As industry moves from fossil fuels to green energy, substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns, depleted hydrocarbon fields, and saline aquifers. Among other criteria, these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is, thus, of utmost importance. In this review, the main factors influencing fluid flow are examined. These are the wettability of the caprock formation, the interfacial tension (IFT) between the rock and the gas or liquid phases, and the ability of gases to diffuse through it. To achieve effective sealing, the caprock formation should possess low porosity, a disconnected or highly complicated pore system, low permeability, and remain strongly water-wet regardless of pressure and temperature conditions. In addition, it must exhibit low rock–liquid IFT, while presenting high rock–gas and liquid–gas IFT. Finally, the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals, the evaporites, low-organic-content shales, mudstones, muscovite, clays, and anhydrite have been identified as highly effective caprocks, offering excellent sealing capabilities and preventing hydrogen leakages.

The rapid expansion of hydrogen production from low-carbon sources requires large-scale, flexible and reliable storage solutions to balance supply and demand and support the integration of hydrogen into future energy systems. Underground hydrogen storage, and particularly storage in salt caverns, offers significant potential due to the favorable characteristics of salt formations and the possibility of storing and recovering large quantities of hydrogen. However, identifying and comparing prospective storage sites requires the simultaneous consideration of geological suitability, uncertainty in the available data, operating characteristics, and project-specific requirements. Existing screening approaches generally address only subsets of these aspects, limiting their applicability to comprehensive site comparison and ranking. This study develops a holistic Decision-Making Tool (DMT) for the preliminary screening and comparative ranking of potential hydrogen storage sites in salt formations. The methodology integrates four complementary information categories: Static, Static-Probabilistic, Dynamic, and Operator’s data. Deterministic suitability assessment, Monte Carlo-based uncertainty propagation, engineering feasibility calculations of hydrogen storage performance, and operator-defined requirements are sequentially combined into a scenario-dependent final ranking. The methodology has been implemented in an Excel-based, transparent tool, allowing multiple candidate sites and alternative storage scenarios to be evaluated without changing the underlying calculation framework. Application to three prospective evaporite areas in western Greece demonstrates the ability of the tool to distinguish between sites not only according to geological suitability but also according to data confidence, storage performance and proximity to hydrogen production and consumption hubs. The resulting framework provides a practical bridge between early-stage geological screening and engineering-oriented site selection, while retaining the flexibility to adapt the ranking to different project objectives and levels of decision-making.

The rapid expansion of hydrogen production from low-carbon sources requires large-scale, flexible and reliable storage solutions to balance supply and demand and support the integration of hydrogen into future energy systems. Underground hydrogen storage, and particularly storage in salt caverns, offers significant potential due to the favourable characteristics of salt formations and the possibility of storing and recovering large quantities of hydrogen. However, identifying and comparing prospective storage sites requires the simultaneous consideration of geological suitability, uncertainty in the available data, operating characteristics, and project-specific requirements. Existing screening approaches generally address only subsets of these aspects, limiting their applicability to comprehensive site comparison and ranking. This study develops a holistic Decision-Making Tool (DMT) for the preliminary screening and comparative ranking of potential hydrogen storage sites in salt formations. The methodology integrates four complementary information categories: Static, Static-probabilistic, Dynamic, and Operator’s data. Deterministic suitability assessment, Monte Carlo-based uncertainty propagation, engineering feasibility calculations of hydrogen storage performance, and operator-defined requirements are sequentially combined into a scenario-dependent final ranking. The methodology has been implemented in an Excel-based, transparent tool, allowing multiple candidate sites and alternative storage scenarios to be evaluated without changing the underlying calculation framework. Application to three prospective evaporite areas in western Greece demonstrates the ability of the tool to distinguish between sites not only according to geological suitability, but also according to data confidence, storage performance and proximity to hydrogen production and consumption hubs. The resulting framework provides a practical bridge between early-stage geological screening and engineering-oriented site selection, while retaining the flexibility to adapt the ranking to different project objectives and levels of decision-making.