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Stability evaluation of salt cavern hydrogen storage and optimization of operating parameters under high frequency injection production
... The first component comprises high-quality solar energy that is transformed into electricity through monocrystalline silicon solar cells [32]. Electricity is provided into the SOEC subsystem to drive hydrogen production, and the hydrogen can be stored [33]. The other part consists of low-grade solar energy, which cannot be utilized by photovoltaic cells. ...
Renewable energy sources, such as wind and solar, can reduce environmental pollution and promote the transformation of the energy structure. However, the intermittency and uncertainty of new energy sources such as wind and photovoltaics pose challenges to large-scale grid integration. Effective utilization of intermittent energy sources requires large-scale energy storage facilities. Salt rock is recognized as an excellent medium for underground large-scale energy storage with a wide range of applications. This paper identifies the potential of salt caverns to be used for large-scale energy storage by analyzing the distribution of wind and solar energy resources in China, taking into account the grid-connected infrastructure of the Chinese power grid and the geographic location of salt mines. The overlapping areas are identified for utilization in compressed air energy storage and hydrogen storage. Through meticulous categorization and analysis of the factors influencing salt cavern underground storage site selection, the AHP-EWM method is introduced to establish an objective hierarchy model for a comprehensive evaluation system of salt cavern underground storage site selection. The comprehensive planning of China's 20 major salt mines is conducted, and the research findings hold significant reference value for facilitating the low-carbon energy transition in China.
Seepage represents a primary factor leading to rock instability, endangering the safety of subterranean structures. Given its prevalence in underground engineering, a comprehensive investigation of marble’s permeability and pore structure is imperative. The coupled thermo-hydro-mechanical (THM) problem often encountered by marble in underground environment has not been studied. The permeability evolution of marble under a wide range of temperature (25–600 °C) and triaxial stress (hydrostatic pressure = 25 MPa) was studied by a high-temperature and high-pressure THM coupling universal testing machine. The changes of pore and fracture properties of marble under different conditions were evaluated by microcomputer tomography and mercury injection. The results show that the changes of pore and fracture properties of marble under THM coupling condition are different from those under high-temperature heat treatment condition. In the THM coupling environment, because of the low confining pressure (25 MPa), there is little difference between the microparameters of the marble rock under THM and HTO (high-temperature-only) conditions. Our findings provide a basis for theoretical approaches that assess the related risks to constructions subjected to high temperatures in the underground environments.
Rock salt formation has a worldwide distribution. In China, a typical area for rock salt formation is in Tarim Basin, Xinjiang Uygur Autonomous Region, Northwest of China. Because of the ultra-deep depth and tectonic movement, the rock salt is interbedded with mudstone and other components. As a result, the creep behavior and mechanism remain uncertain, which brings a big challenge for safe drilling and wellbore integrity. In this paper, we compared different types of rock salt, including fine-grain size pure salt outcrop, composite rock salt outcrop with coarse grain size, and ultra-deep halite core with mudstone interlayer from Tarim basin. The result reveals that the halite core is mainly comprised of salt and clay minerals, highly transparent, and the "hardest" among all the samples. It is hard to define the grain size of the core since the salt crystal seems to be in a whole piece. Besides, we notice distinct fluctuations with composite rock salt in creep tests, which is missed in the fine grain pure rock salt. The halite core is less sensitive to temperature compared with the outcrop. In addition, a finer grain size means a faster creep rate. DIC (Digital Image Correlation) analysis shows that a prominent strain area near the composite interface due to the deformability difference. In addition, it validated the creep fluctuation phenomenon since we could observe it intuitively. The substance of creep doesn't attribute to crystal deformation but fine grain dislocation.
Salt caverns have been successfully used for natural gas storage globally since the 1940s and are now under consideration for hydrogen (H2) storage, which is needed in large quantities to decarbonize the economy to finally reach a net zero by 2050. Salt caverns are not sterile and H2 is a ubiquitous electron donor for microorganisms. This could entail that the injected H2 will be microbially consumed, leading to a volumetric loss and potential production of toxic H2S. However, the extent and rates of this microbial H2 consumption under high-saline cavern conditions are not yet understood. To investigate microbial consumption rates, we cultured the halophilic sulphate-reducing bacteria Desulfohalobium retbaense and the halophilic methanogen Methanocalculus halotolerans under different H2 partial pressures. Both strains consumed H2, but consumption rates slowed down significantly over time. The activity loss correlated with a significant pH increase (up to pH 9) in the media due to intense proton- and bicarbonate consumption. In the case of sulphate reduction, this pH increase led to dissolution of all produced H2S in the liquid phase. We compared these observations to a brine retrieved from a salt cavern located in Northern Germany, which was then incubated with 100% H2 over several months. We again observed a H2 loss (up to 12%) with a concurrent increase in pH of up to 8.5 especially when additional nutrients were added to the brine. Our results clearly show that sulphate-reducing microbes present in salt caverns consume H2, which will be accompanied by a significant pH increase, resulting in reduced activity over time. This potentially self-limiting process of pH increase during sulphate-reduction will be advantageous for H2 storage in low-buffering environments like salt caverns.
The green hydrogen industry, highly efficient and safe, is endowed with flexible production and low carbon emissions. It is conducive to building a low-carbon, efficient and clean energy structure, optimizing the energy industry system and promoting the strategic transformation of energy development and enhancing energy security. In order to achieve carbon emission peaking by 2030 and neutrality by 2060 (dual carbon goals), China is vigorously promoting the green hydrogen industry. Based on an analysis of the green hydrogen industry policies of the U.S., the EU and Japan, this paper explores supporting policies issued by Chinese central and local authorities and examines the inherent advantages of China’s green hydrogen industry. After investigating and analyzing the basis for the development of the green hydrogen industry in China, we conclude that China has enormous potential, including abundant renewable energy resources as well as commercialization experience with renewable energy, robust infrastructure and technological innovation capacity, demand for large-scale applications of green hydrogen in traditional industries, etc. Despite this, China’s green hydrogen industry is still in its early stage and has encountered bottlenecks in its development, including a lack of clarity on the strategic role and position of the green hydrogen industry, low competitiveness of green hydrogen production, heavy reliance on imports of PEMs, perfluorosulfonic acid resins (PFSR) and other core components, the development dilemma of the industry chain, lack of installed capacity for green hydrogen production and complicated administrative permission, etc. This article therefore proposes that an appropriate development road-map and integrated administration supervision systems, including safety supervision, will systematically promote the green hydrogen industry. Enhancing the core technology and equipment of green hydrogen and improving the green hydrogen industry chain will be an adequate way to reduce dependence on foreign technologies, lowering the price of green hydrogen products through the scale effect and, thus, expanding the scope of application of green hydrogen. Financial support mechanisms such as providing tax breaks and project subsidies will encourage enterprises to carry out innovative technological research on and invest in the green hydrogen industry.
Increasing greenhouse gas emissions have put pressure on global economies to adopt strategies for climate-change mitigation. Large-scale geological hydrogen storage in salt caverns and porous rocks has the potential to achieve sustainable energy storage, contributing to the development of a low-carbon economy. During geological storage, hydrogen is injected and extracted through cemented and cased wells. In this context, well integrity and leakage risk must be assessed through in-depth investigations of the hydrogen-cement-rock physical and geochemical processes. There are significant scientific knowledge gaps pertaining to hydrogen-cement interactions, where chemical reactions among hydrogen, in situ reservoir fluids, and cement could degrade the well cement and put the integrity of the storage system at risk. Results from laboratory batch reaction experiments concerning the influence of hydrogen on cement samples under simulated reservoir conditions of North Sea fields, including temperature, pressure, and salinity, provided valuable insights into the integrity of cement for geological hydrogen storage. This work shows that, under the experimental conditions, hydrogen does not induce geochemical or structural alterations to the tested wellbore cements, a promising finding for secure hydrogen subsurface storage.
The concept of “green‐ammonia‐zero‐carbon emission” is an emerging research topic in the global community and many countries driving toward decarbonizing a diversity of applications dependent on fossil fuels. In light of this, electrochemical nitrogen reduction reaction (ENRR) received great attention at ambient conditions. The low efficiency (%) and ammonia (NH 3 ) production rates are two major challenges in making a sustainable future. Besides, hydrogen evolution reaction is another crucial factor for realizing this NH 3 synthesis to meet the large‐scale commercial demand. Herein, the (i) importance of NH 3 as an energy carrier for the next future, (ii) discussion with ENRR theory and the fundamental mechanism, (iii) device configuration and types of electrolytic systems for NH 3 synthesis including key metrics, (iv) then moving into rising electrocatalysts for ENRR such as single‐atom catalysts (SACs), MXenes, and metal–organic frameworks that were scientifically summarized, and (v) finally, the current technical contests and future perceptions are discussed. Hence, this review aims to give insightful direction and a fresh motivation toward ENRR and the development of advanced electrocatalysts in terms of cost, efficiency, and technologically large scale for the synthesis of green NH 3 .
Proton exchange membrane fuel cells (PEMFCs) are becoming a major part of a greener and more sustainable future. However, the costs of high-purity hydrogen and noble metal catalysts alongside the complexity of the PEMFC system severely hamper their commercialization. Operating PEMFCs at high temperatures (HT-PEMFCs, above 120 °C) brings several advantages, such as increased tolerance to contaminants, more affordable catalysts, and operations without liquid water, hence considerably simplifying the system. While recent progresses in proton exchange membranes for HT-PEMFCs have made this technology more viable, the HT-PEMFC viscous acid electrolyte lowers the active site utilization by unevenly diffusing into the catalyst layer while it acutely poisons the catalytic sites. In recent years, the synthesis of platinum group metal (PGM) and PGM-free catalysts with higher acid tolerance and phosphate-promoted oxygen reduction reaction, in conjunction with the design of catalyst layers with improved acid distribution and more triple-phase boundaries, has provided great opportunities for more efficient HT-PEMFCs. The progress in these two interconnected fields is reviewed here, with recommendations for the most promising routes worthy of further investigation. Using these approaches, the performance and durability of HT-PEMFCs will be significantly improved.
This research aims to identify and analyse the challenges faced by the energy–power supply chain (LNG Power) in Pakistan a developing economy from combined perspectives of supply chain sustainability and resilience in the context of the Triple Bottom Line framework, UN SDGs 7, 13 and energy security. The significance of this research increases many folds as energy-power supply chains have been severely disrupted by events such as COVID-19, the Russia–Ukraine war and massive devastation caused by floods in Pakistan. Pakistan meets more than 60% of its energy-power needs from natural gas (including LNG), being less harmful than coal and oil power generation. The industry is in a state of deep crisis as it faces a complex set of challenges. Exploratory research design using a mixed method case study approach was used for the identification and shortlisting of challenges. Later these were ranked using group BWM. Major challenges were lack of strategy, top management commitment, weak compliance to UN SDGs, stalled structural reforms, disasters, lack of supply chain orientation, risk management culture, financial instability, LNG non-availability, demand uncertainty, infrastructure inadequacies and lack of awareness of Industry 4.0. The research enables policy-making besides providing energy practitioners a roadmap to overcome these challenges.
Bangladesh focuses on green energy sources to be a lesser dependent on imported fossil fuels and to reduce the GHG emission to decarbonize the energy sector. The integration of renewable energy technologies for green hydrogen production is promising for Bangladesh. Hybrid renewable plants at the coastline along the Bay of Bengal, Kuakata, Sandwip, St. Martin, Cox'sbazer, and Chattogram for green hydrogen production is very promising to solve the power demand scarcity of Bangladesh. Hydrogen gas turbine and hydrogen fuel cell configured power plant performances are studied to observe the feasibility/prospect to the green energy transition. The Plant's performances investigated based on specification of the plant's units and verified by MATLAB SIMULINK software. Fuels blending (different percent of hydrogen with fossil fuel/NG) technique makes the hydrogen more feasible as turbine fuel. The net efficiency of the fuel cell-based combined cycle configuration (74%) is higher than that of the hydrogen gas turbine-based configuration (51.9%). Moreover, analyses show that the increment of combined cycle gas turbine efficiency (+18.5%) is more than the combined cycle PEMFC configuration (+14%). Long-term storage of renewable energy in the salt cavern as green hydrogen can be a source of energy for emergency. A significant share of power can be generated by a numbers of green power plants at specified places in Bangladesh.
COVID‐19 pandemic is still one of the biggest obstacles to meeting the sustainable development goals (SDGs). Helping the world retrieve from the pandemic and reviving activities require expeditiously examining the comprehensive SDG schemes. This paper draws on existing information and a thorough examination of the research to emphasize continuing challenges confronting the SDGs. It also determines the impact of COVID‐19 on sustainable development goal advancements and suggest a standardized framework to encourage the accomplishment of them in the post‐pandemic era. Before the pandemic started, the advancement toward accomplishing the SDGs was lagging. Global problems and the unequal supply of food, water and energy evidently pose a threat to the achievement of the SDGs. An evaluation is provided on the execution of the SDGs and factors such as the instability of the global political climate, geographical disparities, and exchange. Additionally, an insight is provided for post‐pandemic SDG actions on “Classification‐Coordination‐Collaboration” template in order to better understand the global picture. The current state of advancement is presented based on the emergency of SDG accomplishments considering regulations through categorization with science and research, which can realign the SDGs to their original course. The analysis suggests that attaining the SDGs necessitates a coordinated effort from all stakeholders, and collaboration is crucial to bolstering economic relations, encouraging technical development, and constructing a sustainable world.
The hydrogen economy is one of the possible directions of development for the European Union economy, which in the perspective of 2050, can ensure climate neutrality for the member states. The use of hydrogen in the economy on a larger scale requires the creation of a storage system. Due to the necessary volumes, the best sites for storage are geological structures (salt caverns, oil and gas deposits or aquifers). This article presents an analysis of prospects for large-scale underground hydrogen storage in geological structures. The political conditions for the implementation of the hydrogen economy in the EU Member States were analysed. The European Commission in its documents (e.g., Green Deal) indicates hydrogen as one of the important elements enabling the implementation of a climate-neutral economy. From the perspective of 2050, the analysis of changes and the forecast of energy consumption in the EU indicate an increase in electricity consumption. The expected increase in the production of energy from renewable sources may contribute to an increase in the production of hydrogen and its role in the economy. From the perspective of 2050, discussed gas should replace natural gas in the chemical, metallurgical and transport industries. In the longer term, the same process will also be observed in the aviation and maritime sectors. Growing charges for CO2 emissions will also contribute to the development of underground hydrogen storage technology. Geological conditions, especially wide-spread aquifers and salt deposits allow the development of underground hydrogen storage in Europe.
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.
To meet the requirements of the United Nations Framework Convention on Climate Change, i.e., the Paris Agreement, countries around the world have developed carbon-peaking and carbon–neutral action programs. The use of renewable energy sources is an effective means of meeting this requirement. Compressed air energy storage using salt caverns is an effective way to enhance the efficiency of renewable energy use. To investigate the damage pattern of salt cavern surrounding rocks subjected to cyclic injection and extraction loads during the operation of compressed air energy storage plants, using a MTS815 rock mechanics test system, a series of creep–fatigue mechanics tests on salt rock were carried out, and the effects on the fatigue damage of salt rock were investigated by setting different high stress plateau times and stress levels. (1) The development pattern of the corresponding creep–fatigue stress–strain curve is similar to that of ordinary fatigue, which is also divided into three stages: comb-dense-comb. The cyclic load has a positive effect on creep, but there is a threshold value of plateau time, and the creep deformation is minimal at a plateau time of 15 min. (2) The residual strain before the plateau in A cycle is greater than that after the plateau in B cycle, which is different from the traditional fatigue test, and the difference between the residual strain before and after the plateau is positively correlated with the plateau time. (3) The fatigue life of the salt rock specimens decreases and their creep life increases as the high stress plateau time increases. (4) The effect of the high stress plateau starts to appear under lower stress conditions, and the residual strain difference before and after the plateau increases with increasing stress level. (5) The different responses of the internal structure of the salt rock to fatigue and creep lead to the interaction between creep and fatigue.
Salt caverns are accepted as an ideal solution for high-pressure hydrogen storage. As well as considering the numerous benefits of the realization of underground hydrogen storage (UHS), such as high energy densities, low leakage rates and big storage volumes, risk analysis of UHS is a required step for assessing the suitability of this technology. In this work, a preliminary quantitative risk assessment (QRA) was performed by starting from the worst-case scenario: rupture at the ground of the riser pipe from the salt cavern to the ground. The influence of hydrogen contamination by bacterial metabolism was studied, considering the composition of the gas contained in the salt caverns as time variable. A bow-tie analysis was used to highlight all the possible causes (basic events) as well as the outcomes (jet fire, unconfined vapor cloud explosion (UVCE), toxic chemical release), and then, consequence and risk analyses were performed. The results showed that a UVCE is the most frequent outcome, but its effect zone decreases with time due to the hydrogen contamination and the higher contents of methane and hydrogen sulfide.
Salt caverns are an attractive solution to the growing energy demand in view of their large storage capacity, safety of storage operation and long operation time. The designing process of salt caverns is still considered a complex issue despite progress in geotechnical, construction and exploration methods. Finding the optimal shape and dimensions of a salt cavern in given geological conditions is a difficult engineering problem in view of safety and stability requirements. In this paper, the stability of typical cavern shapes (cylindrical, enlarged top, and enlarged bottom), with each of the three variants differing by their diameter, was evaluated against the stability factors of the geological conditions of the bedded salt deposit. Moreover, the analysed shapes were examined in terms of edges. The three-step smoothing of sharp edges was performed, and its impact on the cavern’s stability performance was studied. Moreover, the analysis aimed to find the optimal cavern shape and volume in the implemented geological conditions. The evaluation was based on the following criteria: the displacement, effective strain, von Mises stress, strength/stress ratio and safety factor. The results of this evaluation can be useful in the design of an optimal cavern shape and volume and for planning new cavern fields for storing natural gas, compressed air or hydrogen in the bedded salt deposits.
China has set ambitious goals to cap its carbon emissions and increase low-carbon energy sources to 20% by 2030 or earlier. However, wind and solar energy production can be highly variable: the stability of single wind/solar and hybrid wind-solar energy and the effects of wind/solar ratio and spatial aggregation on energy stability remain largely unknown in China, especially at the grid cell scale. To address these issues, we analyzed the newly 2007–2014 hourly wind and solar data, which have higher resolution and quality than those used in previous research. The stability of single wind/solar energy production clearly increased as the wind/solar energy capacity factor increased, and there were significant functional relationships between single wind/solar energy stability and the wind/solar energy capacity factor. Highly stable wind energy was concentrated in eastern Inner Mongolia, northeastern China, and northern China while highly stable solar energy was concentrated in the Tibetan Plateau, Inner Mongolia, and northwestern China. Different wind/solar ratios affected the stability of hybrid wind-solar energy through a unimodal relationship, allowing us to produce a map of optimal wind/solar ratios throughout China in order to minimize the variability of hybrid wind-solar energy production. At the optimal wind/solar ratio, the most stable hybrid wind-solar energy was concentrated in eastern Inner Mongolia, northeastern China, and northern China. The variability of single and hybrid wind/solar energy decreased as the aggregated area size increased, especially for wind-dominated energy systems. These results have important practical applications: (a) using the optimal wind/solar ratio to install simple hybrid wind-solar energy systems locally; (b) prioritizing the deployment of large-scale wind farms or centralized solar photovoltaic stations in regions with high hybrid energy stability; and (c) strongly promoting regional cooperation, such as breaking inter-provincial power grid barriers, to reduce the variability of hybrid wind-solar energy production and thus operational costs.
When rock salt is subjected to discontinuous fatigue, time intervals (periods during which the stress remains constant) can accelerate plastic deformation and reduce the fatigue life due to the internal residual stress generated between various defects and the host material. However, the time interval effect on rock salt in a three-dimensional stress state has rarely been investigated despite its great significance in the use of underground salt caverns as storages. In this research, a series of triaxial discontinuous cyclic compression tests were conducted on salt and the residual stress was reproduced through numerical simulations. Experimental results show that the interval effect decreases with the increase of the confining pressure. The change in plasticity caused by time intervals is small and constant when the stress level (ratio of the maximum stress to strength) is below “60%” but then increases as a linear function of the stress level. During simulations, it was observed that the greater the difference in the elasticity modulus between the host material and impurities, the larger the residual stress. The moderate effect of time interval under confinement is the result of the fact that a higher confining pressure strengthens the host material, reduces the volume of impurities and thus leads to a smaller residual stress. In addition, when the stress level is below a certain threshold (which is shown to be at 0.8–0.85 of the critical yield stress), the residual stress is relatively low in magnitude and area of influence. Above that threshold, the residual stress grows rapidly. This is the reason why the interval effect displays a distinct behavior before and after dilatancy point.
Taking Jiangsu province of China as an example, large-scale underground hydrogen storage (UHS) in salt caverns is proposed to realize peak shaving for wind power. A bedded salt rock, Jintan salt mine in Jiangsu, is selected as the potential site for UHS. And the feasibility of UHS in bedded salt rocks is evaluated. Firstly, the regional geological conditions of Jintan salt mine are analyzed. It shows that this mine has good stratigraphic trapping and meets the site-selection requirements for UHS. Then, a numerical simulation model is established to analyze the stability and applicability of the proposed UHS caverns. The tightness of the UHS salt caverns is also investigated. It is indicated that gas tightness can be favorable once the permeability of interlayers is around 10⁻¹⁸ m² or lower. Finally, it is estimated that the salt caverns for 36.9 TWh-scale UHS of Jiangsu can be mainly provided by salt mine enterprises, but more attention should be paid to the usability of caverns during extraction. This study provides a feasible and economical solution for fulfilling the large-scale UHS in the Jiangsu, as well as for the regions that are rich in both renewable energy and salt resources.
Most studies have suggested that aquifers with anticlinal structures are the most favorable structures for compressed air energy storage (CAES) in aquifers because of their trapping ability, but this limits the potential locations for CAES plants, as horizontal aquifers are very common only in offshore areas rich in wind power. The comparison of the characteristics of CAES in dome-shaped and horizontal aquifers can help in understanding the quantitative differences between them. In this study, based on Pittsfield aquifer field test strata and parameters, the characteristics of CAES in dome-shaped and horizontal aquifers were investigated using a numerical simulation method by establishing two comparable conceptual models of a dome-shaped aquifer and a horizontal aquifer. Reasonable matches between the monitored data and simulated results were obtained for the initial air bubble development period of the Pittsfield aquifer field test. Comparisons of the initial air bubble, air cycling performance and energy recovery efficiency were carried out with the same calculation settings for the domeshaped and horizontal aquifers. In the initial air bubble development period, when the same air volume was injected into the dome-shaped and horizontal aquifers, the radius of the air–water interface in the horizontal aquifer was 16.7% larger than that in the dome-shaped aquifer. In the air cycling period, an isothermal cycle type with a constant injection and production air pressure was designed. The energy recovery efficiency of CAES in aquifers is calculated in terms of the concept of exergy. In the case of isothermal compressor work and ignoring the energy loss in the compressor system, the energy recovery efficiency of the horizontal aquifer can reach approximately 80% of that in the dome-shaped aquifer. The effects of wellbore injection/production length and circulation mode on the performance of CAES in both aquifers were investigated. Wellbore injection/production length has obvious impacts on air mass flow rates during initial air bubble development and subsequent cycling, and a longer wellbore injection/production length can provide greater capacity. A comparison between the daily and weekly circulation periods in the dome-shaped and horizontal aquifers showed that the daily circulation has an efficiency advantage at the same energy storage scale, and the energy recovery efficiency of the horizontal aquifer in the weekly circulation can reach approximately 74% of that of the dome-shaped aquifer. In addition, a constant flow rate injection/production gas daily cycle mode was investigated, and the results showed that this mode has higher energy recovery efficiency than the constant pressure cycle mode, and the horizontal aquifer can reach 88.39% of the efficiency of the dome-shaped aquifer. The comparison of the characteristics of CAES in dome-shaped and horizontal aquifers shows that horizontal aquifers may be a potential choice for the storage media of CAES in the case that there are no suitable aquifers with anticlinal structures in offshore areas.
Hydrogen energy will remarkably aid the global energy transition from fossil fuels to renewables. Hydrogen is the lightest molecule. It requires large volume storage facilities only found in geological formations. Salt caverns are a potential geo-storage medium that has been used in practice at a commercial scale. In Australia, several basins, i.e., Advalae, Carnarvon, Amadeus, Officer, and Canning, have been identified with notable salt deposits. The feasibility and potential of storing hydrogen in these salts have yet to be determined by geology, salt thickness, or salt type data. Here, we identified potential hydrogen storage sites. Additionally, hydrogen storage volume was estimated in Mallowa and Minjoo salts (Carribuddy salts: ~95 % halite and ~1 % anhydrite) in Willara Sub-basin, Canning Basin, Western Australia (WA). The results show a high potential for constructing salt caverns for hydrogen storage in these areas. The geochemical data suggest the presence of Bromine (90 to 670 ppm and <150 ppm in some wells), which are favorable for the solution mining process for the development of salt caverns. Our study demonstrates that approximately 28,282 onshore salt caverns (500,000 m 3 each) could be constructed in the Willara Sub-basin salt in WA. The estimated number of caverns can store 14,697 PJ of hydrogen energy. The proposed site would be in the Northwest of WA, ~70 to 80 km from the Indian Ocean, with access to the shore and transportation. The estimated H 2 storage capacity in the salt caverns satisfies Australia's energy consumption (5790 PJ in 2020-21), providing 8900 PJ of H 2 energy for export to ensure a sustainable hydrogen value chain.
Fine particulate matter (PM2.5) poses a major environmental risk to human health. We estimated PM2.5-related premature deaths in 30 Chinese provinces in 2020 using an integrated exposure response model based on monitored concentrations and obtained regional and sectoral contributions based on the atmospheric transport of the atmospheric transport contribution matrix. From the perspective of regional- and sectoral-scale effects, the results revealed that 740,140 [95% confidence interval (CI):646,538-839,968] premature deaths were related to PM2.5 in 2020, mainly in East (30%), Central (18%), and North (15%) China. Manufacturing activity was found to be the major cause of PM2.5-related premature deaths, accounting for over 50% of the deaths. From the perspective of the interregional atmospheric transport effect, although local emissions were the major source of PM2.5-related premature deaths in all regions, non-local emissions contributed approximately 30%. The overall trend in the net atmospheric transport direction was from north to south. In particular, the Guangdong, Guangxi, and Hainan provinces of South China received contributions of more than 40% from non-local provinces, mainly from the East and Central China. Combined with economic data, the regions and sectors with the highest PM2.5-related premature deaths per unit output or consumption include the manufacturing and household sectors in North and Northeast China and transportation, agriculture, and electricity in Central China. Therefore, from the perspective of the above three impacts, although the potential impact of PM2.5 pollution on health in China has decreased with the decrease in PM2.5 concentration in the past decade owing to strict air pollution control, the central and northern parts of China are still the key areas requiring air pollution control. The health impacts of air pollution associated with the rapid development of China's manufacturing industry in the post-pandemic era cannot be ignored.
This paper first measures the level of environmental efficiency (EE) in 72 countries between 2001 and 2019 by adopting the Global Malmquist-Luenberger productivity index in the framework of the super slack-based-measure model. Then, by using the instrument variable-generalized method of moments (IV-GMM) approach, we examine the role of hydrogen development in increasing EE. We also pay attention to the asymmetric effect, the moderating effect, and the mediating effect in the hydrogen development-EE nexus. Several findings are highlighted as follows: (1) Hydrogen development can significantly increase EE. (2) The marginal impact of hydrogen development on EE is significantly positive in countries with a high level of EE, while it is insignificant in countries with a low level of EE, which shows the asymmetric EE enhancement effect of hydrogen development. (3) Foreign direct investment is a key moderating variable in the nexus between hydrogen development and EE, which can strengthen this positive nexus. And (4) mediating effect analysis documents that technological progress is an effective mediating variable through which hydrogen development affects EE. According to these results, we propose several policy implications for the acceleration of hydrogen development and EE.
Complementary renewable technologies support renewable energy use as they can help balance the intermit
tency of solar and wind generation. Previous research has shown that environmental policies directly targeting renewable energy can drive innovation in solar PV and wind technology. This study explores the impact of renewable policies on innovation in complementary renewable technology that assists with integration, including combustion with mitigation potential, efficient power transmission or distribution, and enabling technologies. We use negative binomial models and a panel of 25 OECD countries from 1997 to 2015 to evaluate these relationships. We are not able to find evidence that renewable policies incentivize innovation in complementary combustion or transmission and distribution technologies, and only limited evidence that demand- pull instruments are associated with increased innovation in smart grid technology. Technology-push policies, such as public research and development funds for renewable energy, have had limited impact on grid- supporting energy storage innovation. Our findings suggest that policymakers wishing to accelerate these complementary technologies need to go beyond policies targeting renewable energy in order to drive innovation in complementary fields.
China plans to reach the peak of its CO2 emissions in 2030 and achieve carbon neutrality in 2060. Salt caverns are excellent facilities for underground energy storage, and they can store CO2. Combined with the CO2 emission data of China in recent years, the volume of underground salt caverns in 2030 and the CO2 emission of China are predicted. A correlation model between salt cavern energy storage and CO2 emission is developed. An evaluation model of carbon capture capacity is developed. A method of comprehensive utilization of salt cavern energy storage is proposed. A flow chart of salt cavern energy storage and salt cavern carbon storage is summarized. The research shows that underground salt caverns with a volume of 300 million m3 will be formed in China by 2020-2030, and China’s CO2 emissions will reach 14.4 billion tonnes by 2030. There is a negative correlation between salt cavern development and CO2 emissions. The CO2 reduction percentages of salt cavern comprehensive utilization are: 28.3% for compressed air energy storage; 13.3% for natural gas storage; 10.3% for oil storage; 6.6% for liquid flow battery; 24.8% for hydrogen storage; 16.8% for carbon dioxide storage. The research results have certain reference values for the large-scale development of salt caverns and carbon neutralization.
In response to the Paris Agreement, the transition from fossil fuels to renewable energy resources (RER) is one of the most crucial measures in responding to climate change. Under this context, hydrogen storage with the concept of ‘power to gas’ represents a possible solution for the mismatch problem between fluctuating RER generation and downstream demand in a seasonal time scale. Compared to conventional low storage capacities of salt caverns, widely spread aquifers provide a possibility for safe, cost-effective, and environmentally friendly long-term hydrogen storage. However, current knowledge of hydrogen storage in these aquifers is only limited to a few impure hydrogen projects; understanding their trapping mechanisms as well as how to recover their trapped hydrogen is urgent. In order to fulfil the knowledge gap, not only are the complex underground interactions of hydrogen with rock or a fluid (residual trapping or dissolution trapping) modelled and validated against reliable experimental data, but also multiple cycles and cushion gas injection are integrated to enhance hydrogen recovery in this study. Through powerful numerical studies, the results indicate that: (a) at a seasonal storage time scale, residual trapping has the most effect in reducing hydrogen round-trip efficiency; (b) multiple cycles are helpful for hydrogen storage in an aquifer reservoir with round-trip efficiency increasing from 50.9% in the first cycle to 78.6% at the end; (c) nitrogen as a cushion gas for injection has a better performance compared with carbon dioxide with a capability to unlock residual trapped and dissolution trapped hydrogen; (d) nitrogen as a cushion gas for injection can effectively alleviate insufficient hydrogen production capacity in the first cycle with the hydrogen round-trip efficiency increased from 50% to 70%; and (e) the hydrogen extraction phase ends up with a very high recovery efficiency (around 85%) in a nitrogen injection scenario.
In a world of energy transition and net zero pledges, low-carbon energy solutions are central in the fight against
climate change. Hydrogen plays a key role in a clean energy future, but there are still economic and infrastructural
challenges to be overcome. Hydrogen storage in large volumes is one of the value chains current limitations. This paper presents a feasibility study of an offshore blue or green hydrogen storage in salt caverns created by leaching, within potentially identifiable salt deposits extent of the Gulf of Mexico coastline (US). In this case study, the hydrogen station will have caverns to store hydrogen and some caverns to dispose of CO2 from the blue hydrogen (Carbon Capture and Storage – CCS technology). The construction design includes a fixed platform for the H2 HUB and a jack-up platform for drilling. It presents the conceptual design of wells for leaching the caverns and hydrogen injection and withdrawal cycles.
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 has attracted attention worldwide with its favourable inherent properties to contribute towards a carbon-free green energy future. Australia aims to make hydrogen as its next major export component to economize the growing global demand for hydrogen. Cost-effective and safe large-scale hydrogen storage in subsurface geology can assist Australia in meeting the projected domestic and export targets. This article discusses the available subsurface storage options in detail by first presenting the projected demand for hydrogen storage. Australia has many subsurface formations, such as depleted gas fields, salt caverns, aquifers, coal seams and abandoned underground mines, which can contribute to underground hydrogen storage. The article presents basin-wide geological information on the storage structures, the technical challenges, and the factors to consider during site selection. With the experience and knowledge Australia has in utilizing depleted reservoirs for gas storage and carbon capture and sequestration, Australia can benefit from the depleted gas reservoirs in developing hydrogen energy infrastructure. The lack of experience and knowledge associated with other geostructures favours the utilization of underground gas storage sites for the storage of hydrogen during the initial stages of the shift towards hydrogen energy. The article also provides future directions to address the identified important knowledge gaps to utilize the subsurface geology for hydrogen storage successfully.
The high cost and serious pollution of salt cavern construction (SCC) with fresh water (FW) under oil blanket (OB) poses a major challenge to the development of salt cavern energy storage, and it is of great significance for clean brine mining and efficient SCC to replace FW with light brine (LB) as well as OB with gas blanket (GB). However, the expansion and control of cavern shape after replacement remains unclear, and it also needs to be clarified of the feasibility of SCC with LB. Therefore, the experimental and theoretical research on the physical simulation of SCC with LB under GB was carried out. Firstly, the dissolution test of salt rock in brine was performed, and the effect of brine concentration on the dissolution rate of salt rock was investigated, which provides foundation for the brine preparation of the physical simulation and on-site SCC. Then, based on dimensional analysis and similarity theory, a visual physical simulation platform of SCC under GB was established and five groups of physical simulation experiments were carried out. The effects of tube lifting method and circulation mode on the concentration of withdrawn brine and cavern shape were explored. The relationship between lateral dissolution angle and the effective volume of salt cavern energy storage were analyzed, and the measures and suggestions of controlling lateral dissolution angle and GB were proposed. Finally, the techno-economic analysis of SCC with FW and LB under GB was carried out, which shows that SCC with LB under GB possesses lower cost and better environmental protection. This research can serve as a basis for promoting clean and efficient brine mining and SCC.
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.
Large-scale energy storage methods are required for shaving peak of renewable energy. Because of the good compactness of salt rock, it is proposed to store hydrogen in salt rock caverns to solve this problem. China has abundant salt rock resources, which provide good choices for large-scale hydrogen storage in salt formation. But the salt formations of China are mainly of bedded salt rock, which contain interlayers with various lithologies and different permeability and porosity. Therefore, the tightness of hydrogen storage in different bedded salt formations of China should be investigated. In order to demonstrate the tightness performance of salt cavern hydrogen storage and provide references for site selection and storage management, a series of lab-experiments, theoretical and numerical simulations, and discussions were conducted. Firstly, the porosity and permeability of interlayers with different lithologies were tested and analyzed. Then, a geological model was established, five cases of hydrogen leakage simulation are designed, these cases stand for the typical bedded salt formations of China. In each case, the interlayers have different lithologies, permeability and porosity. The COMSOL Multiphysics software was used to simulate the hydrogen leakage of cavern under different cases, and the leakage range, pore pressure and leakage amount of hydrogen were analyzed. The results show that interlayers are the main positions of hydrogen leakage, and with the decrease of the interlayers' porosity and permeability, the tightness of cavern will be better. It is suggested that when hydrogen is stored in a single cavern, the permeability of interlayers should be less than 1E-17 m², while when stored in a group of caverns, it should be less than 1E-18 m². At the same time, a reflux zone is found in the surrounding rock of storage cavern, hydrogen in the reflux zone will flow back to cavern, which is not conducive to its operation. Leakage coefficient of the surrounding rock of cavern is defined as α, and it is proposed only when α ≤ 1.18E-20 m², can the cavern meet the tightness requirements of hydrogen storage. Finally, some countermeasures are put forward for cavern utilization in bedded salt rock. This research provides guidance and basis for the site selection of hydrogen storage in salt caverns, and promotes the development of underground salt cavern energy storage in China.
As a major greenhouse gas, carbon dioxide (CO2) causes climate warming and weather changes. On the basis of CO2 disposal/storage in salt caverns in this study, a new carbon cycle model is proposed, which provides a new way for carbon capture and storage. The safety and suitability evaluation of CO2 disposal/storage in bedded rock salt caverns in China was carried out. Long-term disposal (Time ≥1000 years), medium-term disposal (several hundred years), and short-term storage (0–30 years) were studied to meet permanent geological isolation of carbon and temporary carbon cycle. The results show that: 1) For long-term and medium-term disposal/storage, it is feasible to carry out permanent geological isolation at proper depth and operating pressure. 2) For short-term storage, the stability of CO2 and CH4 storage in bedded rock salt has a little difference by controlling the operating pressure constant withdrawal-injection cycle. However, the stored CO2 has a much larger storage density and working density than the stored CH4. 3) If dozens of such caverns can be used in a salt mine, the potential for disposal or storage is much considerable. Therefore, the utilization of CO2 storage in salt caverns also acts as an attractive way of carbon neutralization and carbon cycle.
Compared with vertical storage, horizontal storage in bedded salt rock deposits is reasonable and scientific for large-capacity gas storage and for avoiding the risk of interlayer and interfacial oil and gas leaks. The single-well retreating horizontal (SWRH) leaching method is introduced in this paper. After calculating similarity ratios, a physical similarity simulation experiment was conducted for inferring the cavern shape. A numerical model was developed based on the inferred cavern shape, and the stability of the SWRH cavern was analysed. Reasonable values of the cycle frequency and the roof and floor salt layers’ thicknesses were determined. The effects of the pillar width and asynchronous internal gas pressure between adjacent caverns were analysed. The results show that the SWRH cavern satisfies the safety requirements of bedded salt rock districts over the entire design lifetime. A cyclic frequency that is too low and asynchronous internal gas pressure are not conducive to the stability and reliability of the cavern. To ensure stability, the thicknesses of the roof and floor salt rock layers of the horizontal cavern should exceed 16 m and 6 m, respectively. This study opens new vistas for constructing horizontal gas-storage systems in bedded salt rock.
The single well or small-spacing two-well technologies with oil blanket has been gradually applied to construct salt cavern storage in recent years. In order to solve the problems of low efficiency, oil blanket sealing failure, cavern deformity, roof collapses, small volume and brine pollution in salt cavern construction. In this study, a large-spacing two-well (Wellhead spacing is greater than 20 m) with gas blanket (LSTW-GB) method was proposed to construct salt cavern. Firstly, through indoor physical simulation experiment, the feasibility of the LSTW-GB to construct cavern is verified and discussed. The experimental results show that increasing the two-well-spacing effectively increases the effective cavern volume, improve the cavern construction rate and obtain clear brine, but the increase of two-well-spacing will also increase the difficulty of connecting the two wells, so more attention should focus on the technology improvement on connecting the two wells. Secondly, combined with the experimental observations and field geological data in Jintan bedded salt rock of China, the stability of the LSTW-cavern for gas storage under different ratios of long axis to height (RLH) was analyzed by numerical simulations. The simulation results show that as the RLH increasing, the stability of the LSTW-cavern gradually decreases. In addition, under low-internal-pressure operation, the cavern is most likely to lose its stability, so much more attention should be paid to designing the value and duration of minimum operating internal pressure (Pmin). Finally, the working conditions of the LSTW-cavern gas storage are optimized, and it is proposed that the Pmin of the gas storage in the LSTW-cavern should be 33% ∼ 38% of the gravity stress at the casing shoe when RLH varies from 1.60 to 3.10. Comprehensive research results show that the LSTW-cavern has a good application prospect in the construction of gas storage of salt rock in China.
For the sake of safety and stability, a salt roof with certain thickness is usually designed above the cavity. While some rock salt often contains multi-interlayers above the cavity roof in China, which brings new challenges to designing salt roof thickness and evaluating cavity stability. On this basis, the factors affecting the stability of cavity with multiple interlayers above cavity roof is investigated. Combining single factor sensitivity analysis and analytic hierarchy process, the influence of each factor on cavity stability and roof deformation is quantitatively analyzed. Numerical simulation results show that when there are multiple interlayers above cavity roof, the stress and deformation of the cavity are increased compared with general conditions. The rock salt roof thickness has little effect on the stability of the cavity, but the cavity tightness is at risk when it is small. When the operating pressure is setting reasonably, the rock salt roof thickness should be greater than 11 m at around 1000 m deep and 17 m at about 2000 m deep. When the depth of the cavity is less than 1700 m and greater than 2000 m, the minimum operating pressure should be 0.3 and 0.4 times of the gravity stress at the depth of cavity roof. The change of the interlayers stiffness has a little impact on the stability of the cavity. The quantitative analysis indicates that the minimum operating pressure and buried depth are two critical factors that need special attention to ensure the stable operation of the salt cavity gas storage.
The two-well-vertical (TWV) cavern-constructing with gas blanket technology is an important alternative to the single-well (SW) with oil blanket technology. This technology has the advantages of achieving larger cavern volume, clean brine, great water flow rate, and high economic benefits. Promoting and developing its theory and technology will help the future development of salt mining and cavern construction for energy storage in China, as it is in the initial stage. In this paper, a visualized physical simulation platform of water dissolving of the TWV caverns with gas blanket was established, and large size salt rock blocks were used to simulate the constructing process of salt caverns. The similarity ratios of size, flow rate, and time between prototype and model were calculated by using the similarity theory and dimensional analysis. A series of physical simulation tests of water-dissolving caverns were carried out, that the research factors including the two-well-spacing, flow rate, and gas/oil blanket. The results show that: (1) The water flow rate can be increased to 200–400 m³/h by increasing the two-well-spacing when using the TWV technology, which is 2–4 times that of the single-well. (2) It is found that 30–40 m is the optimal size for the two-well-spacing, and the two-well-space is much larger than 40 m may exist risks of roof instability. (3) During the initial stage of cavern construction, it will obtain a smaller lateral solution angle and an ideal cavern bottom groove shape with gas blanket. After the cavern construction is finished, it also will obtain better cavern shape, larger cavern volume and clean brine by comparing with oil blanket. So, the technology of the TWV cavern construction with gas blanket is promising for brine leaching and energy storage cavern construction and it is also worth further study.
In view of the low permeability and good damage self-healing properties of rock salt, salt caverns are thought to be ideal media to hold natural gas. However, widely distributed salt formations in China were formed bedded by lacustrine sedimentation with significant sedimentary rhythm characteristics. The various interlayers in bedded salt formations may cause instability of the cavern pillar due to their uncoordinated deformation, thus threatening the safety of the whole gas storage caverns. Combining theoretical analysis and numerical simulation, the influence of different characteristics of interlayers on the stability of salt cavern pillars were detailed analyzed. Some main conclusions were summarized as follows: 1) In a sedimentary rhythm, the rock salt and the soft interlayers can be considered as one category, and the hard interlayers can be treated as another category. Compared with the hard interlayers, rock salt and the soft interlayers contributes more to the shrinkage of salt cavern; 2) With the decrease of pillar width or the increase of operating time, the principal stress curves (both σ1 and σ3) in the interlayers along the line between the centers of the two caverns generally experience the process of "Bimodal type - Saddle type - Unimodal type"; 3) The entire plastic zone expansion process in hard interlayers of the cavern pillar shows the periodic law of "interfaces - middle interlayer - interfaces - middle interlayer"; 4) As to site selection of salt caverns for gas storage, bedded salt formations with too many interlayers should be avoided. If the interlayers cannot be avoided, the salt cavern should be constructed with interlayers located far away from the cavern center.
In recent decades, creep in salt cavern Underground Gas Storage (UGS) has caused accidents at different locations around the world. Most of them were caused by volume shrinkage of salt caverns. In order to analyze the stability condition of the two-well-horizontal (TWH) salt cavern more realistically, we apply the TWHSMC V2.0 code that was calculated using the cavern geometry, and we used FLAC3D to study the stability of the cavern. Our results show that for a TWH salt cavern: 1) the optimal maximum and minimum operating pressures are 23 MPa and 16 MPa, 2) that the UGS remains stable under static pressure and for a long period of time, and 3) that the horizontal displacement of the cavern is relatively small compared to the vertical displacement. More cycles per unit time and a shorter continuous operation of low-pressure time, result in a smaller volume shrinkage rate and thus less cavern deformation. The recommended casing shoe height should be at least 12 m from the top of the cavern.
to balance the intermittent of renewable power, large-scale energy storage in underground salt caverns can be utilized. And the construction and safety evaluations for these caverns become necessary. Aimed at the bedded salt rocks for energy storage, this study focuses on the effect of different interlayer content on the stability and usability of the underground energy storage caverns in bedded salt of China. Salt caverns with five different interlayer content of 0∼30 % are established for stability and usability comparison. The numerical simulations show that the caverns with high interlayer content have better stability performance than that of the cavern with lower or no interlayer content. A usability evaluation is also discussed by evaluating the effective volume of caverns with different interlayer content. Even though the caverns with high interlayer contents have less volume shrinkage, they have smaller available volume because the collapsed sediments of the interlayer expanded in the cavern bottom. Finally, a method to increase the effective cavern volume is discussed. That is to enlarge the bottom cavern in caverns with high interlayer content.
More and more attentions are being paid to horizontal salt caverns for natural gas storage because of their large working gas capacity and favorable stability. To accelerate the construction of gas storage underground salt caverns, stability analysis of this type of cavern is necessary to assure the safety of such caverns. In this paper, the stability is investigated of a U-shaped horizontal salt cavern under different constant and cyclic internal gas pressures. A 3D geomechanical model is established based on sonar scanning in the field and predicted cavern shape. The stability is analyzed of the rock masses around the cavern under different internal gas pressures and cycle frequencies. Five evaluation criteria are proposed to predict the feasibility and stability of such caverns, including deformation, dilatancy safety factor, volume shrinkage, plastic zone, and equivalent strain. The stability of the rock mass around the cavern under different internal gas pressures is compared to that under different cycle frequencies. The results show that the cavern has a good stability under the constant internal gas pressure of 8 MPa and cyclic internal gas pressures ranging from 8 ~ 18 MPa. The five evaluation indexes of the rock masses around the cavern improve with increasing internal gas pressure. It is proposed that the corner, horizontal-roof center, and external waist positions of the cavern are to be highlighted in the design and construction phases. The cycle frequency has appreciable impact on the stability of the rock mass around the cavern. The difference between the volume shrinkage under cycling compared to constant internal gas pressure is that the cycling simulated results show a rising wave-like curve of creep time. The plastic zone ratio increases with creep time and has a flat peak and a sharp bottom with oscillations. This study provides the design parameters for U-shaped salt cavern in the Huaian salt district and can also be a reference for horizontal salt caverns.
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.
