Passive ranging techniques in borehole surveying

• US 6,937,023 B2
• Filed: 02/18/2003
• Issued: 08/30/2005
• Est. Priority Date: 02/18/2003
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Pathfinder Energy Services LLC (Schlumberger NV)
• Inventors: McElhinney, Graham
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Teresinski, John
• Application Number:
  US10/368,257
• Publication Number:
  US 20040160223A1
• Time in Patent Office: 924 Days
• Field of Search: 324/346, 324/347, 175/73, 175/61, 333/04
• US Class Current: 324/347
• 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 and first and second magnetic field measurement devices disposed at corresponding first and second positions in the borehole, the first and second positions selected to be 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) measuring first and second gravity vector sets using the first and second gravity measurement devices, respectively;

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

(d) measuring a total local magnetic field at each of the first and second positions using the first and second magnetic field measurement devices;

(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 at each of the first and second positions;

(f) re-positioning the tool at new locus for first and second positions in the borehole so that the first and second magnetic field measurement devices 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 first and second interference magnetic field vectors 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 each of the gravity vector sets in (b) comprises first and second gravity vectors.

6. The method of claim 5, 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.

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

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

BoreAzi=RefAzi+DeltaAzi

wherein BoreAzi is the local borehole azimuth, RefAzi is a reference borehole azimuth, and DeltaAzi is a change in azimuth between the first and second gravity measurement devices.

9. The method of claim 8, wherein the local borehole azimuth is determined at the second position and the reference borehole azimuth is determined at the first position.

10. The method of claim 8, wherein the reference borehole azimuth is referenced to a previously surveyed azimuthal reference point in the borehole.

11. The method of claim 10, wherein the reference borehole azimuths at each locus are chain referenced to the previously surveyed azimuthal reference point in the borehole.

12. The method of claim 8, 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.

13. The method of claim 8, wherein the reference borehole azimuth is determined from the measured total local magnetic field.

14. The method of claim 13, wherein the reference borehole azimuth is determined according to the equation:

$\mathrm{RefAzi}=\arctan <br><br>\left(\frac{\left(\mathrm{Gx}*\mathrm{By}-\mathrm{Gy}*\mathrm{Bx}\right)*\sqrt{{\mathrm{Gx}}^2+{\mathrm{Gy}}^2+{\mathrm{Gz}}^2}}{\mathrm{Bz}*\left({\mathrm{Gx}}^2+{\mathrm{Gy}}^2\right)-\mathrm{Gz}*\left(\mathrm{Gx}*\mathrm{Bx}-\mathrm{Gy}*\mathrm{By}\right)}\right)$

wherein RefAzi represents the reference borehole azimuth, Bx, By, and Bz represent first, second, and third magnetic field vectors, Gx, Gy, and Gz, represent first, second, and third gravity vectors measured at the same position as the first, second, and third magnetic field vectors.

15. The method of claim 8, 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.

16. The method of claim 15, 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.

17. The method of claim 15, 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.

18. The method of claim 8, wherein the change in borehole azimuth is determined from the first and second gravity vector sets.

19. The method of claim 18, wherein the change in borehole azimuth is determined according to the equation:

$\mathrm{DeltaAzi}=\frac{\mathrm{Beta}}{1-\mathrm{Sin}<br><br>\left(\left(\mathrm{Inc1}+\mathrm{Inc2}\right)/2\right)}$

wherein;

$\mathrm{Beta}=\arctan <br><br>\left(\frac{\left(\mathrm{Gx2}*\mathrm{Gy1}-\mathrm{Gy2}*\mathrm{Gx1}\right)*\sqrt{{\mathrm{Gx1}}^2+{\mathrm{Gy1}}^2+{\mathrm{Gz1}}^2}}{\mathrm{Gz2}*\left({\mathrm{Gx1}}^2+{\mathrm{Gy1}}^2\right)+\mathrm{Gz1}*\left(\mathrm{Gx2}*\mathrm{Gx1}+\mathrm{Gy2}*\mathrm{Gy1}\right)}\right);<br><br>$$\mathrm{Inc1}=\arctan \left(\frac{\sqrt{({\mathrm{Gx1}}^2+{\mathrm{Gy1}}^2}}{\mathrm{Gz1}}\right);<br><br>$$\mathrm{Inc2}=\arctan \left(\frac{\sqrt{({\mathrm{Gx2}}^2+{\mathrm{Gy2}}^2}}{\mathrm{Gz2}}\right);<br><br>\mathrm{and}$

wherein DeltaAzi represents the change in borehole azimuth, Bx1, By1, and Bz1 represent first, second, and third magnetic field vectors measured at the first position, Gx1, Gy1, and Gz1, represent first, second, and third gravity vectors measured at the first position, Gx2, Gy2, and Gz2, represent first, second, and third gravity vectors measured at the second position, and Inc1 and Inc2 represent inclination values at the first and second positions, respectively.

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

21. The method of claim 20, wherein (d) further comprises deriving a third magnetic field vector based on the first and second magnetic field vectors and the reference magnetic field.

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

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

24. The method of claim 23, wherein the site is disposed in another borehole.

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

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

27. 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 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.

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

29. The method of claim 28, 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.

30. The method of claim 28, wherein (e) further comprises subtracting another magnetic field component from the difference between the total magnetic field and the reference magnetic field.

31. 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.

32. The method of claim 31, wherein a location of a target subterranean structure is determined by determining an average position of a plurality of the intersection points in the two-dimensional viewing plane.

33. The method of claim 31, 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 over ((x_T−

x)²+(y_T−

y)²)}{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.

34. The method of claim 31, wherein a direction from a predetermined point on the borehole to the target subterranean structure may be determined according to the equation:

35. The method of claim 31, wherein a target azimuth and a target inclination of the target subterranean structure are determined from the two-dimensional viewing plane.

36. The method of claim 31, wherein the two-dimensional viewing plane is determined graphically.

37. The method of claim 31, 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

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

38. 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 and first and second magnetic field measurement devices deployed thereon, the tool operable to be positioned in a borehole such that the first and second gravity measurement devices and the first and second magnetic field 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 magnetic field measurement devices disposed 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) total local magnetic fields at the first and second positions for each locus as measured by the magnetic field measurement devices;

(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) interference magnetic field vectors 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).

39. The system of claim 38, wherein:

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

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

40. The system of claim 38, wherein the tool further comprises a gyroscope disposed at one of the first and second positions.

41. 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, 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 first and second magnetic field measurement devices deployed on the tool at the corresponding 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 devices;

(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 interference magnetic field vectors 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).

42. The computer system of claim 41, wherein (b) further comprises determining a local borehole azimuth according to the equation:

BoreAzi=RefAzi+DeltaAzi

wherein BoreAzi is the local borehole azimuth, RefAzi is a reference borehole azimuth, and DeltaAzi is a change in azimuth between the first and second gravity measurement devices.

43. The computer system of claim 42, wherein the reference borehole azimuth is determined according to the equation:

$\mathrm{RefAzi}=\arctan <br><br>\left(\frac{\left(\mathrm{Gx}*\mathrm{By}-\mathrm{Gy}*\mathrm{Bx}\right)*\sqrt{{\mathrm{Gx}}^2+{\mathrm{Gy}}^2+{\mathrm{Gz}}^2}}{\mathrm{Bz}*\left({\mathrm{Gx}}^2+{\mathrm{Gy}}^2\right)-\mathrm{Gz}*\left(\mathrm{Gx}*\mathrm{Bx}-\mathrm{Gy}*\mathrm{By}\right)}\right)$

wherein RefAzi represents the reference borehole azimuth, Bx, By, and Bz represent first, second, and third magnetic field vectors, Gx, Gy, and Gz, represent first, second, and third gravity vectors measured at the same position as the first, second, and third magnetic field vectors.

44. The computer system of claim 43, wherein the change in borehole azimuth is determined according to the equation:

$\mathrm{DeltaAzi}=\frac{\mathrm{Beta}}{1-\mathrm{Sin}<br><br>\left(\left(\mathrm{Inc1}+\mathrm{Inc2}\right)/2\right)}$

wherein;

$\mathrm{Beta}=\arctan <br><br>\left(\frac{\left(\mathrm{Gx2}*\mathrm{Gy1}-\mathrm{Gy2}*\mathrm{Gx1}\right)*\sqrt{{\mathrm{Gx1}}^2+{\mathrm{Gy1}}^2+{\mathrm{Gz1}}^2}}{\mathrm{Gz2}*\left({\mathrm{Gx1}}^2+{\mathrm{Gy1}}^2\right)+\mathrm{Gz1}*\left(\mathrm{Gx2}*\mathrm{Gx1}+\mathrm{Gy2}*\mathrm{Gy1}\right)}\right);<br><br>$$\mathrm{Inc1}=\arctan \left(\frac{\sqrt{({\mathrm{Gx1}}^2+{\mathrm{Gy1}}^2}}{\mathrm{Gz1}}\right);<br><br>$$\mathrm{Inc2}=\arctan \left(\frac{\sqrt{({\mathrm{Gx2}}^2+{\mathrm{Gy2}}^2}}{\mathrm{Gz2}}\right);<br><br>\mathrm{and}$

wherein DeltaAzi represents the change in borehole azimuth, Bx1, By1, and Bz1 represent first, second, and third magnetic field vectors measured at the first position, Gx1, Gy1, and Gz1, represent first, second, and third gravity vectors measured at the first position, Gx2, Gy2, and Gz2, represent first, second, and third gravity vectors measured at the second position, and Inc1 and Inc2 represent inclination values at the first and second positions, respectively.

45. The computer system of claim 41, wherein the portion of the total magnetic field attributable to the subterranean structure at each locus in (d) is determined by 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 determined in (c), and Mex, Mey, and Mez represent the x, y, and z components of the reference magnetic field.

46. The computer system of claim 45, 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.

47. 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 deployed 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 from the subterranean structure, the tool further including first and second magnetic field measurement devices disposed at 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) measuring first and second gravity vector sets at each using the first and second gravity measurement devices;

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

(d) measuring total local magnetic fields at each locus using the magnetic field measurement device;

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

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

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