CRS Methodology to the Realmonte Salt mine, southwestern Sicily: an application for hydrogen storage potential site in Italy.

Giusy Anzelmo , Giovanni Mario Cella, Corrado Magistroni, Andrea Da Pra, DaVID Iacopini

As Sicily expands its renewable energy portfolio, the need for large-scale energy storage becomes increasingly urgent to ensure supply-demand balance. Hydrogen storage in salt caverns represents a promising solution in this context. This study presents the first real-world application of the Common Risk Segment (CRS) methodology, originally developed for oil and gas exploration and recently adapted for CO₂ storage site screening, to underground hydrogen storage in salt caverns, applied to the Realmonte salt mine in southwestern Sicily, Italy. The site's evaporitic sequence was subdivided into two stratigraphic units: the lower "First Cycle" (below -250 m b.s.l.) and the upper "Second Cycle" (above -250 m, encompassing the active mine). For each unit, a site card integrating 20 geological, rock salt, and environmental parameters was compiled, with impact values (-3 to +3), calibrated weights (1-3), and a six-class robustness scale (-2 to +3) quantifying data reliability. Normalised CRS scores were calculated as 95.81% for the First Cycle and 86.91% for the Second Cycle, confirming the deeper salt section as the only viable target for hydrogen storage. The Second Cycle is excluded because of insufficient top-salt depth and caprock thickness, as well as its operational incompatibility with the active mine. A Monte Carlo sensitivity analysis (500 runs per site) demonstrated the stability of the scoring system under data uncertainty, with coefficients of variation below 0.3% for all configurations tested. Cross-site benchmarking against two internationally operational hydrogen storage facilities, Teesside, UK (84.82%) and Clemens Dome, USA (91.62%), validated the methodology and confirmed that the inter-site ranking is preserved in 100% of simulation runs. The high score of the Realmonte First Cycle relative to these operational benchmarks reflects its thick, pure halite (>300 m) at optimal depth (400-600 m), absence of faulting, and strong caprock integrity.
A preliminary storage capacity estimate, based on cavern dimensions of 100-200 m height and 60-80 m diameter with a minimum spacing of three times the cavern diameter, yields a prospective capacity of 1.5-2.5 TWh for the First Cycle, sufficient to meet Sicily's projected hydrogen storage requirements through 2030 and strategically positioned near planned offshore renewable energy hubs. The results identify the Realmonte First Cycle as a priority candidate for pilot cavern development in the Italian hydrogen storage roadmap.