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Hydrothermal numerical model of the Euganean Geothermal System, Veneto, northeastern Italy

The Euganean geothermal field (EGF) is the most important thermal field in the northern Italy (Veneto). At present about 250 wells are active (flow rate = 17 Mm³/y) and the thermal waters (temperature = 65°C-86°C) are mainly use for spa. Recently, a new conceptual model of the Euganean Geothermal System (EGS) has been proposed. The waters are of meteoric origin, infiltrate 80 Km to the north of the EGF in the pre-Alps, flow to the south in a Mesozoic carbonate reservoir, reach a depth of about 3000 m and warm up by a normal geothermal gradient. The active Schio-Vicenza fault system (SVFS) act as a conduit for the hot waters, thanks to higher permeability of the damage zone of faults. In the EGF area, the thermal waters are intercepted by a relay zone, linked to the SVFS, that permits the development of rock fracturing/permeability and enhances the uprising to the surface of waters. The conceptual model is tested in a numerical model. A 82 Km long and 6 Km deep standard cross section is performed. The simulations are developed using the software HYDROTHERM that simulates thermal energy transport in two-phase, hydrothermal, ground-water flow systems. The simulations are divided in two simulation periods: a first period in which the water flux is affected only by the boundary condition ; a second period of 100 years in which the water flux is affected by two extraction-point sources that simulate the flow due to the pumping wells. This is the first numerical model of the EGS and a sensitivity analysis on parameters of formations involved in EGS has been performed. The configuration of parameters that permits the development of an higher temperature in the EGF area is: the mean value of the permeability for all the formations, low values of thermal conductivity for the formation of thermal aquifer, high values of thermal conductivity for the formation below the thermal aquifer. This configuration and the use of an anisotropic permeability (Kz/Kx=0.2) permit to obtain the best result. The simulation period is 55100 years. This period confirms that the EGS has been active since 30 kY (minimum age of the travertine in EGF). This simulation shows an 60-70°C temperature-plume in the EGF area (max. temperature=74°C). This result is according to the temperature of 70-80°C measured in the thermal wells of the EGF, constraining the conceptual model.

Euganean geothermal system ; thermal waters ; numerical modeling ; HYDROTHERM software

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