Focused Electric (Guardlog)
http://www.jensenpartners.com/?klays=%D8%B4%D8%B1%D8%A7%D8%A1-%D9%88%D8%A8%D9%8A%D8%B9-%D8%A7%D9%84%D8%A7%D8%B3%D9%87%D9%85-%D8%B9%D9%86-%D8%B7%D8%B1%D9%8A%D9%82-%D8%A7%D9%84%D8%A7%D9%86%D8%AA%D8%B1%D9%86%D8%AA&f00=37 The focussed resistivity (LL3) measurement provides excellent vertical resolution and a reasonable depth of investigation. The guard log replaces the classic Elog in conditions of low mud resistivity and high formation resistivity.
Principle of Measurement:
خيار ثنائي تجريبي حساب The probe includes a central current-source electrode between two guard electrodes, maintained at the same potential by internal electronics. Current from the centre electrode is constrained to a thin disk by the presence of the guards and returns to the cable armour above a 10m insulated section. The potential of the central electrode with respect to a surface voltage-reference stake and the measured current are combined by a down-hole microprocessor to calculate apparent formation resistivity.