Method for measuring transient electromagnetic components to perform deep geosteering while drilling

• US 20050140374A1
• Filed: 12/24/2003
• Published: 06/30/2005
• Est. Priority Date: 12/24/2003
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Itskovich, Gregory
• Granted Patent: US 7,046,009 B2
• Time in Patent Office: Days
• US Class Current: 324/339
• CPC Class Codes: G01V 3/28 using induction coils

Abstract

A transverse induction transmitter on an instrument induces currents in an earth formation when it is pulsed. Transient measurements made at transverse and axial receivers are used for determination of a distance to a bed boundary. This may be used to control the drilling direction. Alternatively, a transmitter on an instrument having a conductive body induces currents in the earth formation. Transient signals are measured and the effect of the conductive body is removed by using a reference signal measured in a homogenous space.

Claims

1. A method of using an electromagnetic instrument in a borehole in an earth formation comprising:

(a) changing a current through a transmitter on said instrument and inducing currents in said earth formation, said transmitter having a first axial direction;

(b) receiving first and second temporal signals resulting from said induced currents in at least two receivers, a first one of said at least two receivers having an axial direction that is substantially parallel to said first axial direction, and a second one of said at least two receivers having an axial direction inclined to said first axial direction; and

(c) determining from said first and second temporal signals a distance to an interface in said earth formation.

2. The method of claim 1 further comprising determining a direction to said interface.

3. The method of claim 1 wherein said changing of said current through said transmitter comprises turning off said current through said transmitter.

4. The method of claim 1 wherein said changing of said current through said transmitter comprises turning on a current through said transmitter.

5. The method of claim 1 further comprising:

(i) changing a current in an additional transmitter on said instrument, said additional transmitter having an axis inclined to said first axial direction, and inducing additional currents in said earth formation,

(ii) receiving third and fourth temporal signals resulting from said additional induced currents in said first and second receivers, and

(iii) using said third and fourth temporal signals in said determining of said distance.

6. The method of claim 1 wherein said first axial direction is substantially parallel to said axis of said instrument.

7. The method of claim 5 wherein said second one of said at least two eceivers has an axis substantially orthogonal to said first axis.

8. The method of claim 1 wherein said electromagnetic instrument is conveyed on a bottomhole assembly (BHA) into said borehole, the method further comprising using said determined distance for controlling a drilling direction of said BHA.

9. The method of claim 1 wherein said interface comprises a bed boundary.

10. The method of claim 1 wherein said interface comprises a fluid interface selected from:

(i) a gas-oil interface,

(ii) an oil-water interface, and

(iii) a gas-water interface.

11. A method of using an electromagnetic instrument in a borehole in an earth formation comprising:

(a) changing a current through a transmitter on said instrument and inducing currents in said earth formation;

(b) receiving a temporal signal resulting from said induced current in at at least one receiver on said instrument, said received temporal signal including effects of a conductive body of said instrument;

(c) determining from said reference signal and said temporal signal a distance to an interface in sad earth formation, said determination being substantially unaffected by said conductive body.

12. The method of claim 11 further comprising determining a direction to said interface.

13. The method of claim 11 wherein said step of determining further comprises subtracting said reference signal from said temporal signal.

14. The method of claim 11 wherein said changing of said current through said transmitter comprises turning off said current through said transmitter.

15. The method of claim 11 wherein said changing of said current through said transmitter comprises turning on a current through said transmitter.

16. The method of claim 11 wherein said transmitter has an axial direction substantially parallel to an axis of said instrument.

17. The method of claim 11 further comprising obtaining said reference signal by measuring a temporal signal in a substantially homogenous medium.

18. The method of claim 11 wherein said electromagnetic instrument is conveyed on a bottomhole assembly (BHA) into said borehole, the method further comprising using said determined distance for controlling a drilling direction of said BHA.

19. The method of claim 11 wherein said interface comprises a bed boundary.

20. The method of claim 11 wherein said interface comprises a fluid interface selected from:

(i) a gas-oil interface,

(ii) an oil-water interface, and

(iii) a gas-water interface.

21. An apparatus for use in a borehole in an earth formation comprising:

(a) an instrument including a transmitter for inducing currents in said earth formation, said transmitter having a first axial direction;

(b) at least two receivers on said instrument for receiving first and second temporal signals resulting from said induced currents, a first one of said at least two receivers having an axial direction that is substantially parallel to said first axial direction, and a second one of said at least two receivers having an axial direction inclined to said first axial direction; and

(c) a processor for determining from said first and second temporal signals a distance to an interface in said earth formation.

22. The apparatus of claim 21 wherein said processor further determines a direction to said interface.

23. The apparatus of claim 21 further comprising:

(i) an additional transmitter on said instrument, said additional transmitter having an axis inclined to said fist axial direction, said additional transmitter inducing additional currents in said earth formation,

wherein said first and second receivers receive third and fourth temporal signals resulting from said additional induced currents in said first and second receivers, and wherein said processor further uses said third and fourth temporal signals in said determining of said distance.

24. The apparatus of claim 21 wherein said first axial direction is substantially parallel to said axis of said instrument.

25. The apparatus of claim 23 wherein said second one of said at least two receivers has an axis substantially orthogonal to said first axis.

26. The apparatus of claim 21 further comprising a bottomhole assembly (BHA) for conveying said electromagnetic instrument into said borehole, the processor further using said determined distance for controlling a drilling direction of said BHA.

27. The apparatus of claim 21 wherein said interface comprises a bed boundary.

28. The apparatus of claim 21 wherein said interface comprises a fluid interface selected from;

(i) a gas-oil interface,

(ii) an oil-water interface, and

(iii) a gas-water interface.

29. An apparatus for use in a borehole in an earth formation comprising:

(a) an instrument having a conductive body and including a transmitter for inducing currents in said earth formation;

(b) at least one receiver on said instrument for receiving a temporal signal resulting from said induced current, said temporal signal being affected by said conductive body,

(c) a processor for determining from a reference signal and said temporal signal a distance to an interface in said earth formation, said determination being substantially unaffected by said conductive body.

30. The apparatus of claim 29 wherein said processor further determines a direction to said interface.

31. The apparatus of claim 29 wherein said processor subtracts said reference signal from said temporal signal.

32. The apparatus of claim 29 wherein said transmitter has an axial direction substantially parallel to an axis of said instrument.

33. The apparatus of claim 29 wherein said reference signal is obtained by measuring a temporal signal in a substantially homogenous medium.

34. The apparatus of claim 29 further comprising a bottomhole assembly (BHA) for conveying said electromagnetic instrument into said borehole, the processor further uses said determined distance for controlling a drilling direction of said BHA.

35. The apparatus of claim 29 wherein said interface comprises a bed boundary.

36. The apparatus of claim 29 wherein said interface comprises a fluid interface selected from:

(i) a gas-oil interface,

(ii) an oil-water interface, and

(iii) a gas-water interface.

37. The apparatus of claim 29 wherein said instrument comprises a conductive tubular member, and said transmitter is separated from said tabular member by a non-conductive material.

38. The apparatus of claim 37 wherein said non-conductive material comprises a ferrite.