Compensated Deep Propagation Measurements with Differential Rotation

Patent metadata

Field	Value
Publication number	US-2016146967-A1
Application number	US-201414549396-A
Country	US
Kind code	A1
Filing date	Nov 20, 2014
Priority date	Nov 20, 2014
Publication date	May 26, 2016
Grant date	—

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 logging tool 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 logging tool 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 logging tool 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 logging tool of claim 1 , wherein the predefined angle is about 45 degrees.

6 . The logging tool 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 logging tool 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.

8 . A method for making downhole electromagnetic logging while drilling measurements, the method comprising
(a) rotating an electromagnetic logging while drilling tool in a subterranean wellbore, the logging tool including 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, the first sub rotating at a rotation rate greater than a rotation rate of the second sub, each of the first and second transmitters and first and second receivers including an axial antenna and collocated first and second transverse antennas, 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; (b) acquiring a plurality of electromagnetic voltage measurements from the first and second receivers while rotating in (a); (c) processing the voltage measurements acquired in (b) to compute harmonic coefficients; (d) mathematically rotating the harmonic coefficients through at least the predefined angle to obtain rotated coefficients; and (e) processing ratios of selected ones of the rotated coefficients to compute gain compensated measurement quantities.

9 . The method of claim 8 , wherein the processing in (e) is performed by a downhole processor.

10 . The method of claim 9 , further comprising:
(f) transmitting the gain compensated measurement quantities to a surface location; and (g) causing a surface computer to invert the gain compensated measurement quantities to obtain one or more properties of a subterranean formation.

11 . The method of claim 8 , further comprising:
(f) processing the gain compensated measurement quantities to compute compensated phase shift and attenuation quantities.

12 . The method of claim 8 , wherein:
the first and second transverse antennas in the second receiver are rotationally offset by the predefined angle from the first and second transverse antennas in the second transmitter.

13 . The method of claim 8 , wherein the electromagnetic voltage measurements acquired in (b) comprise a three-dimensional matrix of voltage measurements.

14 . The method of claim 8 , wherein the harmonic coefficients computed in (c) comprise DC, first harmonic sine, first harmonic cosine, second harmonic sine, and second harmonic cosine coefficients for measurements acquired in (b) between the first transmitter and the first receiver or between the second transmitter and the second receiver.

15 . The method of claim 8 , wherein the harmonic coefficients computed in (c) comprise a DC coefficient, first and second harmonic cosine coefficients, first and second harmonic sine coefficients, and cosine cosine, cosine sine, sine cosine, and sine sine coefficients of the couplings.

16 . The method of claim 8 , wherein the gain compensated measurement quantities computed in (e) comprise at least one measurement proportional to an xx coupling, a yy coupling, an xy coupling, or a yx coupling.

17 . The method of claim 8 , wherein the gain compensated measurement quantities computed in (e) comprise at least one measurement proportional to a zx coupling, an xz coupling, a zy coupling, or a yz coupling.

18 . The method of claim 8 , wherein the gain compensated measurement quantities computed in (e) comprise at least one measurement sensitive to a product of an xz coupling and a zx coupling or a product of a yz coupling and a zy coupling.

19 . The method of claim 8 , wherein the gain compensated measurement quantities computed in (e) comprise (i) at least one measurement proportional to an xx coupling or a yy coupling, (ii) at least one measurement proportional to an xy coupling or yx coupling, (iii) at least one measurement proportional to a zx coupling, an xz coupling, a zy coupling, or a yz coupling, and (iv) a measurement proportional to an zz coupling.

20 . The method of claim 8 , further comprising:
(f) processing the compensated measurement quantities computed in (e) to compute compensated symmetrized and anti-symmetrized measurement quantities.

21 . The method of claim 8 , wherein:
(b) further comprises acquiring toolface angles of the first and second subs while rotating in (a); and (c) further comprises fitting selected ones of the voltage measurements acquired in (b) to trigonometric functions of the toolface angles acquired in (b) to compute the harmonic coefficients.

22 . A method for making downhole electromagnetic logging while drilling measurements, the method comprising
(a) rotating an electromagnetic logging while drilling tool in a subterranean

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

• G01V3/30

  operating with electromagnetic waves · CPC title