Linking Uncertainty and Risk in Underground Hydrogen Storage: An Expert-Elicited Causal Approach

Hydrogen has increasingly gained attention in the energy transition due to its potential to store intermittent renewable energy and enhance energy system flexibility. In this context, the Netherlands has advanced policies and strategic roadmaps for underground hydrogen storage in depleted gas fields. Alongside these developments, leakage of hydrogen has emerged as a critical environmental and societal risk. The literature on the causal relations governing such uncertainty-driven risks arising from multiple interacting mechanisms remains limited. This study proposes an uncertainty-driven risk characterisation and prioritisation framework to address this gap for underground hydrogen storage in depleted gas fields. It combines a structured pathway identification, Delphi-based expert elicitation through structured questionnaires, a risk matrix, and a site characterisation tool. Possible causes of hydrogen leakage are categorised into caprock, fault/fracture zones, well system, and overall storage structure, and labelled according to their underlying mechanisms. Experts are selected purposely based on their expertise level, and questionnaires assess the importance of each cause and the degree of certainty associated with this assessment. The most relevant causes are then prioritised using a risk matrix. Site characterisation is considered to contextualise how prioritised causes may manifest across different storage settings. The prioritised risks are subsequently represented using bow-tie and fault tree diagrams. Overall, this study provides a structured investigation of the causal relations underlying uncertainty-driven hydrogen leakage risks in Dutch depleted gas fields. 

Keywords: underground hydrogen storage, uncertainty-driven risks, expert elicitation