Apparatus including a magnetometer having a pair of U-shaped cores for extended lateral range electrical conductivity logging
First Claim
1. A magnetometer for use in measuring subsurface AC injected magnetic fields for borehole logging, comprising:
- first and second magnetic field sensors, said first sensor lying in a first plane and said second sensor lying in a second plane;
fastening means for securing said sensors in axial alignment with the plane of said first sensor perpendicular to the plane of said second sensor;
an elongated heat-insulating housing adapted to receive said sensors, said housing having a relatively small diameter and being adapted for insertion vertically into a borehole;
said first and second sensors comprising;
first and second generally U-shaped core segments each having first and second spaced, parallel, elongated leg portions extending from opposite ends of a relatively short base portion, said first and second core segments being mounted in opposite directions with said elongated leg portions of said first core segment being interleaved with said elongated leg portions of said second core segment; and
coil means disposed around said elongated leg portions of each of said first and second core segments;
circuit means connected to said coil means of each of said sensors for producing signals representing AC magnetic field components detected by said first and second sensors; and
means for securing said circuit means to at least one of said sensors.
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Accused Products
Abstract
A method of well logging in petroleum exploration and apparatus for use in the method as described. An improved magnetometer is disposed in a well bore to provide indications of the distribution, filimentation, and distortion of a controlled current flow within adjoining strata of interest. The current flow is excited by a distant alternating source located at the surface or at other boreholes, and perturbations in the current flow and accompanying magnetic field caused by the electrical characteristics of the adjoining strata are registered by the magnetometer.
The magnetometer comprises a pair of elongated U-shaped cores of laminated, high-permeability metal, with portions of each core being surrounded by a sensing coil. The coil output is fed to surface equipment for detection and analysis.
99 Citations
16 Claims
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1. A magnetometer for use in measuring subsurface AC injected magnetic fields for borehole logging, comprising:
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first and second magnetic field sensors, said first sensor lying in a first plane and said second sensor lying in a second plane; fastening means for securing said sensors in axial alignment with the plane of said first sensor perpendicular to the plane of said second sensor; an elongated heat-insulating housing adapted to receive said sensors, said housing having a relatively small diameter and being adapted for insertion vertically into a borehole; said first and second sensors comprising; first and second generally U-shaped core segments each having first and second spaced, parallel, elongated leg portions extending from opposite ends of a relatively short base portion, said first and second core segments being mounted in opposite directions with said elongated leg portions of said first core segment being interleaved with said elongated leg portions of said second core segment; and coil means disposed around said elongated leg portions of each of said first and second core segments; circuit means connected to said coil means of each of said sensors for producing signals representing AC magnetic field components detected by said first and second sensors; and means for securing said circuit means to at least one of said sensors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A magnetometer system for measuring AC injected magnetic fields for borehole logging, comprising:
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surface means for producing in subsurface strata an AC magnetic field; first and second magnetic field sensors, each sensor comprising a generally U-shaped core segment having first and second spaced, parallel, elongated leg portions extending from opposite ends of a relatively short base portion, and coil means disposed around said elongated leg portions of each of said sensors; fastening means for securing said sensors in axial alignment with the plane of said first sensor being perpendicular to the plane of said second sensor and said first sensor being mounted in an opposite direction to said second sensor with said elongated leg portions of said first sensor being interleaved with said elongated leg portions of said second sensor; an elongated housing for said sensors, said housing having a relatively small diameter and being adapted for insertion vertically into a borehole; notch filter means for passing signals having the frequency of said AC magnetic fields; multiplexer switching means connecting the output of a selected one of said sensor coils to the input of said notch filter; surface data processing equipment; cable means for connecting said magnetometer to said surface data processing equipment; and transmitter means responsive to the output from said notch filter to transmit to said surface data processing equipment signals corresponding to said AC magnetic fields. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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Specification