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US 10,948,440 B2Granted
Borehole signal reduction for a side-looking NMR logging tool using a magnet assembly
AssigneeHalliburton Energy Services, Inc.
InventorsLilong Li, Rebecca Jachmann, Arcady Reiderman
Life of this patent
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Abstract
A side-looking Nuclear Magnetic Resonance (“NMR”) logging tool is designed to reduce and/or eliminate a borehole signal. The logging tool includes a magnet assembly having at least two magnets with magnetizations in different directions, thus resulting in a net magnetization that reduces the borehole signal.
Claims8
A method for side-looking nuclear magnetic resonance (“NMR”) logging, the method comprising:
- deploying a logging tool into a wellbore, the logging tool having a radio frequency (“RF”) antenna and a magnet assembly;
- generating a first static magnetic field using a first magnet of the magnet assembly, the first magnet having a magnetization in a first direction;
- generating a second static magnetic field using a second magnet of the magnet assembly, the second magnet having a magnetization in a second direction different from the first direction;
- combining the first and second static magnetic fields to reduce a borehole signal from a total signal of the volume of interest,
- wherein the first and second static magnetic fields combine to result in a combined static magnetic field that results in a sensitive volume of interest where a depth of investigation in front of the logging tool is at a target depth of investigation and a depth of investigation behind the logging tool reduces the borehole signal;
- and
- receiving the total signal from the volume of interest using the RF antenna, wherein:
- the RF antenna is positioned on a front side of the logging tool and the magnet assembly is positioned on a back side of the logging tool opposite the front side, and
- the RF antenna and the magnet assembly are separated from one another along an axis running from the front side to the back side of the logging tool.
6 more elements
A method to design a side-looking nuclear magnetic resonance (“NMR”) logging tool, comprising:
- selecting a magnet assembly to generate a static magnetic field in a volume of interest, the magnet assembly being configured to reduce a borehole signal, wherein the magnet assembly comprises at least two magnets having different directions of magnetizations such that the static magnetic field results in a sensitive volume of interest where a depth of investigation in front of the logging tool is at a target depth of investigation and a depth of investigation behind the logging tool reduces the borehole signal;
- and
- selecting a radio frequency (“RF”) antenna to induce an RF field into the volume of interest and to receive corresponding total signals form the volume of interest, wherein:
- the RF antenna is positioned on a front side of the logging tool and the magnet assembly is positioned on a back side of the logging tool opposite the front side, and
- the RF antenna and the magnet assembly are separated from one another along an axis running from the front side to the back side of the logging tool.
2 more elements
Dependencies are inferred from the claim text.