CO2-REACT is built on a single research platform with tight cooperation of all of the ITN partners. It includes:

- In situ and real time nucleation and growth of minerals from solution – synchrotron-based techniques:

Reaction rates between mixed gas-CO2-H2O fluids and mineral surfaces remain poorly understood mainly because many reactions are extremely fast and strongly pH, ionic strength and temperature dependent. Experimental techniques enabling quantification of such reactions at realistic time and space scales have only recently been developed by UL by taking advantage of synchrotron based small and wide angle X-ray scattering (SAXS/WAXS) and X-ray absorption spectroscopy (XAS)14. These techniques, combined with high resolution imaging and X-ray tomography, will be used in ESR Projects 1, 2 and 4, to quantify CO2-H2O-rock reactions in real time on a molecular scale.

- Atomistic simulation – Atomic scale computational methods for determining free energy and geometric relationships:

Density functional theory (DFT) and molecular dynamics (MD) at KU,15 as well as coarse graining and Monte Carlo methods provide opportunities to test conceptual models constructed from the experimental data. Simulations also allow screening of interesting systems that would take many months in the laboratory and provide insight into higher temperature and pressure systems. ESR Projects 2, 5, 6, and 7 will use simulation.

- Processes at mineral surfaces – Sub-microscopic techniques:

New Atomic Force Microscopy (AFM) techniques developed by MU and KU allow direct observation of reactions at the mineral-fluid interface in real time and under controlled conditions16 and allow changes in surface composition to be monitored17. A particularly exciting possibility is using AFM in a flow through reactor which allows the direct observation of mineral growth with spatial resolution at nanometer scale as a function of time. Nanometer scale observations enable construction of conceptual models that can be used in ESR Projects 1, 2, 6, 7, and to describe what actually happens at mineral surfaces in ESR Projects 12, 13.

- Direct measurement of CO2-H2O-mineral reactivity – Open and closed system reactors:

Dissolution/precipitation rates can be measured by CNRS and UI using techniques that have proven successful for generating robust mineral dissolution rate equations over the past 15 years18. Reactive fluids and solids will be analyzed with classical analytical techniques (i.e., Atomic Absorption, Mass Spectrometry, Ion Chromatography, X-ray diffraction, electron microprobe and scanning electron microscopy), while a new type of in situ pH electrode, which can operate to 220 °C will be used for carbonate ion activity evaluations. Mineral surface chemistry will be measured as a function of solution composition and pCO2, using X-ray photoelectron spectroscopy (XPS), Infrared μ-spectroscopy (FTIR) or μ-XAS. These techniques will be used in ESR Projects 3, 4, 5 and 8.

- CO2-H2O-mineral reactivity in rock cores – Core reactors and X-ray tomography:

CNRS has recently developed flow through core reactors that can operate to 100°C and CO2 pressures up to 60 bars. These reactors allow direct determination of mineral precipitation rates within rock cores and their effect on mineral surface area and rock permeability in response to reactive fluid flow. Using state-of-the-art X-ray microtomography (XMT), 3D XRD and scanning and transmission electron imaging (SEM/TEM) will help quantify the location, and composition of minerals in rock cores19. These are influenced by 1) local supersaturation, 2) mineral orientation within the rocks, and 3) pore size. Each of these factors will be explored. The distribution and reactivity of newly formed minerals is critical for controlling rock permeability, which in turn is fundamental for successful CO2 storage. A drop in permeability in response to mineral precipitation severely limits sequestering capacity. These tools are in particular required for the successful completion of ESR Projects 5 and 10.

- The consequences of CO2-H2O-mineral interaction in time and space -- Reactive transport modelling:

Rate equations developed in CO2-REACT and taken from the literature describing CO2-H2O-rock reactivity, consistent with fundamental theory and experimental evidence will be incorporated into comprehensive reactive transport models20 by A21 and WEST to predict the temporal evolution of chemical/physical properties (e.g. porosity and permeability) of target rock formations. Long term consequences in currently ongoing and proposed CO2 storage sites can be predicted. These tools are the basis for the modelling parts of ESR Projects 10 to 13 and ER 1.

- Assessing the extent of CO2-H2O-mineral CO2 interaction in sedimentary basins and fractured rocks

Industry and field scale applications: CO2-REACT industry partners MOG, RE and LaF are directly involved in the challenges of limiting carbon emission to the atmosphere. Where possible, they will provide CO2-REACT INT fellows with fluid and rock samples and petrophysical, geophysical or chemical data from active CO2 injection sites or interesting reservoirs where the effect of injection needs to be known. In some cases industrial products will be provided for testing. Such samples will make it possible to test reactive transport modelling, assessing the quality of prospective CO2 storage and providing insight into the long term security. Though significant for all projects, this activity will feature in ESR projects 11 to 13

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