Abstract: Variable frequency induction well logging methods and apparatus are disclosed having an approximately constant vertical response function. The frequency of operation is automatically selected to minimize propagation effects. These techniques permit an N point deconvolution of apparent formation conductivity to yield an approximation of the true conductivity of incremental layers of cylindrically symmetrical earth formations, including formations having adjacent layers of arbitrary thicknesses and conductivities.

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 system is disclosed for use in packaging electronic systems for use in high temperature well boreholes. A fluid tight hollow body member or sonde is provided having unique longitudinally extensive hollow support and mounting members for electronic components. The hollow interior of the support and mounting members contain a bismuth eutectic alloy heat absorbant material for evenly distributing heat developed in the electronic componentry throughout the logging tool.

Abstract: In the preferred and illustrated embodiment of a downhole oil well resistivity logging tool having a focused electrode, the current ideally flows from the electrode radially outwardly in a thin sheet deep into the earth's formation adjacent to the well. There is an undesirable vertical current component along the electrodes which distorts the measurement of resistivity. First and second alternate embodiment are set forth which utilize additional balanced electrodes in the electrode array. They establish a vertical current in the adjacent formation. The vertical current is varied by means of an oscillator connected to the balanced electrodes, and the voltage of the electrodes is monitored to detect zero crossing. Zero crossing is indicative of reduced vertical current flowing in the formation.

Abstract: In the disclosed and illustrated embodiment, an improved method and apparatus for obtaining an improved spontaneous potential log is set forth. On a single sonde, multiple spontaneous potential electrodes, aligned vertically along the length of the sonde at spaced location, are positioned to transverse a well bore as the sonde is pulled from the well to obtain a measure of spontaneous potential from each electrode. The apparatus and method further discloses means multiplexing the signals from the several spontaneous potential electrodes whereupon the signals are converted by an analog to digital converter into digital words. By synchronizing with the multiplexing, a digital word is obtained for each electrode at a time such that such electrode is read at a common elevation. The several digital words are then input to delay lines, there being one delay line for each electrode, wherein the delay occurs in multiples of T where T equals the time delay between electrodes.