Submarine storage of CO2
The global ocean is the major natural sink for carbon, nutrients and other biologically active substances. Thus, most of the anthropogenic CO2 will ultimately be removed from the atmosphere and transferred into the oceans to be stored as dissolved inorganic carbon in seawater and particulate organic and inorganic carbon in marine sediments. The rate of atmospheric CO2 uptake is determined by the efficiency of the physical and biological pumps transferring CO2 into the ocean’s interior. Oceans are also deliberately used to dispose CO2 and other waste products from industrial sources. Thus, CO2 separated from natural gas has been stored in sub-seabed geological formations at industrial scale since more than a decade and a large number of new sub-seabed storage sites will be opened in the near future to accommodate CO2 from coal power plants and other industrial sources. Leakage of CO2, displaced formation waters and methane from the storage complex into the overlying water column is the major risk associated with these storage operations.
Against this background, the research unit Marine Geosystems develops and applies new monitoring techniques to survey sub-seabed storage sites. These include improved chemical sensors for the detection of dissolved CO2 and methane in the water column, a membrane-inlet mass spectrometer for the quantification of dissolved gas concentrations, hydro-acoustic techniques for the detection of gas bubbles in the water column, lander systems for in-situ flux measurements at the seabed and numerous additional sea-going instruments. Moreover, the research unit studies the transport behavior of gaseous and dissolved CO2 in sediments and the water column, the dissolution of CO2 in pore fluids, the formation of CO2 hydrates and the geochemical reactions between CO2 and sediments. These studies are performed not only at storage sites but also at CO2 seeps and other natural analogs. The field studies are augmented by experimental studies in the high-pressure lab and by numerical transport-reaction modeling.
The feasibility, environmental risks, costs and legal requirements associated with sub-seabed storage of CO2 in saline aquifers and depleted oil and gas reservoirs are studied in detail within the EU project ECO2 led by the research unit Marine Geosystems (http://www.eco2-project.eu/) while the storage of CO2 in marine gas hydrates is investigated within the SUGAR project.