Induced polarization response of porous media with metallic particles — Part 4: Detection of metallic and nonmetallic targets in time-domain induced polarization tomography

Abstract

Time-domain induced polarization (TDIP) is a nonintrusive imaging technique of the subsurface that can be used to localize polarizable bodies including metallic objects and clay-rich materials. We first reviewed recent advances in the interpretation of induced polarization data. Then, we performed laboratory and sandbox experiments to determine the frequency-domain and TDIP signature of (1) a metal bar in sand, (2) dispersed semiconductors (e.g., pyrite) in sand, and (3) bentonite. In the case of the sandbox experiments, the three types of bodies were localized in the center of the sandbox, which was filled with water-saturated sand. We determined that chargeability was the best parameter to characterize metallic bodies (the metallic bar and the dispersed pyrite), whereas normalized chargeability was the best parameter to characterize the cation exchange capacity and therefore the clay content of the subsurface at a given clay mineralogy. For interpretation purposes, it was therefore important to display the right parameters in TDIP depending on the type of target we wanted to image for engineering applications.