Gain Compensated Tensor Propagation Measurements Using Collocated Antennas

Patent metadata

Field	Value
Publication number	US-2016209540-A1
Application number	US-201414912901-A
Country	US
Kind code	A1
Filing date	Aug 21, 2014
Priority date	Aug 21, 2013
Publication date	Jul 21, 2016
Grant date	—

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
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C

=

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12

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(
0
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xx

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12

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(

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12

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(

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(

β

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1

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Assignees

• Schlumberger Technology Corp

Inventors

• Frey Mark
• Homan Dean M

Classifications

• G01V3/18

  specially adapted for well-logging · CPC title

• G01V3/104

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

• G01V3/28 Primary

  using induction coils · CPC title

• G01V3/38

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