Abstract: In a resistivity logging system, the preferred and illustrated embodiment features a downhole well logging tool utilizing central current emitting electrode flanked symmetrically with a number of small electrodes above and below the central electrode. A switching system is included for switching symmetrical pairs of electrodes into parallel with the central electrode thereby increasing the effective field acting on the current flow. The current flow penetrates radially outwardly into the earth's formations in relation to the relative length of the array of electrodes, thereby enabling a sweep to yield borehole resistivity and deep formation resistivity. The data is preferably presented in a resistogram profile.

Abstract: A reference cell for conducting closely spaced buried structure-to-soil electrical surveys uses a soil contact cell adapted to be mounted on the lower end of a pole or cane to be held by the surveyor walking over the right-of-way of the buried structure such as an underground pipeline. The cell includes a fluid chamber on the lower end of the pole or cane and includes on the lower end of the chamber a ground contact pad. A spring loaded bottom wall or boot closes the chamber and is operative to reduce the volume of the chamber when the lower end of the chamber is forced by the pole into contact with the ground above the buried structure. The reduction in volume of the chamber forces fluid through the contact pad to the ground to insure good electrical contact. Fluid in the chamber may be continuously replenished by a make-up supply carried by the surveyor which is drawn from the supply by return of the boot to its unstressed state.

Abstract: Illustrative embodiments of the present invention include methods and apparatus for processing measurements indicative of the dip and azimuth of formation features at various depths in a borehole to produce three-dimensional representations of the formation features. These three-dimensional representations may be in the form of two-dimensional presentations of apparent dip traces for various depths in one or more planes. The apparent dips may be varied with distance from the borehole in accordance with information derived from dips above and below a selected dip. The three-dimensional representations may also take the form of a contour map of a formation surface around the borehold which represents a three-dimensional structural model derived from dips above and below the contoured formation surface.Dip and azimuth variations over a given interval are used to define a family of surfaces in a three-dimensional reference system.

Abstract: A method of electrically investigating the underground condition by measuring the apparent resistivity in the ground, in which the entire ground region to be investigated is assumed to be an aggregate of a plurality of unit blocks, and the resistivity of each of such unit blocks is analyzed from the measured apparent resistivity thereof to determine the underground condition.

Abstract: A method of magnetotelluric exploration is disclosed which features multiple measurements of the earth's electric field at a plurality of locations and one or more magnetic field measurements being made simultaneously. A specific form of cable for connecting measurement apparatus with recording apparatus is also disclosed.

Abstract: A logging tool in accordance with the invention comprises a unitized electrode assembly adapted to be removably mounted on a central mandrel. The unitized electrode assembly comprises a metallic tube that is encased within an electrically-insulating sheath. An insulating sleeve surrounding the sheath carries various electrodes that are separated from each other by insulating spacers.

Abstract: In the representative embodiment of the invention disclosed herein, an electrical logging tool is arranged to include an axial body around which a plurality of annular electrode members and insulating members are alternately stacked to achieve a particular configuration of formation-measuring electrodes. Fluid seals are arranged between the annular members and the stack is compressed between the ends of the axial body for defining an oil-filled chamber within the tool body.

Abstract: Method and apparatus are disclosed for investigating lateral characteristics of an earth formation penetrated by a borehole. Substantially identical measurement transducers are mounted in a fixed separation, side-by-side relationship on a pad adapted for sidewall application. As a pad traverses the borehole, measurement signals are produced corresponding to the same formation investigation conducted along two side-by-side paths on the borehole wall. The signals are recorded and provide an indication of lateral changes between the side-by-side paths. By comparing the signals with varying depth displacements, the best likeness and corresponding displacement are determined and provided as an indication of lateral inclination of the formation. The best likeness indicates a lateral formation homogeneity characteristic and the displacement the inclination of the lateral characteristic between the side-by-side paths.

Abstract: In a method of investigating the electrical resistivity of the ground, five electrodes are implanted in the ground at equal spacings along a straight line. An electrical current is passed through the ground between one pair of these electrodes and the potential difference between a further pair of the electrodes is measured. The electrode which is not used in this measurement is at one end of the line. A further measurement is then made with the four electrodes which exclude the electrode at the opposite end of the line. The measurements are combined to provide a measurement of apparent resistivity which is almost unaffected by a local resistivity variation.