GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.3 739 electrical resistivity and self-potential measurements have been used as input for generating the conceptual model show in Fig. 2. As the ERT survey consisted in 4 parallel profiles (Fig. 1) of length 470 m and 20 m distant each other, we considered a synthetic model with a length of 470 m, a width of 60 m and a thickness of 120 m. On this model, a computational grid consisted of 4230 regular rectangular cells was built and used to simulate the dynamics of CO 2 along the main fault, modeled by a simple inclined plane with a homogeneous and isotropic permeability. The set of primary variables required by simulator (pressure, temperature and partial pressure of CO 2 ) are identified by gas prospecting in the soil (geochemical analysis) and are used in the EOS2 module to calculate secondary parameters, such as density, viscosity, enthalpy, etc., which are used to assemble mass and energy balance equations. By assuming different geometries for the source system, upward migration of CO 2 was simulated and the flow values within the investigated underground volume were estimated. From the numerical simulations, characteristic times for the upward migration of CO 2 through a thickness of about 40 m of silts and clays were estimated by varying the source geometry and the permeability values of the damage zone. Interestingly, the model is able to predict CO 2 fluxes that are comparable with the observed fluxes in the area, which are on the order of tens of g/s (Fig. 3). Fig. 1 - Map of the CO 2 flux distribution at the Ciorlano site and location of the resistivity profiles (blue lines) (modified after Ascione et al. , 2018). The yellow line in the box indicates the Colle Sponeta fault. Self- Potential measurements were acquired along the profile ERT3. Fig. 2 - Synthetic model of the geology of the study area.