Supplemental referencing techniques in borehole surveying

• US 20040073369A1
• Filed: 02/18/2003
• Published: 04/15/2004
• Est. Priority Date: 10/09/2002
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Pathfinder Energy Services LLC (Schlumberger NV)
• Inventors: McElhinney, Graham
• Granted Patent: US 7,002,484 B2
• Time in Patent Office: Days
• US Class Current: 702/6
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

Abstract

A method for surveying a borehole is disclosed which uses first and second gravity measurement devices disposed at corresponding first and second positions in the borehole and a supplemental reference measurement device disposed at the first position. Exemplary supplemental reference measurement devices include magnetometers and gyroscopes. The method includes determining a reference borehole azimuth at the first position using the supplemental reference measurement device, determining a change in borehole azimuth between the first and second positions using the first and second gravity measurement devices and determining the borehole azimuth at the second position by applying the change in borehole azimuth the reference azimuth. 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 surveying a borehole, 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, the first and second gravity measurement devices being constrained from rotating with respect to one another about a substantially cylindrical borehole axis, the tool further including a supplemental reference measurement device disposed at the first position;

(b) determining a reference borehole azimuth at the first position using the supplemental reference measurement device;

(c) determining a change in borehole azimuth between the first and second positions using the first and second gravity measurement devices; and

(d) determining borehole azimuth at the second position by applying the change in borehole azimuth determined in (c) to the reference borehole azimuth determined in (b).

2. The method of claim 1, wherein the first and second gravity measurement devices comprise accelerometers.

3. The method of claim 1, wherein the supplemental reference measurement device is selected from the group consisting of:

(A) a gyroscope, and (B) a magnetometer.

4. The method of claim 1, wherein the tool further comprises first and second supplemental reference measurement devices disposed at the first and second positions, respectively.

5. The method of claim 4, wherein the first supplemental reference measurement device comprises a magnetometer and the second supplemental reference measurement device comprises a gyroscope.

6. The method of claim 4, wherein each of the first and second supplemental reference measurement devices comprises a magnetometer.

7. The method of claim 1, wherein the supplemental reference measurement device comprises three magnetometers, the magnetometers deployed in mutually orthogonal directions.

8. The method of claim 1, wherein (c) further comprises:

causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets; and

processing the gravity vector sets to determine the change in borehole azimuth.

9. The method of claim 8, wherein the gravity vector sets each comprise first and second gravity vectors.

10. The method of claim 9, wherein (c) 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.

11. The method of claim 10, wherein the third gravity vector is derived according to the equation:

12. The method of claim 8, wherein each gravity vector set comprises first, second, and third gravity vectors.

13. The method of claim 1, wherein (b) comprises measuring a magnetic field.

14. The method of claim 13, wherein (b) comprises measuring first and second magnetic field vectors.

15. The method of claim 14, wherein (b) further comprises deriving a third magnetic field vector based on the first and second magnetic field vectors and a known total magnetic field of the Earth.

16. The method of claim 15, wherein the third magnetic field vector is derived according to the equation:

17. The method of claim 13, wherein (b) comprises measuring first, second, and third magnetic field vectors.

18. The method of claim 13, wherein the reference borehole azimuth determined in (b) is processed according to the equation:

19. The method of claim 1, wherein the borehole azimuth determined in (d) is processed according to the equation:

BoreAzi=RefAzi+DeltaAzi

wherein BoreAzi represents the borehole reference azimuth, RefAzi represents the reference borehole azimuth, and DeltaAzi represents the change in borehole azimuth.

20. The method of claim 19, wherein:

21. The method of claim 1, wherein the first position is located shallower into the borehole than the second position.

22. The method of claim 1, wherein the first position is located deeper into the borehole than the second position.

23. The method of claim 1, wherein the tool comprises a measurement while drilling tool.

24. The method of claim 1, wherein the tool is coupled to a drill string.

25. The method of claim 23, wherein the second position is located in a bottom hole assembly.

26. The method of claim 1, further comprising:

(e) determining the borehole inclination at at least one of the first and second positions.

27. The method of claim 26, wherein (e) comprises determining the inclination of the borehole at the first position according to the equation:

28. The method of claim 26, wherein (e) comprises determining the inclination of the borehole at the second position according to the equation:

29. The method of claim 1, further comprising:

(f) establishing borehole azimuth at one of the first and second positions via reference to a previously surveyed azimuthal reference point in the borehole.

30. The method of claim 1, further comprising:

(e) repeating (a) through (d) to determine borehole azimuth at multiple selected locations in the borehole.

31. The method of claim 30, wherein the borehole azimuth at two or more of said multiple selected locations is chain referenced to a previously surveyed azimuthal reference point in the borehole.

32. The method of claim 30, wherein at least one contiguous pair of said multiple selected locations are selected to be a predetermined borehole distance apart, said predetermined borehole distance exceeding twice the borehole distance between the first position and the second position.

33. The method of claim 1 further comprising:

(f) correcting previously surveyed azimuthal reference points in the borehole with the reference borehole azimuth determined in (b).

34. A method for determining azimuth in a borehole, the method comprising:

(a) positioning first and second gravity measurement devices and a supplemental reference measurement device in the borehole, the first and second gravity measurement devices being positioned at corresponding first and second positions in the borehole, the first and second gravity measurement devices being substantially constrained from rotating with respect to one another about a substantially cylindrical borehole axis, the supplemental reference measurement device being positioned at the first position;

(b) determining a reference borehole azimuth at the first position using the supplemental reference measurement device;

(c) determining a change in borehole azimuth between the first and second positions using the first and second sets of gravity measurement devices; and

(d) determining borehole azimuth at the second position by applying the change in borehole azimuth determined in (c) to the reference borehole azimuth determined in (b).

35. A method for surveying a borehole, 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, the first and second gravity measurement devices being constrained from rotating with respect to one another about a substantially cylindrical borehole axis, and a supplemental reference measurement device disposed at the first position;

(b) causing 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 change in borehole azimuth between the first and second positions;

(d) causing the supplemental reference measurement device to measure a magnetic field vector set at the first position;

(e) processing the first gravity vector set and the magnetic field vector set to determine a reference borehole azimuth at the first position;

(f) determining borehole azimuth at the second position by applying the change in borehole azimuth determined in (e) to the reference borehole azimuth determined in (c) when a difference between a total magnetic field and a magnetic field of the Earth is less than a predetermined threshold value.

36. The method of claim 35, further comprising

(g) determining an azimuth at the second position by referencing an azimuth at the first position to an azimuth of a previously surveyed location in the borehole when a difference between the total magnetic field and the magnetic field of the Earth is greater than a predetermined threshold value.

37. The method of claim 35, wherein the difference between the total magnetic field and the magnetic field of the Earth is a member of the group consisting of a difference in:

(A) magnitude and (B) magnetic dip.

38. The method of claim 35, wherein:

a total magnetic interference is determined from the difference between the total magnetic field and the magnetic field of the Earth; and

the azimuth at the second position is determined by adding the change in borehole azimuth determined in (e) to the reference borehole azimuth determined in (c) when the total magnetic interference is less than a predetermined value.

39. The method of claim 35 further comprising:

(g) determining an interference vector from the total magnetic field and the magnetic field of the Earth; and

(h) repeating (a) through (g) to determine an azimuth value and an interference vectors at each of selected multiple locations in the borehole.

40. The method of claim 39, further comprising:

(i) utilizing the interference vectors at the selected multiple locations in the borehole to determine at least one of a distance and a direction to a source of magnetic interference external to the borehole.

41. The method of claim 40, wherein the source of magnetic interference is an adjacent borehole.

42. The method of claim 39, further comprising:

(i) utilizing the interference vectors at the selected multiple locations in the borehole to determine at least one of an inclination and an azimuth of an adjacent borehole.

43. A system for surveying a borehole, the system comprising:

a downhole tool including first and second gravity measurement devices and a supplemental reference measurement device deployed thereon, the first and second gravity measurement devices disposed at corresponding first and second positions along a substantially cylindrical axis, the gravity measurement devices constrained from rotational movement with respect to one another about the cylindrical axis, the supplemental reference measurement device disposed at the first position, the tool operable to be positioned in a borehole; and

a processor configured to determine;

(A) a change in borehole azimuth between the first and second positions using outputs from the gravity measurement devices;

(B) a reference borehole azimuth at the first position using an output from the supplemental reference measurement device; and

(C) a borehole azimuth at the second position by applying the change in borehole azimuth determined in (A) to the reference borehole azimuth determined in (B).

44. The system of claim 43, wherein:

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

the supplemental reference measurement device comprises first, second, and third magnetometers.

45. The system of claim 43, comprising first and second supplemental reference measurement devices disposed at the first and second positions, respectively.

46. The system of claim 45, wherein one of the supplemental reference measurement devices comprises a gyroscope.

47. The system of claim 45, wherein:

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

each of the supplemental reference measurement devices comprises first, second, and third magnetometers.

48. 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 measurement devices are (1) deployed at corresponding first and second positions in a borehole, and (2) also substantially constrained from rotating with respect to one another about a substantially cylindrical axis along the borehole;

the processor further disposed to receive input from a supplemental reference measurement device when said supplemental reference measurement device is deployed at the first position in the borehole;

the computer-readable logic further configured to instruct the processor to execute a method for determining borehole azimuth, the method comprising;

(a) determining a reference borehole azimuth at the first position using input from the supplemental reference measurement device;

(b) determining a change in borehole azimuth between the first and second positions using input from the first and second sets of gravity measurement devices; and

(c) determining borehole azimuth at the second position by applying the change in borehole azimuth determined in (b) to the reference borehole azimuth measured in (a).

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

50. The computer system of claim 48, wherein the change in borehole azimuth determined in (b) is processed according to the equation:

51. The computer system of claim 48, wherein the borehole azimuth determined in (c) is processed according to the equation:

BoreAzi=RefAzi+DeltaAzi

wherein BoreAzi represents the borehole azimuth, RefAzi represents the reference borehole azimuth, and DeltaAzi represents the change in borehole azimuth.

52. The computer system of claim 51, wherein: