A new biogeochemical method for the monitoring of possible seeps in marine CCS fields

The sub-seabed deep saline aquifer CO2 injection for CCSpurposes requires a reliable monitoring of possible CO2 seepsfrom the bottom sea. A biogeochemical monitoring method ofCO2 seeps in marine environments has been set up by themanufacturing of new in situ and laboratory instruments andtheir use in the marine environment. The new monitoringmethod consists in the determination, before the CO2 geologicalstorage, of benthic fluxes of dissolved inorganic carbon species(pCO2 and DIC) and of other connected parameters (alkalinity,pH and ?13CDIC), in order to characterise the marine carbonatesystem, and by investigating the early diagenesis processes, i. e.the processes originating the benthic fluxes. The knowledge ofthe natural benthic fluxes, before the CO2 injection, will allow thecomparison with data obtained after the storage operations sothat possible occurrences of unexpected leakages of the CO2injected in the geological formations under the sea bottom canbe verified. This method could also be useful employed as an"early warning" system in case of possible failure of the CO2storage. For the set up of this biogeochemical monitoringmethod two new autonomous and automatic benthic fluxmeasurement instruments (the Lander AMERIGO and theCamera Bentica Automatica) and two new laboratory apparatusfor laboratory chemical analysis (pCO2 and DIC analyses) hasbeen realized. The biogeochemical monitoring approach isparticularly sound in the Northern and Central Adriatic Sea wherenumerous previous DIC and other carbonate system chemicalbenthic flux measurements and early diagenesis studies havebeen carried out, where the new monitoring technology is beingapplied and where CO2 sub-seabed storages can be carried out.Previous researches allowed the definitions of nine differentdiagenetic environments in the northern and central Adriatic Sea;each environments is characterized by: 1) homogeneousparticulate matter and dissolved nutrient continental inputs; 2)distances from main sediment sources; 3) bottom sedimentcomposition; 4) organic matter; 5) depths); 6) oxygenation ofwater column. In each diagenetic environment a backgroundvalue of DIC, alkalinity and pH benthic fluxes has been assigned.These background values can be used as baseline in the CCS tomonitoring possible seeps after the injection of CO2 in depth. Atpresent, various researches are in progress in the Adriatic Sea forthe acquisition of new data of DIC and other chemical dissolvedbenthic fluxes by the use of the new technology and for the earlydiagenesis studies that origin the fluxes.