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As argued by the European Commission – Directorate General for Energy and several international bodies, like among the others the Carbon Sequestration Leadership Forum (CSLF), the Carbon Capture and Storage (CCS) is accepted as a reasonable solution for reducing greenhouse gas emissions, figuring in perspective as a countermeasure against the climate change. In particular, there is a general agreement to consider the CO2 storage in geological formations as a feasible technique and Weyburn-Midale CO2 Project (Canada Saskatchewan) and Sleipner Project (Norway-North Sea) seem to demonstrate it. Yet the safe and effective approach in a long-term perspective (500-1000 years) is still largely not proven. Thus the understanding of the long-term transport and fate of CO2 and associated physical processes is still a crucial issue in view of the deployment of the technology. CO2 can be stored in different geological reservoirs as: depleted oil and gas fields, unminable coal seams and deep saline aquifers. The porous rocks with salt waters offer the highest CO2 storage potential and the injection should take place in geological reservoirs located at least 800 meters of deep where the conditions of temperature and pressure are suitable for injecting CO2 in supercritical conditions and with the characteristics of a fluid. The reservoir must be covered by a clay (or equivalent) geological formation, which can prevent the leakage of CO2 into geological formations above. The characterization of the caprock-reservoir system for CO2 geological storage includes several processes as for example: well integrity, chemical reaction, thermal flux, multiphase flow and transport, stress/strain change, induced fracturing and fault reactivation. In this complicated contest, it is undeniable that the numerical modeling is the only tool available for predicting the long-term behavior of CO2. The paper describes the geological models created for three different potential reservoirs in Italy: a) Offshore Sibari basin (denominated Calabria Ionica) where the geological caprock is represented by a thick clay formation (Pleistocene) locally with thin silt or sand layers and the reservoir is represented by high porosity and salt water arenaceous/gravel-sand formation (upper Miocene), b) Offshore North Adriatic sea where the caprock is represented by clay with silt and thin layers of sand (Pleistocene) and the reservoir is represented by high porosity and salt water sands with few thin clay intercalation (Pleistocene-Middle Pliocene), c) Area onshore around Malossa oil and gas field in Lombardia region in which the caprock is represented by a clay formation known as Santerno Clay of Pliocene age and the reservoir is a conglomerate formation with salt water known as Sergnano Gravel of upper Messinian age. The numerical modeling results of CO2 injection and fate by using the Integrated System for Modeling Analysis (SIAM) developed by RSE Company are also shown with particular relevance to CO2 plume extension during the 30 years of supposed injection and extended to more than 500 years after the start of the CO2 injection process itself. The stress conditions generated around the injection wells, inside the reservoirs and at reservoir-caprok interfaces are also shown to verify the safety pressure criteria. The injection of 1 Mton/year of CO2 for a 30 years period is considered for case a) and b) while, for case c) we considered a CO2 injection rate of 0,3 Mton/year. The CO2 storage capacity of each saline-aquifer reservoirs has been estimated by using the method proposed in the EU Geocapacity Project with different values of the storage efficiency factor and compared with the more sophisticated procedures related to numerical modeling.
31 Dicembre 2011
Studi sull’utilizzo pulito dei combustibili fossili e cattura e sequestro della CO2 (P08USI)