Azimuthally sensitive receiver array for an electromagnetic measurement tool
First Claim
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1. A logging while drilling tool comprising:
- a tool body;
at least one transmitter deployed on the tool body and disposed to transmit electromagnetic energy into a subterranean formation;
a receiver array including a plurality of discrete, circumferentially-spaced magnetic field sensors, the receiver array being longitudinally spaced from the at least one transmitter, each of the discrete, circumferentially-spaced magnetic field sensors being disposed to provide an electrical output signal indicative of an electromagnetic field strength proximate to the sensor, a non uniformity in the output signals being indicative of an azimuthal asymmety in an electrical property of the subterranean formation.
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Abstract
An azimuthally sensitive logging while drilling tool is disclosed. The tool may be suitable, for example, to measure azimuthal variations of electrical properties of a subterranean formation. The tool includes at least one transmitter disposed to transmit electromagnetic energy and a longitudinally spaced receiver array. The receiver array includes a plurality of discrete magnetic field sensors deployed about a circumference of the tool body. In one exemplary embodiment, the tool includes six or more magnetic field sensors selected from either giant magnetoresistive sensors or anisotropic magnetoresistive sensors.
51 Citations
22 Claims
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1. A logging while drilling tool comprising:
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a tool body; at least one transmitter deployed on the tool body and disposed to transmit electromagnetic energy into a subterranean formation; a receiver array including a plurality of discrete, circumferentially-spaced magnetic field sensors, the receiver array being longitudinally spaced from the at least one transmitter, each of the discrete, circumferentially-spaced magnetic field sensors being disposed to provide an electrical output signal indicative of an electromagnetic field strength proximate to the sensor, a non uniformity in the output signals being indicative of an azimuthal asymmety in an electrical property of the subterranean formation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A logging while drilling tool comprising:
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a tool body; at least one transmitter deployed on the tool body, the transmitter including a loop antenna having an exposed wire portion deployed about at least a portion of a circumference of the tool body, the transmitter disposed to transmit electromagnetic energy into a subterranean formation; a receiver array including a plurality of discrete magnetoresistive sensors selected from the group consisting of giant magnetoresistive sensors and anisotropic magnetoresistive sensors, the receiver array longitudinally spaced from the transmitter, each of the discrete magnetoresistive sensors being disposed to provide an electrical output signal indicative of an electromagnetic field strength proximate to the sensor, a non uniformity in the output signals being indicative of an azimuthal asymmetry in an electrical property of the subterranean formation. - View Dependent Claims (17, 18, 19, 20)
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21. A logging while drilling tool comprising:
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a substantially cylindrical logging while drilling tool body; at least one pair of longitudinally spaced transmitters deployed on the tool body, the pair of transmitters deployed about a pair of longitudinally spaced receiver arrays; each of the transmitters including a loop antenna having an exposed wire portion deployed about a circumference of the tool body, each of the transmitters disposed to transmit substantially non azimuthally focused electromagnetic energy into a subterranean formation; each of the receiver arrays including a plurality of discrete magnetic field sensors deployed substantially equi-angularly about a circumference of the tool body, each of the magnetic field sensors selected from the group consisting of giant magnetoresistive sensors and anisotropic magnetoresistive sensors; and each of the discrete magnetic field sensors disposed to provide an electrical output signal indicative of an electromagnetic field strength proximate to the sensor, wherein a non uniformity in the output signals is indicative of an azimuthal asymmetry in an electrical property of the subterranean formation. - View Dependent Claims (22)
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Specification