METHODS AND APPARATUS FOR MEASUREMENT OF ELECTRONIC PROPERTIES OF GEOLOGIGAL FORMATIONS THROUGH BOREHOLE CASING

摘要

An apparatus and method for measuring electrochemical phenomena of formations adjacent a cased well borehole. An alternating current is introduced into the casing (4) in the proximity of the formations to be tested. A portion of the current is received at a point (B) sufficiently remote from the current entry point (A) to ensure that a majority of the current introduced at the current entry point (A) enters the formation along the length of the borehole casing (4). A plurality of at least three spaced apart electrodes (C, D and E) disposed along the interior of the casing detect the voltage level at discrete points along the casing. Calibrated differential voltages between discrete pairs of the electrodes allow inference about electrochemical properties of the formation thereby allowing predictions about the formation composition and/or integrity.