Conceptual and numerical models of a tectonically-controlled geothermal system: a case study of the Euganean Geothermal System, Northern Italy

The Euganean Geothermal Field (EGF) is the most important thermal field in northern Italy. It is located in the alluvial plain of the Veneto Region where approximately 17*106 m3 of thermal water with temperatures of 60–86 °C are exploited annually. A regional-scale conceptual model of the Euganean Geothermal System is proposed in this paper using the available hydrogeologic, geochemical and structural data for both the EGF and central Veneto. The thermal water is of meteoric origin and infiltrates approximately 80 km to the north of the EGF in the Veneto Prealps. The water flows to the south in a Mesozoic limestone and dolomite reservoir reaching a depth of approximately 3,000 m and a temperature of approximately 100 °C due to the normal geothermal gradient. The regional Schio-Vicenza fault system and its highly permeable damage zone act as a preferential path for fluid migration in the subsurface. In the EGF area, a geologic structure formed by the interaction of different segments of the fault system increases the local fracturing and the permeability favoring the upwelling of the thermal waters. Numerical simulations are performed to validate the proposed conceptual model using a finite difference code that simulates thermal energy transport in hydrothermal systems. A specific configuration of thermal conductivity and permeability for the formations involved in the thermal system is obtained after calibration of these parameters. This set of parameters is verified in a long-term simulation (55,100 years) obtaining a 60–70 °C plume in the EGF area. The modeled temperatures approach the measured temperatures of 60–86 °C, demonstrating that this conceptual model can be realistically simulated