Large-scale Hydrogen Storage Research Articles

Techno-economic analysis of large-scale green hydrogen production and storage

Producing clean energy and minimising energy waste are essential to achieve the United Nations sustainable development goals such as Sustainable Development Goal 7 and 13. This research analyses the techno-economic potential of waste heat recovery from multi-MW scale green hydrogen production. A 10 MW proton exchange membrane electrolysis process is modelled with a heat recovery system coupled with an organic Rankine cycle (ORC) to drive the mechanical compression of hydrogen. The technical results demonstrate that when implementing waste heat recovery coupled with an ORC, the first-law efficiency of electrolyser increases from 71.4% to 98%. The ORC can generate sufficient power to drive the hydrogen's compression from the outlet pressure at the electrolyser 30 bar, up to 200 bar. An economic analysis is conducted to calculate the levelised cost of hydrogen (LCOH) of system and assess the feasibility of implementing waste heat recovery coupled with ORC. The results reveal that electricity prices dominate the LCOH. When electricity prices are low (e.g., dedicated offshore wind electricity), the LCOH is higher when implementing heat recovery. The additional capital expenditure and operating expenditure associated with the ORC increases the LCOH and these additional costs outweigh the savings generated by not purchasing electricity for compression. On the other hand, heat recovery and ORC become attractive and feasible when grid electricity prices are higher.

The techno-economic potential of large-scale hydrogen storage in Germany for a climate-neutral energy system

The seasonal storage of natural gas is a recognized and reliable technology in the energy industry. Salt caverns are particularly suitable for storing alternative gaseous fuels such as hydrogen. Germany has a great technical potential for expanding its cavern storage capacity, which exceeds the expected demand for hydrogen many times. Regarding the projected long-term decline in natural gas use, the question arises as to whether existing caverns can meet future storage requirements. To this end, a techno-economic model is presented to meet electricity and hydrogen demand in a cost-optimal solution. This analysis focused on the utilization of hydrogen storage in terms of energy throughput and maximum storage capacity. To link the outcome of economic dispatch to the literature, the fundamental assumptions are based on comprehensive capacity expansion models. This study advances the state of the art by evaluating key input parameters of the future energy system. By conducting 192 model runs, the analysis revealed the range of uncertainty in terms of storage use. This indicates a strong dependence of the systemic and economic value of hydrogen storage on boundary conditions such as a consideration of dark doldrums, a flexible hydrogen demand profile, hydrogen import restrictions and a larger electrolyzer capacity. The uncertainty ranged from 0 to 67 TWhH2 for the storage capacity, with an average of 36.6 TWhH2 across all scenarios, and from 0 to 190 TWhH2 for the annual energy throughput. These results are significant for gas storage operators who derive transformation strategies and policymakers evaluating financial funding requirements.

A Mini-Review on Underground Hydrogen Storage: Production to Field Studies

Hydrogen has become increasingly popular as one of the alternative fuels to reduce greenhouse gas emissions. Storing hydrogen in geological structures is a technology that shows great potential in storing large amounts of hydrogen efficiently. However, this technology is relatively new and requires a clear understanding. Therefore, a quick review of underground hydrogen storage is needed to understand its fundamental concepts. This review article presents important components relevant to underground hydrogen storage. First, some currently available hydrogen production methods are discussed followed by hydrogen storage methods. Both small-scale and large-scale hydrogen storage methods are presented. Next, some important factors (fluid properties, rock properties, solid–fluid interactions, and chemical interactions) influencing underground hydrogen storage are summarized. This is followed by presenting various interesting field studies for underground hydrogen storage. Lastly, some challenges and future outlooks pertinent to underground hydrogen storage are reviewed. This article will serve as a useful resource that provides a quick overview of underground hydrogen storage for both researchers and industrialists.

Linking geological and infrastructural requirements for large-scale underground hydrogen storage in Germany

Hydrogen storage might be key to the success of the hydrogen economy, and hence the energy transition in Germany. One option for cost-effective storage of large quantities of hydrogen is the geological subsurface. However, previous experience with underground hydrogen storage is restricted to salt caverns, which are limited in size and space. In contrast, pore storage facilities in aquifers -and/or depleted hydrocarbon reservoirs- could play a vital role in meeting base load needs due to their wide availability and large storage capacity, but experiences are limited to past operations with hydrogen-bearing town gas. To overcome this barrier, here we investigate hydrogen storage in porous storage systems in a two-step process: 1) First, we investigate positive and cautionary indicators for safe operations of hydrogen storage in pore storage systems. 2) Second, we estimate hydrogen storage capacities of pore storage systems in (current and decommissioned) underground natural gas storage systems and saline aquifers. Our systematic review highlights that optimal storage conditions in terms of energy content and hydrogen quality are found in sandstone reservoirs in absence of carbonate and iron bearing accessory minerals at a depth of approx. 1,100 m and a temperature of at least 40°C. Porosity and permeability of the reservoir formation should be at least 20% and 5 × 10−13 m2 (∼500 mD), respectively. In addition, the pH of the brine should fall below 6 and the salinity should exceed 100 mg/L. Based on these estimates, the total hydrogen storage capacity in underground natural gas storages is estimated to be up to 8 billion cubic meters or (0.72 Mt at STP) corresponding to 29 TWh of energy equivalent of hydrogen. Saline aquifers may offer additional storage capacities of 81.6–691.8 Mt of hydrogen, which amounts to 3.2 to 27.3 PWh of energy equivalent of hydrogen, the majority of which is located in the North German basin. Pore storage systems could therefore become a crucial element of the future German hydrogen infrastructure, especially in regions with large industrial hydrogen (storage) demand and likely hydrogen imports via pipelines and ships.

The surface challenges of underground hydrogen storage – pre-feasibility studies at the Otway International Test Centre, Victoria

Underground hydrogen storage (UHS) has the potential to overcome the infrastructure and safety challenges of large-scale hydrogen storage, support long-term supply security and decrease delivery costs through economies of scale. Depleted hydrocarbon reservoirs and saline aquifers are likely to be significant contributors to UHS capacity in Australia. The principles of subsurface hydrogen storage in porous reservoir rocks are based on experience from both natural gas and carbon dioxide storage projects. However, as field-scale testing is required to demonstrate and mature the technology, a pre-feasibility study of the potential for an early UHS demonstration at the Otway International Test Centre (OITC) has been undertaken. Pre-feasibility studies have shown that while the characterisation of the subsurface storage reservoir is the most important aspect of the site-selection process, above-ground factors, such as facilities design, the logistics of hydrogen supply and the regulatory environment, significantly affect project design. Existing technologies require only minor adaptation to provide the surface infrastructure for a UHS project, but the logistics of hydrogen supply may be a significant factor in the scope of a demonstration project.

Hydrogen tightness evaluation in bedded salt rock cavern: A case study of Jintan, China

Hydrogen is regarded as one of the most important energy sources for the future. Safe, large-scale storage of hydrogen contributes to the commercial development of the hydrogen industry. Use of bedded salt caverns for natural gas storage in China provides a new option for underground hydrogen storage (UHS). In this study, the physical properties of multicomponent gases in UHS and salt rock are reviewed and discussed, along with the flow of hydrogen in the surrounding salt rock. Mathematical models of the two-phase multicomponent flow of the gas–brine system in the UHS were established. A numerical model of a simplified elliptical salt cavern was built to simulate the migration of the gas–brine system in the UHS. The hydrogen tightness of the UHS was evaluated through simulation with different storage strategies, salt rock and interlayer permeabilities, and gas components. The results indicate that: (1) Cyclic injection and withdrawal facilitate hydrogen leakage, which is accelerated by increasing the frequency. (2) The huff-n-puff of hydrogen gas in the injection and withdrawal cycles forces the gas into pore space and enhances the relative permeability of the gas phase. The migration of hydrogen and brine weakens the hydrogen tightness. Brine saturation is an important index for evaluating the hydrogen tightness of UHS. (3) The leakage rate of UHS increases with an increase in the permeability of the salt rock and interlayer and the total thickness of the interlayers. The average permeability Kwa weighted by the thickness of layers for the bedded salt formation is proposed to integrate three variables to facilitate field application of the simulation results. The critical Kwa is less than 3.02 × 10−17 m2 if the recommended annual hydrogen leakage rate is less than 1%. (4) The difference between hydrogen and other gas species is another important factor in the leakage rate and should be considered. This study provides theoretical guidance for evaluating the feasibility of UHS in salt caverns and site selection in China.

Utilizing publicly available datasets for identifying offshore salt strata and developing salt caverns for hydrogen storage

Abstract Hydrogen is expected to play a key role in a future climate-neutral economy by decarbonizing ‘hard to abate’ sectors, and importantly act as an energy carrier to balance intermittent renewable energy production, which, if stored, could be used to address grid-scale energy demands. It is evident that for unlocking the vast potential of hydrogen technologies, large-scale hydrogen storage with the capability of fast cyclic operations needs to be secured. Underground salt caverns, where decades of operational experience exist, offer an attractive option for hydrogen storage due to the high hydrogen sealing potential of salt, capability for large injection/withdrawal flow rates and capacity for large volume storage. This study presents a novel methodology for selecting offshore salt cavern sites based on publicly available datasets, which leads to eventually estimating regional hydrogen storage capacities. The Southern North Sea was investigated and a case study detailing a single diapiric salt structure is presented, demonstrating the strength and practicality of the framework as well as highlighting the potential of offshore salt cavern storage of hydrogen in the decarbonization energy journey of the UK.

Role of methane as a cushion gas for hydrogen storage in depleted gas reservoirs

Depleted natural gas reservoirs play an important role as a viable option for large-scale hydrogen storage and production. However, its deployment depends on the accurate knowledge of the cushion gas (such as CH4, CO2, and N2) compositions, which are key components affecting the rock-fluid interfacial phenomenon. In addition, there are currently few reported studies on rock/brine/gas-mixture wettability and gas-mixture/brine surface tension representing this type of reservoir. Hence, we report the feasibility of using CH4 as a cushion gas (in the presence of CO2 and N2) for H2 storage at various pressures (500 up to 3000 psi), temperatures (30 up to 70) oC, and salinities (2 up to 20) wt.% using drop shape analyzer equipment. Contact angle (CA) and surface tension (ST) experiments were extensively conducted for the different gas mixtures (H2–CH4–CO2–N2) to establish relevant data for H2 storage in depleted gas reservoirs.Our result indicates that unless when the rock's initial wetting state is altered, the studied gas-mixture compositions (Test case 1: 80% H2 – 10% CH4 – 5% CO2 – 5% N2; case 2: 70% H2 – 20% CH4 – 5% CO2 – 5% N2; case 3: 60% H2 – 30% CH4 – 5% CO2 – 5% N2; case 4: 50% H2 – 40% CH4 – 5% CO2 – 5% N2; case 5: 40% H2 – 50% CH4 – 5% CO2 – 5% N2; case 6: 30% H2 – 60% CH4 – 5% CO2 – 5% N2; and case 7: 20% H2 – 70% CH4 – 5% CO2 – 5% N2) will exhibit comparable wettability behavior as the CAs ranged between [20 to 41°] irrespective of the reservoir pressure, temperature, and salinity. ST decreases with increasing temperature and linearly with increasing pressure. ST for each gas mixture increased with salinity. ST decreases systematically with increasing CH4 fraction (at any given salinity, temperature, and pressure) with the highest observed in Test case 1 and the lowest in Test case 7 compositions. Test cases 3 and 4 with H2 (50–60%) and CH4 (30–40%) fractions was selected as the optimal gas mixture based on CA and ST for H2 storage and withdrawal. The study's findings offer precise and useful input data for the reservoir-scale simulation used in geo-storage optimization in depleted natural gas reservoirs.

A highly active Pd clusters hosted by magnesium hydroxide nanosheets promoting hydrogen storage

Liquid organic hydrogen carriers (LOHCs) represent promising candidates for large-scale hydrogen storage, yet the design of high-efficiency and low-cost catalysts on the dehydrogenation of LOHCs remains challenging. Herein, we develop a two-dimensional (2D) magnesium hydroxide nanosheet that hosts Pd clusters (Pd/Mg(OH)2) for the dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NEC), an important reaction for H2 transportation. The catalyst boosts the activity up to a 12H-NEC conversion of 100 % and the hydrogen release of 5.72 wt% with a low metal loading of 0.5 wt%, while the hydrogen release on Pd/MgO is only 2.34 wt% with the conversion rate of 71 % under the same conditions. Coupling various characterization technologies (HAADF-STEM, EXAFS, EPR and In-situ DRIFTS) with DFT calculations, it was found that the work function of magnesium hydroxide nanosheets for the dehydrogenation reaction due to the strong metal-support interaction, which makes Pd species have better dispersion, forms Pdn+-OH stable Pd cluster and reduces the dehydrogenation barrier as well, thus enhancing the dehydrogenation performance and improving the hydrogen production greatly. This work provides a new promising way to design advanced dehydrogenation catalyst with high activity for the hydrogen storage.

An Insight into Underground Hydrogen Storage in Italy

Hydrogen is a key energy carrier that could play a crucial role in the transition to a low-carbon economy. Hydrogen-related technologies are considered flexible solutions to support the large-scale implementation of intermittent energy supply from renewable sources by using renewable energy to generate green hydrogen during periods of low demand. Therefore, a short-term increase in demand for hydrogen as an energy carrier and an increase in hydrogen production are expected to drive demand for large-scale storage facilities to ensure continuous availability. Owing to the large potential available storage space, underground hydrogen storage offers a viable solution for the long-term storage of large amounts of energy. This study presents the results of a survey of potential underground hydrogen storage sites in Italy, carried out within the H2020 EU Hystories “Hydrogen Storage In European Subsurface” project. The objective of this work was to clarify the feasibility of the implementation of large-scale storage of green hydrogen in depleted hydrocarbon fields and saline aquifers. By analysing publicly available data, mainly well stratigraphy and logs, we were able to identify onshore and offshore storage sites in Italy. The hydrogen storage capacity in depleted gas fields currently used for natural gas storage was estimated to be around 69.2 TWh.

Effect of Methyl Orange on the Hydrogen Wettability of Sandstone Formation for Enhancing the Potential of Underground Hydrogen Storage

Hydrogen is expected to play a significant role as a clean energy carrier. However, the development of a hydrogen economy requires the use of large amounts of hydrogen; therefore, large-scale hydrogen storage is a considerable problem that needs to be resolved. Hydrogen can be stored underground in aquifers, salt caverns, depleted oil and gas reservoirs, and coal seams. In this context, wettability is a critical parameter in determining the containment security, storage capacity, fluid dynamics, and withdrawal rate during underground hydrogen geo-storage operations. Meanwhile, the toxic soluble dye, methyl orange (MO), is widely used in the textile and other industries and released in large quantities into the surface and subsurface waters. Hence, in the present study, the use of MO to alter the wettability of reservoirs in favor of hydrogen geo-storage is investigated. To this end, model oil-wet rock surfaces are prepared by aging quartz substrates with stearic acid and then treating them with various amounts of aqueous MO for 1 week at 50 °C. The brine contact angles on these model surfaces are then measured in a hydrogen environment under various reservoir conditions to demonstrate that the MO treatment makes the surface more hydrophilic. Moreover, the contact angle is seen to increase significantly with the increase in the temperature, pressure, and salinity. In addition, the importance of pH is assessed, and various brines (NaCl, KCl, MgCl2, and CaCl2) are compared. The proposed treatment is expected to improve the hydrogen trapping efficiency of sandstone reservoirs while simultaneously providing a safe disposal route for MO via deep well injection.

Effect of the cathode catalyst loading on mass transfer in toluene direct electrohydrogenation

Toluene (TL)-methylcyclohexane (MCH) organic hydride is one of the most promising carrier candidates for the large-scale transport and storage of hydrogen. TL Direct electrohydrogenation electrolyzers based on solid polymer electrolyte membrane technology exhibit significant advantages in terms of energy efficiency compared with the conventional TL hydrogenation method. Mass transfer in the catalyst layer is a crucial aspect of the performance of these electrochemical devices. In this study, experiments were conducted using catalyst-coated membranes with various thicknesses to control the catalyst loading (carbon-supported platinum/ruthenium alloy) and investigate its influence on the mass transfer properties and electrolytic performance of a TL direct electrohydrogenation electrolyzers. The current efficiency was also evaluated for TL concentrations between 1% and 100% in the cathode reactant. The results indicated than an optimum thickness of the cathode catalyst layer corresponding to catalyst loadings of 1.4–1.6 mg cm−2 could maximize the current efficiency of the electrolyzer. The presence of hydrogen gas generated as a side reaction in the high-TL concentration range and high MCH concentrations in the low-TL concentration range are the main factors contributing to a decrease in current efficiency.

Atomistic insights into the H2 adsorption and desorption behavior of novel Li-functionalized polycrystalline CNTs

At present, hydrogen storage by physisorption is being investigated on novel polycrystalline carbon nanotubes (PCNTs) in order to utilize them for large-scale applications. Large-sized nanotubes are susceptible to structural flaws known as polycrystallinity, which evolve owing to the inherent constraints of growth kinetics and purification during the synthesis process. In this study, molecular dynamics simulations (MDS) were used to analyze the adsorption and desorption behavior of PCNTs employing hybrid grand canonical Monte Carlo (GCMC) simulations coupled with microcanonical ensembles. Moreover, a distinctive potential energy distribution technique was used to compute the adsorption metrics. We further investigated the size dependency effects, including curvature, length, and grain boundaries (GBs), on hydrogen adsorption functionalities. The MDS revealed that PCNTs with a moderate grain size of 4 nm are energetically stable and adsorption compatible with maximum gravimetric densities of 8.22 and 1.03 wt% at 77 and 300 K, respectively. Furthermore, the optimized PCNTs were functionalized with Li adatoms of varied concentrations and simulated at various temperatures and pressures. Afterward, adsorption/desorption kinetics and isosteric enthalpies of Li-functionalized PCNTs (Li-PCNTs) were computed to assess the synergistic impacts of Li adatoms and GBs. Li-PCNTs have shown remarkable performance in terms of hydrogen storage and deliverability. Consequently, at 77 and 300 K, Li-PCNTs doped with a 25% adatom concentration exhibited the maximum hydrogen uptake of 10.36 wt% and 2.13 wt%, respectively. Additionally, at 300 and 77 K, the averaged isosteric enthalpy of adsorption, estimated from the adsorption isotherms, was about 7.07 kJ/mol and 4.03 kJ/mol, respectively. Therefore, despite their ability to prevent metal clustering, PCNTs have a modest impact on adsorption metrics. Our findings open up new avenues for the utilization of PCNTs in large-scale hydrogen storage applications with suitable functionalization strategies.

Boosting the dehydrogenation efficiency of dodecahydro-N-ethylcarbazole by assembling Pt nanoparticles on the single-layer Ti3C2Tx MXene

As the candidates for large-scale hydrogen storage, liquid organic hydrogen carriers (LOHCs) exhibit evident advantages in hydrogen storage density and convenience of storage and transportation. Among them, NECZ (N-ethylcarbazole)/12H-NECZ (dodecahydro-N-ethylcarbazole) is considered as a typical system with the lower hydrogenation/dehydrogenation temperature. However, the low dehydrogenation efficiency restrict its commercial applications. In this work, the single-layer Ti3C2Tx MXene was employed as the support to load the Pt nanoparticles for the 12H-NECZ dehydrogenation reaction. The effect of transition metals, loading amounts and morphologies of catalysts were analyzed. It was found that the 3 wt% Pt/S–Ti3C2Tx catalyst exhibited the best catalytic performance with 100% conversion, 91.55% selectivity of NECZ and 5.62 wt% hydrogen release amount at 453 K, 101.325 kPa for 7 h. The product distributions and kinetics analysis suggested that the elementary reaction from 4H-NECZ to NECZ was the rate-limiting step. The selectivity of NECZ is sensitive to the dehydrogenation temperature. Combined with the XRD, SEM, HRTEM, XPS, BET and FT-IR results, it could be indicated that the special two-dimension structure of S–Ti3C2Tx and electronic effect between Pt and S–Ti3C2Tx enhanced the dehydrogenation efficiency of 12H-NECZ. The measurements of cyclic dehydrogenation indicated that the Pt/S–Ti3C2Tx catalyst exhibited good stability after 42 h. This work brought a new strategy for the design of efficient catalysts using two-dimensional materials in the applications of the liquid organic storage hydrogen technology.

Large-scale underground hydrogen storage: Integrated modeling of reservoir-wellbore system

Underground Hydrogen Storage (UHS) has received significant attention over the past few years as hydrogen seems well-suited for adjusting seasonal energy gaps.We present an integrated reservoir-well model for “Viking A″ the depleted gas field in the North Sea, as a potential site for UHS. Our findings show that utilizing the integrated model results in more reasonable predictions as the gas composition changes over time. Sensitivity analyses show that the lighter the cushion gas, the more production can be obtained. However, the purity of the produced hydrogen will be affected to some extent, which can be enhanced by increasing the fill-up period and the injection rate. The results also show that even though hydrogen diffuses into the reservoir and mixes up with the native fluids (mainly methane), the impact of hydrogen diffusion is marginal. All these factors will potentially influence the project's economics.

Numerical modelling and heat transfer optimization of large-scale multi-tubular metal hydride reactors

Heat management during the absorption/desorption process is a key aspect in improving the performance of large-scale hydrogen storage systems. In this article, the absorption and desorption performance of a multi-tubular hydride reactor is numerically investigated and optimized for 60 kg mass of LaNi5 alloy. The 90% absorption with 7, 14, and 19 tubes is achieved in 985, 404, and 317 s with an overall reactor weight of 78.46, 88, and 88.2 kg, respectively. The 14-tube reactor performance is investigated by introducing the longitudinal fins inside the tubes. The reactor performance is enhanced by allocating fins into different pairs of half and full fins constrained by overall fin volume. A thermal resistance network model is presented to investigate the effect of fin distribution and coolant velocity on equivalent resistance of the metal hydride reactor. Storage performance obtained from numerical model validates the thermal resistance analysis from heat transfer viewpoint. With six full fins, 90% hydrogen absorption is achieved in 76 s. However, tubes with 6, 8, and 12 pairs of half and full fins require 74, 58, and 54 s, respectively. The 14-tube reactor with 8 pairs of half and full fins is used for quantifying the augmentation in the absorption performance in response to operating conditions (supply pressure and heat transfer fluid temperature). A design methodology is outlined for the development of a large-scale multi-tubular hydride reactor based on a heat transfer optimization strategy.

Numerical simulation of large-scale seasonal hydrogen storage in an anticline aquifer: A case study capturing hydrogen interactions and cushion gas injection

In response to the Paris Agreement, the transition from fossil fuels to renewable energy resources (RER) is one of the most crucial measures in responding to climate change. Under this context, hydrogen storage with the concept of ‘power to gas’ represents a possible solution for the mismatch problem between fluctuating RER generation and downstream demand in a seasonal time scale. Compared to conventional low storage capacities of salt caverns, widely spread aquifers provide a possibility for safe, cost-effective, and environmentally friendly long-term hydrogen storage. However, current knowledge of hydrogen storage in these aquifers is only limited to a few impure hydrogen projects; understanding their trapping mechanisms as well as how to recover their trapped hydrogen is urgent. In order to fulfil the knowledge gap, not only are the complex underground interactions of hydrogen with rock or a fluid (residual trapping or dissolution trapping) modelled and validated against reliable experimental data, but also multiple cycles and cushion gas injection are integrated to enhance hydrogen recovery in this study. Through powerful numerical studies, the results indicate that: (a) at a seasonal storage time scale, residual trapping has the most effect in reducing hydrogen round-trip efficiency; (b) multiple cycles are helpful for hydrogen storage in an aquifer reservoir with round-trip efficiency increasing from 50.9% in the first cycle to 78.6% at the end; (c) nitrogen as a cushion gas for injection has a better performance compared with carbon dioxide with a capability to unlock residual trapped and dissolution trapped hydrogen; (d) nitrogen as a cushion gas for injection can effectively alleviate insufficient hydrogen production capacity in the first cycle with the hydrogen round-trip efficiency increased from 50% to 70%; and (e) the hydrogen extraction phase ends up with a very high recovery efficiency (around 85%) in a nitrogen injection scenario.

Large-scale storage of hydrogen in salt caverns for carbon footprint reduction

This article presents a geomechanical appraisal of green hydrogen (H2) storage in salt caverns opened by solution mining as a technical contribution to carbon footprint reduction. The location of the salt cavern is speculative, within possible limits to be found in the salt deposits in the Gulf of Mexico of the USA, as the aim is to demonstrate the technical feasibility of the concept. It presents the conceptual design of the wells used for the solution mining of the caverns and the operation cycle of injection and withdrawal of hydrogen. The contribution of the study presented stems from the methodology adopted in the simulation of the geomechanical structural behavior of the salt cavern and in its design for storing hydrogen, which has thermomechanical properties more complex than natural gas. The numerical simulation considers the nonlinear physical viscoelastic and elastoplastic phenomena, with different constitutive laws for representing the geomechanical behavior of geomaterials. The constitutive laws based on deformation mechanisms are used (multi-mechanisms of deformation – M.D.) to simulate the creep of the salt rock. The article also presents a protocol for sizing the caverns, considering more than 40 years of experience in the design of conventional and solution mining of rock salt. It presents the concept of admissible halite creep strain and safety factors necessary to establish a stress belt that avoids hydrogen leaks at all stages of cavern construction and hydrogen storage. Using this methodology, the authors found that the cavern studied (220 m in height and 95 m in diameter) can hold 11,968,000 kg of working hydrogen.

Importance of clay-H2 interactions for large-scale underground hydrogen storage

Underground hydrogen storage is considered an option for large-scale green hydrogen storage. Among different geological storage types, depleted oil/gas fields and saline aquifers stand out. In these cases, hydrogen will be prevented from leaking back to the surface by a tight caprock seal. It is therefore essential to understand hydrogen interactions with shale-type caprocks. To this end, natural pure montmorillonite clay was exposed to hydrogen gas at different pressures (0–50 bar) and temperatures (77, 195, 303 K) to acquire data on its adsorption capacity related to UHS and caprock saturation. Montmorillonite was chosen because of its large specific surface area enabling quantification of the adsorption process. Hydrogen adsorption was successfully fitted with a Langmuir isotherm model and yielded small partition coefficients indicating that hydrogen does not preferentially adsorb to the clay surface. Adsorption on montmorillonite goes back to weak physisorption as inferred from minor negative changes in the enthalpy of reaction (−790 J/mol), derived from an Excel Solver approach to the van't Hoff equation. Based on own as well as literature values, adsorption capacities, which were originally reported as mol/kg or wt%, are recast as hydrogen volume adsorbed per specific surface area (μL/m2). The acquired range is surprisingly narrow, with values ranging from 3 to 6 μL/m2, and indicates the normalised volume of hydrogen that can be expected to remain in the shale-type caprock after injected hydrogen migrated upwards through the porous reservoir. This ‘residual’ caprock saturation with hydrogen can be further restrained by considering the geothermal gradient and its effect on the molar volume of hydrogen. The experimental results presented here recommend injecting hydrogen deeper rather than shallower as pressure and temperature work in favour of increased storage volumes and decreased hydrogen loss through clay adsorption in the caprock.

Pore-scale modelling on hydrogen transport in porous media: Implications for hydrogen storage in saline aquifers

Hydrogen energy has tremendous potential as a clean fuel in this energy transition. To build up the full-scale hydrogen energy supply chain, large-scale hydrogen storage is of vital importance. Underground hydrogen storage in saline aquifers has been perceived as an important means to achieve large-scale hydrogen storage. Therefore, we investigated hydrogen transport in pore network in a sandstone porous media at strongly water-wet and weakly water-wet (hydrogen-wet). We performed direct numerical simulation through volume of fluid method to investigate the transport of hydrogen at pore-scale under different wetting conditions with input hydrogen-rock physics data from literature. Our results showed that during primary drainage process (hydrogen injection for storage purpose), increasing hydrogen wetting decreased snap-off effect, enabling a greater pore space for hydrogen storage. During primary imbibition process (hydrogen extraction), increasing hydrogen wetting promoted the size and stability of hydrogen clusters, which is unfavorable to hydrogen extraction process. Given the significant high interfacial tension between brine and hydrogen and low viscous force of hydrogen, snap-off effect dominates the flow in both hydrogen injection and extraction process regardless of wetting conditions. This physical process causes the recovery factor even below 20%. We therefore suggest that storing hydrogen in depleted gas reservoirs under irreducible water saturation would have much less risks in hydrogen trapping during extraction process.