Subsurface technical feasibility studies for a future hydrogen storage in depleted field or aquifer are site specific, as they are for natural gas and for other geological related activities. To provide the best possible insights to project developers of storage sites that are yet to be defined, different strategies have been applied for each of the technical challenges requiring development:
• Based on the experience in screening sites for developing new natural gas storages, scoring and screening criteria have been proposed to support the selection of porous media storage site candidates for pure hydrogen storage. 27 properties have been grouped into three categories: geological and reservoir engineering; geological context and surface environment. For each property, a criteria is proposed and its importance is estimated regarding local impacts, the storage capacity (in Nm3) and the storage performance (in Nm3/h). This is used to advance a database of geological storage opportunities at the European scale by addition of data of specific relevance to geological storage of hydrogen.
• To answer reservoir engineering questions such as effects of mixing, structural trapping for H2, a high mobility gas, a workflow has been set to use results of the above-mentioned database and build synthetic models based on available properties. Estimates of the storage capacity and deliverability are made at a European scale.
• To determine expected microbial activity and impacts, seven different brines and rocks (cores or cuttings) from gas storage sites are being used in a large experimental microbiological investigation. The outcome of this extensive sampling and lab experimental program and data gathering from a wide range of relevant geological conditions is a rare opportunity to propose results across a large variety of possible conditions.
• Determining what steel grade can be used for underground hydrogen storage is a question faced by technical developers of underground hydrogen storage today. Contrarily to hydrocarbons (not corrosive), hydrogen contact with steel creates risks of Hydrogen embrittlement. The project is investigating what material (steel grade) can be used for underground hydrogen storage under which conditions. To cover a diversity of reservoir conditions (temperature and pressure) and gas compositions, tests are done to investigate the mechanical response of several steel grades in reservoir conditions. Autoclave testing are done to observe possible cracking and corrosion attack on specimens, and the Hydrogen uptake in steel coupons is analysed by hot carrier gas extraction. Permeation tests are also conducted to test the effective Hydrogen diffusion in the steel.
Techno-economic feasibility studies are providing insights to support a decision whether to proceed to pilot and large scale demonstration projects. This work aims to inform decision makers in government and industry:
• Energy system modelling has been used to investigate the role of a widespread deployment of underground renewable hydrogen storage in EU-27 + UK in future scenarios across 2025-2050. The scenarios are based on several hypotheses on the hydrogen production (domestic vs. imports from non-EU), storage technologies (salt caverns, porous media, aboveground technologies) and spatial distribution (centralized or distributed storage and production). Preliminary result show that the required long-term hydrogen storage capacities range between 40 to 700 TWhH2 in EU-27 and the UK, i.e. 1.2 to 25 MtH2. As an order of magnitude, assuming it is only done through salt caverns, and that 4000 tons of H2 can be stored per cavern, it is 300 to 6250 salt caverns.
• An assessment of the regulatory framework for Hydrogen Underground Storage in Europe has been done, based on surveys throughout the industry and research institutes. Main barriers are identified and a ranking of countries is proposed according to the status of underground hydrogen legislation.
• Depleted fields or aquifers, salt caverns and possibly other surface technologies will become competing solutions to meet a local storage demand. The cost of developing each of them requires finding the most competitive. Cost model of subsurface storage options have been developed to support these analyses
