The capture, storage and use of CO2 is still in a transitional phase, between research and pilot experiments. Nevertheless it has demonstrated technological know-how, and the large-scale commitment of states or industries to operate sites of significant importance in order to contribute to the reduction of greenhouse gas emissions. The awareness of the impact of atmospheric CO2 emissions on the climate in the 1980s and 1990s naturally led to the deployment of technological solutions. The actors (political, industrial, and academic) mobilized their means, according to more or less economically favorable conditions. Five main domains are concerned by CCUS: 1) the CO2 capture from different industrial plants (refineries, steel making, cement plants, power plants…), 2) CO2 transportation via pipelines towards surface units for (3) CO2 utilization or (4) CO2 injection for (5) CO2 deep storage in geological reservoirs for long term sequestration (Figure 1). CCUS covers a huge domain of competencies from humanities to technological sciences. Separation techniques, estimates of social and environment impact, consequences of fluid-rock interaction for mineralization or mechanical behavior, numerical modelling and monitoring are some of the important topics covered by more than twenty years of intensive research. Figure 1: Domains of interest for academy in the field of CCUS The major technological and scientific advances in geological storage have concerned the development of miniaturized sensors, high pressure - high temperature measurement benches and triaxial cells with percolation of fluids to get as close as possible to in situ conditions, computer tools to model the behavior of complex fluids and the mechanical response of formations subjected to injections. Significant advances have enabled the CCUS sector to reach high levels of technological maturity. Thus the IPCC estimates that the CCUS could contribute to nearly 20% of the reduction in greenhouse gas emissions. It can be seen that the R&D activity is governed by the price per ton of CO2. In 2013, it collapsed to reach € 5, and EU reduced the support to CCUS projects. Today the price goes up and the actors regain hope. New projects are emerging and diversifying even if the fateful breakeven point of € 50 / ton has not yet been reached. Université de Lorraine and CNRS was involved in CCUS for several projects in France as in EU in connection with industrial partners. One of the most important was the TotalEnergies project of Lacq-Rousse. Between 2006 and 2013, TotalEnergies developed the unique on-shore CCS demonstrator in EU in the Southwest of France. CO2 was produced in a boiler using oxy-combustion technique and transported by pipeline on 30 km before to be stored in a deep dolomite reservoir of Jurassic age. The main objectives of this experiment were 1) to demonstrate the technical feasibility of an integrated chain coupling capture, transportation and storage into a depleted gas reservoir, 2) to acquire operating experience for oxy-combustion process and 3) to develop and apply geological storage with efficient monitoring technologies for long term including regulatory aspects and risk assessment [1]. The objective of this paper is to show some scientific results acquired on the CCS demonstrator by the academic teams of Nancy throughout a series of research projects supported by the French Research Agency (ANR), CNRS, Université de Lorraine and TotalEnergies. The reservoir where the CO2 has been stored is the depleted Mano reservoir that is part of the Rousse gas field where CH4 gas was produced for more than 40 years. This fractured dolomitic reservoir discovered in 1967 had an initial pressure of 480 bar at 4500 m depth, the residual pressure being close to 30 bar [2, 3]. Within 2 years of operation, up to 51 000 tons of CO2, produced by oxy-combustion, were injected in the reservoir inducing a recompression of several tens of bar. This injection was operated via the former operating well Rousse-1 (RSE-1) converted into injection well (Figure 2). Figure 2: Cross section of Rousse gas field in the Southwest of France with indications about the targets of research developed at Université de Lorraine/CNRS (GeoRessources lab). The gas reservoir of Rousse is located southward of the Aquitaine basin, specifically in the Adour-Arzacq sub-basin. The Rousse reservoir is located in a deep, isolated, faulted, Triassic to Jurassic siliciclastic and carbonate horst overlain by a 4500m thick overburden, which is composed of a series of turbiditic flysch deposits of Upper Cretaceous (Cenomanian) to Tertiary (Eocene) age. The petrophysical properties of the reservoir, marked by an intense fracture network, were acquired early during an extensional period (Albian), whereas the impact of fluids associated with a period of compression appears to have been limited in space to drainage of tectonic origin (Eocene). CO2 was recorded in fluid inclusions in close association with CH4 at these periods, traces of H2S are suspected to arrive later [4]. Geological studies helped us to reconsider the geodynamic situation of the target reservoir. It was demonstrated that rocks in reservoir were in contact with CO2 in the past [4]. Such observation increases confidence in the project because it is suspected that re-injection of CO2 in the porosity of the rock should not react a lot with the minerals. This conclusion is solid if and only if the injected gas is pure CO2. However this is not always the case because purity of injected gas is depending on the capture strategy and technology. High purity achievement increases the cost of capture and could limit the volume of CO2 to be stored. To tackle the role of impurities co-injected with CO2, different scenarios have been tested in lab using a research pilot mimicking the conditions at great depth (150°C, several hundreds of bar). Geochemical impacts of CO2 and potentially co-injected gases have been tested on the reservoir and the cap-rock. The effect of SOx has been studied because the fuel burned by contact of pure O2 in the boiler can contain some amounts of sulfur [5]. In the same way, the presence of nitrogen oxides have been tested because nitrogen from the air can be present in small quantities in the boiler and can react with O2 to form NOx. And finally, the presence of O2 in excess after oxycombustion has been considered having potential impact on the stability of minerals and on residual hydrocarbons in the depleted gas reservoir [5, 6, 7, 8]. O2 that remains in the flue gas for injection can induce the oxidation of the hydrocarbons contained in the reservoirs. The effect of O2 must be studied in terms of benefit and/or risk for CCS. The top of the geological series is marked by molasses deposits where different shallow wells were drilled to monitor CO2 transfers between geosphere-biosphere-hydrosphere and atmosphere. One of them, of 3.5 m depth at 30 m far from the injection well was equipped with a gas collection chamber isolated from the atmosphere by a packer. Gases were collected through a membrane, non-permeable to water, and driven by a pump up to two spectrometers (FT-IR and Raman) in surface [9]. This equipment was created in cooperation with Solexperts Company. Each 30 minutes, temperature, pressure, and CO2 concentrations were measured into the shallow borehole as into the atmosphere. Water table level is measured in a neighboring piezometer. Gas concentration baseline collected overtime is driven by a limited number of parameters. By consequence, CO2 leakages from the reservoir or the surface devices containing CO2 could be marked by the baseline deviation. Another survey strategy has been developed through a baseline monitoring of the CO2 injection pilot to explore a wide geographical area of 35 km2. The measurements consisted of the joint determination, on a specified number of sites, of CO2 and CH4 gas fluxes at the soil-atmosphere interface and of their concentrations at one meter deep in soil (CO2, CH4, O2, 4He and 222Rn). The emission of CO2 followed an annual cycle with strongest fluxes during summer times and lower during winter ones. This seasonal pattern was consistent with the annual cycle of biological activity in soil. Therefore it was concluded the CO2 at the soil-atmosphere interface was mainly of organic origin [10]. Risk assessment for CCS projects like the Lacq-Rousse project requires efficient tools to demonstrate there is no CO2 emanation in the form of a plume above the storage site. It is the reason why we developed methodologies to perform 2D and 3D cloud chemical imaging using passive remote sensing by Fourier-transform infrared (FTIR) spectrometry for environmental survey of industrial sites like gas storages and natural ecosystems [11]. We used a SIGIS 2 apparatus developed by Bruker Company. Measurements consist in IR emission acquisition over a 2D spatial grid, each pixel of which is converted in brightness temperature spectrum, depending on wavenumber. The identification and quantification of gases are based on radiative transfer equations and on the specific spectroscopic characteristics of each gas. With this equipment, it was possible to build a “cloud” of CO2 in 3D over the injection site of Rousse using a 3D modeler (Gocad software). At each point of the cloud a concentration of CO2 in ppm can be quantified. Research investment around the Lacq pilot which is the first in Europe to implement an end-to-end CO2 capture-transport-storage chain led to several important results: •Development of new remote sensors for survey of industrial sites and reconstruction of gas plumes above a CO2 storage site, •Combination of equipment for baseline acquisition showing high variations of CO2 with time and locations, •New completion/sensor combinations for in situ on-line gas measurements with acquisition of chronicles over time allowing to establish prediction law for CO2 content in soil, •First simulations of annex gas injection in carbonate gas reservoir. SOx, NOx behaviors in deep environment was described for the first time, •Mechanisms of oxidation of CH4 were quantified, improving geochemical models used for combustion risk assessment. All these results must be applied to facilitate the capture of CO2 in a variety of industrial installations, to develop the infrastructure required to transport CO2 from the capture site to a storage site and to qualify geological formations to store the quantities of CO2 necessary to achieve carbon neutrality. Acknowledgements: These works greatly benefited from cooperation or supports of TotalEnergies, BRGM, IFPEN, INERIS, Kaiser Optical Systems, Solexperts, LMD-EPSL, INRA, CREGU, IPGP, Mines ParisTech, ADEME, LRGP, ANR (Sentinelle project), French Ministry of Education and Research. References: 1. Monne J. Carbon Capture and storage, The Lacq Pilot, ©TotalEnergies, 2015, 274 p. 2. Gapillou C., Thibeau S., Mouronval G., Lescanne M. Building a geocellular model of the sedimentary column at Rousse CO2 geological storage site (Aquitaine, France) as a tool to evaluate a theorical maximum injection pressure, GHGT9, Energy Procedia 1, 2009, 2937–2944. 3. 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