Salt Cavern Storage Research Articles

Research on the development of cement slurries for underground hydrogen storage in salt caverns

Artykuł przedstawia wyniki badań nad opracowaniem zaczynów cementowych przeznaczonych do podziemnego magazynowania wodoru w kawernach solnych. Receptury cementowe opracowane zostały w Instytucie Nafty i Gazu – Państwowym Instytucie Badawczym w Laboratorium Zaczynów Uszczelniających. Badania przeprowadzono dla temperatury 45°C i ciśnienia 10 MPa. W badanych zaczynach cementowych jako spoiwo wiążące zastosowano cement wiertniczy G. Zaczyny cementowe sporządzano na solance o pełnym nasyceniu o gęstości 1,2 g/cm3 ze względu na bezpośrednią obecność soli w otworze. Do solanki dodawano kolejno środki: odpieniający, upłynniający i obniżający filtrację. Pozostałe składniki: mikrocement, gips modelowy oraz cement mieszano ze sobą i wprowadzano następnie do wody zarobowej. W przypadku każdego zaczynu cementowego wykonywano badania parametrów technologicznych, takich jak: właściwości reologiczne, gęstość, rozlewność, odstój wody oraz czas gęstnienia zaczynu. Przeprowadzano również badania wytrzymałości na ściskanie po 2 dniach oraz po 3, 5 i 8 miesiącach, a także pomiar porowatości stwardniałych zaczynów cementowych po 8 miesiącach deponowania we w pełni nasyconej solance. Na opracowanych zaczynach wykonano również badanie szczelności stwardniałego zaczynu cementowego dla wodoru. Opracowane zaczyny cementowe charakteryzowały się dobrymi parametrami reologicznymi oraz zerowym odstojem wody. Gęstości zaczynów cementowych wahały się w przedziale od 1900 kg/m3 do 1910 kg/m3. Wszystkie zbadane stwardniałe zaczyny cementowe charakteryzowały się zwartą mikrostrukturą o niskiej zawartości makroporów. Udział porów o średnicy powyżej 10 000 nm wyniósł od 1,9% do 2,5% ilości wszystkich porów. Natomiast udział porów o średnicy poniżej 100 nm w całej matrycy stwardniałego zaczynu cementowego wyniósł od 95,9% do 96,9%. Średni strumień objętości przepływu wodoru przez stwardniały zaczyn cementowy miał wartość od 0,686 cm3/min do 6,85 cm3/min. Dla ustabilizowanych wartości strumienia objętości przepływu obliczono współczynniki przepuszczalności. Średnie wartości współczynnika przepuszczalności dla stwardniałego zaczynu cementowego wynosiły od 0,0000281 mD do 0,000284 mD, co świadczy o dobrej szczelności uzyskanych stwardniałych zaczynów cementowych.

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.

A comprehensive evaluation of wind-PV-salt cavern-hydrogen energy storage and utilization system: A case study in Qianjiang salt cavern, China

With global energy consumption increasing year by year, the industrial sectors of the world’s countries have never been more urgent in achieving carbon reduction. Renewable energy plays a crucial role in the industrial decarbonization process. As the most mature renewable energy technology, wind and photovoltaic power generation have made significant progress in recent years. However, the intermittent characteristics hinder the efficient use of renewable energy. Existing research provides sufficient support for the flexible scheduling of large-scale renewable energy. Hence, this paper proposes a combined energy system composed of wind power-photovoltaic-energy storage salt cavern with hydrogen as the energy scheduling carrier. The system mainly realizes energy conversion through electrolytic water equipment and fuel cells. Then, Qianjiang City, Hubei Province, is taken as the analysis object, and the working conditions of each component in the system are optimized with the help of an improved particle swarm optimization algorithm. According to the results, the system’s contribution to the energy system is discussed, and the system's economy and carbon reduction effect is studied. The analysis proves that the improved particle swarm optimization algorithm has a stronger solving ability. The combined energy system can effectively improve the economy and renewable energy utilization rate, meet the regional electricity demand, and significantly reduce carbon emissions. The economic analysis of the system shows that the operation and maintenance cost of hydrogen storage salt caverns accounts for the largest proportion of the total cost, about 60 %. Compared with several existing large-scale energy storage technologies, it is found that the energy efficiency of the whole system is only about 40 % due to the limitation of technology maturity. Nevertheless, the flexibility of the hydrogen storage system layout is relatively high. The required underground space volume is only equivalent to 1/6 and 1/2 of pumped storage and compressed air storage with the same scheduling capacity. The system will provide a theoretical support for the optimization of energy pattern and layout.

Hydrogen and air storage in salt caverns: a thermodynamic model for phase equilibrium calculations

When storing gas in a salt cavern, it occupies most of the excavated volume, but the lower part of the cavern inevitably contains residual brine, in contact with the gas. The design of hydrogen and compressed air storage in salt caverns requires to have a thermodynamic model able to accurately predict both phase properties such as densities, and phase equilibrium (gas solubility and water content of the vapour phase). This work proposes a parameterization of the e-PPC-SAFT equation of state in this context. Experimental data of pure components and mixtures of light gas + pure water and light gas + salted water are reviewed and used to fit pure component parameters for hydrogen, nitrogen, oxygen, and the brine, and binary interaction parameters between H2, O2, N2 + water and H2, O2, N2 + ions (Na+ and Cl−), for temperature ranging from 273 to 473 K and salinities up to NaCl saturation (6 mol/kg). The model developed delivers good accuracy in reproducing data: the average deviation between experiments and calculated data is between 3% and 9% for gas solubility in saturated brine. More interestingly, the model has been validated on its capability to predict data not included in the parameterization database, including the composition of the vapor phase, and its extension to a mixture, such as air. Finally, it has been used in a case study of Compressed Air Energy Storage (CAES) to evaluate the water content of the gas produced during injection-withdrawing cycles.

Viscoelastic analysis of surface deformation above salt caverns for gas storage based on semi-infinite space

The construction of salt caverns for energy storage is of strategic significance, but the operation of underground gas storages in salt formations will cause surface deformation. The research and analysis of surface deformation is an important part of the stability evaluation of salt caverns for gas storage. From the perspective of classical mechanics theory, the analytical solution of surface deformation above salt caverns for gas storage is deduced. The surface displacement caused by the contraction of a salt cavern is regarded as the boundary displacement caused by the surface force acting on a spherical cavern in a semi-infinite space. The equivalent conversion of load form is carried out based on the mirror principle. The vertical subsidence and horizontal displacement of the surface of the elastic semi-infinite space is obtained. According to the elastic-viscoelastic correspondence principle, the viscoelastic solution of the surface displacement of the semi-infinite body, regarded as Maxwell body, can be obtained. A numerical model of a salt cavern for gas storage is established based on the engineering practice. The results of the analytical solution and the numerical simulation are compared and analyzed to verify the accuracy of the analytical solution. The analytical solution was applied to predict the surface displacement above a group of caverns, and the influence of the layout of salt caverns and cavern center spacing on the surface displacement is analyzed. The research results show that the regular triangular layout is slightly better than the square layout. The larger the cavern center spacing, the smaller the maximum surface subsidence. The proposed theoretical prediction model can provide a theoretical basis for controlling surface deformation for the construction of gas storage caverns.

Analysis of damage characteristics and energy evolution of salt rock under triaxial cyclic loading and unloading

The gas injection, water-soluble excavation, and gas recovery process in the gas storage salt cavern can be regarded as the loading and unloading process of the surrounding rock stress. By conducting triaxial loading and unloading tests on salt rock samples, several findings are presented: 1) The failure formed in the rock sample is a shear failure mode when confining pressure is below 15 MPa, and after confining pressure exceeds 15 MPa, it is bulging in the middle part of sample. The scientific strain is proved to be more suitable for describing the deformation of salt rock sample than the engineering strain. 2) During the unloading-reloading process, the produced stress difference is small at the beginning of unloading, while the rock undergoes more stress loss in the post-peak stage than that in other stages. 3) When the strain increases to reach a specific value, the dissipative energy difference increases with higher confining pressure. 4) Higher confining pressure improves the initial damage degree to the sample. But under different confining pressures, the damage variable has a similar evolution trend, which reaches a steady growth stage with the loading/unloading cycles gradually.

Failure mode of cement sheath in salt cavern gas storge wellbore based on coupling plasticity and damage evolution

In this paper, the failure mechanism of the cement sheath in gas storage salt caverns under the cyclic internal pressure and cavity shrinkage was explored. First, an elastoplastic damage evolution model for the completion cement was established and further developed as a constitutive equation for numerical calculation. Second, the verification of the model is completed by mechanical tests and numerical examples, respectively. The uniaxial and triaxial compression tests, Brazilian splitting tests, and cyclic loading tests were performed to verify the theoretical stress-strain curves. Numerical examples were performed to verify the stability of the constitutive equation in numerical simulations. Finally, the constitutive equation is applied to the engineering, and the numerical model calculation of wellbore fatigue damage and salt cavity shrinkage was performed. The following conclusions are obtained: cyclic loading will increase the plastic strain of the cement sheath, and micro-annuluses will form on the inner surface after 25 years of operation. The shrinkage of the salt cavity will debond the outer side of the cement sheath near the open well. With the increase of cavity shrinkage, the range of wellbore failure increases upwards. When the cavity shrinkage rate exceeds 10%, partial debonding will occur on the cemented surface between the cement sheath and the rock salt formation, which may provide a channel for natural gas leakage.

Blowout Prediction on a Salt Cavern Selected for a Hydrogen Storage Pilot

To prevent climate change, Europe and the world must shift to low-carbon and renewable energies. Hydrogen, as an energy vector, provides viable solutions for replacing polluting and carbon-emitting fossil fuels. Gaseous hydrogen can be stored underground and coupled with existing natural gas pipe networks. Salt cavern storage is the best suited technology to meet the challenges of new energy systems. Hydrogen storage caverns are currently operated in the UK and Texas. A preliminary risk analysis dedicated to underground hydrogen salt caverns highlighted the importance of containment losses (leaks) and the formation of gas clouds following blowouts, whose ignition may generate dangerous phenomena such as jet fires, unconfined vapor cloud explosions (UVCEs), or flashfires. A blowout is not a frequent accident in gas storage caverns. A safety valve is often set at a 30 m depth below ground level; it is automatically triggered following a pressure drop at the wellhead. Nevertheless, a blowout remains to be one of the significant accidental scenarios likely to occur during hydrogen underground storage in salt caverns. In this paper, we present modelling the subterraneous and aerial parts of a blowout on an EZ53 salt cavern fully filled with hydrogen.

Shape design and safety evaluation of salt caverns for CO2 storage in northeast Thailand

Salt caverns are an adequate solution for the sequestration of CO2 (large capacity, safety and long-term operation). The large rock salt deposits of the Maha Sarakham Formation represent a very promising location. Designing salt caverns is still a complex issue. In this paper, the stability of typical cavern shapes (spherical, cylindrical, teardrop, bulb, and pear) was evaluated based on displacement, von Mises stress, safety factor, and volume change. The analysis aimed to find the optimal cavern shape for salt deposits at Ban Nong Plue, Borabue district, Maha Sarakham province, northeast Thailand. The Finite Element simulations investigating the cavern stability are carried out for a time span of 600 years (> 500 years is considered permanent storage). The bulb-shaped cavern yielded the best results, indicating that it constitutes the optimal shape in the given geological conditions. The stability of all analyzed caverns showed a dependence on the operating stage. Each stability factor exhibited large differences between the periods of cavern construction/brine discharge and pre-pressurization by CO2 injection. A lower cavern pressure negatively affected the evaluated factors. The results can be useful in planning future cavern fields for CO2 storage (and other gases) in salt deposits.

Mathematic modeling of the salt deposits growing on the tubing during debrining for gas storage salt cavern

Salt deposits growth during debrining of salt cavern construction may block the debrining inner tubing (DIT) and influence the efficiency of debrining. A novel coupled model for the salt deposits growing on the DIT during debrining is built according to the salt deposits growth mechanisms and heat transfer principle. A finite element model is proposed, which considers the coupling of salt deposits growth and of brine heat transfer. A device used to simulate the salt deposits growing on the tubing during debrining was developed and a simulating experiment was carried out. The model is validated by experimental results. The relative error of salt deposits total masses on the debrining tubing between the model result and the experimental result is 3 %. A-1 cavern of Jintan UGS is taken as an example. The rules of salt deposits growing and brine temperature changing were researched. Results show that the salt deposits thicknesses increase with the decrease of depth. It is similar to the experimental results. The salt deposits thicknesses maximum is 6.86 mm after continuous debrining for 24 h, much less than the radius of the DIT. It is suggested to increase the continuous debrining time to 24 h for increase the efficiency of the debrining. This study can provide a theoretical foundation and a technological reference for predicting the salt deposits growth during debrining.

Study on thermodynamic behaviour of natural gas and thermo-mechanical response of salt caverns for underground gas storage

Using salt caverns for underground gas storage (UGS) is an important energy storage solution. A coupled aero-thermo-mechanical (ATM) model with an integrated wellbore–3D realistic cavern geometry was established to investigate the thermodynamic behaviour of natural gas and the thermo-mechanical response of rock salt for UGS caverns. Unlike classical thermo-gas-mechanical (TGM) models that assume the cavern gas is an ideal gas and in an isotropic thermodynamic state, the ATM model solved thermodynamic properties for the real gas, and revealed the tempo-spatial varying gas state and its mechanism. Predictions of gas temperature, pressure and flux by ATM modelling well captured the in-situ measurements obtained by the distributed optical cable monitoring system during a one-month field testing at Jintan UGS site. Effects of the tempo-spatial varying gas state on the mechanical response were unveiled by ATM modelling. Predictions of mechanical response by TGM modelling shared similar patterns as that by ATM modelling, however, the TGM model tended to underestimate the risk of creep failure, tensile failure, fatigue failure and plastic damage due to the isotropic gas state. The proposed model could be used to improve the thermodynamic and mechanical predictions that are pertinent to the optimal design and the stability of caverns.

Failure mechanism of gas storage salt cavern cement sheath under the coupling effect of plasticity and fatigue damage

Due to their good air tightness and stability, gas storage salt caverns are widely used in rapid peak shaving of natural gas. The wellbore is used to connect the cavern to the surface pipeline, and its integrity can usually be guaranteed after cementing and can be verified by logging. In gas injection and production, the tightness of the cement sheath will deteriorate, which may lead to gas leakage accidents. To explore the wellbore integrity during operations, a theoretical model considering fatigue damage and plasticity is established, and constitutive equations are developed for numerical simulation. The model in this paper has been verified by mechanical tests and has good stability and accuracy. Through experiments and simulations, the following conclusions are drawn: (1) The coupling of plasticity and damage can rapidly lead to failure of the wellbore cement sheath interface. Only calculating plasticity or damage may overestimate the integrity of the cement sheath. (2) Fatigue damage and plastic strain under cyclic loading will be concentrated locally, mainly at the interface between the cement sheath and the casing, that is, the inner cemented surface is more likely to fail. (3) The plasticity and damage evolution of the cement sheath have different sensitivities to different cementing defects. Low-quality cementing such as lack of cement sheath will lead to rapid accumulation of wellbore plastic strain and damage. However, casing deviation does not increase plasticity and damage evolution.

Projecting the levelized cost of large scale hydrogen storage for stationary applications

Hydrogen as an energy vector is considered to be an attractive solution for sustainable energy systems - provided, of course, that the energy is from renewable resources. As for all energy systems, this would require energy storage to alleviate the supply and demand disparity within the energy value chain. Despite a great deal of effort to reduce the cost of hydrogen generation, there has been relatively little attention paid to the cost of hydrogen storage. This article determines the levelized cost of hydrogen storage (LCHS) for seven technologies based on the projected capital expenditure (CapEx), operational expenditure (OpEx), and decommissioning cost. Our analysis quantitatively demonstrates the impact of different storage cycle lengths on storage system economics, with LCHS dramatically increasing for long-term storage despite a radical decrease in OpEx cost. For example, the LCHS of above-ground compressed gaseous storage for a daily and 4-monthly storage cycle length is ∼$0.33 and ∼$25.20 per kg of H2, respectively. On the other hand, globally, most green hydrogen is produced by low-carbon electricity primarily based on intermittent solar and wind, and the average levelized cost of hydrogen production ranges from ∼$3.2 to ∼$7.7 per kg of H2. Thus, the storage costs are much higher than the generation cost for long-term storage. Storage in salt caverns exhibits the lowest LCHS at ∼$0.14/kg of H2 for daily storage, followed by above-ground compressed gaseous storage. On the other hand, ammonia has the highest LCHS ∼$3.51/kg of H2, followed by methanol ∼$2.25/kg of H2. These costs are expected to stay relatively high; our CapEx prediction suggests that by 2050 the LCHS of ammonia and methanol could decrease by 20–25%. Furthermore, storage efficiency for ammonia is the lowest at ∼42%, followed by methanol at ∼50%, while compressed gaseous shows the highest storage efficiency, at ∼92%. Overall the analysis shows that the cost of hydrogen storage would need to be significantly reduced for applications in long-term storage or if ammonia/methanol are used (due to, for example, compatibility with existing infrastructure). These insights could increase transparency around the future competitiveness of stationary storage technologies and help to guide research, policy, and investment activities to ensure cost-efficient deployment in a low-emission economy.

Nonlinear creep-damage constitutive model of surrounding rock in salt cavern reservoir

Salt cavern energy storage is a key technology to promote the optimization of China's energy reserve structure, but the surrounding rock of the reservoir cavity is prone to creep and damage during the long-term injection production process, which seriously endangers the safety of the reservoir operation. Therefore, it is urgent to carry out salt rock creep test research to reveal the creep mechanical properties and damage evolution failure mechanism of the surrounding rock of the reservoir cavity, so as to provide a theoretical basis for the safe construction and operation of the salt cavern reservoir. In order to deeply study the creep mechanical properties of salt rock, a long-term graded loading creep test was carried out on salt rock specimens. The loading time of each stage was about 30 days, and the total creep time exceeded 3 months. The long-term strength of salt rock is determined to be about 8 MPa by the improved isochronous stress-strain method and steady-state creep rate method. A nonlinear creep-damage constitutive model of salt rock based on elastic element and dashpot element is established and compared with the fitting results of several models for the sake of describing the creep behavior of salt rock more accurately. The local and global sensitivity analysis methods are applied to the model to verify its robustness and the rationality of parameter setting. The results showed that the fitting results of the model were in good agreement with the test data, and could well describe the whole creep process of salt rock, especially the nonlinear accelerated creep stage. In addition, the constitutive relation of the established model is simple, and the meaning of the model parameters is clear, which provides a theoretical basis for the study of the creep law of salt rock and the safe operation of the salt cavern storage.

Influence of loading history on creep behavior of rock salt

Creep is a vital factor that affects the long-term stability of gas storage salt caverns. When we conduct a laboratory creep test of rock salt, compared with the single-stage loading method, the multi-stage loading method is used more frequently as it eliminates the discreteness of the sample. However, the early loading history affects the later creep behavior when the multi-stage loading method is used. To study the influence of loading history on the creep behavior of rock salt, the multi-stage loading triaxial creep test of rock salt and synchronous acoustic emission test were performed. Then, the numerical sample is established based on the laboratory test results and the discrete element numerical simulation is carried out. Single-stage loading and multi-stage loading creep tests were carried out on the initial numerical samples, respectively. Finally, the multi-stage loading data processing methods were compared using numerical simulation data. The results indicate that: (1) the improved multi-stage loading data processing method works well and it is recommended to use this method to process the multi-stage loading creep data. (2) Cracks are more developed in multi-stage loading sample, which experienced an early loading history, than in samples under single-stage loading. The damage accumulation in rock salt leads to its mechanical properties deterioration, which makes the creep deformation more prone to occur in the later stage. (3) The steady-state creep rate of rock salt is independent of loading history, only related to stress and temperature. The effect of damage accumulation in the loading history is mainly reflected in the transient strain and the strain in the transient creep phase. The study is helpful to further understanding the influence of loading history of rock salt on its creep, and provides an important basis for the design, construction, and operation of gas storage salt caverns.

Communicating leakage risk in the hydrogen economy: Lessons already learned from geoenergy industries

Hydrogen is set to play a part in delivering a net zero emissions future globally. However, previous research finds that risk perception issues are particularly challenging for emerging and potentially unfamiliar technologies. Hydrogen as a fuel falls into this category. Thus, while the hydrogen value chain could offer a range of potential environmental, economic and social benefits, it is imperative that the roll-out of hydrogen fits with societal expectations of how risk ought to be managed—and by whom. Communication and engagement are critical to ensure 1) communities and stakeholders are able to come to informed decisions on hydrogen and 2) developers, operators and regulators are able to respond to societal concerns and adapt practices appropriately.Within the hydrogen value chain, geological storage may be an important step, but could present challenges in terms of perceived safety. Lessons can be learned from international research and practice of CO2 and natural gas storage in geological formations [for carbon capture and storage (CCS) and power respectively] which may be relevant to hydrogen storage in salt caverns or porous sandstones. We draw on these analogues to present potential societal risk perception issues which may arise for geological storage of hydrogen. We argue that site-specific communication and engagement strategies, underpinned by broad-based principles covering the entire span of the project and a clear rationale for how hydrogen benefits the climate and the most vulnerable members of society under an energy crisis, will be critical to fostering societal support for geological hydrogen storage.

Theoretical research on gas seepage in the formations surrounding bedded gas storage salt cavern

When constructing salt cavern gas or petroleum storage in lacustrine sedimentary salt formations rich in mudstone interlayers, the influence of the sealing performance of interlayers and salt-mud interface on the storage tightness should be considered adequately. In order to reveal the gas seepage in deep formations surrounding bedded salt cavern underground storage, a leakage analysis model was established based on the characteristics of a low dip angle and the interbedded structure of bedded rock salt. The gas seepage governing equations for one-dimensional and plane radial flow were derived and solved. A gas seepage simulation experiment was conducted to demonstrate the accuracy and reliability of the theoretical calculation results. The error of the seepage range was approximately 6.70%, which is acceptable. The analysis and calculation results indicate that the motion equation of gas in deep formations satisfies a non-Darcy's law with a threshold pressure gradient and slippage effect. The sufficient condition for the gas flow to stop is that the pressure gradient is equal to the threshold pressure gradient. The relationship between the leakage range and operating time is a positive power function, that is, the leakage range gradually increases with time and eventually stabilizes. As the seepage range increases, the seepage pressure decreases sharply during the early stage, and then decreases gradually until the flow stops. Combining the research results with engineering applications, three quantitative evaluation indexes named the maximum admissible leakage range, leakage volume and leakage rate are proposed for the tightness evaluation of gas storage salt cavern during their operating stage. These indexes can be used directly in actual engineering applications and can be compared with the key design parameters stipulated in the relevant specifications. This work is expected to provide theoretical and technical support for the gas loss and tightness evaluation of gas storage salt caverns.

Does the United Kingdom have sufficient geological storage capacity to support a hydrogen economy? Estimating the salt cavern storage potential of bedded halite formations

Hydrogen can be used to enable decarbonisation of challenging applications such as provision of heat, and as a fuel for heavy transport. The UK has set out a strategy for developing a new low carbon hydrogen sector by 2030. Underground storage will be a key component of any regional or national hydrogen network because of the variability of both supply and demand across different end-use applications. For storage of pure hydrogen, salt caverns currently remain the only commercially proven subsurface storage technology implemented at scale. A new network of hydrogen storage caverns will therefore be required to service a low carbon hydrogen network. To facilitate planning for such systems, this study presents a modelling approach used to evaluate the UK's theoretical hydrogen storage capacity in new salt caverns in bedded rock salt. The findings suggest an upper bound potential for hydrogen storage exceeding 64 million tonnes, providing 2150 TWh of storage capacity, distributed in three discrete salt basins in the UK. The modelled cavern capacity has been interrogated to identify the practical inter-seasonal storage capacity suitable for integration in a hydrogen transmission system. Depending on cavern spacing, a peak load deliverability of between 957 and 1876 GW is technically possible with over 70% of the potential found in the East Yorkshire and Humber region. The range of geologic uncertainty affecting the estimates is approximately ±36%. In principle, the peak domestic heating demand of approximately 170 GW across the UK can be met using the hydrogen withdrawn from caverns alone, albeit in practice the storage potential is unevenly distributed. The analysis indicates that the availability of salt cavern storage potential does not present a limiting constraint for the development of a low-carbon hydrogen network in the UK. The general framework presented in this paper can be applied to other regions to estimate region-specific hydrogen storage potential in salt caverns.

Optimization of hydrogen supply from renewable electricity including cavern storage

Abstract The present study introduces a methodology to model electricity based hydrogen supply systems as a Mixed Integer Linear Programming (MILP) problem. The novelty of the presented approach lies especially in the linear formulations of the models for electrolysis and salt cavern storage. The proposed linear electrolysis model allows for an accurate consideration of operating limits and operating point-specific efficiencies, while the two-dimensional cavern model treats the cavern volume as a decision variable. The developed formulations are implemented in the open energy modeling framework (oemof) and applied to representative case studies with 2020 marginal conditions. Thereby, it has been confirmed that the individual consideration of power supply and hydrogen demand is crucial for optimal system design and operation. If electricity is drawn exclusively from the German grid, hydrogen costs of 2.67 € kg H 2 − 1 $€{\text{kg}}_{{\text{H}}_{2}}^{-1}$ are identified along with an increased CO2 footprint compared to natural gas based hydrogen. By contrast, a significantly reduced CO2 footprint results from autarkic wind power supply at costs of at least 4.28 € kg H 2 − 1 $€{\text{kg}}_{{\text{H}}_{2}}^{-1}$ . Further findings on autarkic operation include optimal ratios of electrolyzer and wind farm nominal power, as well as power curtailment strategies. Evidence is provided that salt cavern interim storage is beneficial. With grid connection, it serves to exploit electricity price fluctuations, while with renewable autarkic operation, it is essential to compensate for seasonal fluctuations in generation.

A Thermodynamic Model for Carbon Dioxide Storage in Underground Salt Caverns

In the context of green energy and decarbonization, carbon dioxide storage in underground facilities, such as salt caverns, is one promising technical solution that has aroused attention. However, the thermodynamic behavior of CO2 and the geomechanical response of salt cavities have not been studied comprehensively. In this study, we proposed a thermomechanical model that integrated a salt cavity and wellbore and implemented a series of simulations for carbon dioxide storage in a salt cavern. The model was verified by gas capacity calculations using field testing data. The thermodynamic behaviors of CO2 were determined and compared to methane. The results showed that the critical point coordinates of carbon dioxide were within the storage operation conditions, a phase transition could occur, and the thermodynamic properties around the critical point varied dramatically. For a short CO2 withdrawal operation, the salt cavity remained stable, while the near-wellbore area (NWA) was prone to fracture due to tensile stress concentration. Thus, we concluded that the proposed thermomechanical coupling numerical simulation method provided a comprehensive and quantitative tool for the feasibility analysis of CO2 storage in underground salt caverns.