Abstract: In order to increase the angular field of observation of a logging sonde usable, in particular for dip metering, the sonde is equipped with measuring pads each comprising two independent flaps. The flaps of the same pad are hinged to a central element which is held permanently parallel to the axis of the sonde body, and they are applied against the wall of a borehole by blade springs. Each of the flaps carries an array of electrodes. The flaps of each of the measuring pads are circumferentially offset relative to each other so that the angular field of observation is increased without increasing the diameter of the sonde, once the pads have been retracted.

Abstract: A device for centering a tool forming a part of a tool string, inside a cased well, comprises a central bar suitable for being integrated in a tool string for lowering the tool inside the tubing, two slides which are slidable over a limited range of said central bar, and a series of wheel-carrying structures of generally triangular geometry defined by arms which are hinged to said slides. The device further comprises a series of wheels with each wheel being mounted to rotate freely on a respective one of said wheel-carrying structures in a plane which is inclined relative to a radial plane through the wheel-carrying structure in such a manner that its periphery projects radially outwardly. When the wheel-carrying structures are fully retracted against the central bar, the wheels are received in recesses provided in the outer surface of the central bar. Resilient return means are provided to urge the wheels radially outwardly.

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.