Real‐time electrical monitoring of reagent delivery during a subsurface amendment experiment

• Published in: Near surface geophysics (Online) 2014-02, Vol.12 (1), p.151-163
• Main Authors: Rucker, Dale F., Crook, Nigel, Winterton, Jeffrey, McNeill, Michael, Baldyga, Chris A., Noonan, Gillian, Fink, James B.
• Format: Article
• Language: English
• ISSN: 1569-4445; 1873-0604
• DOI: 10.3997/1873-0604.2013017

ABSTRACT An electrical resistivity monitoring survey was conducted on a mine heap to track reagent movement during high‐pressure injections. The injections were designed to increase the dissolution of metallic gold from low‐grade ore and enhance recovery after surface leaching had ceased. The main objective of the geoelectrical monitoring was to observe the effectiveness of the injection technique and provide feedback to optimize injection parameters in real time. Real‐time assessment was achieved by monitoring the raw output current and transfer resistance on a network of borehole electrodes installed around the injection well. It was demonstrated that the output current increased significantly on particular borehole electrodes after commencement of reagent injection, when the wetting front arrived at the electrodes. When injection ceased, the electrical current returned to the initial baseline current values. The timing and distribution of the electrodes demonstrating this behaviour varied with injection depth. The internal structure of the heap was likely a controlling factor in reagent movement. Resistance, converted to apparent resistivity, was also shown to change significantly in the region near the injection. Verification of the real‐time assessment was conducted with post‐injection time‐lapse 3D tomographic inversion. While inverse modelling provides a truer 3D representation of reagent injection, the cost was shown to be a time‐lag of 3.5 days to complete the modelling. The simplicity of monitoring the raw current output and voltage can make this a powerful tool for real‐time tracking of fluid movement in the subsurface.