MAGNETIC HEAD FOR CONDUCTIVITY IMAGING FOR USE IN BOREHOLES

Abstract

A sensor for performing micro-conductivity measurements during well logging measurements in a borehole includes a magnetic core having a conductive insert wherein windings are driven with alternating current. Some embodiments include a sensor further having a conductive case. Various aspects of the sensor, such as dimensions and conductive properties of fabrication materials are selected to maximize performance of the sensor. Methods for using the sensor call for, among other things, placing the sensor in a well logging tool, and placing the tool in a well bore. A substantial focusing of the magnetic field on the wall of the borehole is achieved and provides for high quality data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alike in the several Figures:

FIG. 1 depicts aspects of well logging and a sampling tool;

FIG. 2 depicts aspects of a sensor for micro-conductivity measurements;

FIG. 3A and FIG. 3B, collectively referred to as FIG. 3, depict aspects of performance of the sensor disclosed herein;

FIG. 4 depicts aspects of a sensor having a differential magnetic head;

FIG. 5 depicts aspects of a sensor for use with DC;

FIG. 6 depicts aspects of the sensor with a button electrode included therein; and,

FIG. 7 depicts aspects of the sensor having a conductive insert and a conductive case combined with sensor windings.

Claims

1. A magnetic sensor adapted for making micro-conductivity measurements in a borehole, the sensor comprising: a magnetic core supporting windings wound around portions thereof and at least one conductive insert disposed within a core gap of the magnetic core wherein the windings are adapted for receiving a current and providing measurement data for the measurements.

2. The magnetic sensor of claim 1, being comprised within at least one conductive case.

3. The magnetic sensor of claim 2, wherein at least one of the conductive insert and the conductive case are fabricated from one of copper and a copper alloy.

4. The magnetic sensor of claim 1, wherein the magnetic core comprises a soft magnetic ferrite material.

5. The magnetic sensor of claim 1, wherein the magnetic core comprises a shape for focusing a magnetic field of the sensor.

6. The magnetic sensor of claim 1, wherein the magnetic core comprises a C-shape.

7. The magnetic sensor of claim 6, wherein the windings are wound around parallel portions of the C-shape.

8. The magnetic sensor of claim 1, wherein the windings are adapted for coupling to a source of alternating current (AC).

9. The magnetic sensor of claim 1, wherein the windings are adapted for coupling to a source of direct current (DC) and the sensor is adapted for operation by at least one of a lateral translation and a vibration.

10. The magnetic sensor of claim 1, wherein a length L of the core-gap is between about one times and about two times a standoff distance S between a sensing portion of the sensor and a wall of a borehole into which the logging tool is inserted.

11. The magnetic sensor of claim 1, wherein a first conductive insert is disposed opposite to a second conductive insert and is adapted for providing a magnetic bridge.

12. The magnetic sensor of claim 1, further comprising a button electrode coupled to the conductive insert and is adapted for use as at least one of a galvanic transmitter and receiver.

13. The magnetic sensor of claim 12, further comprising an electrode coupled to the conductive case for providing galvanic signals.

14. The magnetic sensor of claim 1, wherein the sensor comprises at least one of a design and a construction for maximizing an operational aspect of the sensor.

15. A magnetic sensor adapted for making micro-conductivity measurements in a borehole, the sensor comprising: a magnetic core comprising an inner conductor disposed within a core gap thereof, the magnetic core being comprised within an outer conductor, wherein, a combination of the inner conductor and the outer conductor effectively form a single-turn winding adapted for generating a magnetic field of the magnetic sensor.

16. A tool for performing micro-conductivity measurements in a borehole, the tool comprising: a magnetic sensor comprising a magnetic core supporting windings wound around portions thereof and at least one conductive insert disposed within a core gap of the magnetic core wherein the windings are adapted for receiving a current and providing measurement data for the measurements.

17. A method for performing micro-conductivity measurements in a borehole, comprising: selecting a tool comprising at least one magnetic sensor comprising a magnetic core supporting windings wound around portions thereof and at least one conductive insert disposed within a core gap of the magnetic core wherein the windings are adapted for receiving a current and providing measurement data for the measurements; and,performing micro-conductivity measurements with the tool in the borehole.

18. The method of claim 17, wherein performing comprises using a differential magnetic head of the tool to obtain a first signal and another signal.

19. The method of claim 18, wherein the measurements comprise a comparison of the first signal and the another signal.

20. The method as in claim 17, wherein performing comprises applying an alternating current (AC) signal to the windings.

21. The method as in claim 17, wherein performing comprises applying direct current (DC) signal to the windings and at least one of laterally translating the sensor and vibrating the sensor.

22. The method as in claim 21, wherein each one of translating and vibrating provides for at least one of generating a signal and detecting a signal.

23. A method for fabricating a magnetic sensor adapted for making micro-conductivity measurements in a borehole, the method comprising: selecting components for the sensor comprising at least one magnetic core, at least one conductive insert, at least one set of windings and optionally at least one conductive case;determining aspects of the components for maximizing performance of the magnetic sensor for making the micro-conductivity measurements;assembling the components so that the magnetic core comprises windings wound around portions thereof, the magnetic core also comprising at least one conductive insert disposed within a core gap of the magnetic core.