The COCONUT project aims at developing predictive capabilities to understand how colloids (nanometals, fine particles, bacteria, viruses, asphaltenes..) control immiscible two-phase flow in complex geological formations. Colloids (including nanoparticles) have an incredible potential to remobilize non-aqueous phase trapped by capillary forces in soils and the subsurface, and then to remediate contaminated ground-water or enhance oil recovery. Their use in daily engineering, however, is still underexploited because the lack of knowledge regarding their transport mechanisms is an obstacle to precise control of two-phase flow. Importantly, the presence of colloidal particles flowing in the subsurface challenges the standard modeling viewpoint of flow and transport based on Darcy’s law. We posit that the precise control of colloids on the motion of two-phase flow can only be achieved by developing a deep knowledge of the coupled hydro-electro-chemical processes at the pore-scale. The COCONUT project uses a combined modelling-experimental strategy focusing on the pore-scale mechanisms and on the upscaling to the continuum-scale. The project is multi-disciplinary and uses computational and experimental sciences, fluid dynamics, electrochemistry, and mathematics. The project will require the development of hydro-electro-chemical computational models at different scales of interest (WP1). We will use high-resolution simulations to interrogate emergent physico-chemical processes and characterize the surface attractive and repulsive forces at the nanoscale (WP2). Then, we will decipher the mechanisms leading to the displacement of fluids trapped in an unsaturated porous medium in the presence of colloids using pore-scale modelling and microfluidic experiments (WP3). Finally, we will demonstrate and optimize the two-phase flow colloidal control in geological systems at the column-scale (WP4).

Planetary growth, differentiation and the social impacts from volcanic activity are all linked to the poorly understood dynamics of magmatic systems. MECAMUSH will rationalize the behavior of crystal-rich magmas (mush) by combining novel experimental and numerical modeling techniques. Geological observations point towards two crucial aspects of mush dynamics. 1) Ubiquitous differentiation by melt extraction, which produces mobile, crystal-poor magmas and crystal-rich residues, seems controlled by the dynamics of force chains in the network of crystals. MECAMUSH aims at characterizing these force chains and how they regulate mush rheology from 1-12 Kbars. 2) MECAMUSH will explore the subsequent transition of the mobile magma into a microlite-charged mush during eruption by experimentally characterizing the permeability of three-phase magmas combined with new rheological insights of bimodal suspension to update existing numerical models for volcanic hazard assessment.

The recent geophysical data acquired to describe subduction zones revealed the very variable mechanical behaviour of the plate interface fault zone, from aseismic slip to megaearthquakes. So far, there is no model to describe the processes controlling these deformation modes. The fault cores contain in many cases a large proportion of smectite. This clay mineral incorporates a variable proportion of water in interlayer space. Dehydration reactions are a potential trigger of mechanical instabilities, and the aim of SMEC is to unravel possible connections between dehydration reactions and slip instabilities. Understanding smectite dehydration in fault rocks requires first a new conceptual framework to be applied. All available experimental data, as well as thermodynamic models, consider a system where the same pressure is applied to the solid and the free fluid. On the contrary, fault rocks are best described as a two-phase system composed of a solid skeleton that includes fluid-filled cavities, with two independent pressures. Based on this fundamental assumption, we propose to reassess smectite dehydration by combining experiments and modelling (WP1). Dehydration reactions in the space (Pfluid-Psolid-T conditions) will be analysed using X-ray diffraction experiments in a semi-transparent high-pressure vessel at ISTO, along with Synchrotron experiments. These experimental results will then constitute inputs to a model of dehydration, which includes molecular simulations at the clay interlayer scale, and upscaling to a macroscopic thermodynamic model. This analysis of dehydration will form the ground of an experimental study of smectite deformation (WP2), to unravel potential connections between slip instabilities and dehydration. Frictional properties of smectite revealed by the experiments will be modelled using a combination of molecular simulations at the interlayer scale and thermo-poro-mechanics to retrieve macroscopic properties and to establish instability criteria. Last, in WP3, the same approach of WP1 and WP2 will be applied to natural fault rocks, to validate and extend the hydration and frictional behaviour characterized on synthetic, pure smectite samples to natural material with a larger complexity, in particular in terms of mineralogy. The hydration and frictional properties obtained from the analysis of synthetic and natural samples will finally be used as inputs of numerical models of the slip behaviour of large-scale fault zones, able to reproduce the seismic cycle and to catch a large scope of slip behaviour, from slow slip events to regular earthquakes.

The response of tropical wetlands to climate change in terms of carbon storage remains highly uncertain, in particular because the mineralization of organic matter as a function of bacterial activity and the reduction of iron over time is still debated. The objective of this project is therefore to better understand the coupled dynamics of organic matter, iron oxyhydroxides and water in these wetlands and the black water rivers they feed. Based on existing experimental and theoretical studies, our objective is to quantify, through a several years monitoring, the relative share of the different processes proposed for the transformations and transfers by (sub)surface waters of carbon and iron from these wetlands. We will notably combine for the first time long term observations on hydrochemistry, the stable isotopes Fe-C-O-H for the tracing of sources and dominant reactions, the study of organo-metallic speciations and the search for functional genes in the field. We thus expect to show, among the possible mechanisms identified during laboratory experiments, those which really play an important role for the balances of these elements. This knowledge, acquired in the context of the Rio Negro basin in Brazil (SO HyBam) which remains relatively untouched by human activity, will help reduce the uncertainties of climate change modeling mentioned in the 2019 IPCC report on Climate Change and Land. It will also provide a baseline to better highlight the effect of other major anthropogenic disturbances in Amazonia, such as deforestation.

France is committed to reducing its greenhouse gas emissions, which in particular includes the transposition of the European Directive on the geological storage of CO2. Indeed, groundwater protection is not explicitly taken into account in the European Directive on CO2 storage, although it is indirectly covered by the global philosophy of the text summarized in Article 1.2: “prevent and, where this is not possible, eliminate as far as possible negative effects and any risks to the environment and human health”. The main actions mentioned in the text in relation to groundwater protection are data collection and monitoring. In this context, the CIPRES project focuses on the characterization of potential impacts of CO2 leakage on groundwater quality. The first objective is to characterize the biogeochemical mechanisms that may impair the quality of groundwater resources, especially in deep aquifers, such as the Albian in the Paris Basin in France, as yet little explored. The microbial composition of such deep aquifers and their role in controlling water quality is unknown. Another aspect already highlighted by previous studies is the role of sorption-desorption processes on the mobility of trace elements. The presence of glauconite in the Albian sands may play a role in the mobility of trace elements in the Albian aquifer. The second objective, in view of the fact that future groundwater monitoring will be confronted with several issues, is to validate a monitoring methodology. The thresholds values of the parameters to be monitored will be validated in a natural context during an experimental CO2 leakage and our methods will be tested by equipping a monitoring observation well in a deep aquifer, the Albian aquifer (0 to 1000 m deep). The major parameters to be monitored in the case of CO2 leakage are pH, alkalinity and dissolved CO2. In deep conditions, pH sensors are not stable, CO2 sensors are not validated and measuring alkalinity requires particular sampling conditions to avoid degasing before analysis. To reach the abovementioned objectives, this project proposes three complementary study contexts: (i) the laboratory for the characterization of biochemical and geochemical (sorption / desorption) processes that may impact water quality, and experiments carried out on Albian samples (ii) an experimental site to validate the monitoring methodology by experimental CO2 leakage in groundwater and to characterize the in situ mechanisms having an impact on water quality and (iii) a deep well to apply deep monitoring methodology for deep aquifers. The characterization of mechanisms in the laboratory and in situ will be based partly on the acquisition of experimental data and partly on the calibration of numerical models that take into account the diffusion of CO2 into the environment (unsaturated zone and aquifer) and reactive transport. This numerical calibration is designed to reinforce the numerical modelling work carried out for predictive purposes during the site characterisation, impact studies and design of monitoring networks. One outcome of the project will be to integrate the results in order to propose recommendations for (i) taking into account the impacts on groundwater in the future characterization of geological storage sites, (ii) defining the mechanisms to be considered in the studies to qualify and quantify the impacts on groundwater quality, and (iii) setting up groundwater monitoring networks.