Quantifying Gas and Thermal Energy Emissions in an Active Geothermal Area: Insights From Le Biancane (Larderello Field, Italy)

Abstract The Larderello‐Travale area in the northern Apennines of Italy hosts the world's oldest exploited geothermal field. Its success lies primarily in the presence of an extraordinary geothermal resource housed in a large vapor‐dominated fractured reservoir that produces superheated steam. We present results from an integrated study at Le Biancane area (∼80,000 m 2 ) in the southern sector of the Larderello‐Travale geothermal field, where the impermeable caprock is absent and the shallowest reservoir outcrops. Maps of soil diffuse CO 2 and soil temperature, based on measurements at 345 locations, highlight focused zones of high CO 2 flux (>500 g m −2 day −1 ) and soil temperature (>60°C), likely controlled by NNE‐SSW and NE‐SW trending fractures and normal to strike‐slip faults. Convective heat flux from high‐enthalpy vapor is estimated using the H 2 O/CO 2 molar ratio of local fumaroles and the total CO 2 output (∼10 t day −1 ) as a degassing tracer. The field study is supplemented by laboratory measurements of soil properties (thermal conductivity, porosity, water and air content, bulk and solid‐phase densities). Combined data sets allow us to demonstrate that the heat associated with the ascent and condensation of vapor is predominantly transferred by conduction in the uppermost portion of the soil at Le Biancane, generating linear thermal profiles, which we measured in 41 locations. Ultimately, the analysis of the heat exchange within the soil and its dynamic interaction with the atmosphere offers a clearer understanding of the relative roles of the various heat flux components in a vapor‐dominated geothermal field.