Controlling particle flow driven by local concentration gradients in geological porous media

Project Information

TRACE-it

Grant agreement ID: 101039854

DOI

10.3030/101039854

EC signature date 21 February 2022

Start date 1 June 2022

End date 31 May 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 499 985,00

EU contribution

€ 1 499 985,00

Coordinated by

UNIVERSITE D'ORLEANS
France

Periodic Reporting for period 1 - TRACE-it (Controlling particle flow driven by local concentration gradients in geological porous media)

Reporting period: 2022-06-01 to 2024-11-30

Summary of the context and overall objectives of the project

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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The aim of TRACE-it project is to control the displacement of colloidal particles in subsurface geological environments using in situ solute concentration gradients for subsurface remediation. The objective is to understand the origin of concentration gradients and the transport by diffusiophoresis in geological porous media. Diffusiophoresis refers to the transport of charged particles driven by solute concentration gradients without application of any external force; So far very little consideration has been conducted on diffusiophoresis transport in porous media. The project uses a combined experimental-modelling strategy focused on pore-scale phenomena (the scale of a single pore and of a network of pores) and their upscaling to the reservoir scale (continuum scale).

The project integrates the usage of microfluidic experiments, direct and indirect observation techniques, and computational microfluidics. The major achievements are described below.

One objective is to surpass the current measurement capabilities from the pore-scale to the column-scale. An indirect method to measure pore-scale processes has been developed. For the first time, the Spectral Induced Polarization method is miniaturized at the microfluidic scale, and applied to monitor calcite dissolution, a common geochemical reaction. The technological advancement can now be applied to various geochemical processes for a further understanding of the monitoring of subsurface processes. In addition, we demonstrate that large-scale models classically used in geophysics applies to pore-scale monitoring. This is a strong result because field scale survey is challenging due to the superposition of the couplings and the heterogeneity of the natural environment.

A second aim is to predict the location and magnitude of local concentration gradients that are generated in geological porous media due to contaminants or mineral reactions. We designed microfluidic devices where a contaminant is trapped in a dead-end pore while an aqueous phase is flowing around. These devices allow to monitor the dissolution of the contaminant in the aqueous phase. One crucial parameter in the dissolution process is the wettability of the device, indeed the wettability of the walls of the porous media affects the trapping of the contaminant and the mean dissolution rate. We developed a new method to control and modify the wettability of the inner surface of our micromodels. The method is based on atmospheric pressure plasma technology. We are now ready to use this method to characterize contaminant dissolution and the effects of wettability, and to confront it to numerical models.

The project also aims at describing diffusiophoretic transport of colloids in porous media from the pore-scale to the macroscale, both numerically and experimentally. Using microfluidic experiments, we assessed the effect of a local source of concentration gradient on the transport of colloidal particles. We discovered that a chemical reaction can be inhibited by the colloids that form a passivation layer around the source of concentration gradient. This breakthrough proves that remediation through diffusiophoresis can now be designed.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Microscale geophysics using microfluidics is a new tool that couples direct visualization of the pore-scale dynamics and chemical reactivity with geoelectrical response. To the best of our knowledge we are the first team to provide microfluidics chips equipped with electrodes for geo-electrical monitoring. In addition, we show that petrophysical models apply to microscale geoelectrical monitoring and are consistent with optical observations. Showing that the electrical signal measured on an investigated volume accounts for the average behaviour of pore-scale processes is a major asset for our community. Indeed, we prove that coupling microfluidics with integrative monitoring methods is essential for characterization across scales. We did not expect that a simple petrophysical model like the one we used will agree with pore-scale observations. The outcomes of this methodology are beneficial for the physics-based advancement of pore-scale modeling of complex electrical conductivity.

We assessed the impact of a source of concentration gradient on the transport of colloids, we show that colloids form a passivation layer around a dissolving mineral leading to the inhibition of the dissolution. Indeed, this phenomenon was not reported before in the literature. Moreover, we show that diffusiophoresis effect lead to the focusing of colloids around a dissolving mineral even in the presence of strong pressure gradients, as it is mostly the case in geological environment. These results prove that we can now design remediation through diffusiophoresis by choosing the properties of the particles to target a chemical reaction and stop it

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