Well logging pad devices having differential pressure relief

Abstract From the Canadian patent

Abstract of the Disclosure. A well logging instrument comprises a focus section having a focus upper guard a center, electrode and lower focus guard. The bottom section of the instrument includes a pad device having electrodes on its borehole wall-engaging surface and adapted to be urged against the borehole wall and also having a plurality of pressure relief holes formed therein to reduce differential pressure which might otherwise build up between the surface of the pad and the borehole wall. The remote electrode of the focus portion of the instrument is the armor surrounding the logging cable. The lower focus guard serves a dual function in that it is also the minifocus remote electrode. …