LOGGING PROBE FOR MAKING REDOX POTENTIAL MEASUREMENTS

摘要

Method and apparatus for electrical logging in a mud-filled borehole by sensing redox potential and other formation characteristics. An elongated, tubular probe body contains spaced-apart reference and potential measuring electrodes which extend longitudinally thereof and are adapted to make external contact with the borehole fluid at the streamlined surface of the probe nose. The reference electrode is a chemical type formed of a metal electrode immersed in an electrolyte-filled compartment separated from the external borehole fluid by a pressure-compensating diaphragm in the probe side wall. A fluid bridge is established between the lower end of the reference electrode and the mud of the borehole through the insertion of a permeable ceramic wick. The diaphragm substantially equalizes pressure between the borehole fluid and the electrolyte so as to prevent either loss or contamination of the electrolyte, a feature not found in prior art devices. An optional heavy electrolyte compartment within the probe body may be interposed between the sidewall diaphragm and the reference electrode, thus maintaining a positive leak pressure into the mud even under high pressure borehole conditions.