GNGTS 2019 - Atti del 38° Convegno Nazionale

738 GNGTS 2019 S essione 3.3 MODELING OF NON-VOLCANIC CO2 EARTH DEGASSING. APPLICATION TO A CASE STUDY FROM CIORLANO AREA (SOUTHERN APENNINES, ITALY) R. Di Maio 1 , E. Piegari 1 , R. Salone 1 , C. De Paola 1,2 1 Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse, Università di Napoli Federico II, Napoli, Italy 2 SOCOTEC Italia s.r.l., Lainate, Milano, Italy Introduction. In the last twenty years a growing interest is noticed in studying the process of carbon dioxide degassing from the geosphere in various field of Earth Sciences, with the aim of defining relationship between gas flux on the ground and tectonic structures, quantifying deeply derived CO 2 released into the atmosphere and studying volcanic and non-volcanic degassing processes (Frondini et al. , 2018). While it is already recognized that volcanic degassing can introduce huge quantities of carbon dioxide into the atmosphere, only recent studies (Kerrick and Seward, 1996; Chiodini et al. , 2000) have shown that non-volcanic degassing may be a globally significant input of CO 2 into the atmosphere and that many areas where large emissions of non-volcanic carbon dioxide take place are also characterized by a some degree of permeability of the crust that often coincides with seismically active zones. Indeed, seismic data demonstrate the existence of a positive spatial correlation between gas discharges and extensional tectonic regimes and confirms that such processes would play a key role in creating pathways for the rising gases at micro- and macro-scales, increasing the rock permeability and connecting the deep crust to the earth surface. Therefore, the identification and the geometric characterization of the CO 2 -permeable active faults is fundamental, not only for the definition of the seismic-active zone geometry, but also for the understanding of the processes that govern the flow of fluids along the damage zone that convey the gases towards the surface. In this framework, numerical simulations of fluid flow in three-dimensional faulted models can help to identify the primary control parameters of fault-related fluid flow, their interactions, and to model the temporal evolution of the investigated system. In this work, we present the results of a numerical simulation of CO 2 flow along an active fault in the Ciorlano area of Matese Ridge (Southern Apennines, Italy), which recent accurate geological and geochemical analyses classify as the area with the highest non-volcanic natural emissions of CO 2 ever measured on Earth (Ascione et al. , 2018). Modeling of non-volcanic CO 2 earth degassing. The study presented here aims to reproduce the observed flux of non-volcanic CO 2 along an active fault to get insight on the geometry of the source. The first step of the modeling consists in building of a 3D realistic petrophysical model of the investigated system and identifying possible geometries of the system source. To this aim, we used the results of a geophysical survey, specifically consisting in electrical resistivity tomography (ERT), self-potential (SP) and horizontal to vertical spectral ratio (HVSR) measurements, whose integration with borehole data allowed to define the physical properties of the rock layers. Then, two possible scenarios for the source system were identified and the software TOUGH2 was used to perform numerical simulations of CO 2 flow. In particular, the EOS2 module was chosen as it describes the thermodynamic equation for a mixture of water and CO 2 and accounts for non-ideal behavior of gaseous CO 2 and dissolution of CO 2 in the aqueous phase with heat of solution effects. Application to the Ciorlano area (Southern Apennines, Italy). The study area is located in the Campania-Molise sector of the Southern Apennines (Italy) (Fig. 1) on a high terrace at about 300 m above sea level (a.s.l.), and is characterized by an advective and localised gas leakage associated with gas vents. The strong gas emissions (gas vents) and bubbling phenomena in springs or sinkholes with dominant CO 2 are aligned with the main tectonic elements (e.g. Colle Sponeta Fault Scarp). In the study site, different geophysical methods, among which ERT and SP surveys (De Paola et al. , 2019), were applied with the aim to define the electro- stratigraphic sequence of the site and to identify anomalous sectors correlated to presence of possible migration pathways of non-volcanic carbon dioxide. The integration of data from