Method and apparatus for azimuthal resistivity measurements in a borehole
First Claim
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1. An apparatus for making measurements of a parameter of interest of an earth formation comprising:
- (a) an elongated body;
(b) a first guard electrode on the body;
(c) a central electrode on the body;
(d) two pairs of monitor electrodes on the body, one of the two pairs of monitor electrodes on a first side of the central electrode, and a second of the two pairs of monitor electrodes on a second side opposite the first side of the central electrode, and(e) a second guard electrode including at least one electrically conducting pad mechanically coupled to an adjacent portion of the elongated body by an extension device, the at least one electrically conducting pad at substantially the same electrical potential as the adjacent portion of the body, and wherein the second guard electrode is on the same side of the central electrode as the first guard electrode.
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Abstract
An azimuthal resistivity logging tool includes one or more pads for making azimuthal resistivity measurements of earth formation. Current from the pads, guard electrodes and a measure electrode are measured while monitoring the voltage difference between pairs of monitor electrodes. The pads and an adjacent portion of the tool body form a guard electrode. In addition, microelectrodes are provided on the pads for obtaining high resolution resistivity measurements.
47 Citations
26 Claims
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1. An apparatus for making measurements of a parameter of interest of an earth formation comprising:
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(a) an elongated body; (b) a first guard electrode on the body; (c) a central electrode on the body; (d) two pairs of monitor electrodes on the body, one of the two pairs of monitor electrodes on a first side of the central electrode, and a second of the two pairs of monitor electrodes on a second side opposite the first side of the central electrode, and (e) a second guard electrode including at least one electrically conducting pad mechanically coupled to an adjacent portion of the elongated body by an extension device, the at least one electrically conducting pad at substantially the same electrical potential as the adjacent portion of the body, and wherein the second guard electrode is on the same side of the central electrode as the first guard electrode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of making measurements of a parameter of interest of an earth formation comprising:
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(a) conveying a logging tool including body into a borehole in said earth formation; (b) emitting a first current from a first guard electrode on the body; (c) emitting a measure current into the earth formation using a central electrode on the body; (d) monitoring voltages of a first pair of monitor electrodes on the body, the first pair of monitor electrodes on a first side of the central electrode; (e) monitoring voltages of a second pair of monitor electrodes on the body, the second pair of monitor electrodes on a second side of the central electrode; (f) emitting a second current from an electrically conducting pad mechanically coupled to the body by an extension device, the electrically conducting pad and the adjacent portion of the body forming part of a second guard electrode; and (g) controlling emission of currents from the first guard electrode and the electrically conducting pad in response to the monitored voltages. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification