Underground Hydrogen Storage Research Articles

Techno-economic analysis of developing an underground hydrogen storage facility in depleted gas field: A Dutch case study

Underground hydrogen storage will be an essential part of the future hydrogen infrastructure to provide flexibility and security of supply. Storage in porous reservoirs should complement storage in salt caverns to be able to meet the projected high levels of required storage capacities. To assess its techno-economic feasibility, a case study of hydrogen storage in a depleted gas field in the Netherlands is developed. Subsurface modelling is performed and various surface facility design concepts are investigated to calculate the levelized cost of hydrogen storage (LCOHS). Our base case with hydrogen as cushion gas results in an LCOHS of 0.79 EUR/kg (range of 0.58–1.04 EUR/kg). Increasing the number of full-cycle equivalents from 1 to 6 lowers the storage cost to 0.25 EUR/kg. The investment cost of the cushion gas represents 76% of the total cost. With nitrogen as cushion gas, LCOHS is reduced to 0.49 EUR/kg (range of 0.42–0.56 EUR/kg).

Experimental investigation of shale/hydrogen geochemical interactions

Underground Hydrogen Storage (UHS) is an effective technique that provides safe storage and recovery of the stored hydrogen for long-term energy storage. Shale caprocks are regarded as effective seals of the stored gas, however, one of the key challenges is the in-situ geochemical shale/hydrogen reactions that can impact the seal integrity during injection/production of hydrogen. To address this issue, this work investigates the geochemical reactions between hydrogen and shales, and evaluates the possible alterations in shales’ petro-physical properties. Calcite-rich shale samples are collected from EagleFord (EFS) and Wolfcamp (WCS) shale formations and exposed to pure hydrogen for 108 days under 9.65 MPa at 348 K. Analytical methods including X-ray diffraction, X-ray fluorescence and Scanning Electron Microscope analysis are performed. The results indicate calcite precipitation after hydrogen treatment in both samples due to the presence of organic contents. Sulfate and pyrite reduction reactions with hydrogen are not observed as hydrogen did not all react with sulfate minerals. Consequently, minor changes in the surface pore structure and pore spaces are observed after the treatment, confirming the low reactivity of calcite-rich shale rocks with hydrogen. Gas chromatography analysis shows neither considerable hydrogen loss nor the generation of other gases such as CH4 or CO2 occurred during the experiments. The obtained results suggest that the integrity of shale-caprocks are expected to remain strong during the injection and production of hydrogen, which is favorable for UHS. This work can be a suitable experimental framework to assist in evaluating the hydrogen reactivity to different types of shales with various mineralogy, and assessing the suitability of shale rock for UHS.

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.

GIS-based analysis of rock salt deposits’ suitability for underground hydrogen storage

The paper discusses the suitability of bedded salt deposits for underground hydrogen storage facilities. The presented research is an example of multi-criteria decision analysis coupled with spatial data analysis undertaken using GIS (Geographic Information System). The aim of this study is to develop a methodology for selecting the best locations for hydrogen storage in salt caverns. In the analysis, we take into account the results of previous studies of the storage capacity of rock salt deposits. The presented methodology allows the creation of rock salt deposit suitability maps for underground hydrogen storage. The results show that the applied method significantly influences the resulting map image, helping to identify optimal locations for hydrogen storage facilities. The presented approach may be of value to governmental institutions considering underground hydrogen storage, geological services, power plants producing electricity from renewable energy sources, and chemical and petrochemical plants.

Role of geochemical reactions on caprock integrity during underground hydrogen storage

Underground hydrogen storage in depleted gas reservoirs is a promising and economical option for large-scale renewable energy storage to achieve net-zero carbon emission. While caprock plays an important role in sealing capacity, current knowledge is still limited on the effect of H2-brine-rock geochemical interactions on caprock integrity, raising concerns about the viability of long-term UHS. To address this problem, we developed kinetic batch models to characterize the time-dependent redox-reactions which are unique for underground hydrogen storage. This is combined with analytical estimates for the extent of hydrogen penetration into caprock. Our results show that the dissolution degrees of all tested minerals in three types of shales are <1 % in 30 years, indicating a strong caprock integrity and containment ability during underground hydrogen storage from a geochemical perspective. Reactive transport calculations indicate that hydrogen only affects a few metres of the caprock above the reservoir, so that storage integrity of thick caprocks will be unaffected. Similarly, the overall amount of hydrogen penetrating into caprock is likely to be a tiny fraction of the amount stored, typically much <1 %. Overall, our results suggest that H2-brine-shale geochemical interactions may not compromise caprock integrity during underground hydrogen storage.

Underground hydrogen storage to balance seasonal variations in energy demand: Impact of well configuration on storage performance in deep saline aquifers

Grid-scale underground hydrogen storage (UHS) is essential for the decarbonization of energy supply systems on the path towards a zero-emissions future. This study presents the feasibility of UHS in an actual saline aquifer with a typical dome-shaped anticline structure to balance the potential seasonal mismatches between energy supply and demand in the UK domestic heating sector. As a main requirement for UHS in saline aquifers, we investigate the role of well configuration design in enhancing storage performance in the selected site via numerical simulation. The results demonstrate that the efficiency of cyclic hydrogen recovery can reach around 70% in the short term without the need for upfront cushion gas injection. Storage capacity and deliverability increase in successive storage cycles for all scenarios, with the co-production of water from the aquifer having a minimal impact on the efficiency of hydrogen recovery. Storage capacity and deliverability also increase when additional wells are added to the storage site; however, the distance between wells can strongly influence this effect. For optimum well spacing in a multi-well storage scenario within a dome-shaped anticline structure, it is essential to attain an efficient balance between well pressure interference effects at short well distances and the gas uprising phenomenon at large distances. Overall, the findings obtained and the approach described can provide effective technical guidelines pertaining to the design and optimization of hydrogen storage operations in deep saline aquifers.

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.

Cavern integrity for underground hydrogen storage in the Brazilian pre-salt fields

Over the years, energy has depended on petroleum-based fuels. However, global warming and the energy crisis have drastically impacted the markets. It urges investing in renewable energy resources, such as hydrogen. Therefore, this work focuses on the hydrogen storage process in salt caverns, as these rocks have relevant properties, such as low permeability, relevant creep, and self-healing. A workflow for cavity integrity analysis is proposed. Hydrogen storage provokes variations in temperature and pressure inside the cavern. The gas thermodynamics is represented through a diabatic solution, which updates the gas pressure and temperature at each time step. The thermomechanical formulation is implemented into an in-house framework GeMA, which couples different physics. Four case studies are analyzed, and the discussions compared mechanical and thermomechanical models. Results demonstrate the importance of thermal effects, as temperature amplitudes may compromise rock integrity, for instance, inducing tensile stresses and affecting permeability.

Assessing and modeling hydrogen reactivity in underground hydrogen storage: A review and models simulating the Lobodice town gas storage

Underground Hydrogen storage (UHS) is a promising technology for safe storage of large quantities of hydrogen, in daily to seasonal cycles depending on the consumption requirements. The development of UHS requires anticipating hydrogen behavior to prevent any unexpected economic or environmental impact. An open question is the hydrogen reactivity in underground porous media storages. Indeed, there is no consensus on the effects or lack of geochemical reactions in UHS operations because of the strong coupling with the activity of microbes using hydrogen as electron donor during anaerobic reduction reactions. In this work, we apply different geochemical models to abiotic conditions or including the catalytic effect of bacterial activity in methanogenesis, acetogenesis and sulfate-reduction reactions. The models are applied to Lobodice town gas storage (Czech Republic), where a conversion of hydrogen to methane was measured during seasonal gas storage. Under abiotic conditions, no reaction is simulated. When the classical thermodynamic approach for aqueous redox reactions is applied, the simulated reactivity of hydrogen is too high. The proper way to simulate hydrogen reactivity must include a description of the kinetics of the aqueous redox reactions. Two models are applied to simulate the reactions of hydrogen observed at Lobodice gas storage. One modeling the microbial activity by applying energy threshold limitations and another where microbial activity follows a Monod-type rate law. After successfully calibrating the bio-geochemical models for hydrogen reactivity on existing gas storage data and constraining the conditions where microbial activity will inhibit or enhance hydrogen reactivity, we now have a higher confidence in assessing the hydrogen reactivity in future UHS in aquifers or depleted reservoirs.

Evaluating the hydrogen storage potential of shut down oil and gas fields along the Norwegian continental shelf

The underground hydrogen storage (UHS) capacities of shut down oil and gas (O&G) fields along the Norwegian continental shelf (NCS) are evaluated based on the publicly available geological and hydrocarbon production data. Thermodynamic equilibrium and geochemical models are used to describe contamination of hydrogen, loss of hydrogen and changes in the mineralogy. The contamination spectrum of black oil fields and retrograde gas fields are remarkably similar. Geochemical models suggest limited reactive mineral phases and meter-scale hydrogen diffusion into the caprock. However, geochemical reactions between residual oil, reservoir brine, host rock and hydrogen are not yet studied in detail. For 23 shut down O&G fields, a theoretical maximum UHS capacity of ca. 642 TWh is estimated. We conclude with Frigg, Nordost Frigg, and Odin as the best-suited shut down fields for UHS, having a maximum UHS capacity of ca. 414 TWh. The estimates require verification by site-specific dynamic reservoir models.

Sulfate reduction and homoacetogenesis at various hypersaline conditions: Implications for H2 underground gas storage

While interest in underground gas storage (UGS) of hydrogen (H2) in salt caverns is increasing in a growing H2 economy, knowledge of the microbial communities inhabiting those hypersaline environments is still scarce. High salt concentrations and limited availability of carbon (C) sources in cavern environments reduce microbial growth rates and metabolic activities. Growth conditions potentially change once H2 is stored in salt caverns. H2 is a universal electron donor that can facilitate autotrophic growth and subsequently growth of heterotrophs. In this study, a mixed culture enriched from hypersaline UGS sites was investigated in microcosm experiments with H2 atmosphere, testing the effect of different salt concentrations and C sources on methanogenesis, sulfate reduction and homoacetogenesis. Sulfate, acetate and lactate concentrations were quantified throughout a time span of 125 days of incubation and correlations with the microbial community structure and function were explored through 16S rRNA gene-based amplicon sequencing at the end of the experiment. Many of the amplicon sequence variants (ASVs) were only assigned to family or order level, reflecting that a large number of ASVs belong to previously undescribed taxa. At 4.4 M NaCl, close to cavern brine salinity, members of the Desulfovibrionales were absent when no C source other than CO2 was offered as the sole C source. This is in line with the finding that no sulfate reduction occurred at these conditions. Acetogenic Halanaerobiia dominated in these high salinity levels. Based on metagenome sequencing of four selected samples, we found that acetogenesis at autotrophic conditions relies on the activity of a halophilic homoacetogen, Acetohalobium sp. and that sulfate reduction can most likely be associated with a so far undescribed member of the Desulfonatronovibrionales. We further discuss the discrepancy between sulfate reduction at heterotrophic conditions, while no sulfate reduction was observed under autotrophic conditions although acetate was produced through the homoacetogenic activity of Acetohalobium. For the application of UGS of H2, this means that the presence and activity of the aforementioned microorganisms must be investigated, as they can eventually lead to the formation of acetate and allow sulfate reduction at relevant concentrations.

Coupled model for microbial growth and phase mass transfer in pressurized batch reactors in the context of underground hydrogen storage.

A rising interest in a strong hydrogen economy as a part of the future net-zero economy results in an increasing necessity to store hydrogen as a raw material or an energy carrier. Experience and studies show that storing hydrogen in deep underground sites could enable microbial conversion of hydrogen. To predict and examine the loss of hydrogen, laboratory studies, and analysis are essential. A growth model is required to interpret batch or chemostat experiments. With this model, the parameters of microbial growth, and the conversion of hydrogen can be specified. This study presents experiments with methanogens and a hydrogen/carbon dioxide gas mixture performed in batch reactors. Further, the microbial growth was modeled by a double Monod model with hydrogen and carbon dioxide as the limiting substrates. As the amount of carbon dioxide dissolved in the water phase can not be neglected, both phases were considered in the proposed model. The mass-transfer rate between the gas and water phase was implemented by a linear relation including the concentrations in both phases and the mass-transfer coefficient. With the resulting coupled model, it was possible to match the pressure behavior in the reactor and conclude the microbial growth kinetics. Two types of methanogenic species were tested to validate the model. The mass transfer coefficient proves to impact the growth behavior in porous media. The mathematical model and experimental data are necessary to determine the growth rate and yield coefficient.

The drillstring dynamic frequency domains modes and mode shapes characteristics of compound drilling for the high-quality slim borehole

High-quality borehole is crucial to hydrogen underground storage (HUS) and oil & gas development, while compound drilling plays an important role in improving borehole quality. The modal model of compound drillstring in slim borehole is established by using finite element method to analyze the modal of longitudinal vibration, lateral vibration and torsional vibration. The results shows that as the number of order increases, the intrinsic frequency of the three vibrations increases. The amplitude of axial vibration is the largest, and the amplitude of lateral vibration is smallest. The natural frequency of drillstring in slim borehole decreases as drillstring length increasing. The longer drillstring is, the smaller the interval frequency between the intrinsic frequencies of orders will be, and it is easier to cause resonance. The axial vibration will cause minimal damage to the HUS quality. Lateral vibration has the greatest damage to wellbore quality, and is the most unfavorable for the establishment of HUS channels. The damage of torsional vibration to the HUS is less than the lateral vibration and larger than axial vibration. The higher the vibration frequency and amplitude, the harder it is to improve the HUS quality. In order to improve the quality of HUS, the weight on bit (WOB) and rotary per minutes (RPM) should be adjusted at the same time for lateral shock, and the WOB should be mainly reduced for controlling the axial and torsional vibration. The results are benefit for the drillstring design, improving the wellbore quality and HUS quality.

Guest Editorial: How To Leverage E&amp;P Expertise for the New Energy Economy

_ The term “new energy economy” broadly refers to the transition to a low-carbon future for sustaining human development while reducing CO2 emissions. Such a shift is considered to be the third energy transition of the modern era, after the shift from biomass to coal as the primary source of energy in the early 1900s, followed by oil overtaking coal’s dominant position in the 1960s–1970s. This trend towards decarbonization (i.e., diversification from carbon-intensive fossil fuels to sustainable greener energy feedstocks and carriers) is motivated by the understanding that emissions need to be reduced to moderate the potential impacts of global temperature rise on future climatic changes. Strategies common to proposed decarbonization pathways include - Improving energy efficiency (i.e., slower increase in energy demand compared to GDP/population increase). - Increasing energy supply from renewable sources (i.e., wind, solar, geothermal, nuclear) coupled with hydrogen underground storage (HUS) as a way of storing surplus electrical energy. - Switching to low-carbon energy carriers (i.e., hydrogen) for end-use applications in transportation, buildings, and industry. - Removing carbon emissions, via carbon capture, utilization, and storage (CCUS), from fossil-fuel-fired power plants and hard-to-abate industrial sources. The key takeaway for readers is how the two subsurface-oriented decarbonization strategies—CCUS and HUS—are relevant for application/adaptation of expertise from the exploration and production (E&amp;P) sector of the oil and gas industry. Their rise will be built upon decades of experience with CO2-EOR, gas injection, produced-water disposal, and underground natural gas storage (NGS). Carbon Capture, Utilization and Storage (CCUS) As shown in Fig. 1, CCUS involves capturing CO2 from a fossil-fuel-fired power plant or industrial facility and processing it to a practically pure form, transporting it to a nearby geologic storage site using pipelines, and injecting it into saline aquifers for long-term sequestration or depleted oil/gas fields for enhanced oil recovery (EOR) and associated storage. Research and field demonstration projects over the past few decades have demonstrated that CCUS is a viable technology for curtailing atmospheric CO2 emissions buildup. Some of the key elements of CCUS projects and their overlap with corresponding E&amp;P expertise are summarized below.

The drillstring dynamic time domains harmonic response and acceleration characteristics of compound drilling for the high-quality slim borehole

The harmonic response and acceleration characteristic of drillstring is established to improve borehole quality for the hydrogen underground storage (HUS). The harmonic response laws of drillstring is discussed. Harmonic response analysis includes non-failure case and failure case. Absorber control measure is simulated to lower vibration amplitude of drillstring. The drill string collides violently with the wellbore reduces the wellbore quality and increases the unreliability of the HUS. Lateral harmonic response has the greatest damage to well wall. Torsional harmonic response causes less damage than lateral vibration. High WOB (weight on bit) and high RPM (rotary per minute) are not conducive to the quality of HUS. In course of designing drilling parameter, it is required to avoid or reduce drillstring resonance under low-order inherent frequency as much as possible. The research result is of much significance to improve wellbore quality of hydrogen underground storage.

The Uncertain Bright Future of Underground Hydrogen Storage

The most obvious obstacles to a big ramp-up in global hydrogen production are well known. They include technological breakthroughs to bring down production costs along with new sources of demand from the power and transportation sectors. Less obvious is that a small army of reservoir engineers, geologists, and other subsurface experts will be needed to understand where and how tomorrow’s hydrogen hubs will store their clean-burning fuel. Bulk storage on the surface is considered by many experts to be simply out of the question. That means large hydrogen projects will need a subsurface component, and some think depleted oil and gas fields—with an emphasis on the latter—may fit the bill. Saline aquifers are being eyed for the role too. But as this all suggests, no one has ever attempted to use these formations for hydrogen storage. Just four shallow salt formations, three salt domes in Texas and one salt field in the UK, represent the totality of the world’s hydrogen underground storage (HUS) capacity. Research is underway to expand HUS in salt formations but that will not solve for the fact that they are not a geologic option for many locations where big industrial players are hoping to produce hydrogen. This includes most of Europe and most of the US outside of its Gulf Coast states. By contrast, deeper sedimentary structures of various flavors are in no short supply but lack any material field experience that might help jumpstart the de-risking of storing several Bcf of hydrogen. The upstream industry’s extensive experience in operating what are the closest analogues—natural gas storage and carbon capture and storage (CCS)—will help that process but there are new challenges when it comes to injecting the universe’s smallest molecule into porous media. Topping the list is hydrogen’s strong propensity to migrate inside a reservoir (laterally and vertically) along with the potential for troublesome chemical and biological reactions. Hydrogen may also be clean burning but it offers only about a third of the energy density as methane, which means it needs roughly three times the storage volume to deliver the same energy output to a gas-fired power plant. Among those working to bring clarity to such issues is Mojdeh Delshad, a reservoir engineer and professor at The University of Texas at Austin. Her latest research involved using commercial reservoir simulators to model what would happen if selected gas fields and saline aquifers in the US used for CCS or natural gas storage were instead used to store hydrogen. “We wanted to know about the challenges of hydrogen, which because of its properties—very low density, very low viscosity—is going to move in the reservoir much more quickly than CO2 and methane. And that’s exactly what we found, which means we’re going to have to do something differently with hydrogen storage in order to capture and produce what is injected,” said Delshad.

Research of cement slurries for sealing casing strings in underground hydrogen storage facilities in depleted hydrocarbon reservoirs

Prezentowany artykuł omawia zagadnienia dotyczące technologii zaczynów cementowych proponowanych do uszczelniania kolumn rur okładzinowych w podziemnych magazynach wodoru w sczerpanych złożach węglowodorów. Do badań laboratoryjnych wytypowano dziesięć receptur zaczynów zawierających różne dodatki i domieszki (m.in. nanomateriały, tj. nano-SiO2, nano-Al2O3, lateksy, polimery wielkocząsteczkowe). Badania receptur prowadzono w temperaturze 60°C pod ciśnieniem 25 MPa, stosując w składach zaczynów domieszkę odpieniającą, upłynniającą, antyfiltracyjną oraz opóźniacz wiązania. Badania wykonywano na dwóch rodzajach cementów: portlandzkim CEM I 42,5 oraz wiertniczym klasy G. Określano parametry technologiczne świeżych i stwardniałych zaczynów cementowych, badając: gęstość, odstój wody (wolną wodę), reologię, czasy gęstnienia, a także wytrzymałość na ściskanie, porowatość oraz szczelność rdzeni cementowych względem wodoru. Płynne zaczyny cementowe posiadały prawidłowe parametry technologiczne (były dobrze przetłaczalne w warunkach HPHT, a ich gęstości wynosiły 1,80–1,91 g/cm3). Wytrzymałości na ściskanie stwardniałych zaczynów cementowych po okresie od 2 dni do 28 dni hydratacji, zwłaszcza w przypadku próbek z dodatkiem nanokomponentów, przyjmowały bardzo wysokie wartości (po 28 dniach przekraczając 40 MPa). Próbki kamieni cementowych posiadały bardzo niską zawartość porów kapilarnych, co ogranicza możliwość tworzenia się kanalików w płaszczu cementowym otworu wiertniczego. W większości próbek pory o najmniejszych rozmiarach (poniżej 100 nm) stanowiły zdecydowaną większość (powyżej 95–97%) ogólnej ilości porów występujących w matrycy cementowej. Najkorzystniejsze parametry technologiczne uzyskano w przypadku próbek zawierających nano-SiO2 (nanokrzemionkę), a optymalny współczynnik wodno-cementowy dla takich zaczynów kształtował się na poziomie około 0,46–0,48 – w zależności od rodzaju zastosowanego cementu. Najniższe wartości przenikalności dla wodoru zanotowano dla receptur zawierających nanokrzemionkę (nano-SiO2). Receptury o najlepszych parametrach technologicznych, zawierające nanokomponenty (po wykonaniu szczegółowych testów), będą mogły znaleźć zastosowanie podczas uszczelniania rur okładzinowych w otworach wierconych w celu magazynowania wodoru.

Comprehensive study of the underground hydrogen storage potential in the depleted offshore Tapti-gas field

Comprehensive study of the underground hydrogen storage potential in the depleted offshore Tapti-gas field

Effect of relative permeability hysteresis on reservoir simulation of underground hydrogen storage in an offshore aquifer

Underground hydrogen storage (UHS) in porous media is proposed to balance seasonal fluctuations between demand and supply in an emerging hydrogen economy. Despite increasing focus on the topic worldwide, the understanding of hydrogen flow in porous media is still not adequate. In particular, relative permeability hysteresis and its impact on the storage performance require detailed investigations due to the cyclic nature of H2 injection and withdrawal. We focus our analysis on reservoir simulation of an offshore aquifer setting, where we use history matched relative permeability to study the effect of hysteresis and gas type on the storage efficiency. We find that omission of relative permeability hysteresis overestimates the annual working gas capacity by 34 % and the recovered hydrogen volume by 85 %. The UHS performance is similar to natural gas storage when using hysteretic hydrogen relative permeability. Nitrogen relative permeability can be used to model the UHS when hysteresis is ignored, but at the cost of the accuracy of the bottom-hole pressure predictions. Our results advance the understanding of the UHS reservoir modeling approaches.

Calcite–Fluid Interfacial Tension: H2 and CO2 Geological Storage in Carbonates

Underground hydrogen storage (UHS) and CO2 geological storage (CGS) are two outstanding techniques for meeting the universal energy demand and reducing anthropogenic greenhouse gases (GHGs). In this context, the calcite–fluid interfacial tension (γcalcite–fluid) is a critical parameter for gas s torage in carbonate formations as it affects the spreading and flow of fluids in porous media, gas injection/withdrawal rate, gas storage capacity, and containment safety. However, there is a scarcity of γcalcite–fluid data (e.g., γcalcite–gas and γcalcite–water for carbonate/gas/water systems) at geological conditions in the literature. In addition, there is no independent experimental method to measure γrock–fluid; thus, advancing and receding contact angles are often used to calculate it by a combination of Neumann’s equation of state and Young’s equation. We, therefore, theoretically calculated γcalcite–fluid as a function of the main geological parameters, including temperature, pressure, organic acid concentration, and salinity for calcite/H2/water and calcite/CO2/water systems. We recognized that γcalcite–gas decreased with pressure, salinity, and organic acid concentration but increased with temperature. Also, a slight increase in γcalcite–water with organic acid concentration and salinity was noticed at 15 MPa, 323.15 K, and 10 MPa, 323.15 K, respectively. However, γcalcite–water slightly decreased with temperature, assuming that it remained constant with pressure. Furthermore, the values of γcalcite–fluid for a H2/brine system were more than those for a CO2/brine system. This work thus provides a deep understanding of the wetting characteristics at calcite/H2/water and calcite/CO2/water interfaces and leads to a better investigation of H2/CO2 storage in carbonate formations.