Method and apparatus of using magnetic material with residual magnetization in transient electromagnetic measurement
First Claim
1. An electromagnetic transient apparatus configured to generate a transient magnetic field in a material to be analyzed, comprising:
- a magnetic core having magnetic hysteresis and configured to generate the transient magnetic field when a pulsed current through a coil proximate to the magnetic core reverses a state of magnetization of the magnetic core, wherein the magnetic core is made of at least one permeable magnetic material, the at least one material and dimensions of the magnetic core being selected to make a residual magnetization of the core substantially equal to a saturation magnetization of the core and the at least one magnetic material having a substantially rectangular hysteresis loop when measured in a closed magnetic loop configuration; and
an antenna configured to receive signals from the material to be analyzed, the signals caused by the reversal of the state of magnetization of the magnetic core.
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Accused Products
Abstract
A transmitter antenna assembly for transient electromagnetic well logging instrument comprises an antenna coil coupled with a current source and a magnetic core having residual magnetization. Switching current in the antenna coil results in magnetization reversal in the magnetic core and change in magnetic dipole moment of the antenna. After the magnetization reversal is complete the current is removed and the new vector of magnetic dipole of the antenna maintains constant (steady-state phase of the antenna dipole) due to magnetic hysteresis of magnetic material employed for the magnetic core. No power expenditure during the steady-state phase of the magnetic dipole facilitates highly effective generation and fast switching of a large magnetic dipole. The magnetic core also serves as a shield between the antenna coil and any conductive part of the antenna assembly. Embodiments suitable for measurement-while-drilling or measurements through casing make use of residual magnetization of magnetic drill collar or magnetic casing respectively.
35 Citations
22 Claims
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1. An electromagnetic transient apparatus configured to generate a transient magnetic field in a material to be analyzed, comprising:
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a magnetic core having magnetic hysteresis and configured to generate the transient magnetic field when a pulsed current through a coil proximate to the magnetic core reverses a state of magnetization of the magnetic core, wherein the magnetic core is made of at least one permeable magnetic material, the at least one material and dimensions of the magnetic core being selected to make a residual magnetization of the core substantially equal to a saturation magnetization of the core and the at least one magnetic material having a substantially rectangular hysteresis loop when measured in a closed magnetic loop configuration; and an antenna configured to receive signals from the material to be analyzed, the signals caused by the reversal of the state of magnetization of the magnetic core. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of analyzing an earth formation comprising:
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selecting at least one permeable magnetic material for a magnetic core, the at least one magnetic material having a coercive force and dimensions selected to make a residual magnetization of the core substantially equal to a saturation magnetization of the core and the at least one material having a substantially rectangular hysteresis loop when measured in a closed magnetic loop configuration; using the magnetic core which is made of the at least one permeable magnetic material and has magnetic hysteresis to produce a transient magnetic field in the earth formation when a pulsed current through at least one coil proximate the magnetic core reverses a state of magnetization of the magnetic core; and measuring an electromagnetic signal caused by eddy currents in the earth formation induced by the produced transient magnetic field. - View Dependent Claims (19, 20, 21, 22)
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Specification