Summary Quantification and control of the in situ mechanics of calcite precipitation in the subsurface are notorious problems often encountered in hydrogeological and engineering applications. Difficulties arise here due to the general inaccessibility and texture of pore spaces, as well as the precipitation reaction’s dependence on fluid chemistry and the composition of the pore surfaces. To mitigate the uncertainties introduced by these inaccessible variables, we propose the use of spectral induced polarization (SIP) as a non-invasive tool to gain insight into the textural and electrochemical parameters controlling the precipitation rate within confined pore spaces and incorporate the gained information into a reactive transport model for quantification. We present SIP monitoring data from three laboratory experiments on diffusive mixing, inducing CaCO3 precipitation in sandstone. During the experimental runs, we identify a clear pattern showing the onset of the chemical reaction in the low-frequency ( 0.1 Hz) response of the imaginary conductivity and the formation of an associated high-frequency peak ( 10 Hz) in the later stages of the experiment. The changes to pore space geometry and precipitation yield were estimated with multiple independent methods. Using information gained from the monitoring data, we predict the dynamics of the precipitation reaction by including textural information, the inner surface area, and the grain size of the precipitate, as well as constraints on the effective diffusivity. These parameters were determined for each sample, based on empirical relations to the polarization response, and incorporated into an accompanying reactive transport model (phreeqc). The experimental results highlight the benefits SIP monitoring can provide to reactive transport models, even if precipitation yield is close to the detection limit of commonly applied methods, such as X-ray powder diffraction or fluorescence.
Mansfeld et al. (Thu,) studied this question.