the location of said sensor means in the borehole.

26. In borehole survey apparatus wherein magnetic sensor means and acceleration sensor means are suspended and effectively rotated in a borehole and at a cant angle γ

relative to the borehole axis, the magnetic sensor means having amplitude output GA and rotation related phase output GP, and the acceleration sensor means having amplitude output AA and rotation related phase output AP, there also being means supplying a signal value Ω

_v proportional to earth'"'"'s angular rate of rotation, and means supplying a value derived from γ

the improvement which comprises

(a) first means for combining AA, AP, GA, GP said value derived from γ and

Ω

_v to derive a value ψ

for borehole azimuth at the level of said sensor means in the borehole.

27. The apparatus of claim 26 including

(b) second means operatively connected with said first means for employing AA modified by said value derived from γ

to derive a value φ

for borehole tilt from vertical at the level of said sensor means in the borehole.

28. The apparatus of claim 26 wherein said first means includes (c) means responsive to GA modified by said value derived from γ

, GP and AP to derive

(i) a first component Ω

_x of the magnetic sensor output, and

(ii) a second component Ω

_y of the magnetic sensor output.

29. The apparatus of claim 28 wherein said (c) means to derive Ω

_x and Ω

_y includes (d) means responsive to GP and AP to produce a phase angle value α

representative of the difference in phase of said modified GP and AP outputs, (e) means responsive α

to to produce sin α and

cos α

values, (f) means to multiply modified GA and said sin α

value to produce Ω

_y, and (g) means to multiply modified GA and said cos α

value to produce Ω

_x.

30. The apparatus of claim 28 wherein said first means includes (h) means responsive to Ω

_x, modified AA and Ω

_x to derive a value Ω

'"'"'_B and (j) means responsive to Ω

_y and Ω

'"'"'_B to derive said value ψ

for borehole azimuth.

31. The apparatus of claim 30 wherein said (h) means includes:

(h₁) an arc sin generator responsive to modified AA to generate an output,

(h₂) sin and cos generator means responsive to said output of the arc sin generator to generate an output sin φ and

an output cos φ

,

(h₃) multiplier means responsive to sin φ and

Ω

_v to produce a product thereof,

(h₄) substractor means responsive to said product and Ω

_x to obtain a difference value,

(h₅) divider means to divide said difference value by said output cos φ

to obtain said value Ω

'"'"'_B.