Rate gyro wells survey system including nulling system

• US 5,806,195 A
• Filed: 06/17/1997
• Issued: 09/15/1998
• Est. Priority Date: 12/19/1994
• Status: Expired due to Term

• Current Assignee: Eric Wright, Gary Uttecht, Greg Allen Neubauer, James Brosnahan
• Original Assignee: Eric Wright, Gary Uttecht, Greg Allen Neubauer, James Brosnahan
• Inventors: Wright, Eric, Neubauer, Greg Allen, Uttecht, Gary, Brosnahan, James
• Primary Examiner(s): Fulton, Christopher W.
• Application Number:
  US08/877,159
• Time in Patent Office: 455 Days
• Field of Search: 33/304, 33/301, 33/302, 33/303, 33/312, 33/313, 33/114
• US Class Current: 33/304
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

Abstract

A method for well borehole survey is set out. A sonde supports X and Y accelerometers and X and & sensors on a rate gyro having a Z axis aligned with the sonde. On a slickline, or within a drill string, the sonde is used to measure four variables, these being G_x and G_y, A_x and A_z. This enables well azimuth and inclination to determined. Measuring depth enables a survey to be made.

Claims

1. A method of performing a survey of a well borehole comprising the steps of:

(a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°

of housing rotation, and

(i) a first output indicative of north comprises N measurements is determined at said first sonde position,

(ii) said housing is then rotated by 180° and

a second output indicative of north comprising another N measurements is determined at said second sonde position, and

(iii) N is an integer;

(b) combining said first and second outputs indicative of north to yield a measure of north in which systematic instrument error is reduced;

(c) positioning the sonde at spaced locations along a well borehole; and

(d) repeating step a) at each said spaced location.

2. The method of claim 1, wherein N is greater than 1 and said first output indicative of north is obtained from an average of said N measurements and said second output indicative of north is obtained from an average of said N measurements with said housing rotated 180°

.

3. The method of claim 2 wherein rate gyro housing rotation occurs after N measurements are made, thereby enabling said N measurements to be made in a selected time interval and a second set of measurements to be made in a second selected time interval.

4. The method of claim 2 wherein each said spaced location is at evenly spaced locations along said well borehole so that the borehole survey has a desired set of data points.

5. The method of claim 1, wherein;

(a) said first output indicative of north is defined in a first X-Y quadrant which is orthogonal to the major axis of said elongated sonde;

(b) said second output indicative of north is defined in a second X-Y quadrant; and

(c) said first and second X-Y quadrants lie in a common plane and are azimuthally spaced at 180°

.

6. The method of claim 1 wherein said sonde is lowered to the bottom of a drill string in the well borehole on a slickline and the slickline is retrieved leaving the sonde in said well borehole.

7. The method of claim 6 including the additional step of measuring the direction of said sonde along said well borehole at each said spaced location, and determining therefrom gravity direction at each said spaced location while tripping said drill string out of the borehole.

8. The method of claim 7 wherein said measurements of north and said gravity direction measurements are made spaced along said well borehole by the length of a stand of pipe in the drill string.

9. The method of claim 1 wherein said sonde is lowered to the bottom of said well borehole to enable a survey to be conducted, retrieving the sonde along the borehole, and making said measurements along the borehole said spaced locations.

10. The method of claim 9 wherein said sonde is stopped at said spaced locations along said well borehole and said measurements are made and stored in the sonde until retrieval to the surface.

11. A method of obtaining a survey in a well borehole subject to deviation from the vertical which comprises the steps of:

(a) positioning in a well borehole a rate gyro having an axis of rotation coincident with the major axis of a sonde which supports said rate gyro;

(b) moving said sonde along the well borehole and making two orthogonal signal measurements at spaced locations;

(c) combining said two orthogonal signals measurements to obtain a reference north measurement;

(d) reducing systematic instrument error ill said orthogonal signal measurements by making measurements differing by 180°

;

(e) measuring the direction of gravity along the sonde during movement in the well borehole by making an additional two orthogonal signal measurement; and

(f) determining from said additional two orthogonal measurements at least two dimensions of the position of the sonde in the well borehole.

12. The method of claim 11 including the step of determining sonde depth within said well borehole.

13. The method of claim 12 including the step of determining well borehole azimuth for said survey.

14. The method of claim 13 including the step of determining well borehole inclination for said survey.

15. The method of claim 14 including the step of making said signal measurements recorded in memory within said sonde and retrieving the sonde to obtain data recorded in memory.

16. A method of performing a survey of a well borehole comprising the steps of:

(a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°

of housing rotation, and

(b) making a first gyro measurement indicative of north;

(c) moving said gyro and making second, third and fourth measurements indicative of north and wherein

(i) said first and said third measurements arc at 180°

;

(ii) said second and said fourth measurements are at 180°

; and

(iii) said measurements are made after 90°

rotation;

(d) summing said measurements indicative of north to yield a measure of north;

(e) reducing instrument error in said summation of north by combining said measurements;

(f) moving said sonde between spaced locations along a well borehole; and

(g) repeating steps (b)-(e) at each said spaced location.

17. The method of claim 16 wherein said first, second, third and fourth measurements are each defined by an average of N measurements, where N is an integer greater than 1.

18. The method of claim 17 wherein rate gyro housing rotation occurs after N measurements are made, thereby enabling said N measurements to be made in a selected time interval.

19. The method of claim 16 wherein each said spaced location is at evenly spaced locations along said well borehole so that the borehole survey has a desired set of data points.

20. The method of claim 16 wherein said sonde is lowered to the bottom of a drill string in the well borehole on a slickline and the slickline is retrieved leaving the sonde in said well borehole.

21. The method of claim 20 including the additional step of measuring the direction of said sonde alone said well borehole at each said spaced location, and determining therefrom gravity direction at each said spaced location while tripping said drill string out of the borehole.

22. The method of claim 21 wherein said measurements of north and said gravity direction measurements are made spaced along said well borehole by the length of a stand of pipe in the drill string.

23. The method of claim 16 wherein said sonde is lowered to the bottom of said well borehole to enable a survey to be conducted, retrieving the sonde along the borehole, and making said measurements along the borehole said spaced locations.

24. The method of claim 23 wherein said sonde is stopped at said spaced locations along said well borehole and said measurements are made and stored in the sonde until retrieval to the surface.

25. A method for measuring the position of a survey sonde in a well borehole, comprising the steps of:

(a) positioning a rate gyro in a well survey sonde;

(b) moving the sonde to a survey position in the well borehole;

(c) making a first and a second gyro reading at that survey position, wherein said first and second gyro readings provide information useful in determining north;

(d) positioning a pair of accelerometers at right angles in said sonde wherein one accelerometer is located in a plane at right angles to the major axis of said sonde;

(e) moving the sonde to a second survey position along the well borehole;

(f) making accelerometer measurements as the sonde moves along the well borehole; and

(g) determining from said gyro measurements and said accelerometer measurements the path of the well borehole in the earth.

26. The method of claim 25 wherein said sonde is lowered to the bottom of a drill string in the well borehole on a slickline and the slickline is retrieved leaving the sonde in said well borehole.

27. The method of claim 26 wherein said sonde is moved along the well borehole while tripping said drill string out of the borehole.

28. The method of claim 25 wherein said gyro measurements and said accelerometer measurements are made at spaced locations along said well borehole by the length of a stand of pipe in a drill string.

29. The method of claim 25 wherein said sonde is lowered to the bottom of said well borehole, retrieving the sonde along the borehole, and making said gyro and accelerometer measurements along the borehole said spaced locations.

30. The method of claim 29 wherein said sonde is stopped at said spaced locations along said well borehole and said gyro and accelerometer measurements are made and stored in the sonde until retrieval to the surface.

31. The method of claim 30 wherein said direction measurements are made at a plurality of spaced locations within said well borehole.

32. A method of performing a survey of a well borehole comprising the steps of:

(a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°

of housing rotation, and wherein power to operate components within said sonde is supplied by a power supply within said sonde, and

(i) a first output indicative of north comprises N measurements is determined with said gyro in said first position,

(ii) said housing is then rotated by 180° and

a second output indicative of north comprising another N measurements is determined with said gyro in said second position, and

(iii) N is an integer; and

(b) combining said first and second outputs indicative of north to yield a measure of north which contains reduced systematic instrument error.

33. The method of claim 32 wherein N is greater than 1 and said first output indicative of north is obtained from an average of said N measurements and said second output indicative of north is obtained from an average of said N measurements with said housing rotated 180°

.

34. The method of claim 33 wherein rate gyro housing, rotation occurs after N measurements are made, thereby enabling, said N measurements to be made in a selected time interval and a second set of measurements to be made in a second selected time interval.

35. The method of claim 33 including the additional step of;

(a) providing two accelerometers within said sonde;

(b) measuring the inclination of said sonde within said well borehole using, the responses of said accelerometers; and

(c) determining therefrom gravity direction.

36. A method claim 35 including the additional steps of:

(a) making a third and a forth measurement, both of which are responsive to north and which are 180°

apart and wherein

(i) said first and said third measurements are at 180°

, and

(ii) said second and said fourth measurements are at 180°

;

(b) summing, said measurements responsive to north to yield a measure of north; and

(c) reducing instrument error in said measurement of north by combining said first and third measurements responsive to north.

37. The method of claim 36 wherein said first and third measurements are made with said gyro, and said second and fourth measurements are made with one of said two accelerometers.

38. The method of claim 32 wherein;

(a) said first output indicative of north is defined in a first X-Y quadrant which is orthogonal to the major axis of said elongated sonde;

(b) said second output indicative of north is defined in a second X-Y quadrant; and

(c) said first and second X-Y quadrants lie in a common plane and are azimuthally spaced at 180°

.

39. A method of obtaining a survey in a well borehole, comprising the steps of:

(a) positioning in a well borehole a rate gyro;

(b) obtaining direction measurements X, Y, -X and -Y from the response of said rate gyro, wherein X and -X differ by 180° and

Y and -Y differ by 180°

;

(c) obtaining a reference direction measurement from said direction measurements; and

(d) combining pairs of said direction measurements to reduce systematic instrument error in said reference direction measurement.

40. The method of claim 39 wherein;

(a) said rate gyro comprises at least one axis; and

(b) said rate gyro is positioned such that X+90°

=Y.

41. The method of claim 40 wherein each of said direction measurements are repeated N times at at least one spaced location within said well borehole.

42. The method of claim 41 where N is an integer greater than one.

43. The method of claim 39 wherein said reference measurement is true north.

44. The method of claim 39 wherein said reference measurement is a high side of a sonde containing said rate gyro.

45. A method for obtaining the orientation of a sonde within a well borehole, comprises the steps of:

(a) positioning a rate gyro having at least one axis within said sonde;

(b) with said gyro, making at least two orthogonal signal measurements at at least one location within said well borehole;

(c) obtaining a measure of true north from said two orthogonal signal measurements;

(d) measuring the direction of gravity at said at least one location within said well borehole; and

(e) determining from said at least two orthogonal signal measurements and said measure of gravity the azimuthal orientation of said sonde within said well borehole.

46. The method of claim 45 wherein said orientation of said sonde comprises the position of the high side of the sonde with respect to true north.

47. The method of claim 45 further comprising the steps of:

(a) moving said sonde along the well borehole;

(b) obtaining said measures of true north and of gravity at M spaced locations within said well borehole, where M is an integer greater than 1; and

(c) determining said azimuthal orientation of said sonde within said borehole at each said spaced location.

48. The method of claim 45 wherein said sonde is affixed to a second borehole instrument, and the orientation of said second borehole instrument within said borehole is obtained from said orientation of said sonde within said borehole.

49. The method of claim 45 wherein an additional two signal measurements are made and combined with said two orthogonal signal measurements to reduce systematic instrument error in said measure of true north.

50. The apparatus of claim 49 wherein said means for conveying said sonde comprises affixing said sonde to a borehole instrument which is conveyed by means of a wireline.

51. The apparatus of claim 50 wherein said sequence of data defines the azimuthal orientation of said borehole instrument within said well borehole.

52. The apparatus of claim 51 wherein said azimuthal orientation is defined with respect to said measure of true north.

53. An apparatus for measuring a sequence of data from within a well borehole, comprising;

(a) a sonde which is conveyed within said borehole, wherein said sonde comprises

(i) a rate gyro comprising at least one axis,

(ii) a power supply to operate said rate gyro,

(iii) a memory for recording response of said rate gyro, and

(iv) means for measuring the direction of gravity acting upon said sonde;

(b) a CPU for

(i) combining a first and a second measurement from said rate gyro to obtain a measure of true north,

(ii) combining a third and a fourth measurement from said rate gyro with said first and second measurements to reduce systematic instrument error in said measure of true north; and

(iii) combining said measure of gravity direction and said measure of true north to obtain said measured sequence of data; and

(c) means for conveying said sonde within said well borehole.

54. The apparatus of claim 53 wherein said means for conveying said sonde comprises a slick line.

55. The apparatus of claim 53 wherein said means for conveying said sonde comprises a drill string.

56. The apparatus of claim 53 wherein said means for conveying said sonde comprises the force of gravity.

57. The apparatus of claim 53 further comprising means for measuring the depth of said sonde within said well borehole.

58. The apparatus of claim 53 wherein said sequence of data defines a three dimensional path of said well borehole within the earth.

59. The apparatus of claim 53 wherein said sequence of data defines the azimuthal orientation of said sonde within said well borehole.

60. The apparatus of claim 59 wherein said azimuthal orientation is defined with respect to said measure of true north.