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. TwoDimensional reactive transport modeling of CO2 injection in a saline aquifer at the Sleipner site, North sea. American journal of science, American Journal of Science, 2007Science, , 307, pp.974-1008Science, . <10.2475Science, /07.2007

The sequestration of CO 2 in the deep geosphere is one potential method for reducing anthropogenic emissions to the atmosphere without a drastic change in our energy-producing technologies. Immediately after injection, the CO 2 will be stored as a free phase within the host rock. Over time it will dissolve into the local formation water and initiate a variety of geochemical reactions. Some of these reactions could be beneficial, helping to chemically contain or 'trap' the CO 2 as dissolved species and by the formation of new carbonate minerals; others may be deleterious, and actually aid the migration of CO 2. It will be important to understand the overall impact of these competing processes. However, these processes will also be dependent upon the structure, mineralogy and hydrogeology of the specific lithologies concerned and the chemical stability of the engineered features (principally, the cement and steel components in the well completions). Therefore, individual storage operations will have to take account of local geological, fluid chemical and hydrogeological conditions. The aim of this paper is to review some of the possible chemical reactions that might occur once CO 2 is injected underground, and to highlight their possible impacts on long-term CO 2 storage.If sequestration of CO 2 is to be a practicable largescale disposal method, the CO 2 must remain safely underground, and not return to the atmosphere within relatively short timescales (e.g. thousands of years), so that natural buffering processes (e.g. oceanic and forestry sinks) have sufficient time to reduce global atmospheric CO 2 levels to environmentally acceptable levels. Indeed, acceptable performance will need to be demonstrated in order to satisfy operational, regulatory and public acceptance criteria. The track record of CO2-assisted enhanced oil recovery (EOR) operations and purposedesigned underground storage of natural gas shows that underground storage can be practicable and leakage minimized over 'industrial' time periods (e.g. tens of years). However, there is much less information for longer-term processes, and these must be understood, especially as CO 2 is more chemically reactive than methane.The injection of a relatively reactive substance such as CO 2 into the deep subsurface will result in chemical disequilibria and the initiation of various chemical reactions. It is important to understand the direction, rate and magnitude of such reactions both in terms of their impact upon the ability of a host formation to contain the injected CO 2 safely, and in terms of the longevity of CO 2 containment (e.g. Rochelle et al. 1999). Some reactions, such as the precipitation of CO 2 in secondary carbonate minerals, may be beneficial and aid containment. However, other reactions may result in mineral dissolution -facilitating the formation of migration pathways and so act to reduce containment. The aim of this paper is to highlight some of these processes, and to illustrate their possible impact on long-term CO 2 storage. It is hoped that...

International audienceGeochemistry plays an important role when assessing the impact of CO2 storage. Due to the potential corrosive character of CO2, it might affect the chemical and physical properties of the wells, the reservoir and its surroundings and increase the environmental and financial risk of CO2 storage projects in deep geological structures. An overview of geochemical and solute transport modelling for CO2 storage purposes is given, its data requirements and gaps are highlighted, and its progress over the last 10 years is discussed. Four different application domains are identified: long-term integrity modelling, injectivity modelling, well integrity modelling and experimental modelling and their current state of the art is discussed. One of the major gaps remaining is the lack of basic thermodynamical and kinetic data at relevant temperature and pressure conditions for each of these four application domains. Real challenges are the coupled solute transport and geomechanical modelling, the modelling of impurities in the CO2 stream and pore-scale modelling applications

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