Resistivity imager for conductive and non-conductive mud

Patent metadata

Field	Value
Publication number	US-9746574-B2
Application number	US-201615003630-A
Country	US
Kind code	B2
Filing date	Jan 21, 2016
Priority date	Jan 21, 2016
Publication date	Aug 29, 2017
Grant date	Aug 29, 2017

Abstract

Methods and apparatus configured to evaluate a volume of interest of an earth formation intersected by a borehole. Apparatus comprise a transceiver electrode on the tool body configured to provide electrical current to the earth formation; a return electrode configured to receive the electrical current returning from the earth formation; a multi-function electrode on the resistivity imager tool; and an electrical system configured to provide current measurements at the transceiver electrode. In the first operational mode, the electrical system maintains the tool body at a first electrical potential, and maintains the multi-function electrode and the transceiver electrode at a second electrical potential; and in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at the second potential.

First claim

We claim:

1. An apparatus configured to evaluate a volume of interest of an earth formation intersected by a borehole, the apparatus comprising:
a tool body configured to be conveyed in the borehole, the tool body having thereon:
a transceiver electrode on the tool configured to provide electrical current to the earth formation;
a return electrode configured to receive the electrical current returning from the earth formation;
a multi-function electrode on the resistivity imager tool, the multi-function electrode configured to be switched between a guard mode and a return mode; and
a shield electrode between the transceiver electrode and the multi-function electrode; and

an electrical system configured to provide current measurements at the transceiver electrode indicative of a resistivity parameter of the volume of interest, the electrical system configured to be switched between a first operational mode and a second operational mode, wherein:
in the first operational mode, the electrical system maintains the tool body at a first electrical potential, and maintains the multi-function electrode and the transceiver electrode at a second electrical potential different than the first potential; and
in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at the second potential different than the first potential.

2. The apparatus of claim 1 wherein the current measurements comprise current amplitude measurements and current phase measurements.

3. The apparatus of claim 2 comprising at least one processor configured to:
estimate complex impedance values from the current measurements and the corresponding second electrical potential in the first operational mode;
estimate complex impedance values from the measured current and the corresponding second electrical potential in the second operational mode; and
estimate a resistivity parameter of the volume of interest using the estimated complex impedance values.

4. The apparatus of claim 3 wherein the tool body is associated with a bottom hole assembly (BHA) and the transceiver electrode is configured for rotation through a plurality of azimuthal orientations during measurement.

5. The apparatus of claim 4 wherein the resistivity parameter comprises a complex impedance of the volume of interest, and the at least one processor is configured to estimate the complex impedance of the volume of interest at the plurality of azimuthal orientations while the BHA is performing drilling operations.

6. The apparatus of claim 2 wherein the at least one processor is configured to estimate a complex impedance of the volume of interest from the current measurements and to provide a standoff image using an imaginary part of the complex impedance.

7. The apparatus of claim 2 wherein the at least one processor is configured to estimate a complex impedance of the volume of interest from the current measurements and to provide a resistivity image using a real part of the complex impedance.

8. The apparatus of claim 1 wherein in the first operational mode, the electrical system provides current to the transceiver electrode at an operational frequency of less than 20 kHz; and, in the second operational mode, the electrical system provides current to the transceiver electrode at an operational frequency of greater than 1 MHz.

9. The apparatus of claim 1 wherein in the first and second operational modes the electrical system maintains the shield electrode at substantially the second electrical potential.

10. A method of evaluating a volume of interest of an earth formation intersected by a borehole, the method comprising:
conveying a logging tool disposed on a carrier into the borehole, the logging tool including a tool body configured to be conveyed in the borehole, the tool body having thereon:
a transceiver electrode on the tool configured to provide electrical current to the earth formation;
a return electrode configured to receive the electrical current returning from the earth formation;
a multi-function electrode on the resistivity imager tool, the multi-function electrode configured to be switched between a guard mode and a return mode; and
a shield electrode between the transceiver electrode and the multi-function electrode; and

using an electrical system to take current measurements at the transceiver electrode indicative of a resistivity parameter of the volume of interest, the electrical system configured to be switched between a first operational mode and a second operational mode, wherein:
in the first operational mode, the electrical system maintains a tool body at a first electrical potential, maintains the multi-function electrode and the transceiver electrode at a second electrical potential different than the first potential; and
in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at a second potential different than the first potential.

11. The method of claim 10 wherein the current measurements comprise current amplitude measurements and current phase measurements.

12. The method of claim 11 comprising using at least one processor to:
estimate complex impedance values from the current measurements and the corresponding first electrical potential in the first operational mode;
estimate complex impedance values from the measured current and the corresponding fourth electrical potential in the second operational mode; and
estimate a resistivity parameter of the volume of interest using the estimated complex impedance values.

13. The method of claim 11 comprising taking the current measurements in a plurality of azimuthal orientations by rotation of the transceiver electrode around a central axis of the tool body and taking the current measurements during the rotation.

14. The method of claim 12 wherein the resistivity parameter comprises a complex impedance of the volume of interest, the method comprising using the at least one processor to estimate the complex impedance of the volume of interest at the plurality of azimuthal orientations while the BHA is performing drilling operations.

15. The method of claim 10 comprising using the electrical system to provide current to the transceiver electrode at an operational frequency determined responsive to a selection of the operational mode from among the first operational mode and the second operation mode, the operational frequency being of at least one of i) less than 20 kHz; and ii) greater than 1 MHz.

16. The method of claim 10 comprising using the electrical system to maintain the shield electrode at the second electrical potential in both operational modes.

17. The method of claim 10 comprising using the at least one processor to estimate a complex impedance of the volume of interest from the current measurements and to provide a standoff image using an imaginary part of the complex impedance.

18. The method of claim 10 comprising using the at least one processor to estimate a complex impedance of the volume of interest from the current measurements and to provide a resistivity image using a real part of the complex impedance.

19. The method of claim 10 comprising injecting an electric current into the volume of interest of the earth formation.

Assignees

• Baker Hughes Inc

Inventors

• Itskovich Gregory B
• Forgang Stanislav
• Krueger Sven
• Le Fei

Classifications

• E21B49/00

  Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells · 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

• G01V3/18

  specially adapted for well-logging · CPC title

• G01V3/24 Primary

  using AC · CPC title