Compensated deep propagation measurements with differential rotation

Patent metadata

Field	Value
Publication number	US-9784880-B2
Application number	US-201414549396-A
Country	US
Kind code	B2
Filing date	Nov 20, 2014
Priority date	Nov 20, 2014
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

A method for making downhole electromagnetic logging while drilling measurements includes rotating an electromagnetic logging while drilling tool in a subterranean wellbore. The logging tool includes a first transmitter and a first receiver deployed on a first sub and a second transmitter and a second receiver deployed on a second sub. Rotating the logging tool causes the first and second subs to rotate at different rates. A plurality of electromagnetic voltage measurements are acquired from the first and second receivers while rotating. The acquired voltage measurements are processed to compute harmonic coefficients which are mathematically rotated to obtain rotated coefficients. Ratios of selected ones of the rotated coefficients are processed to compute gain compensated measurement quantities.

First claim

What is claimed is:

1. A bottom hole assembly comprising:
a downhole drilling motor deployed axially between first and second electromagnetic logging while drilling subs, the motor configured to rotate the first sub with respect to the second sub;
the first sub including a first transmitter and a first receiver axially spaced apart from one another;
the second sub including a second transmitter and a second receiver axially spaced apart from one another;
each of the first and second transmitters and first and second receivers including an axial antenna and collocated first and second transverse antennas; and
the first and second transverse antennas in the first receiver being rotationally offset by a predefined angle from the first and second transverse antennas in the first transmitter and the first and second transverse antennas in the second receiver being rotationally offset by the predefined angle from the first and second transverse antennas in the second transmitter.

2. The bottom hole assembly of claim 1 , wherein each of the first and second subs comprises:
corresponding first and second sets of magnetometers; and
downhole processors configured to (i) acquire magnetic field measurements from the first and second sets of magnetometers and (ii) process the magnetic field measurements to compute corresponding toolface angles and rotation rates of the first and second subs.

3. The bottom hole assembly of claim 1 , wherein the first and second transverse antennas in each of the first and second transmitters and the first and second receivers comprise saddle coils.

4. The bottom hole assembly of claim 1 , wherein the axial antenna and the first and second transverse antennas in each of the first and second transmitters and first and second receivers are collocated.

5. The bottom hole assembly of claim 1 , wherein the predefined angle is about 45 degrees.

6. The bottom hole assembly of claim 1 , further comprising a downhole processor configured to (i) acquire voltage measurements from the first and second receivers and (ii) process ratios of selected ones of the voltage measurements to obtain gain compensated measurement quantities.

7. The bottom hole assembly of claim 6 , wherein (ii) comprises:
(iia) processing the voltage measurements acquired in (i) to compute harmonic coefficients;
(iib) processing selected ones of the harmonic coefficients computed in (iia) to obtain transmitter and receiver gain matrices;
(iic) applying the gain matrices to the harmonic coefficients;
(iid) mathematically rotating the harmonic coefficients through at least the predefined angle to obtain rotated coefficients;
(iie) processing combinations of the rotated coefficients to obtain rotated combinations; and
(iif) processing ratios of selected ones of the rotated combinations to obtain the gain compensated measurement quantities.

Assignees

• Schlumberger Technology Corp

Inventors

• Frey Mark

Classifications

• E21B47/13 Primary

  by electromagnetic energy, e.g. radio frequency · CPC title

• G01V3/26 Primary

  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