Mittwoch, 08.03.2022 (09:00 - 10:00 Uhr)

Experience and acquired knowledge of Larderello geothermal system (Italy): an overview

Geoffrey Giudetti

(ENEL Green Power, Pisa, Italy)

ENEL is among the major utilities worldwide producing from geothermal resource. To date, Enel Green Power is the only geo-electricity producer in Italy, with an installed capacity of 915.5 MWe (807 MWe efficient capacity), 37 generating units and over 500 wells managed, where the gross electricity generation reached about 6.1 billion kWh. Power plants are located in Tuscany, in the two “historical” areas of Larderello-Travale (first geoplant in the world in operation since 1904) and Mount Amiata.
Larderello is one of the few steam dominated geothermal system known in the world, where two distinct reservoirs have been identified. The upper reservoir is relatively shallow (the top can be within 1000m below ground level) and consists of mesozoic carbonates, dolostones and anhydrites. The lower reservoir, formed by metamorphic basement rocks such as schists, phyllites, micaschists and gneisses, extends to a depth of 3500m and more. Mean temperatures reach 150°-180°C in the first reservoir and about 250 – 300°C in the metamorphic basement. A temperature of 515°C was recorded close to the so called K-horizon, a seismic reflector present at depth, in the root of the system.
During years the installed capacity always increased thanks to the acquired knowledge leading to a strategic vision of reservoir management, new technologies, digitalization, and environmental leadership. The latter is achieved among others through monitoring plans, like the seismicity network implementation (which covers an area of about 820 km2 ensuring the detection of microseismic events with magnitude often also near 0), and innovative research and application like the European DESCRAMBLE project, aimed at reaching the K-horizon testing new materials for superhot systems, or the utilization of spectral gamma ray log analyses (SGR) to identify different granitic bodies in the Travale area to reconstruct their shape and geometry.
In more than 60 years of exploitation, geological and geophysical data coming from drilled wells together with geophysical surveys (2D-3D profiles) and geochemical characterization allow deciphering the architecture of the Larderello-Travale geothermal field, although permeability distribution in the reservoir remains somehow puzzling.
Together with knowledge in parallel we achieved sustainability of the system and transparency with local population and authorities.