Abstract: Logging apparatus for measuring alternating magnetic fields generated by electric current flow on a subterranean target near a borehole is disclosed. Electric current of a predetermined temporal form is made to flow on the target; the resulting magnetic field is measured by magnetometers in a downhole sonde. The orientation of the sonde is fixed by various combinations of gyroscope, accelerometer, magnetometer measurements, and borehole survey data.

Abstract: Logging apparatus for measuring magnetic fields while drilling is disclosed. An electrode is located within a drill string and receives alternating current which is conducted to the drill string and from the drill string is injected into the earth surrounding the well. This current is concentrated in anomalies of interest, such as the casing of a target well which is to be intercepted by, or to be avoided by, the well being drilled. A sensitive magnetometer is located within a nonmagnetic portion of the drill string, near the bottom thereof, to detect the alternating magnetic field generated by the current flow in the target and to produce output signals corresponding to the detected field. The output from the magnetometer is used to determine the relative locations of the well being drilled and the target.

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.

Abstract: A method and an apparatus for determining the exact direction of and distance to a nearby target well having a steel casing from a bore hole are disclosed. A long solenoid having a coil wound on a high permeability core for generating a source magnetic field which, in the absence of a target well, has axial symmetry and is characterized by having a magnetic pole at each end of the core is provided. Directly adjacent to one end of the core is a 3-component ring-type fluxgate magnetometer to detect magnetic field components perpendicular to the axis of the solenoid. The detection apparatus is located in a bore hole, and the magnetic field generated thereby is distorted when the solenoid approaches a target well.The magnetic field source is mounted in a drill stem which includes one or more nonmagnetic drill collars, the solenoid source being mounted so that its lower end is located within the nonmagnetic collar while the upper end is magnetically connected to the rest of the drill stem.

Abstract: A method of locating a deep well casing at substantial distances below the earth's surface, and for directing the drilling of a second relief well to intersect the first well at substantial distances below the earth's surface is disclosed. A low frequency alternating electric current flow is produced in the casing of the well to be detected by means of current injected into the earth surrounding the first well. The current flow in the casing produces a magnetic field which is detectable by a sensitive magnetic field sensor suspended in the relief hole and spaced a substantial distance from the current source. The magnetic field sensor detects the magnitude and apparent direction of the alternating field, and this measurement is combined with a concurrent measurement of the earth's magnetic field to determine the direction and distance of the casing from the relief well.

Abstract: A method of well logging in petroleum exploration and apparatus for use in the method is 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 two pairs of elongated U-shaped cores of laminated, high-permeability metal, adjacent portions of each pair being surrounded by a sensing coil. The coil outputs are fed to surface equipment for detection and analysis.