In a scenario where energy is produced in excess during peak production period from renewable sources, a solution for large-scale storage is essential. A promising solution can be the conversion of the excess energy in hydrogen, using it as energy carrier, and temporarily store it underground, in depleted gas/oil reservoirs, salt caverns or saline aquifers. The scope of this study is to investigate the feasibility of underground hydrogen storage (UHS) in depleted fields and develop a screening protocol to identify possible storage opportunities in Eni operated assets.
The first phase of work was to explore the state of art of underground hydrogen storage from literature review. Literature analysis allowed to identify the factors that must be considered for the suitability of a field for underground hydrogen storage. A total of 21 parameters have been selected as key factors. To each of them, a general weight (W) has been assigned following the importance of the parameter for a feasible storage. In addition, a general uncertainty, associated to the agreement of the scientific community on the ideal range for that parameter has been set up. Furthermore, the specific value of the field for each parameter must be considered. Therefore, we defined ranges of optimal values for each key factor, to which correspond a high positive impact (I), while more negative influence is given as we move far away from them.
In conclusion, the screening methodology developed in this study, allowed to define a ranking of Eni almost depleted assets ordered by decreasing score and increasing uncertainty. In this way, it is possible to identify the most potential fields in terms of features and associated risks.