Resistivity logging systems and methods employing ratio signal set for inversion

Patent metadata

Field	Value
Publication number	US-9547102-B2
Application number	US-201214410543-A
Country	US
Kind code	B2
Filing date	Jun 25, 2012
Priority date	Jun 25, 2012
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

Electromagnetic resistivity logging systems and methods yielding formation anisotropy and dip from a signal set that closely approximates the response of a idealized tool. One illustrative method embodiment derives from an azimuthally-sensitive tool's measurements a full set of orthogonal direct couplings (Vxx, Vyy, Vzz) and a cross-coupling sum (Vxz+Vzx) or (Vyz+Vzy). These values are converted into a signal set as a function of borehole position, the set including: a first signal representing a ratio between Vzz coupling components at different spacing distances, a second signal representing a ratio between Vxx and Vzz coupling components, a third signal representing a ratio between Vyy and Vzz coupling components, a fourth signal representing a ratio between Vxx and Vyy coupling components, and a fifth signal representing a ratio between a cross-coupling sum and a sum of the direct couplings. From this signal set, formation parameters can be accurately determined by inversion.

First claim

What is claimed is:

1. A resistivity logging method that comprises:
obtaining signal measurements collected by an azimuthally sensitive electromagnetic logging tool as a function of position in a borehole, the tool having at least two spacing distances (d 1 , d 2 ) between transmit and receive antennas;
deriving from the signal measurements: orthogonal direct couplings (Vxx, Vyy, Vzz) and a cross-coupling sum (Vxz+Vzx) or (Vyz+Vzy);
generating a set of signals as a function of position in the borehole, the set including:
a first signal representing a ratio between Vzz coupling components at different spacing distances,
a second signal representing a ratio between Vxx and Vzz coupling components,
a third signal representing a ratio between Vyy and Vzz coupling components,
a fourth signal representing a ratio between Vxx and Vyy coupling components, and
a fifth signal representing a ratio between a cross-coupling sum and a sum of the direct couplings; and

determining a formation dip log and a formation anisotropy log based at least in part on said set of signals.

2. The method of claim 1 , further comprising determining a formation resistivity log and a formation strike angle log based at least in part on said set of signals.

3. The method of claim 2 , further comprising displaying at least one of said logs to a user.

4. The method of claim 1 , wherein said determining is performed via inversion by iterative estimation of model parameters.

5. The method of claim 1 , wherein said signal measurements represent averaged measurements for measurement bins.

6. The method of claim 5 , wherein said signal measurements are calibrated, combined, and/or compensated to improve their reliability.

7. The method of claim 1 , wherein the tool is a logging while drilling tool having one or more tilted antennas.

8. The method of claim 1 , wherein the tool is a wireline tool having at least one triad of orthogonal transmit antennas and at least one triad of orthogonal receive antennas.

9. The method of claim 1 , wherein the first signal is representable as S1=Vzz(d 1 )/Vzz(d 2 ), the second signal is representable as S2=Vxx/Vzz, the third signal is representable as S3=Vyy/Vzz, and the fourth signal is representable as Vxx/Vyy.

10. The method of claim 9 , wherein the fifth signal is expressible as

S
5

=

1
+

V
xz

+

V
zx

1
2

⁢

V
xx

+

1
2

⁢

V
yy

+

V
zz

.

11. The method of claim 1 , further comprising steering a drill bit based on the determined formation dip log.

12. A resistivity logging system that comprises:
a memory that stores logging software; and
at least one processor coupled to the memory to execute the logging software, the software causing the at least one processor to:
obtain signal measurements collected by an azimuthally sensitive electromagnetic logging tool as a function of position in a borehole, the tool having at least two spacing distances (d 1 , d 2 ) between transmit and receive antennas;
derive from the signal measurements: orthogonal direct couplings (Vxx, Vyy, Vzz) and a cross-coupling sum (Vxz+Vzx) or (Vyz+Vzy);
generate a set of signals as a function of position in the borehole, the set including:
a first signal representing a ratio between Vzz coupling components at different spacing distances,
a second signal representing a ratio between Vxx and Vzz coupling components,
a third signal representing a ratio between Vyy and Vzz coupling components,
a fourth signal representing a ratio between Vxx and Vyy coupling components, and
a fifth signal representing a ratio between a cross-coupling sum and a sum of the direct couplings; and

determine a formation dip log and a formation anisotropy log based at least in part on said set of signals.

13. The system of claim 12 , wherein the software further causes the at least one processor to determine a formation resistivity log and a formation strike angle log based at least in part on said set of signals.

14. The system of claim 13 , wherein the software further causes the at least one processor to display at least one of said logs to a user.

15. The system of claim 12 , wherein as part of said determining, the software causes the processor to iteratively estimate formation dip and anisotropy until the generated set of signals is matched by a modeled set of signals.

16. The system of claim 12 , wherein said signal measurements represent averaged measurements for measurement bins.

17. The system of claim 16 , wherein said signal measurements are calibrated, combined, and/or compensated to improve their reliability.

18. The system of claim 12 , wherein the tool is a logging while drilling tool having one or more tilted antennas.

19. The system of claim 12 , wherein the tool is a wireline tool having at least one triad of orthogonal transmit antennas and at least one triad of orthogonal receive antennas.

20. The system of claim 12 , wherein the first signal is expressible as S1=Vzz(d 1 )/Vzz(d 2 ), the second signal is expressible as S2=Vxx/Vzz, the third signal is expressible as S3=Vyy/Vzz, and the fourth signal is expressible as Vxx/Vyy.

21. The system of claim 20 , wherein the fifth signal is expressible as

S
5

=

1
+

V
xz

+

V
zx

1
2

⁢

V
xx

+

1
2

Assignees

• Wu Hsu-Hsiang
• Bittar Michael S
• Donderici Burkay
• Halliburton Energy Services Inc

Inventors

• Wu Hsu-Hsiang
• Bittar Michael S
• Donderici Burkay

Classifications

• G01V3/30 Primary

  operating with electromagnetic waves · CPC title

• G01V3/38 Primary

  Processing data, e.g. for analysis, for interpretation, for correction · CPC title