Cone-based electrical resistivity tomography

Abstract

Determining the 3D spatial distribution of subsurface properties is a challenging, but critical, part of managing the cleanup of contaminated sites. We have developed a minimally invasive technology that can provide information about the 3D distribution of electrical conductivity. The technique, cone-based electrical resistivity tomography ͑C-bert͒, integrates resistivity tomography with cone-penetration testing. Permanent current electrodes are emplaced in the subsurface and used to inject current into the subsurface region of interest. The resultant potential fields are measured using a surface reference electrode and an electrode mounted on a cone penetrometer. The standard suite of cone penetration measurements, including high-resolution resistivity logs, are also obtained and are an integral part of the C-bert method. C-bert data are inverted using an inexact Gauss-Newton algorithm to produce a 3D electrical conductivity map. A major challenge with the inversion is the large local perturbation around the measurement location, due to the highly conductive cone. As the cone is small with respect to the total model space, explicit modeling of the cone is cost prohibitive. We have developed a rapid method for solving the forward model which uses iteratively determined boundary conditions ͑IDBC͒. This allows us to generate a computationally feasible, preinversion correction for the cone perturbation. We assessed C-bert by performing a field test to image the conductivity structure of the Kidd 2 site near Vancouver, British Columbia. A total of nine permanent current electrodes were emplaced and five C-bert data sets were obtained, resulting in 6516 data points. These data were inverted to obtain a 3D conductivity image of the subsurface. Furthermore, we demonstrated, using a synthetic experiment, that C-bert can yield high quality electrical conductivity images in challenging field situations. We conclude that C-bert is a promising new imaging technique.

The use of non-conventional CPTe data in determination of 3-D electrical resistivity distribution

“…To overcome these problems, Pidlisecky et al (2006) have developed a cone-based electrical resistivity tomography system.…”

“…On the other hand, ERT data which can be inverted to determine the subsurface electrical conductivity structure are increasingly being used to help the development of subsurface models. Data can be used to derive the existence of contaminants and to obtain flow directions of contaminants due to their electrical conductivity differences from the background environment (Pidlisecky et al, 2006;Daily and Ramirez, 1995;LaBrecque and Yang, 2001;Versteeg et al, 2000;Kemna et al, 2002;Slater et al, 2002;Singha and Gorelick, 2005).…”

The use of reference models from a priori data to guide 2D inversion of electrical resistivity tomography data

“…In a further example, Pidlisecky, et al (2006) combine ERT and RCPT to image a saltwater plume. An ERT survey was carried out using the fixed subsurface electrodes as current sources.…”

Resistivity and induced polarization monitoring of biogas combined with microbial ecology at a brownfield site

“…Current and potential electrodes can be distributed along profiles or grids at the ground surface (Revil et al, 2012;Loke et al, 2013), within adjacent boreholes (Pidlisecky et al, 2006;Danielsen and Dahlin, 2010), or making combinations between surface and borehole electrodes (Bergmann et al, 2012;Power et al, 2015;Mendonça et al, 2015).…”

“…Once evaluated, potential values of ߮ is selected for points with measurements and used to evaluate the transfer resistance or apparent resistivity. This model response can then be compared to real data set and the resistivity model iteratively updated to provide data fitting (Pidlisecky et al, 2006;Karaoulis et al, 2013). Model response for IP also implies the solution of a Poison equation to evaluate a potential ߮ ୍ by replacing medium property ߪ in equation (3) by conductivity ߪ , such that (Oldenburg and Li, 1994)…”