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High resolution resistivity earth imager

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High resolution resistivity earth imager


An imaging tool made includes a pad whose curvature is chosen based on the expected range of borehole radius and the pad size so as to maintain the maximum standoff below a desired value. The curvature may be adjusted using fasteners.

Browse recent Baker Hughes Incorporated patents - Houston, TX, US
Inventors: Stanislav W. Forgang, Randy Gold, Peter J. Nolan, Carlos A. Yanzig
USPTO Applicaton #: #20120299595 - Class: 324346 (USPTO) - 11/29/12 - Class 324 


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The Patent Description & Claims data below is from USPTO Patent Application 20120299595, High resolution resistivity earth imager.

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CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 12/199,278 filed Aug. 27, 2008 the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This disclosure generally relates to exploration for hydrocarbons involving electrical investigations of a borehole penetrating an earth formation. More specifically, this disclosure relates to a method and apparatus having the flexibility to provide an image of a borehole wall for a wide range of borehole sizes.

2. Background of the Art

Electrical borehole logging is often used to provide images of an electrical property of boreholes. There are two categories of devices typically used as electrical logging devices for imaging boreholes. In the first category (galvanic devices), a measure electrode (current source or sink) is used in conjunction with a return electrode (such as the tool body). A current flows from a current source in the tool to a measure electrode through the earth formation. The current returns to the source via another electrode. The second category relates to inductive measuring tools in which an antenna within the electrical logging tool induces a current flow within the earth formation. The magnitude of the induced current is detected using either the same antenna or a separate antenna.

There are several modes of operation of a galvanic device. In one mode, the current at a current electrode is maintained constant and a voltage is measured between a pair of monitor electrodes. In another mode, the voltage of the measure electrode is fixed and the current flowing from the measure electrode is measured.

The galvanic devices are contact devices, in that the measure electrodes generally come in contact with the borehole wall during logging of the wellbore. Such devices are sensitive to the effects of borehole rugosity, borehole size, and the standoff of the pad carrying the measure electrodes. The present disclosure provides an improved electrical logging tool that reduces the effects of the pad offset.

SUMMARY

OF THE DISCLOSURE

One embodiment of the disclosure provides a method of generating an image of a resistivity property of an earth formation. In one aspect, a method may include: determining a size of a borehole in which a resistivity imaging instrument is to be used; selecting a radius of curvature of a pad of the resistivity imaging instrument based on a pad size, the size of the borehole, and a selected value for a maximum standoff of the pad; conveying the resistivity imaging instrument into the borehole; using a plurality of sensors on the pad responsive to a formation resistivity to obtain measurements indicative of the resistivity property; and providing the image of the resistivity property of the earth formation using the measurements obtained by the plurality of sensors.

Another embodiment of the disclosure includes an apparatus for providing an image of a resistivity property of an earth formation. In one aspect, the apparatus may include a resistivity imaging instrument configured to be conveyed into a borehole, wherein the he resistivity imaging instrument includes a pad having a radius of curvature that is determined by using a pad size, a borehole size, and a selected value for a maximum standoff of the pad between the pad and inside of the borehole. The apparatus may further include at least one processor configured to: use an output of each of a plurality of sensors on the pad responsive to a resistivity property of the earth formation to provide an image of the resistivity property.

Another embodiment according the disclosure provides a computer-readable-medium for use with an apparatus for providing a resistivity image of an earth formation, wherein the apparatus comprises a resistivity imaging instrument configured to be conveyed into a borehole, the resistivity imaging instrument having a pad with a radius of curvature determined using a pad size, a borehole size, and a defined value for a maximum standoff of the pad; wherein the computer-readable-medium comprises instructions that enable at least one processor to: use an output of each of a plurality of sensors on the pad responsive to a resistivity property of the earth formation to provide an image of the resistivity property.

BRIEF DESCRIPTION OF THE FIGURES

The present disclosure is best understood with reference to the accompanying figures in which like numerals generally refer to like elements and in which:

FIG. 1 shows an exemplary logging tool that includes an imaging tool made according to one embodiment of the disclosure in a borehole.

FIG. 2A is a schematic diagram of an exemplary imaging tool made according to one embodiment of the disclosure for use in a logging tool, such as the logging tool of FIG. 1;

FIG. 2B is a detailed view of a pad made according to one embodiment of the disclosure for use in an imaging tool, such as the imaging tool shown in FIG. 2A;

FIG. 3A illustrates a pad having a smaller radius of curvature than a borehole;

FIG. 3B illustrates a pad having a larger radius of curvature than a borehole;

FIG. 4 shows a relation between pad radius, borehole radius and maximum standoff according to one aspect of the disclosure for use in an imaging tool, such as the imaging tool shown in FIG. 2;

FIG. 5 shows a pad for which the radius of curvature may be adjusted; and

FIG. 6 shows an exemplary image obtained with a resistivity imaging tool.



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stats Patent Info
Application #
US 20120299595 A1
Publish Date
11/29/2012
Document #
13565533
File Date
08/02/2012
USPTO Class
324346
Other USPTO Classes
324347
International Class
/
Drawings
6



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