Geothermal fluid circulation in a caldera setting: The Torre Alfina medium enthalpy system (Italy)

The Torre Alfina medium enthalpy geothermal field is located about 10 km north of the Bolsena caldera (Italy). The reservoir is a buried structural high consisting of fractured Meso-Cenozoic carbonate sequences and sealed by clayey flysch successions and Pliocene marine clays. We performed TOUGH2 numerical simulations, testing different model designs based on contrasting conceptual models. Results indicate that deep circulation is forced by the geometry of the reservoir and by the applied T and P gradients. We interpret the Torre Alfina field as a “blind” system, mostly recharged by lateral advection of heat and fluids from the Bolsena caldera deep high-enthalpy system, through the permeable caldera faults.