Well logging appts. measuring resistivity of formation - with survey current and potential difference measured with vertical narrow electrode array

摘要

Well logging appts. comprises a tool having a narrow wall-engaging pad with an array of long vertical electrodes. The pad is less than 4 inches wide and the array length to width ratio is 3-5. A circuit produces between two electrodes a survey current primarily through the zone of the formation likely to be washed by borehole fluid. A second circuit measures the survey current and the potential difference between a remote reference electrode and a point between the two electrodes to indicate zone resistivity. The pad pref. carries three pairs of electrodes respectively short-circuited and symmetrically located relative to a central electrode at increasing distances. The pad is e.g. of neoprene.