Method and Apparatus for Well-bore Proximity Measurement While Drilling

• US 20080018334A1
• Filed: 08/31/2007
• Published: 01/24/2008
• Est. Priority Date: 01/18/2005
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Reiderman, Arcady
• Granted Patent: US 8,294,468 B2
• Time in Patent Office: Days
• US Class Current: 324/346
• CPC Class Codes: E21B 47/092 by detecting magnetic anomalies
• CPC Class Codes: G01N 24/081 Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
• CPC Class Codes: G01R 33/3808 Magnet assemblies for single-sided MR wherein the magnet assembly is located on one side of a subject only; Magnet assemblies for inside-out MR, e.g. for MR in a borehole or in a blood vessel, or magnet assemblies for fringe-field MR
• CPC Class Codes: G01R 33/381 using electromagnets
• CPC Class Codes: G01V 3/32 operating with electron or nuclear magnetic resonance

Abstract

A rotating, transversely magnetized, magnet on a drill collar induces magnetization in a casing of a preexisting well. A coil rotating synchronously with the magnet produces a current at twice the frequency of rotation and having an amplitude that depends upon the distance from the magnet to the preexisting well. Alternatively, a variable magnetic field is produced in the casing using a switchable magnet. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. A method of determining a distance to a first borehole from a second borehole, the method comprising:

(a) producing a time varying magnetic field in the first borehole using a magnet in the second borehole and inducing a magnetization in a magnetic object in the first borehole;

(b) using a coil in the second borehole for producing a signal responsive to a magnetic flux resulting from the magnetization; and

(c) estimate the distance using the signal.

2. The method of claim 1 wherein the magnetic object in the first borehole comprises a casing.

3. The method of claim 1 further comprising using the estimated distance to maintain a trajectory of the second borehole in a desired relation to the first borehole.

4. The method of claim 3 wherein the desired relation is one of:

(i) substantially parallel, and (ii) intersecting.

5. The method of claim 1 further comprising conveying the magnet on a bottomhole assembly on a drilling tubular into the second borehole.

6. The method of claim 1 wherein producing the time varying field further comprises rotating a magnet having a substantially transverse magnetization in the second borehole at a first rotational speed;

and wherein producing the signal further comprises rotating the coil synchronously with the magnet.

7. The method of claim 6 wherein estimating the distance further comprises filtering the signal to remove an effect of a magnetic field of the earth.

8. The method of claim 6 further comprising:

(i) measuring the first rotational speed,

(ii) determining a second harmonic component of the first rotational speed, and

(iii) using the determined second harmonic component to correct the signal.

9. The method of claim 6 further comprising:

(i) measuring an additional signal using a split coil responsive to the magnetic flux, and

(ii) using the additional signal as an indicator of an inclination between an axis of the first borehole and an axis of the second borehole.

10. The method of claim 6 wherein the first rotational speed is substantially the same as a rotational speed of a bottomhole assembly.

11. The method of claim 1 wherein producing the time varying field further comprises switching a polarity of a magnet having a substantially longitudinal magnetization in the second borehole, and wherein producing the signal further comprises using a coil with an axis that is substantially longitudinal.

12. The method of claim 11 further comprising estimating the distance further comprises using a portion of the signal substantially excluding a component of the signal due to a direct coupling of the magnet and coil, and substantially excluding a component of the signal due to eddy currents in the formation and a conductive body in the second borehole.

13. An apparatus for determining a distance to a first borehole from a second borehole, the apparatus comprising:

(a) a magnet configured to be conveyed in the second borehole, produce a time varying magnetic field in the first borehole and induce a magnetization in a magnetic object in the first borehole;

(b) a coil in the second borehole configured to produce a signal responsive to a magnetic flux resulting from the magnetization; and

(c) a processor configured to estimate the distance usng the signal.

14. The apparatus of claim 13 wherein the magnetic object in the first borehole comprises a casing.

15. The apparatus of claim 13 wherein the processor is further configured to use the estimated distance to maintain a trajectory of the second borehole in a desired relation to a trajectory of the first borehole.

16. The apparatus of claim 15 wherein the desired relation is one of:

(i) substantially parallel, and (ii) intersecting.

17. The apparatus of claim 13 further comprising a bottomhole assembly on a drilling tubular configured to conveyed the magnet into the second borehole.

18. The apparatus of claim 13 wherein the magnet further comprises a rotating magnet having a substantially transverse magnetization configured to rotate at a first rotational speed;

and wherein the coil is configured to rotate synchronously with the magnet.

19. The apparatus of claim 18 wherein the processor is configured to determine the distance by further filtering the signal to remove an effect of a magnetic field of the earth.

20. The apparatus of claim 18 further comprising an accelerometer configured measure the first rotational speed;

and wherein the processor is further configured to;

(i) determine a second harmonic component of the first rotational speed, and

(ii) use the determined second harmonic component to correct the signal.

21. The apparatus of claim 18 further comprising a split coil responsive to the magnetic flux configured to produce an additional signal, and

the processor is further configured to use the additional signal as an indicator of an inclination between an axis of the first borehole and an axis of the second borehole.

22. The apparatus of claim 18 wherein the first rotational speed is substantially the same as a rotational speed of a bottomhole assembly.

23. The apparatus of claim 13 further comprising:

(i) a switchable magnet having a substantially longitudinal magnetization in the second borehole configured to produce the time varying field; and

(ii) a coil with an axis that is substantially longitudinal configured to produce the signal.

24. The apparatus of claim 23 wherein the processor is further configured to estimate the distance using a portion of the signal substantially excluding a component of the signal due to a direct coupling of the magnet and coil, and substantially excluding a component of the signal due to eddy currents in the formation and a conductive body in the second borehole.

25. A computer-readable medium for use with an apparatus for determining a distance to a first borehole from a second borehole, the apparatus comprising:

(a) a magnet configured to be conveyed in the second borehole, switched to produce a time varying magnetic field in the first borehole and induce a magnetization in a magnetic object in the first borehole; and

(b) a coil in the second borehole configured to produce a signal responsive to a magnetic flux resulting from the magnetization;

the medium comprising instructions which enable a processor to;

(c) estimate the distance using the signal.

26. (canceled)