GB544676A - Magnetic field well logger - Google Patents

Abstract

544,676. Magnetic tests and measurements. STANDARD OIL DEVELOPMENT CO. Oct. 15, 1940, No. 15286. Convention date, Oct. 28, 1939. [Class 37] Bore holes and wells are logged by determining the vanation of the magnetic field in the different formations penetrated. At the surface of the earth 5 is placed a frequency meter 6 and a detector 7. Conductors 8 are contained within a cable 9 and connected to a D.C. motor 10 suspended within the bore hole 1, which passes through strata 2, 3, 4. A battery 11 is connected to the conductors 8 at the earth's surface and provides power to operate the motor 10, to the shaft of which is attached a coil 12 connected by slip-rings 13 and conductors 14 contained in a cable 15 to the detector 7, which may be an A.C. voltmeter. The frequency meter 6 enables the speed of the motor 10 to be kept constant. A commutator may be substituted for the slip-rings 13 and a D.C. voltmeter employed as detector. The motor 10, which rotates the coil 12 at a constant speed about a diameter is lowered down the bore-hole 1 and the magnetic field at different levels is measured by observing the voltage generated by the coil 12. In a modification the motor rotates a disc about a diameter within a fixed coil so that an alternating current is induced in the coil when the coil and disc are in a magnetic field. The motor and coil may be enclosed in a fluid-tight container of non- magnetic material. The D.C. motor may be replaced by an A.C. synchronous motor. Instead of a motor producing a rotary movement a device producing a uniformly recurring movement may be attached to the coil 12 or the disc.