Bulk electric conductivity response to soil and rock CO2 concentration during controlled CO2 release experiments: Observations and analytic modeling

Abstract

To develop monitoring technologies for geologic [Formula: see text] storage, controlled [Formula: see text] release experiments at the Zero Emissions Research and Technology (ZERT) site in Bozeman, Montana, USA, were carried out in 2009–2011. To understand the impact on the electric properties of soil and sediment rock due to possible [Formula: see text] leakage, we have developed an analytical model to explain and predict the electric conductivity (EC) for [Formula: see text] impacted soil and sedimentary rock. Results from the model were compared with the measurements at the ZERT site during 2009–2011 and the [Formula: see text]-Vadose Project site in France in 2011–2012 after model calibration at each site. The model was calibrated using the saturation ([Formula: see text]) and cementation ([Formula: see text]) exponents contained in Archie’s equation, and a chemistry coefficient ([Formula: see text]) as tuning parameters that minimized the misfit between observed and modeled soil/rock bulk conductivity data. The calibration resulted in [Formula: see text], [Formula: see text], and [Formula: see text] for the ZERT site, which was within the range of values in the literature. All the ZERT data sets had rms errors of 0.0115–0.0724. For the [Formula: see text]-Vadose site, calibration resulted in [Formula: see text]–9.85 and [Formula: see text]–4.2, [Formula: see text]–5.65, and the rms error of 0.0002–0.0003; the cementation exponents were consistent with the literature. These results found that the model predicted the bulk EC reasonably well in soil and rock once the unmeasurable model parameters ([Formula: see text], [Formula: see text], and [Formula: see text]) were calibrated.