Analisi di fattibilità e delle prestazioni di sistemi di scambiatori di calore a circuito chiuso per l’estrazione di energia in ambienti geologici ad alta temperatura

Geothermal energy represents a key resource for the decarbonization of energy systems, yet conventional hydrothermal and enhanced geothermal technologies are often constrained by exploration risk, fluid-related challenges, and environmental concerns, particularly in high-temperature volcanic and protected regions. Closed-loop geothermal systems, which extract heat through conductive exchange without hydraulic interaction with the subsurface, offer a low-risk alternative but remain insufficiently assessed in such environments. This thesis evaluates the feasibility and thermal performance of closed-loop borehole heat exchanger systems in high-temperature geological settings, with a focus on coaxial configurations. Vulcano Island (Aeolian Archipelago, Italy) is adopted as a representative volcanic case study. An integrated approach combining geological characterization, laboratory-derived rock thermo-physical properties, and advanced numerical modelling is developed to simulate coupled fluid flow and heat transfer processes under extreme geothermal gradients. Finite-element models are implemented to investigate the influence of borehole depth, well geometry, flow rate, injection temperature, insulation strategy, well spacing, and operational mode on long-term system performance. Model validation against published deep borehole field data confirms the reliability of the numerical framework. The results demonstrate that closed-loop systems can sustain stable heat extraction in volcanic environments, with borehole depth and geometric configuration exerting the dominant control on performance, while operational parameters play a secondary role over long time scales. Array and multilateral configurations significantly enhance thermal recovery at shallow to medium depths, whereas insulation effectiveness is shown to be depth-dependent. Under favourable thermal conditions, closed-loop systems exhibit potential for binary power generation, providing a technically viable and environmentally safe alternative to conventional geothermal exploitation in volcanic and island contexts.