Logging method and apparatus for investigating geometrical characteristics of a borehole.

摘要

The invention relates to a logging method and apparatus for investigating the geometrical characteristics of a borehole. The apparatus comprises an array of circumferentially spaced apart azimuthal current electrodes (Aazi) disposed on a sonde (21), and an annular current electrode (A) longitudinally spaced apart from the array of azimuthal electrodes. Currents (Ici) are emitted between the azimuthal electrodes and the annular electrode (A). Monitor electrodes (M, Mazi) are respectively associated with the current electrodes (A, Aazi). The potential differences ( DELTA Vci) between the annular monitor electrode (M) and each of the azimuthal monitor electrodes (Mazi) are detected. In response to the detected potential differences, output signals (Rci) are generated indicative of the distances between the sonde and the wall of the borehole in a plurality of directions around the sonde. The invention also relates to the application of such a technique to azimuthal resistivity measurements of earth formations for correcting said measurements for sonde eccentring and/or for the irregular shape of the section of the borehole. <IMAGE>