Carbon Release in Italy through Volcanic, Tectonic and Other Styles of Degassing: Implication for Carbon Dioxide Sequestration and Storage.

Abstract:

One of the key criteria for successful geological storage of CO₂ is that the target reservoir must not leak the stored gases over extended periods. Due to the peculiarity of its geological and geodynamic setting, which results in the production, accumulation, and leakage of large volumes of natural CO₂, the Italian peninsula can be used as a natural laboratory as it provides to study gas migration mechanisms in large-scale geological systems, as well as to determine whether and how much sequestered CO₂ could hypothetically leak from a subsurface reservoir.

Moving from west to east, the Italian peninsula includes several geodynamic settings: the Tyrrhenian back arc basin and associated volcanic arcs, the Apennines fold and thrust belt, and the Adriatic foredeep. All of them are characterized by a diffuse and/or massive degassing of deeply derived CO₂, which is usually emitted by vents or dissolved and transported by large aquifers. In the volcanic islands, in the south of the Tyrrhenian Sea, large areas are characterized by leakage from the sea floor.

Based on the statistical and geo-spatial interpretation of more than 40,000 soil gas samples collected in central and southern Italy by the Fluid Chemistry Laboratory of “La Sapienza” University of Rome over more than 30 years of activity, different migration patterns related to the different geodynamic settings are distinguished and described. This very large database has been organised and managed in a GIS environment that allows the calculation of fundamental statistical parameters, the analysis of distribution patterns, the study of spatial autocorrelation and spatial heterogeneity, and the elaboration of maps. The interpretation of these data allow us to define background values of CO₂, strongly related to geological setting, and other minor (CH₄) and trace gases (He and Rn), that characterise the different geological scenarios. A common feature is that anomalous gas concentrations occur in restricted zones, both aligned along preferential pathways (i.e. faults and fractures) and/or as spot anomalies. This database and associated studies constitutes a unique tool for studying the various physical and chemical processes involved, as well as for the development of new sampling strategies for site assessment and monitoring of any CO₂ geological storage site.