Systems and methods for deep-looking NMR logging
First Claim
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1. A system for NMR logging of an underground formation traversed by a borehole, the system having a longitudinal axis and comprising:
- means for imparting a static magnetic field in the formation surrounding the borehole, the static magnetic field being substantially radially-oriented with respect to the longitudinal axis in a portion of the formation;
means for applying a first oscillating magnetic field having magnetic field lines substantially orthogonal to the static magnetic field in substantially all azimuthal directions;
means for applying one or more directional oscillating magnetic fields being substantially orthogonal to the static magnetic field in corresponding one or more angular sectors of a volume in the formation surrounding the system; and
means for directionally sensitive detection of NMR signals from the formation surrounding the system.
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Abstract
An NMR logging tool for conducting NMR measurements in a plurality of sensitive volumes ranging up to a meter from the tool. The tool comprises a magnetic assembly using one or more permanent magnets and at least one pole piece for extending a magnet pole and shaping the magnetic field to simulate a magnetic monopole in a sensitive volume within the formation. Different embodiments of a segmented antenna enable directional NMR logging. The tool embodiments and methods of their use are suitable for wireline or LWD logging, and can be used for directional drilling.
279 Citations
26 Claims
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1. A system for NMR logging of an underground formation traversed by a borehole, the system having a longitudinal axis and comprising:
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means for imparting a static magnetic field in the formation surrounding the borehole, the static magnetic field being substantially radially-oriented with respect to the longitudinal axis in a portion of the formation; means for applying a first oscillating magnetic field having magnetic field lines substantially orthogonal to the static magnetic field in substantially all azimuthal directions; means for applying one or more directional oscillating magnetic fields being substantially orthogonal to the static magnetic field in corresponding one or more angular sectors of a volume in the formation surrounding the system; and means for directionally sensitive detection of NMR signals from the formation surrounding the system. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for NMR logging a borehole in a geologic formation by means of a tool having longitudinal axis, the method comprising the steps of:
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imparting a static magnetic field having substantially radial orientation with respect to the tool axis in a volume of the formation surrounding the borehole; imparting a plurality of oscillating magnetic fields substantially orthogonal to the static magnetic field in the volume of the formation in which the static magnetic field has substantially radial orientation, the plurality of oscillating magnetic fields being azimuthally directional; detecting NMR signals from the formation in a plurality of directionally sensitive antenna segments; and processing of the detected NMR signals to obtain directionally sensitive information about at least one property of the formation. - View Dependent Claims (15)
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16. A method for determining an NMR property of formation surrounding a borehole with the aid of a logging device, comprising the steps of:
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providing a magnetic configuration producing a substantially radial static magnetic field into a portion of the formation; providing a plurality of directionally sensitive antenna segments disposed along a longitudinal axis of the logging device generating RF pulsed magnetic fields in the formation, the RF fields being substantially orthogonal to the static magnetic field; receiving NMR signals from a sensitive region of the formation at two adjacent antenna segments; and determining a property of the formation in a direction based on orientation of both the adjacent antenna segments. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification