Term by term gain calibration of triaxial propagation measurements

Patent metadata

Field	Value
Publication number	US-9804292-B2
Application number	US-201414339959-A
Country	US
Kind code	B2
Filing date	Jul 24, 2014
Priority date	Jul 25, 2013
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

A method for obtaining gain corrected triaxial electromagnetic propagation measurements with an offset correction includes deploying an electromagnetic logging tool in a subterranean borehole. The logging tool includes at least first and second axially spaced triaxial transmitters and at least first and second axially spaced triaxial receivers. A plurality of full tensor voltage measurements may be acquired and processed tensor term by tensor term to obtain a full tensor, gain corrected quantity. The processing may optionally include (i) removing a full tensor voltage offset from the acquired full tensor voltage measurements to obtain a corresponding plurality of offset corrected voltage tensors and (ii) processing the offset corrected voltage tensor term by tensor term to obtain the full tensor, gain and offset corrected quantity.

First claim

What is claimed is:

1. A method for obtaining a gain corrected triaxial electromagnetic antenna measurement, the method comprising:
(a) rotating an electromagnetic logging tool in a subterranean borehole, the logging tool including at least first and second axially spaced triaxial transmitters and at least first and second axially spaced triaxial receivers, each of the triaxial transmitters including a plurality of mutually independent transmitting antennas and each of the triaxial receivers including a plurality of mutually independent receiving antennas;
(b) applying a time varying electrical current to each of the plurality of transmitting antennas in each of the axially spaced transmitters to transmit corresponding electromagnetic waves while rotating in (a);
(c) causing each of the plurality of receiving antennas in each of the axially spaced receivers to measure voltages corresponding to each of the electromagnetic waves transmitted in (b) to acquire a plurality of full tensor voltage measurements;
(d) causing a downhole processor to remove a full tensor voltage offset from the full tensor voltage measurements acquired in (c) to obtain a corresponding plurality of offset corrected voltage tensors; and
(e) causing the downhole processor to process the offset corrected voltage tensors tensor term by tensor term to compute a full tensor, gain corrected quantity.

2. The method of claim 1 , further comprising:
(f) causing the downhole processor to process the full tensor, gain corrected quantity to obtain a full tensor attenuation and a full tensor phase shift.

3. The method of claim 1 , further comprising:
(f) transmitting the full tensor, gain corrected quantity to the surface; and
(g) causing a surface computer to invert the full tensor, gain corrected quantity to obtain one or more properties of a subterranean formation.

4. The method of claim 1 , wherein off-diagonal terms of the full tensor voltage offset are set equal to corresponding off-diagonal voltage measurements obtained during an air hang calibration of the logging tool.

5. The method of claim 4 , wherein the full tensor voltage offset V tr off for a transmitter t and a receiver r in the logging tool is expressed as follows:

V
tr
off

=

[

0
⁢

V
trxy
air

V
trxz
air

V
tryx
air

⁢
0

V
tryz
air

V
trzx
air

V
trzy
air

0
⁢

]

wherein V trxy air , V trxz air , V tryx air , V tryz air , V trzx air , and V trzy air represent the off-diagonal terms of the full tensor voltage offset.

6. The method of claim 1 , wherein the full tensor voltage offset is obtained from a tilted test loop calibration of the logging tool.

7. The method of claim 6 , wherein the tilted test loop calibration comprises:
(i) acquiring a first voltage tensor calibration measurement with a conductive ring electrically open about the logging tool;
(ii) acquiring a second voltage tensor calibration measurement with the conductive ring electrically closed about the logging tool;
(iii) processing the first voltage tensor calibration measurement to obtain diagonal terms of the full tensor voltage offset; and
(iv) processing a difference between the first voltage tensor calibration measurement and the second voltage tensor calibration measurement to obtain diagonal terms of the full tensor voltage offset.

8. The method of claim 7 , wherein the full tensor voltage offset V tr off for a transmitter t and a receiver r in the logging tool is expressed as follows:

V
tr
off

=

[

V
trxx
off

⁡

(
TTL
)

⁢

V
trxy
air

V
trxz
air

V
tryx
air

V
tryy
off

⁡

(
TTL
)

⁢

V
tryz
air

Assignees

• Schlumberger Technology Corp

Inventors

• Bertrand Paul
• Homan Dean M
• Frey Mark
• Argentier Luc

Classifications

• G01V3/26

  operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device (with electromagnetic waves G01V3/30) · CPC title

• G01V3/28

  using induction coils · CPC title

• G01V3/108 Primary

  the emitter and the receiver coils or loops being uncoupled by positioning them perpendicularly to each other · CPC title

• G01V13/00 Primary

  Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00 · CPC title