Microfluidics for geosciences: application to detection and targeting of mineral dissolution in porous media

Sophie Roman

maître de Conférences à l’université d’Orléans

ISTO (Institut des Sciences de la Terre d’Orléans) , CNRS, BRGM, Université d’Orléans

Colloids and small particles are ubiquitous in the soils and subsurface geological formations. Many engineering applications foreseen their usage for groundwater remediation or for sealing damaged geological confinement barriers. However, colloid injection methods remain for now at the stage of prototypes as the delivery of the particles to the contaminated or damaged regions is not well controlled. Unlike well-known fluid and particle transport processes driven by gradients of pressure, or gravity, diffusiophoretic transport of charged particles is only driven by chemical concentration gradients without application of any external force. The ability of diffusiophoresis to reroute colloids and small particles trajectory offer an appealing solution to deliver healing materials towards target regions of the porous formations since the solute concentration gradients are very often localized at the vicinity of the regions of interest. To control colloid flow at the reservoir-scale for remediation, we need to characterize the localization and magnitude of concentration gradients and the diffusiophoresis effects associated with these gradients. In subsurface environments, local concentration gradients originate from a number of physico-chemical processes, e.g. salt dissolution, drying, chemical reactions. The objective of this work is to characterize local concentration gradients generated during mineral dissolution through indirect geo-electrical method implementation, and to investigate colloid transport in the vicinity of a dissolving mineral.

We use microfluidic experiments that enable direct visualization of flows, reactions, and transport at the pore-scale to study the water-mineral-colloid interactions. We propose a new kind of micromodels equipped with electrodes for SIP (Spectral Induced Polarization) monitoring of calcite dissolution. We show a strong correlation between SIP response and dissolution through electrical signal examination and image analysis. In the presence of negatively charged particles, the colloids tend to aggregate around the dissolving calcite crystal, thus slowing down the reaction process. We show the complex interplay between flow, reaction, and colloid transport in geological porous media.