Multi-array laterolog tools and methods with differential voltage measurements

Patent metadata

Field	Value
Publication number	US-9547100-B2
Application number	US-201113884034-A
Country	US
Kind code	B2
Filing date	Nov 2, 2011
Priority date	Nov 15, 2010
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

Multi-array laterolog tool systems and methods acquire a set of array measurements sufficient to provide laterolog tool measurements of differing array sizes. Such systems and method offer multiple depths of investigation while offering greater measurement stability in borehole environments having high resistivity contrasts. In at least some system embodiments, a wireline or LWD tool body has a center electrode positioned between multiple pairs of guard electrodes and a pair of return electrodes. The tool's electronics provide a current from the center electrode to the pair of return electrodes and currents from each pair of guard electrodes to the pair of return electrodes. Each of the currents may be distinguishable by frequency or distinguishable by some other means. This novel arrangement of currents provides a complete set of measurements that enables one tool to simultaneously emulate a whole range of laterolog tools.

First claim

What is claimed is:

1. A resistivity logging system that comprises:
a tool body having:
a center electrode positioned between multiple pairs of guard electrodes, wherein said multiple pairs of guard electrodes are positioned between a pair of return electrodes on said tool body, each said pair being a set of two electrodes symmetrically located relative to the center electrode; and
between each adjacent pair of guard electrodes, a dyad of monitor electrode pairs, each dyad being two monitor electrode pairs that form a set of four monitor electrodes symmetrically located relative to the center electrode, the set of four monitor electrodes including, on each side of the center electrode, two monitor electrodes between adjacent guard electrodes in the adjacent pair of guard electrodes; and

electronics that provide a primary current from the center electrode to the pair of return electrodes and provide a respective guard current from each pair in said multiple pairs of guard electrodes to the pair of return electrodes, the electronics further operating to acquire a differential voltage measurement from at least one dyad of monitor electrode pairs.

2. The system of claim 1 , wherein said multiple pairs of guard electrodes includes at least three pairs, and wherein the electronics further operate to acquire a differential voltage measurement from each dyad of monitor electrode pairs.

3. The system of claim 2 , wherein the tool body further includes a dyad of monitor electrode pairs between the center electrode and an innermost pair of guard electrodes.

4. The system of claim 1 , wherein the electronics drive all of said primary and guard currents concurrently.

5. The system of claim 4 , wherein the primary current and each of the respective guard currents has a spectral signature that distinguishes it from other currents.

6. The system of claim 4 , wherein each of the guard currents has a unique signal frequency.

7. The system of claim 6 , wherein the primary current has at least one signal frequency different than each of the guard current signal frequencies.

8. The system of claim 7 , wherein the primary current further includes a signal frequency that matches a signal frequency of an innermost pair of guard electrodes.

9. The system of claim 1 , wherein the guard electrodes in each pair are shorted together, and the monitor electrodes in each pair are shorted together.

10. The system of claim 1 , further comprising:
a processor that receives that receives measurements indicative of electrical resistances associated with the primary current and the guard currents, wherein the processor processes the measurements to determine measurements corresponding to a tool having a reduced number of guard electrodes.

11. The system of claim 1 , wherein the tool body is a drilling collar.

12. The system of claim 1 , wherein the tool body is a wireline sonde.

13. A resistivity logging method that comprises:
receiving from a logging tool measurements indicative of a differential voltage between each dyad of monitor electrode pairs positioned between adjacent guard electrode pairs, each pair being a set of two electrodes located symmetrically relative to a center electrode and each dyad being two monitor electrode pairs that form a set of four monitor electrodes symmetrically located relative to the center electrode, the set of four monitor electrodes including, on each side of the center electrode, two monitor electrodes between adjacent guard electrodes in each adjacent pair of guard electrodes;
processing said measurements to determine a localized formation resistivity at a position associated with a location of the center electrode during collection of said measurements; and
displaying said localized formation resistivity as a function of position.

14. The method of claim 13 , wherein said processing comprises:
deriving measurements indicative of electrical resistances between the center electrode and each pair of guard electrodes; and
combining said derived measurements in a manner that enforces an assumption of commensurate voltages on the center electrode and at least one pair of guard electrodes.

15. The method of claim 13 , further comprising driving said guard electrode pairs and center electrode with respective current sources.

16. The method of claim 15 , wherein the respective current sources provide currents with different signal frequencies.

17. A resistivity logging tool that comprises:
a tool body having a center electrode positioned between symmetrically-spaced pairs of guard electrodes, symmetrically-spaced pairs of voltage monitor electrodes, and a pair of return electrodes, the voltage monitor electrodes being positioned in dyads between adjacent ones of the center electrode and guard electrodes, each dyad being two symmetrically-spaced pairs forming a set of four monitor electrodes that includes, on each side of the center electrode, two monitor electrodes between said adjacent electrodes;
respective current sources that drive the center electrode and each pair of guard electrodes relative to the pair of return electrodes;
one or more analog to digital converters that digitize representations of differential voltage signals between said dyads; and
at least one processor that processes said digitized representations to determine a resistivity measurement associated with a tool having a reduced number of guard electrodes.

18. The tool of claim 17 , comprising at least five symmetrically-spaced pairs of guard electrodes.

19. The tool of claim 17 , wherein the current sources drive all of said primary and guard currents concurrently.

20. The tool of claim 19 , wherein each current source provides a current with a spectral signature that distinguishes it from the currents from the other current sources.

Assignees

• Li Shanjun
• San Martin Luis E
• Bittar Michael S
• Li Jing
• Halliburton Energy Services Inc

Inventors

• Li Shanjun
• San Martin Luis E
• Bittar Michael S
• Li Jing

Classifications

• G01V3/28

  using induction coils · CPC title

• E21B47/102

  Fixed Constructions · mapped topic

• G01V2200/16

  Measure-while-drilling or logging-while-drilling · CPC title

• 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

• G01V3/24 Primary

  using AC · CPC title