Well logging tool for bore hole investigations

Well logging tool for insertion into a borehole with an elongated cylinder-shaped permanent magnet which is magnetized perpendicularly to its cylinder axis, to produce a magnetic field outside the borehole, which in an axial range is directed essentially perpendicular to the cylinder axis and whose magnitude in this range depends essentially only on the radial distance from the cylinder axis, with at least one high frequency transmission and detection coil to transmit and to detect high frequency signals for the excitation and the detection, respectively, of proton nuclear resonance signals in material outside the borehole, whereby a high frequency magnetic field which is produced by the transmission coil comprises components which are inside that range perpendicular to the cylinder axis as well as to the magnetic field

• characterized in that
• transmission and detection coils are used whose axes are essentially perpendicular to the cylinder axis and perpendicular to each other, that means are provided to apply to the transmission coil a continuous high frequency excitation current with the Larmor frequency of the hydrogen nuclei of the material at a predetermined distance from the cylinder axis, and that the magnetization direction of the permanent magnet is at least intermittently at an angle of about 45.degree. between the axes of the transmission and detection coil.