Radosław Tarkowski

Underground hydrogen storage (UHS) is poised to emerge as a pivotal technology for large-scale and seasonal energy storage in future low-carbon energy systems. Nevertheless, ensuring its safe deployment necessitates implementation of monitoring strategies that account for the distinct physicochemical and microbiological characteristics of hydrogen. These characteristics cannot be directly transposed from underground gas storage (UGS) or carbon capture and storage (CCS) applications. In this study, we propose an integrated multi-domain monitoring framework for UHS developed through a thorough evaluation of European regulations; ISO and DNV standards; monitoring practices; and representative CCS, UGS, and UHS case studies. The framework includes a conceptual digital twin architecture for integrating heterogeneous monitoring data and supporting model updating, anomaly screening, and operational interpretation. It comprises five complementary monitoring domains: subsurface, near-surface, surface, remote, and digital. The integration of geophysical, geochemical, microbiological, atmospheric, and digital monitoring techniques, including 4D seismic surveys, fiber-optic sensing, hydrogen leakage detection systems, and satellite- and UAV-based observations, is a key aspect of this study. The analysis demonstrates that monitoring approaches developed for CCS and UGS provide a solid foundation for UHS but require adaptation to account for hydrogen’s high diffusivity, low viscosity, limited geochemical footprint, flammability, material compatibility issues, and potential for microbial conversion. The digital domain is proposed as an integration layer for monitoring data, model updating, anomaly screening, and decision support. Predictive and real-time capabilities require future field-scale implementation and validation. The proposed framework may provide a structured conceptual basis for the development of future UHS monitoring guidance, pilot applications, and regulatory requirements.

Underground hydrogen storage (UHS) is emerging as a key enabler of the green energy transition, ensuring energy system stability and supporting large-scale integration of renewable sources. Despite its technological readiness, UHS deployment in Europe faces significant barriers due to the absence of a clear legal status and a dedicated regulatory framework. Current EU energy, climate, and environmental directives do not explicitly define hydrogen as a storage medium, creating legal ambiguity. Lessons from underground gas storage (UGS) and Carbon Capture and Storage (CCS) provide valuable reference points; however, direct transfer of these frameworks is insufficient due to hydrogen’s the distinct physicochemical characteristics and associated safety and monitoring challenges. Major regulatory gaps have been identified in legislation, liability, ownership, technical standards, and monitoring. To address these issues, a hybrid UHS model is proposed—combining the operational practices of UGS with the regulatory rigour of CCS—to accelerate safe and efficient implementation of UHS in Europe and support the broader transition to green energy.

The efficiency of underground hydrogen storage (UHS) in an anticlinal dome structure in a saline aquifer largely depends on the geometry of the dome structure and the placement of injection wells, which determine both the dynamic capacity and the migration of the gas plume. In this study, we aimed to assess the impact of well location within the Jeżów anticlinal dome structure (central Poland) on storage capacity and hydrogen plume migration. A geological model of the structure was developed and used in TOUGH2 (version 2.0) software to simulate nine injection scenarios with different well placements. The results indicate that storage capacity increases with both the secant dip angle relative to the top of the dome structure and the tangent dip angle at the well location, reaching a maximum in areas with the steepest dip. During injection, the hydrogen plume migrates upward toward the top of the structure; afterwards, it gradually stabilizes and partially redistributes toward the top of the dome structure. Injection wells located in steeper parts of the anticline promote upward hydrogen migration, which may limit hydrogen recovery during the withdrawal phase. This study confirms that both structural dip and well placement are key factors determining UHS efficiency.

Underground hydrogen storage (UHS) is a relatively new technology that demonstrates notable potential for the efficient storage of large quantities of green hydrogen. Its large-scale implementation requires a comprehensive understanding of numerous factors, including safe and effective storage methods, as well as overcoming various thresholds and challenges. This article presents strategies for accelerating the implementation of this technology, identifying the thresholds and challenges affecting the development and future scale-up of UHS. It characterises challenges and constraints related to geology (including the type and geological characterisation of structures, hydrogen storage capacity, and hydrogen interactions with underground environments), the technological aspects of hydrogen storage (such as infrastructure, management, and monitoring), and economic and legal considerations. The need for the rapid implementation of demonstration projects has been emphasised. The identified thresholds and challenges, along with the resulting recommendations, are crucial for paving the way for the large-scale implementation of UHS. Addressing these issues will significantly influence the implementation of this technology post-2030.

Podziemne składowanie dwutlenku węgla jest uważane za technologię pozwalającą na redukcję znaczących ilości emisji tego gazu do atmosfery. Poprzedzone wychwyceniem CO2 u dużych przemysłowych emitentów, wdrożenie tej technologii staje się coraz bardziej pilne na globalnej drodze do zerowej emisji netto. Wymaga to poszukiwań odpowiednich struktur spełniających wymagania podziemnego składowania CO2. Przydatność struktury geologicznej wynika z jej pojemności dynamicznej zapewniającej przyjęcie jak największej ilości zatłoczonego gazu. Jej określenie wymaga przeprowadzenia każdorazowo symulacji zatłaczania CO2 w oparciu o wiarygodny model geologiczny struktury. Zbudowano model geologiczny struktury Jeżów dedykowany do składowania CO2 w warstwach jury dolnej oraz przeprowadzono symulacje zatłaczania dla 36 różnych lokalizacji otworu zatłaczającego. Z wykorzystaniem mapy pojemności składowania CO2 przedstawiono dynamiczną pojemność składowania CO2 dla rozważanych lokalizacji otworu zatłaczającego. Odnotowano przestrzenną zmienność wielkości potencjału magazynowania CO2. Wynika ona z ograniczeń związanych z ciśnieniem (zarówno szczelinowania, jak i kapilarnego nadkładu) i zmienia się ona w przypadku struktury Jeżów, w zależności od lokalizacji otworu zatłaczającego, od 94,36 do 147,37 mln ton CO2. Na otrzymany wynik mają wpływ zarówno parametry geologiczno-złożowe warstw zbiornikowych oraz nadkładu, ich ułożenie, oddalenie otworu zatłaczającego od szczytu struktury, jak i nachylenie warstw. Przedstawione rezultaty pozwalają na bardziej efektywne i bezpieczne planowanie składowania tego gazu, podkreślają znaczenie optymalnego rozmieszczenia otworów zatłaczających dla maksymalizacji pojemności oraz efektywnego wykorzystania struktury i ograniczenia ryzyka wycieku gazu.

This article presents the findings of a bibliometric analysis of scientific publications in journals and materials indexed in the SCOPUS and Web of Science databases, covering the broad topic of underground hydrogen storage (UHS). The use of VOSviewer software for keyword analysis enabled the identification of four key research areas related to UHS. These areas include hydrogen and hydrocarbon reservoir engineering; hydrogen economy and energy transformation; processes in hydrogen storage sites, including lessons from CO₂ sequestration; and the geology, engineering, and geomechanics of underground gas storage. The interdisciplinary nature of UHS research emphasises the synergy of research across diverse fields. A bibliographic analysis allowed for the identification of areas of intensive research and new directions of work related to UHS, key research centres, and the dynamics of the development of research topics related to UHS. This study revealed the chronological dispersion of the research results, their geographical and institutional variability, and the varying contributions of major publishing journals. The research methodology used can serve as an inspiration for the work of other researchers.

The successful commercialisation of underground hydrogen storage (UHS) is contingent upon technological readiness and social acceptance. A lack of social acceptance, inadequate policies/regulations, an unreliable business case, and environmental uncertainty have the potential to delay or prevent UHS commercialisation, even in cases where it is ready. The technologies utilised for underground hydrogen and carbon dioxide storage are analogous. The differences lie in the types of gases stored and the purpose of their storage. It is anticipated that the challenges related to public acceptance will be analogous in both cases. An assessment was made of the possibility of transferring experiences related to the social acceptance of CO₂ sequestration to UHS based on an analysis of relevant articles from indexed journals. The analysis enabled the identification of elements that can be used and incorporated into the social acceptance of UHS. A framework was identified that supports the assessment and implementation of factors determining social acceptance, ranging from conception to demonstration to implementation. These factors include education, communication, stakeholder involvement, risk assessment, policy and regulation, public trust, benefits, research and demonstration programmes, and social embedding. Implementing these measures has the potential to increase acceptance and facilitate faster implementation of this technology.

Underground hydrogen storage facilities require cushion gas to operate, which is an expensive one-time investment. Only some of this gas is recoverable after the end of UHS operation. A significant percentage of the hydrogen will remain in underground storage as non-recoverable cushion gas. Efforts must be made to reduce it. This article presents the results of modeling the cushion gas withdrawal after the end of cyclical storage operation. It was found that the amount of non-recoverable cushion gas is fundamentally influenced by the duration of the initial hydrogen filling period, the hydrogen flow rate, and the timing of the upconing occurrence. Upconing is one of the main technical barriers to hydrogen storage in deep saline aquifers. The ratio of non-recoverable cushion gas to cushion gas (NRCG/CG) decreases with an increasing amount of cushion gas. The highest ratio, 0.63, was obtained in the shortest 2-year initial filling period. The lowest ratio, 0.35, was obtained when utilizing the longest initial filling period of 4 years and employing the largest amount of cushion gas. The presented cases of cushion gas recovery can help investors decide which storage option is the most advantageous based on the criteria that are important to them.

Underground hydrogen storage in geological structures is considered appropriate for storing large amounts of hydrogen. Using the geological Konary structure in the deep saline aquifers, an analysis of the influence of depth on hydrogen storage was carried out. Hydrogen injection and withdrawal modeling was performed using TOUGH2 software, assuming different structure depths. Changes in the relevant parameters for the operation of an underground hydrogen storage facility, including the amount of H2 injected in the initial filling period, cushion gas, working gas, and average amount of extracted water, are presented. The results showed that increasing the depth to approximately 1500 m positively affects hydrogen storage (flow rate of injected hydrogen, total capacity, and working gas). Below this depth, the trend was reversed. The cushion gas-to-working gas ratio did not significantly change with increasing depth. Its magnitude depends on the length of the initial hydrogen filling period. An increase in the depth of hydrogen storage is associated with a greater amount of extracted water. Increasing the duration of the initial hydrogen filling period will reduce the water production but increase the cushion gas volume.