Method and apparatus of using magnetic material with residual magnetization in transient electromagnetic measurement
First Claim
1. An electromagnetic transient transmitter to generate a magnetic field in materials to be analyzed, comprising:
- a magnetic core made of a permeable magnetic material having magnetic hysteresis, said core magnetically coupled with the materials to be analyzed;
at least one coil to change magnetization in the magnetic core; and
a source of current driving the coil, said source of current is switched between zero and at least one non-zero steady current in the coil, said magnetic core remaining substantially magnetized when the source of current is switched to zero current.
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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.
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Citations
24 Claims
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1. An electromagnetic transient transmitter to generate a magnetic field in materials to be analyzed, comprising:
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a magnetic core made of a permeable magnetic material having magnetic hysteresis, said core magnetically coupled with the materials to be analyzed;
at least one coil to change magnetization in the magnetic core; and
a source of current driving the coil, said source of current is switched between zero and at least one non-zero steady current in the coil, said magnetic core remaining substantially magnetized when the source of current is switched to zero current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. An electromagnetic transient transmitter for logging of oil wells having a metal casing comprising:
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at least one magnetic core, the magnetic core comprising an axial fragment of the casing;
at least one coil to change magnetization in the magnetic core; and
a source of current driving the coil, the source of current is switched between zero current and at least one non-zero steady current in the coil, the magnetic core remaining substantially magnetized when the source of current is switched to zero current.
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19. A method of energizing of earth formations to study transient electromagnetic induction effects comprising:
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using a magnetic core made of at least one type of permeable magnetic material having magnetic hysteresis, the core magnetically coupled with the earth formations;
using at least one coil to change magnetization of the magnetic core; and
using a source of current driving the coil, the source of current is switched between zero current and a non-zero steady current in the coil, the magnetic core remaining substantially magnetized when the source of current is switched to zero current. - View Dependent Claims (20, 21, 22, 23, 24)
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Specification