Method and apparatus for borehole wall resistivity imaging with full circumferential coverage

Patent metadata

Field	Value
Publication number	US-9709692-B2
Application number	US-28817108-A
Country	US
Kind code	B2
Filing date	Oct 17, 2008
Priority date	Oct 17, 2008
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

Abstract

A logging tool for performing resistivity measurements on the sidewall of a borehole in an earth formation is provided with a circumferential series of evenly-spaced measurement electrodes providing complete circumferential coverage of resistivity measurements. In one embodiment, the measurement electrodes are carried on a conductive pad circumferentially surrounding an elongate mandrel or tubular. The conductive pad is held at a voltage adapted to focus measurement current into the sidewall of the borehole. Preferably, the pad has dimensions relative to the measurement electrodes and a standoff distance between the measurement electrodes and said borehole wall to effectively focus the measurement current into the borehole wall. In accordance with one aspect of the invention, the measurement electrodes are spaced apart by a distance that is less than the width of each measurement electrode, thereby ensuring full circumferential resolution.

First claim

What is claimed is:

1. An apparatus for performing electrical logging in a borehole through an earth formation, comprising:
a mandrel; and
a circumferential pad disposed upon said mandrel and carrying a plurality of individual measurement electrodes evenly spaced around the entire circumference of said pad and configured to supply measurement current to the formation, the circumferential pad extending continuously around the mandrel;
at least one focusing electrode held at a potential sufficient to focus said measurement current into said borehole wall, thereby reducing the flow of current through fluid surrounding said tool;
wherein said focusing electrode has dimensions sufficient to focus said measurement current into said borehole wall when said measurement electrodes are spaced apart from said borehole wall by a standoff of at least one-half inch.

2. The apparatus in accordance with claim 1 , wherein the distance between each pair of said plurality of measurement electrodes is less than the width of each electrode.

3. The apparatus in accordance with claim 2 , wherein the ratio of the length of said circumferential pad and a standoff between said electrodes and the sidewall of said borehole is at least 10:1.

4. The apparatus in accordance with claim 2 , wherein the ratio of the length of said pad to the length of each of said plurality of electrodes is at least 50:1.

5. The apparatus in accordance with claim 1 , wherein the pad is one unitary pad that extends around the mandrel.

6. The apparatus in accordance with claim 1 , wherein the mandrel is configured to be conveyed by a cable.

7. The apparatus in accordance with claim 1 , comprising at least one processor configured to model the measurement electrodes as a conductive ring carried by the pad.

8. The apparatus in accordance with claim 1 , comprising an insulation layer disposed upon and circumferentially surrounding said mandrel and axially separating the pad from a return electrode.

9. A method for performing resistivity measurements in a borehole through an earth formation, comprising:
(a) using a measurement tool to inject a measurement current into said borehole wall;
(b) providing at least one focusing electrode held at a potential sufficient to focus said measurement current into said borehole wall, thereby reducing the flow of current through fluid surrounding said tool;
(c) taking resistivity measurements at a plurality of measurement electrodes arranged circumferentially around said measurement tool, said measurement electrodes being carried on a circumferential pad that extends continuously around said tool and being evenly spaced apart by a distance that is less than the width of each of said measurement electrodes, such that the tool has full circumferential resolution;
(d) using the resistivity measurements to generate a resistivity image of the borehole; and
(e) using the resistivity image to conduct at least one of: i) hydrocarbon exploration, and
ii) hydrocarbon production;

wherein said focusing electrode has dimensions sufficient to focus said measurement current into said borehole wall when said measurement electrodes are spaced apart from said borehole wall by a standoff of at least one-half inch.

10. The method in accordance with claim 9 , wherein the pad is one unitary pad that extends around the tool.

11. The method in accordance with claim 9 , further comprising conveying the tool through the borehole using a cable.

12. The method in accordance with claim 9 , comprising modeling the measurement electrodes as a conductive ring carried by the pad.

13. The method in accordance with claim 9 , comprising using an insulation layer to circumferentially surround said mandrel and axially separate the pad from a return electrode.

Assignees

• Itskovich Gregory B
• Bespalov Alexandre N
• Shaikh Farhat A
• Nolan Peter John
• Baker Hughes Inc

Inventors

• Itskovich Gregory B
• Bespalov Alexandre N
• Shaikh Farhat A
• Nolan Peter John

Classifications

• G01V3/20 Primary

  operating with propagation of electric current · CPC title