GNGTS 2021 - Atti del 39° Convegno Nazionale

109 GNGTS 2021 S essione 1.2 unrests have been characterized by increases in magmatic component and in temperature of the gas fumaroles. In particular, fumaroles temperature, that generally are on the average of 350 °C, shows pulses reaching values up to 700 °C (Nuccio et al., 1999; Diliberto, 2011; 2013). These unrest episodes are also accompanied by an increase in CO 2 content, the most abundant anhydrous component in the fumarolic gases at Vulcano Island (Inguaggiato et al., 2012), and by the occurrence of superficial micro-seismicity at a depth of about 500-1500 m below the La Fossa crater (Alparone et al., 2010). On the other hand, no significant ground deformations have been observed during the unrest episodes (Alparone et al., 2019), just as there is no correlation between temperature increases and gravity changes (Di Maio and Berrino, 2017). In order to simulate fluid circulation at high temperature and in supercritical conditions, we have used the BINMIXT module of the MUFITS numerical code (Afanasyev, 2013a, b), as hydro- thermal model, which works in the temperature range to 0-1000 °C and pressure range to 0-100 MPa, to compute the temperature, poro-pressure and density variations of a non-isothermal three-phase flows of a mixture of water and carbon dioxide. MUFITS has the advantages (i) of simulating both the sub- and super-critical condition of CO 2 (Afanasyev, 2012), (ii) of simulating two different phases of CO 2 (liquid like and gas like) and (iii) of being numerically stable as it does not present singularity in the vicinity of the critical thermodynamic conditions of the mixture, avoiding the reduction of the time step and ensuring faster convergence (Afanasyev, 2013a). 2. Numerical Simulations and Results In order to analyze the different scenarios that can occur under fluid-rock interaction, particular attention was paid to the permeability, by studying two different configurations, and to the size of the conduit and of the injection area. We have obtained that an unrest phase characterized only by a rise in the flow and CO 2 content engender temperature variations in the proximity of the injection zone (Fig. 1a-c), regardless of the permeability configuration and the size of the conduit. Positive Fig. 2 - Radial distributions of horizontal (U) and vertical (V) displacements and of gravity changes (∆g) on the ground surface over time, induced by the injection of a mixture of H 2 O and of CO 2 at a temperature of 600 °C. The unrest phase was simulated for three different sizes of inlet: 40 m (left panels), 100 m (central panels) and 200 m (right panels), maintaining the same permeability configuration.