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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

nowadays, hydrogen is considered a potential successor to the current fossil-fuel-based energy. within a few years, it will be an essential energy carrier, and an economy based on hydrogen will require appropriate hydrogen storage systems. Due to their large capacity, underground geological structures (deep aquifers, depleted hydrocarbon fields, salt caverns) are being considered for hydrogen storage. their use for this purpose requires an understanding of geological and reservoir conditions, including an analysis of the preparation and operation of underground hydrogen storage. the results of hydrogen injection and withdrawal modeling in relation to the deep Lower Jurassic, saline aquifer of the Konary geological structure (trap) are presented in this paper. A geological model of the considered structure was built, allowable pressures were estimated, the time period of the initial hydrogen filling of the underground storage was determined and thirty cycles of underground storage operations (gas injection and withdrawal) were simulated. the simulations made it possible to determine the essential parameters affecting underground hydrogen storage operation: maximum flow rate of injected hydrogen, total capacity, working gas and cushion gas capacity. the best option for hydrogen storage is a two-year period of initial filling, using the least amount of cushion gas. Extracted water will pose a problem in relation to its disposal. the obtained results are essential for the analysis of underground hydrogen storage operations and affect the economic aspects of uHS in deep aquifers. [ABSTRACT FROM AUTHOR]

The subject of this study is the analysis of influence of capillary threshold pressure and injection well location on the dynamic CO 2 and H 2 storage capacity for the Lower Jurassic reservoir of the Sierpc structure from central Poland. The results of injection modeling allowed us to compare the amount of CO 2 and H 2 that the considered structure can store safely over a given time interval. The modeling was performed using a single well for 30 different locations, considering that the minimum capillary pressure of the cap rock and the fracturing pressure should not be exceeded for each gas separately. Other values of capillary threshold pressure for CO 2 and H 2 significantly affect the amount of a given gas that can be injected into the reservoir. The structure under consideration can store approximately 1 Mt CO 2 in 31 years, while in the case of H 2 it is slightly above 4000 tons. The determined CO 2 storage capacity is limited; the structure seems to be more prospective for underground H 2 storage. The CO 2 and H 2 dynamic storage capacity maps are an important element of the analysis of the use of gas storage structures. A much higher fingering effect was observed for H 2 than for CO 2 , which may affect the withdrawal of hydrogen. It is recommended to determine the optimum storage depth, particularly for hydrogen. The presented results, important for the assessment of the capacity of geological structures, also relate to the safety of use of CO 2 and H 2 underground storage space. • Capillary threshold pressure as an important factor for UHS and CCS is introduced. • The dynamic storage capacity of CO 2 and H 2 at different well locations is estimated and compared. • Dynamic capacity maps of the CO 2 and H 2 as important element of storage assessment are presented. • Variable impact of the fingernig effect on the underground storage of CO 2 and H 2 is shown. [ABSTRACT FROM AUTHOR]

Using the Konary anticlinal structure in central Poland as an example, a geological model has been built of the Lower Jurassic reservoir horizon, and CO2 injection was simulated using 50 various locations of the injection well. the carbon dioxide storage dynamic capacity of the structure has been determined for the well locations considered and maps of CO2 storage capacity were drawn, accounting and not accounting for cap rock capillary pressure. though crucial for preserving the tightness of cap rocks, capillary pressure is not always taken into account in CO2 injection modeling. It is an important factor in shaping the dynamic capacity and safety of carbon dioxide underground storage. When its acceptable value is exceeded, water is expelled from capillary pores of the caprock, making it permeable for gas and thus may resulting in gas leakage. Additional simulations have been performed to determine the influence of a fault adjacent to the structure on the carbon dioxide storage capacity. the simulation of CO2 injection into the Konary structure has shown that taking capillary pressure at the summit of the structure into account resulted in reducing the dynamic capacity by about 60%. the greatest dynamic capacity of CO2 storage was obtained locating the injection well far away from the structure's summit. A fault adjacent to the structure did not markedly increase the CO2 storage capacity. A constructed map of CO2 dynamic storage capacity may be a useful tool for the optimal location of injection wells, thus contributing to the better economy of the enterprise. [ABSTRACT FROM AUTHOR]

An analysis of the influence of injection well location on CO2 storage efficiency was carried out for three well-known geological structures (traps) in deep aquifers of the Lower Jurassic Polish Lowlands. Geological models of the structures were used to simulate CO2 injection at fifty different injection well locations. A computer simulation showed that the dynamic CO2 storage capacity varies depending on the injection well location. It was found that the CO2 storage efficiency for structures with good reservoir properties increases with increasing distance of the injection well from the top of the structure and with increasing depth difference to the top of the structure. The opposite is true for a structure with poor reservoir properties. As the quality of the petrophysical reservoir parameters (porosity and permeability) improves, the location of the injection well becomes more important when assessing the CO2 storage efficiency. Maps of dynamic CO2 storage capacity and CO2 storage efficiency are interesting tools to determine the best location of a carbon dioxide injection well in terms of gas storage capacity. [ABSTRACT FROM AUTHOR]