Gain compensated tensor propagation measurements using collocated antennas

Patent metadata

Field	Value
Publication number	US-9835753-B2
Application number	US-201414912901-A
Country	US
Kind code	B2
Filing date	Aug 21, 2014
Priority date	Aug 21, 2013
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

A method for obtaining full tensor gain compensated propagation measurements includes processing a full tensor voltage measurement to obtain a fully gain compensated tensor quantity. An electromagnetic logging tool including at least first and second axially spaced transmitters and at least first and second axially spaced receivers is rotated in a subterranean borehole. A plurality of voltage measurements are acquired while rotating to obtain a full tensor voltage measurement which is in turn processed to obtain the fully gain compensated tensor quantity.

First claim

What is claimed is:

1. A method for obtaining full tensor gain compensated propagation measurements, the method comprising:
(a) rotating an electromagnetic logging tool in a subterranean borehole, the logging tool including at least first and second axially spaced transmitters and at least first and second axially spaced receivers, each of the receivers including a set of collocated linearly independent antennas, each of the transmitters including first and second collocated antennas, at least the first transmitter antenna having a tilted moment with respect to a longitudinal axis of the tool;
(b) acquiring a plurality of voltage measurements while rotating the tool in (a), the plurality of voltage measurements obtained using a corresponding plurality of pairs of the transmitters and receivers;
(c) fitting the voltage measurements to a harmonic expression to obtain harmonic coefficients;
(d) causing a processor to process the harmonic coefficients to construct a full tensor voltage measurement; and
(e) causing the processor to process the full tensor voltage measurement to obtain a fully gain compensated tensor quantity.

2. The method of claim 1 , wherein the processor is a downhole processor.

3. The method of claim 2 , further comprising:
(f) transmitting the fully gain compensated tensor quantity to the surface; and
(g) causing a surface computer to invert the fully gain compensated tensor quantity to obtain one or more properties of a subterranean formation.

4. The method of claim 2 , further comprising:
(f) causing the downhole processor to process the fully gain compensated tensor quantity to obtain a fully gain compensated tensor attenuation and a fully gain compensated tensor phase shift.

5. The method of claim 1 , wherein the second transmitter antenna in each of the first and second transmitters has a transverse moment with respect to the longitudinal axis of the tool.

6. The method of claim 1 , wherein:
(d) further comprises causing the processor to process the harmonic coefficients to obtain first and second sets of full tensor voltage measurements; and
(e) further comprises (i) causing the processor to process the first set of full tensor voltage measurements to obtain a first full tensor quantity, (ii) causing the processor to process the second set of full tensor voltage measurements to obtain a second full tensor quantity, and (iii) causing the processor to process the first and second full tensor quantities to obtain the fully gain compensated tensor quantity.

7. The method of claim 6 , wherein the first set of full tensor voltage measurements are obtained at a toolface angle of zero degrees and the second set of full tensor voltage measurements are obtained at a toolface angle of ninety degrees.

8. The method of claim 7 , wherein the fully gain compensated tensor quantity 12C is computed in (e) as follows:

12
⁢
C

=

[

12

⁢

(
0
)

xx

⁢

12

⁢

(

π
2

)

xx

12

⁢

(
0
)

xy

⁢

12

⁢

(

π
2

)

xy

cot
⁡

(

β

T
⁢

⁢
1

)

⁢

12

⁢

(
0
)

xz

12

⁢

(
0
)

yx

⁢

12

⁢

(

π
2

)

yx

12

⁢

(
0
)

yy

Assignees

• Schlumberger Technology Corp

Inventors

• Frey Mark
• Homan Dean M

Classifications

• G01V3/28 Primary

  using induction coils · CPC title

• G01V3/38

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

• G01V3/18

  specially adapted for well-logging · CPC title

• G01V3/104

  using several coupled or uncoupled coils (G01V3/101 takes precedence) · CPC title