Rotating magnet for distance and direction measurements from a first borehole to a second borehole

• US 5,589,775 A
• Filed: 12/05/1995
• Issued: 12/31/1996
• Est. Priority Date: 11/22/1993
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Vector Magnetics, Inc.
• Inventors: Kuckes, Arthur F.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/567,578
• Time in Patent Office: 392 Days
• Field of Search: 324/338, 324/346, 324/326, 324/207.11, 324/207.13, 324/207.14, 324/207.15, 324/207.22, 324/207.23, 324/207.26, 175/40, 175/45, 175/50, 166/66.5
• US Class Current: 324/346
• CPC Class Codes: E21B 47/0228 using electromagnetic energy or detectors therefor
• CPC Class Codes: G01V 3/26 operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device with electromagnetic waves G01V3/30

Abstract

A method for determining the distance and direction from a first borehole to a second borehole includes generating, by way of a rotating magnetic field source at a first location in a second borehole, and elliptically polarized magnetic field in the region of the first borehole. First and second sensors positioned at an observation point in the first borehole measure the amplitude and relative phase of respective first and second components of the polarized magnetic field and from these measurements, the direction, relative to the sensors, from the observation point to the first location is determined. The distance between these points is determined by measuring at plural observation points amplitude variations with depth of the rotating magnetic field in the first borehole, and computing theoretical variations in the amplitude for different assumed distances between the observation points and the location of the magnetic field source. The measured amplitude variations are compared with theoretical variations to determine the distance between the first and second boreholes.

Claims

1. A method for determining the direction from a magnetic field source to an observation point, comprising:

generating, by way of a rotating magnetic field source at a first location, an elliptically polarized magnetic field in the region of an observation point;

measuring, by first and second sensors at said observation point the amplitude and relative phase of respective first and second perpendicular vector components of said ellipticity polarized rotating magnetic field; and

determining from said measurements the direction, relative to said sensors, from said observation point to said first location.

2. The method of claim 1, further including:

determining the total field strength of said polarized magnetic field at said observation point;

determining the strength of said magnetic field source; and

determining from the measured total field strength and from the strength of said magnetic field source, the distance from said observation point to said source.

3. The method of claim 2, wherein the step of determining the strength of said source comprises measuring said source prior to its placement in said first borehole.

4. The method of claim 1, further including:

determining the orientation of said first and second sensors to obtain an absolute direction from said observation point to said first location.

5. The method of claim 4, wherein the step of determining the orientation of said first and second sensors includes determining their orientation with respect to the earth'"'"'s magnetic field.

6. The method of claim 4, further including locating said observation point in an existing borehole, and said rotating magnetic field source in a second borehole, and wherein the step of determining the orientation of said first and second sensors includes determining their orientation with respect to the high side of said existing borehole.

7. The method of claim 4, wherein the step of determining the orientation of said first and second sensors includes providing a gyroscope at said observation point and establishing therefrom reference axes for said sensors, the direction from said observation point to said first location being relative to said sensor reference axes.

8. The method of claim 1, further including determining from said measurements the distance from said observation point to said first location.

9. A method for determining the distance and direction from a magnetic field source to an observation point, comprising:

generating from a rotating magnetic field source at a first location an elliptically polarized magnetic field in the region of an observation point;

measuring, by first and second sensors at the observation point, variations in amplitude and relative phase of respective first and second components of said polarized magnetic field;

determining from said measurements the direction, relative to said sensors, from said observation point to said first location;

measuring at plural observation points amplitude variations of the rotating magnetic field;

computing theoretical variations in the amplitude of the rotating magnetic field for different selected distances between said observation points and said first location; and

comparing the measured amplitude variations with the computed theoretical variations to determine the distance between said first location and said observation points.

10. The method of claim 9, further including locating said rotating magnetic field source in a first borehole and said observation points in a second borehole and measuring said amplitude variations at plural observation points in a second borehole to thereby determine the distance between said first and second boreholes.

11. The method of claim 10, further including measuring first and second perpendicular vector components of said polarized magnetic field by said first and second sensors, determining the orientation of said sensors, and determining from said measured components and said orientation an absolute direction from said second borehole to said first borehole.

12. A method for determining the distance from a first borehole to a second borehole, comprising:

generating, by way of a rotating magnetic field source at a first location in a first borehole, an elliptically polarized magnetic field in the region of a second borehole;

measuring at plural observation points in said second borehole, variations with depth in the amplitude of said polarized magnetic field;

computing theoretical variations in the amplitude of the total magnetic field for different selected distances between said observation points and said first location; and

comparing the measured amplitude variations with the computed theoretical variations to determine the distance between said first and second boreholes.

13. A method for determining the distance from a first borehole to a second borehole, comprising:

generating by way of a rotating magnetic field source at a first location in a first borehole, a rotating elliptically polarized magnetic field extending to the region of a second borehole;

measuring, by first and second sensors at an observation point in said second borehole, the total rotating magnetic field;

measuring at plural observation points in said second borehole the amplitude variations with depth of the total magnetic field in the second borehole;

computing theoretical variations in the amplitude of the total magnetic field for different selected distances between said observation points and said first location;

comparing the measured amplitude variations with the computed theoretical variations to determine the distance between said first and second boreholes;

obtaining from the determined distance between said first and second boreholes and from said measured total magnetic field at said second borehole the strength of said magnetic field source; and

determining from said magnetic field source strength and from the measured total magnetic field the distances from plural observation points in said second borehole to source locations in said first borehole.

14. Apparatus for determining the direction from a magnetic field source to an observation point, comprising:

a rotating magnetic field source at a first location, said source producing a rotating, elliptically polarized magnetic field in the earth;

an observation point located in said rotating magnetic field;

first and second sensors located at said observation point to measure first and second vector components of said rotating elliptically polarized magnetic field; and

means for determining, from measurements of the amplitude and phase of said first and second measured components, the direction of said source with respect to said sensors.

15. The apparatus of claim 14, wherein said source is located in a first borehole and said observation point is in a second borehole, and wherein said first and second boreholes are generally horizontal and are spaced apart.

16. The apparatus of claim 15, wherein said boreholes are parallel.

17. The apparatus of claim 15, wherein said first and second boreholes are generally vertical and spaced apart.

18. The apparatus of claim 17, wherein said first and second boreholes are parallel.

19. The apparatus of claim 14, wherein said magnetic field source is a permanent magnet mounted for rotation on a drill string in a borehole being drilled for measurement while drilling.

20. The apparatus of claim 19, wherein said permanent magnet has a north-south axis mounted perpendicular to an axis of rotation of said drill string.

21. The apparatus of claim 14, further including means for orienting said first and second sensors.

22. The apparatus of claim 21, wherein said source is located in a first borehole and said observation point is in a second borehole, and wherein said orienting means includes means for determining the direction of a high side of said second borehole with respect to said sensors.

23. The apparatus of claim 21, wherein said orienting means includes gyroscope means.

24. The apparatus of claim 14, further including means for measuring the strength of said magnetic field at said observation point and for determining the distance between said observation point and said first location.

25. A method for determining the direction from a target borehole to a borehole being drilled, comprising:

generating a rotating elliptically polarized magnetic field in said borehole being drilled;

measuring the amplitude and relative phase of perpendicular vector components of said rotating magnetic field at an observation location in said target borehole; and

determining from said vector components the direction from said borehole being drilled to said borehole being drilled.

26. The method of claim 25, further including generating said magnetic field at a source location in said borehole being drilled and positioning a magnetic field sensor at said observation location, said source location being coplanar with said sensor in a plane substantially perpendicular to said target borehole.

27. The method of claim 25, further including:

generating said magnetic field at a first depth in said borehole being drilled;

positioning a magnetic field sensor at said observation location in said target borehole;

measuring the amplitude and relative phase of vector components of said rotating magnetic field in a plane perpendicular to a longitudinal axis of said target borehole.

28. The method of claim 27, further including positioning said sensor to include said first depth in said plane.

29. The method of claim 27, further including measuring the field gradient of said rotating magnetic field along said target borehole longitudinal axis and determining the relative depth of said sensor in said target borehole with respect to said first depth.

30. The method of claim 29, further including determining the distance between said target borehole and said borehole being drilled.

31. The method of claim 27, further including positioning an axial magnetic field sensor at a location along said target borehole axis for measuring the axial vector component of said rotating magnetic field.

32. The method of claim 31, further including:

generating said rotating magnetic field at a source location on a drill assembly, whereby said first depth of said source location varies during drilling;

positioning said sensor at a fixed observation location in said target borehole; and

measuring said perpendicular and axial vector components during drilling.