System and method for EM ranging in oil-based mud

• US 8,844,648 B2
• Filed: 05/26/2011
• Issued: 09/30/2014
• Est. Priority Date: 06/22/2010
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Bittar, Michael S., Li, Jing, Li, Shanjun, Finke, Michael D.
• Primary Examiner(s): Thompson, Kenneth L
• Application Number:
  US13/116,069
• Publication Number:
  US 20110308859A1
• Time in Patent Office: 1,223 Days
• Field of Search: 175/45, 175/61, 175/62, 175/320, 175/323, 731/520.3
• US Class Current: 175/45
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

Abstract

Nearby conductors such as pipes, well casing, etc., are detectable from within a borehole filled with an oil-based fluid. At least some method embodiments provide a current flow between axially-spaced conductive bridges on a drillstring. The current flow disperses into the surrounding formation and causes a secondary current flow in the nearby conductor. The magnetic field from the secondary current flow can be detected using one or more azimuthally-sensitive antennas. Direction and distance estimates are obtainable from the azimuthally-sensitive measurements, and can be used as the basis for steering the drillstring relative to the distant conductor. Possible techniques for providing current flow in the drillstring include imposing a voltage across an insulated gap or using a toroid around the drillstring to induce the current flow.

Claims

1. A method for detecting a conductive feature from a borehole filled with an oil-based fluid, the method comprising:

providing current flow between two axially-spaced conductive bridges on a conductive tubular in the borehole, said current flow dispersing into a surrounding formation and causing a secondary current flow in the conductive feature;

detecting a magnetic field from the secondary current flow with at least one azimuthally-sensitive antenna in the borehole; and

obtaining magnetic field measurements at multiple azimuths from the borehole and, based at least in part on said measurements, determining a direction of the conductive feature from the borehole.

2. The method of claim 1, wherein the bridges comprise stabilizer fins having an outer diameter substantially equal to a nominal diameter of the borehole.

3. The method of claim 1, wherein the bridges comprise centralizer springs or other compliant conductors that maintain contact with a wall of the borehole.

4. The method of claim 1, wherein said obtaining includes making said measurements with antennas having different azimuthal sensitivities.

5. The method of claim 1, wherein said obtaining includes rotating said at least one antenna to make said measurements.

6. The method of claim 1, further comprising adjusting a drilling direction based at least in part on said direction.

7. The method of claim 1, further comprising estimating a distance to the conductive feature from the borehole.

8. The method of claim 1, wherein said current flow is an alternating current.

9. The method of claim 1, wherein said providing includes imposing a voltage across an insulated gap in the conductive tubular.

10. The method of claim 1, wherein said providing includes employing a toroid around the conductive tubular to induce the current flow.

11. The method of claim 1, wherein the conductive feature is an existing well.

12. A system for detecting a conductive feature from a borehole filled with an oil-based fluid, the system comprising:

a tool that induces a current flow between two axially-spaced conductive bridges on a conductive tubular in the borehole so as to cause a secondary current flow in the conductive feature; and

at least one azimuthally-sensitive antenna that detects a magnetic field from the secondary current flow,

wherein the tool obtains magnetic field measurements at multiple azimuths from the borehole, and wherein the system further comprises a processor that determines a direction of the conductive feature from the borehole based at least in part on said measurements.

13. The system of claim 12, wherein the bridges comprise stabilizer fins having an outer diameter substantially equal to a nominal diameter of the borehole.

14. The system of claim 12, wherein the bridges comprise centralizer springs or other compliant conductors that maintain contact with a wall of the borehole.

15. The system of claim 12, wherein tool obtains said measurements with antennas having different azimuthal sensitivities.

16. The system of claim 12, wherein said at least one antenna rotates to make said measurements.

17. The system of claim 12, further comprising a steering mechanism that adjusts a drilling direction based at least in part on said direction.

18. The system of claim 12, wherein the processor further determines a distance to the conductive feature from the borehole.

19. The system of claim 12, wherein said current flow is an alternating current.

20. The system of claim 12, wherein the tool includes a power source that imposes a voltage across an insulated gap in the tool body.

21. The system of claim 12, wherein the tool includes a toroid around the conductive tubular to induce the current flow.

22. The system of claim 12, wherein the conductive feature is an existing well.