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After the Paris Agreement in which 195 countries are involved, the Carbon Capture and Storage (CCS) is now an accepted technology in the United Nations Framework Convention on Climate Change (UNFCCC). In Spain, Fundación Ciudad de la Energía (ClUDEN) has successfully completed the full CCS chain, being C02 captured in the Technology Development Centre in Cubillos del Sil (León, Spain) whereas that it is geologically stored in a deep saline aquifer, formed by fractured carbonates with poor matrix porasity, located in the Technology Development Plant (TDP) at Hontomín (Burgos, Spain).The results of the field tests, in which up to 150t of CO 2 and synthetic air (5%v of N 2 and O 2 ) were co-injected on site, are analyzed in this paper comparing the operational parameters gained during the injection of impure CO 2 (pressures, temperatures and flow ranges) with its corresponding baseline previously determined (Le. 1500tons of pure C02 were injected during the reservoir hydraulic characterization). Besides that, the geochemical reactivity analysis of impure C02 injected in this saline aquifer and its correlation with the results fram laboratory tests were assessed.As main conclusions fram laboratory scale results, a porasity diminution was measured after the injection of CO 2 with 5%v of S02; apart fram that, without S02, the effluent pH was in the range of 7-8 whereas in case of CO 2 and S02, a pH of 1-2 was obtained. Otherwise and focused on field scale tests, a density decrease was detected comparing the base case (pure CO 2 ) with the CO 2 injection containing 5.1%v of synthetic air. On the other hand, Ca 2 +, S04 2 -, Mg2+ and K+ migration effects in the rack were also detected and analyzed. ObjectiveThe main objective was to carry out field scale injection tests of C02 and synthetic air (i.e. 02 and N2) into fractured carbonates with poor primary porosity and transmissivity through the fracture network, to identify and assess the impacts ofthese impurities Abbreviations: BHP, bottom-hole pressure; BOP, balance of plant; CCS, carbon capture and storage; ClUDEN, Fundation Ciudad de la Energía; DOT, pressure vessel used to store fluids at aboye atmospheric pressure, the acronym is department oftransport; DTS, distributed temperature sensing; ERT, electrical tomography system; Fm, formation; FIlR, Fourier Transform lnfrared (analyzer); HA well, Hontomín observation (or auscultation) well; Hl well, Hontomín injection well; lEA, lnternational Energy Agency; I&C, instrumentation and control; LoT, leak-off-test (pressure); PFD, process flow diagram; TDP, Technology Development Plant; WHP, well-head pressure. * Corresponding author.E-mail addresses:jc.dedios@ciuden.es.jcdediosgonzalez@gmail.com U.e. de Dios).in the short-term stability of C02 storage and their inf!uences on site operation. Laboratory scale test campaign was previously conducted in order to study the chemical interactions between impure C02/brine and carbonates reservoir.

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Carbon dioxide is the main Greenhouse Gas (GHG) due to its abundance in the atmosphere. CO2 capture and storage (CCS) technologies contribute to mitigate the effects of climate change by reducing their emissions. This requires appropriate geological environments such as deep saline aquifers with great potential on an industrial scale in Spain. They must have appropriate characteristics to ensure the tightness of CO2 and the technical viability of the injection process. The capacity of the storage is conditioned by the trap mechanisms that take place in depth. In this work, the static configuration of the ATAP (High Temperature-High Pressure) test device has been developed to reproduce the mineralization trap mechanism or mineral sequestration by applying it to a sandstone aquifer for supercritical CO2 storage (SCCO2). The equipment allows to observe the changes produced in a rock sample after it has been saturated with the fluids existing in the store (brine and SCCO2), under the pressure and temperature conditions characteristic of storage (up to 120ºC and 500 bar). To verify these changes, the technique of computed axial tomography and He pycnometry were used. The variations of porosity produced in the storage rock are compared with those obtained in studies of SCCO2 saturation by injection and in reactor carried out by other authors. Keywords: Mineral trapping, deep saline aquifer, sandstone storage, supercritical CO2, high pressure and temperature equipment