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1 Alberta Research Council, Edmonton, Alberta, T6N 1E4, Canada gunter{at}arc.ab.ca
2 Alberta Geological Survey, Edmonton, Alberta, T6B 2X3, Canada
3 Lawrence Berkeley National Laboratories, Berkeley, California, 94720, USA
Sedimentary basins throughout the world are thick piles of lithified sediments that, in many cases, are the hosts for fossil fuel resources. They may become even more important in the future if they are used for the storage of anthropogenic carbon dioxide. The efficiency of CO2 geological storage is determined by the structure of the sedimentary basins, which have an intricate plumbing system defined by the location of high and low permeability strata that control the flow of fluids throughout the basin and define ‘hydrogeological’ traps. The most secure type of hydrogeological trapping is found in ‘stratigraphic’ and ‘structural’ traps in oil and gas reservoirs that have held oil and gas for millions of years. Another form of hydrogeological trapping is ‘hydrodynamic’ trapping which has been recognized in saline aquifers of sedimentary basins that have extremely slow flow rates. A volume of carbon dioxide injected into a deep hydrodynamic trap may take millions of years to travel by buoyancy forces updip to reach the surface before it leaks back into the atmosphere. Moreover, as the carbon dioxide migrates towards the surface, it dissolves in the surrounding brine (‘solubility’ trapping) and may react geochemically with rock minerals to become permanently trapped in the sedimentary basin by ‘ionic’ or ‘mineral’ trapping. The efficiency of the CO2 geological storage in sedimentary basins depends on many factors, among the most important being CO2 buoyancy, formation water density, lithological heterogeneity and mineralogy. A risk analysis must be completed for each site chosen for the geological storage of CO2 to evaluate the trapping security.
