In-situ hydrogen wettability characterisation for underground hydrogen storage

Hydrogen storage in subsurface aquifers or depleted gas reservoirs represents a viable long-term energy storage solution. There is currently a scarcity of subsurface petrophysical data for the hydrogen system. In this work, we determine the wettability and Interfacial Tension (IFT) of the hydrogen-brine-quartz system using captive bubble, pendant drop and in-situ 3D micro-Computed Tomography (CT) methods. Effective contact angles ranged between 29° and 39° for pressures 6.89–20.68 MPa and salinities from distilled water to 5000 ppm NaCl brine. In-situ methods, novel to hydrogen investigations, confirmed the water-wet system with the mean of the macroscopic and apparent contact angle distributions being 39.77° and 59.75° respectively. IFT decreased with increasing pressure in distilled water from 72.45 mN/m at 6.89 MPa to 69.43 mN/m at 20.68 MPa. No correlation was found between IFT and salinity for the 1000 ppm and 5000 ppm brines. Novel insights into hydrogen wetting in multiphase environments allow accurate predictions of relative permeability and capillary pressure curves for large scale simulations.     

Hydrogen wettability in carbonate reservoirs: Implication for underground hydrogen storage from geochemical perspective

Hydrogen has been considered as a promising renewable source to replace fossil fuels to meet energy demand and achieve net-zero carbon emission target. Underground hydrogen storage attracts more interest as it shows potential to store hydrogen at large-scale safely and economically. Meanwhile, wettability is one of the most important formation parameters which can affect hydrogen injection rate, reproduction efficiency and storage capacity. However, current knowledge is still very limited on how fluid-rock interactions affect formation wettability at in-situ conditions. In this study, we thus performed geochemical modelling to interpret our previous brine contact angle measurements of H₂-brine-calcite system. The calcite surface potential at various temperatures, pressures and salinities was calculated to predict disjoining pressure. Moreover, the surface species concentrations of calcite and organic stearic acid were estimated to characterize calcite-organic acid electrostatic attractions and thus hydrogen wettability. The results of the study showed that increasing temperature increases the disjoining pressure on calcite surface, which intensifies the repulsion force of H₂ against calcite and increases the hydrophilicity. Increasing salinity decreases the disjoining pressure, leading to more H₂-wet and contact angle increment. Besides, increasing stearic acid concentration remarkably strengthens the adhesion force between calcite and organic acid, which leads to more hydrophobic and H₂-wet. In general, the results from geochemical modelling are consistent with experimental observations that decreasing temperature and increasing salinity and organic acid concentration increase water contact angle. This work also demonstrates the importance of involving geochemical modelling on H₂ wettability assessment during underground hydrogen storage.     

Hydrogen-induced calcite dissolution in Amaltheenton Formation claystones: Implications for underground hydrogen storage caprock integrity

With the rising potential of underground hydrogen storage (UHS) in depleted oil and gas reservoirs or deep saline aquifers, questions remain regarding changes to geological units due to interaction with injected hydrogen. Of particular importance is the integrity of potential caprocks/seals with respect to UHS. The results of this study show significant dissolution of calcite fossil fragments in claystone caprock proxies that were treated with a combination of hydrogen and 10 wt% NaCl brine. This is the first time it has been experimentally observed in claystones. The purpose of this short communication is to document the initial results that indicate the potential alteration of caprocks with injected hydrogen, and to further highlight the need for hydrogen-specific studies of caprocks in areas proposed for UHS.     

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.     

Thermodynamic characterization of H2-brine-shale wettability: Implications for hydrogen storage at subsurface

Large-scale underground hydrogen storage (UHS) appears to play an important role in the hydrogen economy supply chain, hereby supporting the energy transition to net-zero carbon emission. To understand the movement of hydrogen plume at subsurface, hydrogen wettability of storage rocks has been recently investigated from the contact angles rock-H₂-brine systems. However, hydrogen wettability of shale formations, which determines the sealing capacity of the caprock, has not been examined in detail. In this study, semi-empirical correlations were used to compute the equilibrium contact angles of H₂/brine on five shale samples with various total organic content (TOC) at various pressures (5–20 MPa) and at 343 K. The H₂ column height that can be securely trapped by the shale and capillary pressures were calculated. The shale's H₂ sealing capacity decreased with increasing pressure, increasing depth and TOC values. The CO₂/brine equilibrium contact angles were generally higher than H₂/brine equilibrium, suggesting that CO₂ could be used as favorable cushion gas to maintain formation pressure during UHS. The utmost height of H₂ that can be safely trapped by shale 3 (with TOC of 23.4 wt%) reduced from 8950 to 8750 M while that of shale 5 (with TOC of 0.081 wt%) reduced slightly from 9100 M to 9050 M as the pressure was increased from 5 to 20 MPa. The capillary entry pressure decreased with increasing depth and shale TOC, implying that the capillary trapping effect, as well as the over-pressure required to move brines from the pores by hydrogen displacement, reduces with increasing depth, and shale TOC. However, the shales remained at strongly water-wet conditions, having an equilibrium contact angles of not more than 17° at highest pressure and TOC. The study suggests that the increasing contact angles with increasing pressure and shale TOC, as well as decreasing column height and capillary pressure with increasing depth for H₂-brine-shale systems might not be sufficient to exert significant influence on structural trapping capacities of shale caprocks due to low densities of hydrogen.     

Geochemical reactions-induced hydrogen loss during underground hydrogen storage in sandstone reservoirs

Underground hydrogen storage (UHS) appears to be an important means as a large-scale and long-term energy storage solution. A primary concern of UHS is the in-situ geochemical reactions-induced hydrogen loss. In this context, we performed geochemical modelling to examine the hydrogen loss associated with hydrogen dissolution and fluid-rock interactions using PHREEQC (Version 3) as a function of temperature and pressure. We also performed geochemical modelling with kinetics to investigate the potential hydrogen loss in two commercial gas storage reservoirs (Tubridgi and Mondarra) in Western Australia against the reservoir mineralogy, fluid properties, depth and temperature.Our results show that increasing pressure and temperature only slightly increases hydrogen solubility in brines without minerals. Increasing salinity slightly decreases the solubility of hydrogen in brines. The saturated hydrogen aqueous solution almost does not react with silicate and clay minerals, which is favorable for underground hydrogen storage in quartz-rich sandstone reservoirs. However, unlike silicate and clay minerals, carbonates like calcite triggers up to 9.5% hydrogen loss due to calcite dissolution induced hydrogen dissociation process. Kinetic simulations show that Tubridgi only leads to 0.72% of hydrogen loss, and Mondarra causes 2.76% of hydrogen loss as a result of reservoir calcite dissolution and hydrogen dissociation in brines in 30-year time. Nearly over 87% of calcite cement from Mondarra may be dissolved in 30-year, suggesting potential risks associated with wellbore stability. In conclusion, geochemical reactions-induced hydrogen loss would be minor for UHS in porous media, and we argue that deep calcite-free reservoirs together with calcite-free caprocks would be preferable for underground hydrogen storage.     

Experimental investigation of hydrogen-carbonate reactions via computerized tomography: Implications for underground hydrogen storage

The underground hydrogen storage (UHS) in depleted hydrocarbon reservoirs, aquifers, and saline caverns is regarded as a vital component of hydrogen economy value-chains, meant to tackle carbon emissions and global warming. The caprock integrity and storage capacity of the carbonate formations can be altered by the reaction between the injected hydrogen and the calcite/dolomite minerals during UHS. However, experimental investigations of hydrogen-calcite/dolomite reactions at underground storage temperature are rarely reported in literature. Thus, we conducted X-ray computed micro-tomography (μCT) scans of limestone and dolomite cores before and after pressurization with hydrogen for 75 days at 700 psi and 75 °C. For the first time, a significant calcite expansion was observed and led to reduction in storage capacity (i.e., effective porosity) by 47%. However, the storage capacity of the dolomite rock slightly increased (～6%) because the grain expansion effects canceled out the dissolution effects. The study suggests that reduction in storage capacity of carbonate formation due to hydrogen reactivity with calcite is possible during UHS in carbonate formations. Thus, hydrogen reactivity with carbonate minerals should be evaluated to de-risk hydrogen storage projects in carbonate formations.     

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.     

Hydrogen underground storage in Romania,potential directions of development,stakeholders and general aspects

Romania is a country with relatively good opportunities to manage the transition from the dependence on fossil energy to an energy industry based on renewable energy sources (RES), supported by hydrogen as an energy carrier. In order to ensure Romania's energy security in the next decades, it will be necessary to consider a fresh approach incorporating a global long-term perspective based on the latest trends in energy systems. The present article focuses on an analysis of the potential use of salt caverns for hydrogen underground storage in Romania. Romanian industry has a long technical and geological tradition in salt exploitation and therefore is believed to have the potential to use the salt structures also in the future for gas and specifically hydrogen underground storage. This paper indicates that more analysis works needs to be undertaken in order to value this potential, based on which macroeconomic decisions then can be taken. The present work examines the structures of today's energy system in Romania and features an analysis of Romania's current potential of hydrogen underground storage as well as, reports on the potential use of this hydrogen in chemical industry, the transport sector and salt industry in Romania and highlighting issues implied by a possible introduction and use of hydrogen and fuel cell technologies.     

Bulk storage of hydrogen

The technical aspects and economics of bulk hydrogen storage in underground pipes, lined rock caverns (LRC) and salt caverns are analyzed. Hydrogen storage in underground pipes is more economical than in geological caverns for useable amounts <20-t-H₂. However, because the pipe material is a major cost factor, the capital and operating costs for this storage method do not decrease appreciably with an increase in the amount of stored H₂. Unlike underground pipes, the installed capital cost of salt caverns decreases appreciably from ~$95/kg-H₂ at 100 t-H₂ stored to <$19/kg-H₂ at 3000 t-H₂ stored. Over the same scale, the annual storage cost decreases from ~$17/kg-H₂ to ~$3/kg-H₂. Like salt caverns, the installed capital cost of lined rock caverns decreases from ~$160/kg-H₂ at 100 t-H₂ stored to <$44/kg-H₂ at 3000 t-H₂ stored. Storing >750-t useable H₂ requires multiple caverns. The cost of salt caverns scales more favorably with size because the salt caverns are larger than lined rock caverns and need to be added at a slower rate as the storage capacity is increased.     

Assessment of feasible strategies for seasonal underground hydrogen storage in a saline aquifer

Renewable energies fluctuate, resulting in temporary mismatches between demand and supply. The conversion of surplus energy to hydrogen and its storage in geological formations is one option to counteract this energy imbalance. This study evaluates the feasibility of seasonal storage of hydrogen produced from wind power in Castilla-León region (northern Spain). A 3D multiphase numerical model is used to test different extraction well configurations during three annual injection-production cycles in a saline aquifer. Results demonstrate that underground hydrogen storage in saline aquifers can be operated with reasonable recovery ratios. A maximum hydrogen recovery ratio of 78%, which represents a global energy efficiency of 30%, has been estimated. Hydrogen upconing emerges as the major risk on saline aquifer storage without using other cushion gases. However, shallow extraction wells can minimize its effects. Steeply dipping geological structures are key for an efficient hydrogen storage.     

Assessment of the potential for underground hydrogen storage in bedded salt formation

Salt formations of an appropriate thickness and structure, common over the globe, are potential sites for leaching underground caverns in them for storage of various substances, including hydrogen. Underground hydrogen storage, considered as underground energy storage, requires, in first order, an assessment of the potential for underground storage of this gas at various scales: region, country, specific place.The article presents the results of the assessment of the underground hydrogen storage potential for a sample bedded salt formation in SW Poland. Geological structural and thickness maps provided the basis for the development of hydrogen storage capacity maps and maps of energy value and heating value. A detailed assessment of the hydrogen storage capacity was presented for the selected area, for a single cavern and for the cavern field; a map of the energy value of stored hydrogen has also been presented. The hydrogen storage potential of the salt caverns was related to the demand for electricity and heat. The results show the huge potential for hydrogen storage in salt caverns.     

Large-vscale hydrogen production and storage technologies: Current status and future directions

Over the past years, hydrogen has been identified as the most promising carrier of clean energy. In a world that aims to replace fossil fuels to mitigate greenhouse emissions and address other environmental concerns, hydrogen generation technologies have become a main player in the energy mix. Since hydrogen is the main working medium in fuel cells and hydrogen-based energy storage systems, integrating these systems with other renewable energy systems is becoming very feasible. For example, the coupling of wind or solar systems hydrogen fuel cells as secondary energy sources is proven to enhance grid stability and secure the reliable energy supply for all times. The current demand for clean energy is unprecedented, and it seems that hydrogen can meet such demand only when produced and stored in large quantities. This paper presents an overview of the main hydrogen production and storage technologies, along with their challenges. They are presented to help identify technologies that have sufficient potential for large-scale energy applications that rely on hydrogen. Producing hydrogen from water and fossil fuels and storing it in underground formations are the best large-scale production and storage technologies. However, the local conditions of a specific region play a key role in determining the most suited production and storage methods, and there might be a need to combine multiple strategies together to allow a significant large-scale production and storage of hydrogen.     

Geologic feasibility of underground hydrogen storage in Canada

Electricity production in the majority of Canada's regions is characterized by high proportions of nuclear and renewable sources such as hydroelectricity. Future plans to phase out coal-fired power plants by 2030 and decrease fossil fuel use in favor of increased integration of renewables highlight the need to develop strategies which can match intermittent and base-load electricity output with market demand. The use of hydrogen gas generated through off-peak electrolysis has been highlighted by the Canadian government as a potential avenue forward in managing electrical grids with surplus and intermittent electricity generation. This technology can be supported in a safe and cost-effective manner by underground hydrogen storage in geological formations. In this article, an overview of Canadian geology, as well as an assessment of the potential application of underground storage methods and associated safety concerns in Canada is presented. Favorable locations for pilot projects are found in the sedimentary basins of western and Atlantic Canada as well as southern Ontario, or the crystalline rocks of the Canadian Shield.     

Hydrogen storage in Majiagou carbonate reservoir in China: Geochemical modelling on carbonate dissolution and hydrogen loss

Underground hydrogen storage (UHS) appears to be promising means for large-scale hydrogen storage. Carbonate reservoirs can play an important role in hydrogen storage in particular in Western China and Middle East region. However, little work has been done to address the potential risks and uncertainties associated with carbonate dissolution and hydrogen loss as a result of hydrogen-brine-carbonate geochemical reactions. We thus performed geochemical modelling to assess the potential of UHS in Majiagou carbonate formation, China. Kinetic models of the dissolution/precipitation of calcite, dolomite and quartz were developed to characterize hydrogen loss, mineral dissolution and water chemistry variations up to 500 years.The results show that the percentage of hydrogen loss due to fluid-rock interactions is only 6.6% for the first year, but could increase to 81.1% at the end of 500 years during UHS in Majiagou formation, indicating that carbonate reservoirs is suitable for hydrogen seasonal storage but may not be a good candidate for long-term storage. Meanwhile, totally 0.0646% of calcite would dissolve into formation brine over 500 years, bringing potential risks on caprock and wellbore stability and formation integrity. Besides, we observed a considerable amount of methane generated along with H₂-brine-carbonate interactions. Our works provide a framework to assess the hydrogen storage capacity of carbonate reservoirs using geochemical modelling, and can be also applied to other types of storage deposits.     

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.     

A review on worldwide underground hydrogen storage operating and potential fields

Overreliance on fossil fuels for human energy needs, combined with the associated negative environmental consequences in terms of greenhouse gas emissions, has shifted our focus to renewable energy sources. Hydrogen has been identified by researchers as an energy source. Hydrogen is a non-carbon-based energy resource that has the potential to replace fossil fuels. This resource is seen as an alternative fuel since it may be produced using environmentally friendly methods.Hydrogen storage is a critical component of the hydrogen economy, particularly when hydrogen utilization on a large scale is required. This paper presents a review of worldwide underground operating and potential sites to provide a clear understanding of the current status of hydrogen storage in the world.The literature survey indicated that underground geological structures have been used to successfully store hydrogen. Some of the criteria used to select these sites for underground hydrogen storage include but are not limited to geological conditions, storage location, availability of brine, presence of insoluble impurities such as dolostone, limestone, or shale, and socio-economic characteristics.The key issues with the hydrogen storage in the subsurface geological structures include but are not limited to microbial, hydrogeological, hydrodynamics, geomechanics, and geochemical facilitated by injected hydrogen which significantly impact the success and operational efficiency of the projects.     

Salinity,temperature and pressure effect on hydrogen wettability of carbonate rocks

Hydrogen had been injected into the geologic formations, and the geologic formation wettability would influence the hydrogen storage. Hydrogen wettability of sandstone reservoirs (quartz), mica and other rocks have been explored in the previous study. However, the research on hydrogen wettability of carbonate rocks was lacked. In this study, we studied the carbonate rock wettability alteration when exposed to the hydrogen environments. Salinity, temperature and pressure effect on H₂/carbonate rock/brine wettability were explored. When the solutions ions concentration increased, the advancing/receding contact angle would increase, and divalent ions could make the contact angle higher than monovalent ion, which was because ions could compress the electric double layer. The carbonate rock powder in brine showed negative charge, and the zeta potential increased with higher ions concentration. When temperature increased and the pressure decreased, the contact angle would decrease, which was related to the H₂ gas density and molecular interactions.     

Impact of experimentally measured relative permeability hysteresis on reservoir-scale performance of underground hydrogen storage (UHS)

Underground Hydrogen Storage (UHS) is an emerging large-scale energy storage technology. Researchers are investigating its feasibility and performance, including its injectivity, productivity, and storage capacity through numerical simulations. However, several ad-hoc relative permeability and capillary pressure functions have been used in the literature, with no direct link to the underlying physics of the hydrogen storage and production process. Recent relative permeability measurements for the hydrogen-brine system show very low hydrogen relative permeability and strong liquid phase hysteresis, very different to what has been observed for other fluid systems for the same rock type. This raises the concern as to what extend the existing studies in the literature are able to reliably quantify the feasibility of the potential storage projects. In this study, we investigate how experimentally measured hydrogen-brine relative permeability hysteresis affects the performance of UHS projects through numerical reservoir simulations. Relative permeability data measured during a hydrogen-water core-flooding experiment within ADMIRE project is used to design a relative permeability hysteresis model. Next, numerical simulation for a UHS project in a generic braided-fluvial water-gas reservoir is performed using this hysteresis model. A performance assessment is carried out for several UHS scenarios with different drainage relative permeability curves, hysteresis model coefficients, and injection/production rates. Our results show that both gas and liquid relative permeability hysteresis play an important role in UHS irrespective of injection/production rate. Ignoring gas hysteresis may cause up to 338% of uncertainty on cumulative hydrogen production, as it has negative effects on injectivity and productivity due to the resulting limited variation range of gas saturation and pressure during cyclic operations. In contrast, hysteresis in the liquid phase relative permeability resolves this issue to some extent by improving the displacement of the liquid phase. Finally, implementing relative permeability curves from other fluid systems during UHS performance assessment will cause uncertainty in terms of gas saturation and up to 141% underestimation on cumulative hydrogen production. These observations illustrate the importance of using relative permeability curves characteristic of hydrogen-brine system for assessing the UHS performances.