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Summary of the project

TRACE-it: Controlling particle flow driven by local concentration gradients in geological porous media

Many engineering applications foreseen the usage of small particles for groundwater remediation or for sealing damaged geological confinement barriers, however, delivering materials to a contaminated or damaged region is challenging. TRACE-it aims at controlling the flow of colloidal particles in subsurface geological environments using in situ solute concentration gradients. The phenomenon, known as diffusiophoresis, has a tremendous potential to move colloids to regions that are inaccessible by conventional transport. Diffusiophoretic transport in porous media, however, has received very little attention so far, especially in standard transport in porous media models where it remains unconsidered.

What is the magnitude and location of solute concentration gradients produced during subsurface processes? How to use these gradients to transport colloids towards target regions? The answers will be found through a combined experimental-modelling approach to: (i) measure coupled hydro-electro-chemical dynamics, (ii) characterize concentration gradients generated in situ in geological porous media, (iii) identify the influence of concentration gradients on particle transport and develop a macroscale model of transport in porous media that includes diffusiophoresis. TRACE-it integrates the usage of microfluidic experiments, observation techniques, and multi-scale computational fluid dynamics to describe the transport mechanisms at the pore-scale before upscaling to the continuum-scale.

The experimental-modelling toolset will open new ways for moving colloidal particles by sensing chemical gradients generated naturally or from human activity, leading them to their target such as oil, contaminants, or reacting minerals. During column-scale experiments, controlling colloid transport will be achieved through the characterization of solute concentration gradients and the use of specifically designed particles.

Principle of diffusiophoresis: charged particles move in the presence of a gradient of solute concentration either to higher solute concentration, or to lower concentrations.

Origin of concentration gradients for diffusiophoresis in geological environements:

(a) Chemical and physical processes associated with the process of CO2 injection and sequestration at the pore-scale, the aqueous phase (brine) is in blue, from Steefel et al. (2013), (b) numerical simulations of mineral dissolution from a pore-scale perspective (Soulaine et al. 2017), (c) examples of field-scale processes associated with the generation of local chemical gradients, (d) conceptual model of trapped NAPL (Non-Aqueous Phase Liquid) in a porous matrix that undergoes dissolution by interphase mass transfer, nanoiron particles are targeting NAPL for remediation purposes, from Saleh et al. (2006).

Scientific program

The core objective of the project is to progress towards a deeper understanding of colloid transport driven by chemical gradients in geological porous media. The project is multi-disciplinary and uses computational and experimental sciences,
fluid dynamics, electrokinetics, geochemistry, and technological developments of observation techniques. The project is organized in four work packages (WP).

 

WP1: Experimental developments

Development of direct and indirect measurement of coupled hydro-electro-chemical dynamics at the different scales of interest. The development of our Nanoμlab platform coupled with computational microfluidics will allow the evaluation of concentration gradients and surface properties at the micrometer-scale, and their temporal evolution. By coupling these direct observations to indirect geo-electrical techniques, we will characterize the electrical signature of concentration gradients at the pore-scale toward geo-electrical monitoring at larger scales. 

WP2: Origin of chemical gradients

This WP aims at characterizing local concentration gradients generated in porous media. By combining experimental and computational microfluidics we will predict the magnitude and location of concentration gradients in porous media that are generated by local processes, i.e. during the dissolution of a contaminant or during mineral reactions. To overcome the complexity of coupled geochemical systems, the approach will be iterative starting from analysis at the scale of a single pore, to network of pores, and to real-rock systems for various pH, salinity, and flow conditions.

WP3: Diffusiophoresis in porous media

We will investigate the impact of concentration gradients on particle transport in porous media. We will assess the transport of particles in porous media under controlled chemical gradients coupled with advective flow. We adopt a step-wise strategy that focus first on well-controlled geometries before investigating the complex coupling between diffusiopheresis and porous media properties (permeability, pore size distribution). Microfluidic experiments will support the development of models for diffusiophoretic transport in porous media, then allowing the upscaling towards macroscale models.

WP4: Column-scale demonstrator

We will use column experiment to achieve the control of particles transport driven by concentration gradient generated in situ. Key physical parameters (e.g. concentration gradients, particle size, coating, suspension concentration and injection flow rate) will be optimized to propose enhanced remediation processes.