PASSIVE RANGING TECHNIQUES IN BOREHOLE SURVEYING

• US 20040160223A1
• Filed: 02/18/2003
• Published: 08/19/2004
• Est. Priority Date: 02/18/2003
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Pathfinder Energy Services LLC (Schlumberger NV)
• Inventors: McElhinney, Graham
• Granted Patent: US 6,937,023 B2
• Time in Patent Office: Days
• US Class Current: 324/346
• 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
• CPC Class Codes: G01V 7/00 Measuring gravitational fields or waves; Gravimetric prospecting or detecting

Abstract

A method for determining the location of a target subterranean structure from within an adjacent borehole is disclosed which uses first and second gravity measurement devices disposed at corresponding first and second positions in the adjacent borehole and a magnetic field measurement device disposed one of the first and second positions. The method includes processing a total local magnetic field, a reference magnetic field, and a local azimuth determined using the gravity measurement devices to determine a portion of the total magnetic field attributable to the subterranean structure multiple points in the adjacent borehole. The location of the subterranean structure is determined using the portion of the total magnetic field attributable thereto. A system adapted to execute the disclosed method and a computer system including computer-readable logic configured to instruct a processor to execute the disclosed method are also provided.

Claims

1. A method for determining the location of a target subterranean structure from within an adjacent borehole, said subterranean structure generating magnetic flux, the method comprising:

(a) providing a downhole tool including first and second gravity measurement devices disposed at corresponding first and second positions in the borehole, at least one of the first and second positions selected to be within sensory range of magnetic flux from the subterranean structure, the tool further including a magnetic field measurement device disposed at one of the first and second positions and within sensory range of magnetic flux from the subterranean structure, the first and second gravity measurement devices constrained from rotating with respect to one another about a substantially cylindrical borehole axis;

(b) using the first and second gravity measurement devices to measure corresponding first and second gravity vector sets;

(c) processing the first and second gravity vector sets to determine a local borehole azimuth;

(d) measuring a total local magnetic field using the magnetic field measurement device;

(e) processing the total local magnetic field, the local azimuth and a reference magnetic field to determine a portion of the total magnetic field attributable to the target subterranean structure;

(f) re-positioning the tool at new locus for first and second positions in the borehole so that the magnetic field measurement device remains within sensory range of the magnetic flux from the subterranean structure;

(g) repeating (b), (c), (d), (e), and (f) for a predetermined number of cycles;

(h) generating an interference magnetic field vector for each locus for first and second positions, each of the interference magnetic field vectors corresponding to the portion of the total magnetic field determined in (e) at the corresponding locus; and

(j) extending the interference magnetic field vectors to determine a location of the target subterranean structure.

2. The method of claim 1, wherein the subterranean structure is a borehole.

3. The method of claim 1, wherein the subterranean structure is a cased borehole.

4. The method of claim 1, wherein the tool further includes a gyroscope disposed at one of the first and second positions.

5. The method of claim 1, wherein the tool further includes magnetic field measurement devices disposed at each of the first and second positions.

6. The method of claim 1, wherein each of the gravity vector sets in (b) comprises first and second gravity vectors.

7. The method of claim 6, wherein (b) further comprises deriving a third gravity vector for each of the gravity vector sets, each third gravity vector derived from processing the corresponding first and second gravity vectors and a known total gravitational field of the Earth.

8. The method of claim 1, wherein each of the gravity vector sets in (b) comprises first, second, and third gravity vectors.

9. The method of claim 1, wherein (c) further comprises determining the local borehole azimuth according to the equation:

10. The method of claim 9, wherein the local borehole azimuth is determined at the second position and the reference borehole azimuth is determined at the first position.

11. The method of claim 9, wherein the reference borehole azimuth is referenced to a previously surveyed azimuthal reference point in the borehole.

12. The method of claim 11, wherein the reference borehole azimuths at each locus are chain referenced to the previously surveyed azimuthal reference point in the borehole.

13. The method of claim 9, wherein the reference borehole azimuth is determined with a supplemental reference measurement device disposed at one of the first and second positions on the downhole tool.

14. The method of claim 9, wherein the reference borehole azimuth is determined from the measured total local magnetic field.

15. The method of claim 14, wherein the reference azimuth is determined according to the equation:

16. The method of claim 9, wherein the reference borehole azimuth is determined from the total magnetic field when a difference between the total magnetic field and the reference magnetic field is less than a predetermined threshold.

17. The method of claim 16, wherein the reference borehole azimuth is determined from the total magnetic field when a difference between a magnitude of the total magnetic field and a magnitude of the reference magnetic field is less than the predetermined threshold.

18. The method of claim 16, wherein the reference borehole azimuth is determined based on the total magnetic field when a difference between a magnetic dip of the total magnetic field and a magnetic dip of the reference magnetic field is less than the predetermined threshold.

19. The method of claim 9, wherein the change in borehole azimuth is determined from the first and second gravity vector sets.

20. The method of claim 19, wherein the change in borehole azimuth is determined according to the equation:

21. The method of claim 1, wherein (d) comprises measuring first and second magnetic field vectors.

22. The method of claim 21, wherein (d) further comprises deriving a third magnetic field vector based on the first and second magnetic field vectors and the reference magnetic field.

23. The method of claim 1, wherein (d) comprises measuring first, second, and third magnetic field vectors.

24. The method of claim 1, wherein:

the downhole tool comprises first and second magnetic field measurement devices disposed at the first and second positions, respectively; and

(d) comprises measuring the total local magnetic field at each of the first and second positions.

25. The method of claim 24 wherein (d) comprises measuring first, second, and third magnetic field vectors at each of the first and second positions.

26. The method of claim 1, wherein the reference magnetic field is measured in substantially real time at a site substantially free of magnetic interference.

27. The method of claim 26, wherein the site is disposed in another borehole.

28. The method of claim 1, wherein the reference magnetic field is known based on a historical geological survey.

29. The method of claim 1, wherein the reference magnetic field is determined from on a numerical model.

30. The method of claim 1, wherein x, y, and z components of the reference magnetic field are determined according to the equations:

M_EX=H_E(cos D sin Az cos R+cos D cos Az cos Inc sin R−

sin D sin Inc sin R) M_EY=H_E(cos D cos Azl cos Inc cos R+sin D sin Inc cos R−

cos D sin Az sin R) M_EZ=H_E(sin D cos Inc−

cos D cos Az sin Inc)

wherein Mex, Mey, and Mez represent the x, y, and z components of the reference magnetic field, respectively, He represents a magnitude of the reference magnetic field, D represents a magnetic dip of the reference magnetic field, Inc represents a local borehole inclination, Az represents the local borehole azimuth, and R represents a local rotation of the downhole tool.

31. The method of claim 1, wherein (e) comprises determining a difference between the total magnetic field and the reference magnetic field.

32. The method of claim 31, wherein:

x, y, and z components of the reference magnetic field are determined according to the equations;

M_EX═

H_E(cos D sin Az cos R+cos D cos Az cos Inc sin R−

sin D sin Inc sin R) M_EY═

H_E(cos D cos Az cos Inc cos R+sin D sin Inc cos R−

cos D sin Az sin R) M_EZ=H_E(sin D cos Inc−

cos D cos Az sin Inc)

wherein Mex, Mey, and Mez represent the x, y, and z components of the reference magnetic field, respectively, He represents a magnitude of the reference magnetic field, D represents a magnetic dip of the reference magnetic field, Inc represents a local borehole inclination, Az represents the local borehole azimuth, and R represents a local rotation of the downhole tool; and

the portion of the total magnetic field attributable to the subterranean structure is determined according to the equations;

M_IX=B_X−

M_EX M_IY=B_Y−

M_EY M_IZ=B_Z−

M_EZ

wherein Mix, Miy, and Miz represent x, y, and z components, respectively, of the portion of the total magnetic field attributable to the subterranean structure, and Bx, By, and Bz represent x, y, and z components of the total magnetic field, respectively.

33. The method of claim 31, wherein (e) further comprises subtracting another magnetic field component from the difference between the total magnetic field and the reference magnetic field.

34. The method of claim 1, comprising at least four predetermined cycles in (g).

35. The method of claim 1, wherein (i) further comprises:

projecting said extended interference magnetic field vectors onto a two-dimensional view;

determining intersection points in the two-dimensional view at which the interference magnetic field vectors intersect one another; and

determining a two-dimensional viewing plane at which a distance between the intersection points is substantially at a minimum.

36. The method of claim 35, wherein a location of a target subterranean structure is determined by averaging positions of a plurality of the intersection points in the two-dimensional viewing plane.

37. The method of claim 36, wherein a distance from a predetermined point on the borehole to the target subterranean structure may be determined according to the equation:

D={square root}{square root over ((x_T−

x)²+(y_T−

y)²)}

wherein D represents the distance, X_T and Y_T represent x and y coordinates, respectively, in the two-dimensional viewing plane of the location of the target subterranean structure, and x and y represent the x and y coordinates, respectively, in the two-dimensional viewing plane of the predetermined point on the borehole.

38. The method of claim 36, wherein a direction from a predetermined point on the borehole to the target subterranean structure may be determined according to the equation:

39. The method of claim 35, wherein a target azimuth and a target inclination of the target subterranean structure are determined from the two-dimensional viewing plane.

40. The method of claim 35, wherein the two-dimensional viewing plane is determined graphically.

41. The method of claim 35, further comprising:

transposing the interference magnetic field vectors into azimuth, magnetic dip, and magnitude components;

rotating the interference magnetic field vectors by adding angle increments to the azimuth component thereof;

rotating the interference magnetic field vectors by adding angle increments to the magnetic dip component thereof; and

projected the interference magnetic field vectors onto a two-dimensional view at each of said angle increments.

42. A system for determining the location of a target subterranean structure from within an adjacent borehole, said subterranean structure generating magnetic flux, the system comprising:

a down hole tool including first and second gravity measurement devices deployed thereon, the tool operable to be positioned in a borehole such that the first and second gravity measurement devices are located at a preselected series of corresponding first and second positions in the borehole, each first and second position in the series corresponding to a predetermined locus of the tool in the borehole, at least one of the first and second positions selected to be within sensory range of magnetic flux from the subterranean structure at each locus, the tool further including a magnetic field measurement device disposed at one of the first and second positions and within sensory range of magnetic flux from the subterranean structure at each locus, the first and second gravity measurement devices constrained from rotating with respect to one another about a substantially cylindrical borehole axis; and

a processor configured to determine;

(A) first and second sets of gravity vectors from measurements of the first and second gravity measurement devices, respectively, at the first and second positions, respectively, at each locus;

(B) a local borehole azimuth at each locus from the first and second gravity vector sets in (A);

(C) a total local magnetic field for each locus as measured by the magnetic field measurement device;

(D) a portion of the total magnetic field attributable to the subterranean structure at each locus, said portion determined from the total local magnetic field in (C), the local azimuth in (B), and a reference magnetic field made available to the processor;

(E) an interference magnetic field vector for each locus, each of the interference magnetic field vectors corresponding to the portion of the total magnetic field determined in (D) at the corresponding locus; and

(F) a location of the target subterranean structure based on extension of the interference magnetic field vectors determined in (E).

43. The system of claim 42, wherein:

each of the gravity measurement devices comprises first, second, and third accelerometers; and

the magnetic field measurement device comprises first, second, and third magnetometers.

44. The system of claim 42, comprising first and second magnetic field measurement devices disposed at the first and second positions, respectively.

45. The system of claim 44, wherein:

each of the gravity measurement devices comprises first, second, and third accelerometers;

each of the magnetic field measurement devices comprises first, second, and third magnetometers.

46. The system of claim 42, wherein the tool further comprises a gyroscope disposed at one of the first and second positions.

47. A computer system comprising:

at least one processor; and

a storage device having computer-readable logic stored therein, the computer-readable logic accessible by and intelligible to the processor;

the processor further disposed to receive input from first and second gravity measurement devices when said first and second gravity measurement devices are deployed on a down hole tool at a preselected series of corresponding first and second positions in a borehole, each first and second position in the series corresponding to a predetermined locus of the tool in the borehole, at least one of the first and second positions selected to be within sensory range, at each locus, of magnetic flux generated by a target subterranean structure located outside the borehole, the first and second gravity measurement devices constrained, when deployed on the tool, from rotating with respect to one another about a substantially cylindrical borehole axis,

the processor further disposed to receive input from a magnetic field when said magnetic field measurement device is deployed on the tool at one of the first and second positions and within sensory range at each locus of magnetic flux from the subterranean structure,

the computer-readable logic further configured to instruct the processor to execute a method for determining the location of the target subterranean structure, the method comprising;

(a) determining first and second sets of gravity vectors based on input from the first and second gravity measurement devices, respectively, at the first and second positions, respectively, at each locus;

(b) calculating a local borehole azimuth at each locus from the first and second gravity vector sets determined in (a);

(c) determining a total local magnetic field for each locus based on input from the magnetic field measurement device;

(d) determining a portion of the total magnetic field attributable to the subterranean structure at each locus, said portion determined from the total local magnetic field in (c), the local azimuth in (b), and a reference magnetic field made available to the processor;

(e) calculating an interference magnetic field vector for each locus, each of the interference magnetic field vectors corresponding to the portion of the total magnetic field determined in (d) at the corresponding locus; and

(f) determining a location of the target subterranean structure based on extension of the interference magnetic field vectors determined in (e).

48. The computer system of claim 47, wherein (b) further comprises determining a local borehole azimuth according to the equation:

49. The computer system of claim 48, wherein the reference borehole azimuth is determined according to the equation:

50. The computer system of claim 49, wherein the change in borehole azimuth is determined according to the equation:

51. The computer system of claim 47, wherein the portion of the total magnetic field attributable to the subterranean structure at each locus in (d) is determined by the equations:

52. The computer system of claim 51, wherein the x, y, and z components of the reference magnetic field are determined by the equations:

M_EX=H_E(cos D sin Az cos R+cos D cos Az cos Inc sin R−

sin D sin Inc sin R) M_EY=H_E(cos D cos Az cos Inc cos R+sin D sin Inc cos R−

cos D sin Az sin R) M_EZ=H_E(sin D cos Inc−

cos D cos Az sin Inc)

wherein He represents a magnitude of the reference magnetic field, D represents a magnetic dip of the reference magnetic field, Inc represents a local borehole inclination, Az represents the local borehole azimuth determined in (b), and R represents a local rotation of the downhole tool.