Improved Understanding of the Spectral Induced Polarization Response of Reactive Transport Through Millifluidic Experiments

Abstract : Spectral induced polarization (SIP) has shown potential to detect subsurface reactive transport processes. However, previous laboratory experiments could not associate the SIP response with the temporal development and spatial distribution of reactive transport processes in detail due to the opaque nature of porous media. We developed a novel experimental setup that consists of a millimeter scale 2D transparent porous medium and electrodes for SIP measurements to visually observe reactive transport processes down to the pore scale while performing SIP measurements (i.e. a 2D millifluidic setup). We used this setup to investigate the SIP response of calcite precipitation (CaCO₃). The image analysis and SIP measurements highlight that the SIP response does not necessarily represent the total mass of calcite precipitation in the measurement region. In addition, we numerically simulated the electric field distribution based on the observed calcite precipitation. The results suggested that the heterogeneous distribution of calcite precipitation within the investigated volume had an important influence on the SIP response. Given the heterogeneous and localized nature of many reactive processes, these findings clearly demonstrate the importance of investigating sub-resolution reactive processes for SIP measurements. The proposed novel experimental setup was shown to be suitable for this purpose.