Abstract: Apparatus for continuously recording, as a function of the depth, the residual magnetization of the rocks through which a well hole passes, comprising, on the one hand, a measurement probe which contains means for measuring the magnetic susceptibility and the magnetic field and, in a cryostat, three gradiometers and, on the other hand, a processing unit which incorporates an integrator (81) for carrying out integration of the data from the gradiometers, a multiplier (76) for multiplying the magnetic field by the magnetic susceptibility, and a subtractor (83) for deducting this product from the result of the integration.

Abstract: A geomechanical probe for a drilling well comprises a logging box located between two inflatable preventers and including a plurality of tracers movable radially and urged outwards by springs for engaging the well wall. The tracers are mounted on pistons which are received in cylinders and urged radially inwards by springs for retracting the tracers, the pistons being driven outwardly to displace the tracers into working positions abutting the well wall by supply of actuating fluid to the cylinders. The positions of the tracers is determined by differential transformers having cores fixed for radial movement with respective tracers.The preventers are inflated with pressurised fluid which is supplied thereto along passages in the probe which also supply pressurized fluid to the well space between the preventers to act upon the well wall.