Abstract: A well logging instrument for measuring the resistivity of relatively thin formation beds. A well logging instrument includes an elongated body member, serving as a single guard electrode, and a point current emitting measure electrode recessed therein. The instrument is lowered into a borehole and urged into contact with the wall of the borehole. A measure current emanates from the measure electrode into the formation for determining the resistivity thereof.

Abstract: A well logging instrument is attached at its first end to a well logging cable and is connected at its second end through a flex joint to a shaft section which through another flex joint is connected at its lower end to a centralizing section. As the well logging instrument traverses an earth borehole, the lower centralizer section maintains the guide nose of the centralizer section away from the ledges encountered along the borehole walls and a shaft flexibly connected between the well logging instrument and the centralizer section ties the gravity decentralized logging instrument to the lower centralizing section and steers the lower guide nose away from the ledges which are encountered.

Abstract: The system consists of means for running a logging instrument and a long semi-rigid extension on a logging cable through open-ended drill pipe. A head on the upper end of the extension conforms sufficiently close to the inside diameter of the drill pipe that pump pressure down the drill pipe develops thrust across the head to push the extension and logging instrument down the well bore. A catcher sub at the lower end of the drill pipe prevents the extension from being pumped out the bottom of the drill pipe. As the extension and logging instrument are pulled back into the drill pipe by the logging cable, well bore measurements are made and recorded over the interval below the bottom of the drill pipe. The extension consists of a number of sections that are joined together on top of the instrument as the instrument is lowered into the drill pipe on the logging cable, the extension sections each having a slot along their entire length in order that the extension will fit around the logging cable.

Abstract: The system consists of means for running a logging instrument connected to a long rigid extension on a logging cable through open-ended drill pipe. The extension consists of a number of sections of tubing that are joined together on top of the instrument as the instrument is lowered into the drill pipe prior to the logging cable being connected to the well logging instrument. As soon as the last section of the tubing has been added, the well logging cable, having an electrical probe member attached to its lower end and having weighting means to cause the probe to lower itself through the tubing, is fed down through the tubing and into a circulation and electrical connection sub connected to the well logging instrument itself.

Abstract: Circuitry is provided for establishing the points in time at which radiation is detected following each neutron burst in pulsed neutron logging. Means are provided to generate a signal indicative of the arithmetic mean to then compute the macroscopic thermal neutron capture cross section of the formation of interest surrounding the borehole. In one embodiment, an indeterminate number of gates provides a means of establishing the point in time of each pulse indicative of detected radiation. In another embodiment, only a predetermined number of such gates are used. In yet another embodiment, a weighting factor is applied to pulses occurring either before or after the arithmetic mean such that the number of pulses before the arithmetic mean are a multiple of the number occurring after such time.