(Pre)feasibility study of underground hydrogen storage potential in depleted gas fields and salt caverns in the Netherlands

Hydrogen is expected to play an important role in our future energy system. It is a versatile energy carrier that can be produced from renewable electricity and then be used as a CO₂-neutral fuel for (re)generating electricity and/or heat, or as feedstock for the chemical industry. Hydrogen can be stored underground in large quantities and therefore has the potential to take over the role of natural gas in securing the supply of energy. Although depleted gas fields can potentially store larger volumes of hydrogen than current clusters of salt caverns, UHS in porous reservoirs is not yet a proven technology. To enable future demonstration/pilot projects, screening studies are needed for the identification and characterization of potential underground candidates.

Since 2012, the Dutch Ministry has funded several national (pre)feasibility studies to estimate the potential for underground natural gas and hydrogen storage (UGS & UHS) and flow performance of depleted natural gas fields and salt caverns clusters in the Netherlands. Various methodologies and criteria are being utilized. Analog methods provide first-order estimates on UHS capacities based on the volume of natural gas originally contained in fields and clusters of salt caverns. This reveals a total theoretical maximum storage capacity onshore of up to a few hundred TWh for fields and tens of TWh for clusters of salt caverns. More accurate estimates were obtained from nodal analyses using the analytical inflow performance relationship (IPR) and the vertical flow performance (VFP) curves. Surface limitations were considered for onshore areas such as groundwater, protected and urban areas, which shows a significant reduction, on average around 60%, in the total theoretical storage capacity. Because of that, and in order to search for alternative UHS sites, more attention has been paid to depleted fields and salt pillars in offshore areas. For this, realistic technical limitations were assumed, such as the working pressure range of transmission systems between 150  and 250 bar. This reveals a significant reduction in the storage capacity and flow performances, as many fields would not be filled to their maximum working capacity. For a better understanding of the difference between the performance of UGS and UHS, three UGSs currently in operation in the Netherlands were investigated in more detail. Results show that the range of working pressures at which they may operate significantly determines the amount of energy that a UHS can store. Results from ongoing numerical modelling (Eclipse 300) for some of the best depleted gas fields allow quantifying the efficiency of different operating strategies and the number of wells required based on injection/withdrawal cycles at various timescales (daily-weekly-monthly), distinct ranges of working pressures and types of cushion gas (e.g. nitrogen/hydrogen). Other aspects such as geochemical reactions, microbial activity and type of residual gas in the different fields are also being considered as selection criteria. These ongoing studies are expected to facilitate the screening and design of future demonstration/pilot projects for UHS in gas fields and salt caverns in the Netherlands beyond 2030.