A preliminary site selection system for underground hydrogen storage in salt caverns and its application in Pingdingshan, China
Highlights
In this study, a preliminary site selection method for underground hydrogen storage in salt cavern was established.
Dynamic demands for hydrogen energy were considered as key influencing factors.
The significance of each index in the site evaluation method for underground hydrogen storage in salt mines was investigated.
The Pingdingshan salt mine was identified as a suitable location for underground hydrogen storage in China.
1 INTRODUCTION
The world is facing energy transition by the adoption of green hydrogen as an important energy source. More than 20 countries and regions such as Japan, South Korea, Germany, and the United States have formulated national hydrogen energy development strategies. Hydrogen energy is internationally recognized as an important clean energy source for addressing climate change and achieving “carbon neutrality” (Abe et al., 2019). China has firmly implemented the Paris Agreement to address climate change issues. The declaration of carbon peak by 2030 and carbon neutrality by 2060 also demonstrates confidence in participating in global climate governance. The development of China's hydrogen energy industry has boomed in recent years, and the coordinated development capability of the hydrogen energy industry supply chain has been enhanced (Gao & An, 2022). By the end of 2021, China's hydrogen production capacity was about 4.1 × 107 tons/year, and the output was about 3.342 × 107 tons/year. China has built 255 hydrogen refueling stations. The number of hydrogen fuel cell vehicles is about 9315. It has become the world's largest hydrogen-producing country and fuel cell commercial vehicle market (China Hydrogen Energy Alliance, 2021). In March 2022, the “Medium and Long-Term Plan for the Development of Hydrogen Energy Industry (2021–2035)” formally incorporated hydrogen energy into China's energy strategy system (National Development and Reform Commission, National Energy Administration, 2022). The implementation of this policy indicates that rapid and dynamic development of hydrogen energy is taking place in China. A large-scale hydrogen storage site and a related site selection method are necessary for the hydrogen industry in China.
Due to its extremely low permeability, damage-healing ability, good creep behavior, and inertia with respect to storage medium, rock salt has been recognized as an ideal medium for underground energy storage and nuclear waste disposal (Hou, 2003; Xing et al., 2015). Underground hydrogen storage (UHS) in salt caverns has been proposed for large-scale hydrogen storage. There are four existing UHS facilities in salt caverns in operation around the world, with three in the United States and one in the United Kingdom. The first UHS facility in a salt cavern was built in 1972 in Tesside, with three salt caverns for storage of hydrogen with 95% purity. These three salt caverns are at a depth of 365 m with a constant operating pressure of 4.5 MPa. The second pure UHS facility in salt cavern was set up in 1983, with a cavern volume of 5.80 × 105 m3, in Clemens Dome. The last two salt caverns were set up in 2007 and 2014, with a cavern volume of 5.66 × 105 and 5.80 × 105 m3, respectively. Except for the Tesside salt cavern, the other three salt caverns were constructed underground with more than 1000 m depth. Compared to natural reservoirs (e.g., depleted oil and gas reservoirs, aquifer), salt caverns are a preferred option for storage of pure hydrogen (Fang et al., 2022). In natural reservoirs, ancient microorganisms may react with stored hydrogen under certain conditions (Strobel et al., 2020; Xiong et al., 2023). These microbiological reactions could result in hydrogen loss and methane regeneration. The reactants may further block the pores of reservoir, which is not favorable for long-term storage of pure hydrogen. The rapid development of hydrogen energy in China has made it imperative to promote the development of UHS in salt caverns. In addition, a comprehensive site selection method for UHS in salt caverns is the first step to achieve this goal.
Site selection is the primary consideration in the construction of a UHS site and has been receiving increasing attention from investors and builders (Tarkowski, 2019). Hydrogen molecules are smaller and more chemically reactive than methane, and may thus leak more easily through tight spaces or react with other substances. Thus, compared with methane storage in salt caverns, hydrogen storage in salt caverns has higher requirements of stability and sealing properties of caverns (Liu et al., 2020). In addition, geological conditions, technical conditions, and economic benefits also need to be considered (Lankof et al., 2022; Lewandowska-Śmierzchalska et al., 2018). Most UHS facilities in salt caverns in the United States, the European Union, and the United Kingdom were built in stable salt domes or thick salt-bearing formations (Caglayan et al., 2020; Małachowska et al., 2022; Williams et al., 2022). However, the salt mines available for UHS in China are limited due to the nature of salt-bearing formations. Rock salt in China is known as bedded salt instead of salt dome. Bedded rock is characterized by a large number of salt layers and interlayers, small thickness of a single salt layer, low content of sodium chloride, and high content of water-insoluble substances (Qiu et al., 2020; Wang et al., 2015). Therefore, when developing a UHS site selection system and determining the specific evaluation parameters of a potential site, all the factors mentioned above must be considered, especially keeping in mind the unique characteristics of hydrogen itself and bedded rock salt in China.
In this paper, a comprehensive site selection system considering the unique features of hydrogen, bedded rock salt, and the dynamic development of the hydrogen energy industry in China was developed. First, hot research topics and keywords of salt cavern storage were explored and analyzed using CiteSpace software. Second, based on the analyzed and filtered keywords, four important influencing factors of UHS in salt caverns were investigated; these factors are dynamic demands of hydrogen energy, geological, hydrological, and ground factors of salt mines. Then, a preliminary site selection method of UHS in salt caverns was developed by building a site selection index system based on the selected influencing factors and index weight determined by the analytic hierarchy process (AHP) method. Lastly, considering the Pingdingshan salt mine in China as a case study, a validation of the developed system was conducted.
2 METHODOLOGY
2.1 Bibliometric analysis by CiteSpace
The bibliometric analysis method can systematically and clearly analyze the development status of a certain field. CiteSpace is a bibliometric software that can identify and display scientific research development trends and the latest developments in the selected database. It can analyze the dynamic mechanism of discipline evolution and predict the development of disciplines through exploration of literature data and construction of visualization maps (Chen, 2006). Its significant advantages have led to its widespread application in visual analysis across various research domains (Ahsan et al., 2022; Geng et al., 2022). CiteSpace was used as the analysis tool to explore the advances, development status, and trend of salt cavern storage in China through keyword co-occurrence analysis. Based on the keyword co-occurrence analysis, references for building a site selection system for UHS in salt cavern were provided. The relevant parameters in CiteSpace were configured as follows: the time span was set from 2000 to 2022, with time slices representing 1-year intervals, and a threshold was applied to include the “TOP 50” items. Additionally, the “Pruning” method was selected to simplify the network structure and highlight important features.
Web of Science (WoS) is a widely used database that offers access to an extensive collection of scholarly literature. In this study, WoS was chosen as the data source. The search terms used were TS = (“salt cave*” and “storage”), with the time frame selected as 2000–2022 (salt cave* including salt cave and salt cavern). Nonrelevant scientific categories were excluded, and a total of 516 studies were retrieved.
2.2 The AHP
AHP is a systematic analysis method combining qualitative and quantitative analyses that was initially applied in the site selection of underground salt caverns for gas storage and hydrogen storage (Lewandowska-Śmierzchalska et al., 2018). In this paper, AHP was used to evaluate the site selection of salt caverns for UHS in China. The main steps are as follows:
When applying AHP to analyze decision-making problems, the problem must be organized and hierarchical. Thus, a hierarchical structural model needs to be created. In this paper, the target layer is the site selection evaluation of salt caverns for UHS in China. The criterion layer is the geological features of the salt mine, roof and floor properties of rock salt, and the hydrological and ground factors in the salt mine area. The measure layer is each evaluation index.
Then, the second step is to present a judgment matrix. According to the experiment conducted by Saaty (1990), a scale of 1–9 was used to compare elements in each layer. Table 1 lists the scale assignment references for 1–9.
| Scaling | The number of occurrences |
|---|---|
| 1 | Both factors are of equal importance |
| 3 | Compared with the two factors, the former is slightly more important than the latter |
| 5 | Compared with the two factors, the former is obviously more important than the latter |
| 7 | Compared with the two factors, the former is much more important than the latter |
| 9 | Compared with the two factors, the former is extremely important compared to the latter |
| 2, 4, 6, 8 | Intermediate value of the above adjacent judgment |
| Reciprocal | If the ratio of importance of factor i to factor j is aij, then, the ratio of importance of factor j to factor i is the reciprocal of aij |
3 SITE SELECTION SYSTEM AND EVALUATION INDEX FOR UHS IN SALT CAVERNS
3.1 Bibliometric analysis of salt cavern storage
In this section, bibliometric software, CiteSpace, was used to analyze the research hotspots and keywords in the field of salt cavern storage, providing a foundation for the subsequent analysis of the factors affecting the site selection for UHS in salt caverns.
The keywords not only can indicate the core contents of the paper but also indicate the research trend in the related field. The keyword co-occurrence of the 516 studies chosen was analyzed using CiteSpace and thus a knowledge map of the key co-occurrence of salt cavern gas storage was obtained (Figure 1). An overview of the high-frequency keywords of research in salt cavern storage is listed in Table 2. The first five keywords show the research trend of salt caverns in energy storage, which is favorable for salt caverns. In recent years, the prominence of hydrogen storage has been gradually increasing, reaching a centrality measure of 0.21. The keywords of feasibility analysis, renewable energy, technology, and safety indicated that the research of salt caverns was transformed into the industry application stage rather than remaining a theoretical concept. This indicates the increasing demand for hydrogen energy. The storage of hydrogen is also important. Keywords such as permeability, stability, creep deformation, pressure, and mechanical property were indicative of research on geological, hydrological, and ground factors of UHS.
 |
3.2 Influencing factors of site selection for salt cavern UHS
Based on the analysis of the hot topics and keywords in the last section and consideration of the geological characteristics of bedded rock in China, four influencing factors were summarized: dynamic demands for hydrogen energy, and geological, hydrological, and ground factors of the salt mine (Figure 2). Different from the existing site selection system for natural gas storage in salt caverns, the dynamic demands for hydrogen energy were considered as a factor for the first time. The construction and implementation of natural gas storage in China depend on the national strategy, but not for hydrogen, as hydrogen is not a national strategic energy in China currently. Thus, the demand for hydrogen in nearby areas should be included when selecting a potential storage site. Given that hydrogen development in China is in the early stages and hydrogen has diverse terminal applications, the demand for hydrogen is expected to be dynamic. Therefore, unlike the previous site selection system for natural gas storage, in this paper, as a novel approach, the dynamic demands of hydrogen energy were considered as influencing factors for site selection.
3.2.1 Dynamic demands for hydrogen energy
1.
Transportation
Hydrogen is considered a promising and eco-friendly substitute compared to traditional fossil fuels in the transportation industry, including fuel cell electric vehicles (FCEVs), hydrogen-fueled buses and trains, and other applications in the aerospace sector. It can be anticipated that hydrogen energy will play a significant role in decarbonization, particularly in the transportation sector. The potential demand for hydrogen energy in the transportation sector of the province where the salt mine is located is measured by using the increase in the value of transportation in the area.
2.
Industry
Hydrogen is used as a raw material or fuel in many industrial processes, such as for the refinement of petroleum, production of chemicals, and manufacture of fertilizers. As the demand for clean and sustainable energy sources increases, the use of hydrogen in the industry is likely to grow in the coming years. The potential demand for hydrogen in the industrial sector of the province where the salt mine is located is based on the increase in the value of industry in the area.
3.
Grid storage and stationary power generation
Hydrogen has great potential as a grid storage solution and a power generation source due to its high energy density, long-term storage capability, versatility, compatibility with existing infrastructure, and ability to improve grid stability. The potential for hydrogen to be used for grid storage in the province where the salt mine is located is measured according to the installed capacity of renewable energy in the area. The electricity consumption in the province where the salt mine is located indicates the electricity demand of the area, which can be used to measure the potential of hydrogen as a power generation source.
4.
Residential heating
Hydrogen can be used as a clean, efficient, and versatile fuel for heating homes and buildings, providing an alternative to traditional fossil fuel-based heating solutions and reducing greenhouse gas emissions while also improving air quality. The potential for hydrogen use in residential heating in the province where the salt mine is located is indicated by the heating area in that region.
5.
Hydrogen blending in natural gas
Blending of hydrogen into natural gas can improve the energy efficiency of natural gas-fired power plants and other energy-consuming systems. As the demand for clean energy continues to grow and the cost of producing hydrogen from renewable sources decreases, it is likely that hydrogen doping in natural gas will become an increasingly important tool for reducing greenhouse gas emissions and improving energy efficiency in the future. The potential for hydrogen to be used for hydrogen-mixed natural gas in the evaluated area is linked to the total amount of natural gas supplied in the area.
The Five-Year Plan for National Economic and Social Development of China has played a remarkably effective role in steering the country's economic and social development (Wang, 2020). Therefore, based on the latest Five-Year Plan, the dynamic demand phases for hydrogen energy in China are divided into three stages: 2021–2025, 2026–2030, and 2031–2035 (Table 3). In China, the construction of hydrogen storage facilities is primarily used for peak shaving and meeting supply needs in the respective provinces. As a result, the strategic demand for hydrogen energy is assessed by various indicators specifically for the province where the salt mine is located. The stage from 2021 to 2025 is determined based on the 2021 target data, while the stages from 2026 to 2030 and from 2031 to 2035 are determined based on the relevant target data of the long-term plans in various provinces of China or the average growth rate of the corresponding targets.
| Site classes | ||||
|---|---|---|---|---|
| Preferred location | Suitable location | Medium location | Unsuitable location | |
| 2021–2025 | ||||
| The increase in the value of transportation (108 CNY) | >3000 | 2000–3000 | 1000–2000 | <1000 |
| The increase in the value of industry (1012 CNY) | >1.5 | 1.0–1.5 | 0.5–1.0 | <0.5 |
| Installed capacity of renewable energy (104 kWh) | >3000 | 1500–3000 | 1000–1500 | <1000 |
| The electricity consumption (108 kWh) | >3000 | 2000–3000 | 1000–2000 | <1000 |
| Heating area (108 m2) | >8 | 5–8 | 1–5 | <1 |
| Total amount of natural gas supplied (108 m3) | >60 | 30–60 | 15–30 | <15 |
| 2026–2030 | ||||
| The increase in the value of transportation (108 CNY) | >3500 | 2500–3500 | 1500–2500 | <1500 |
| The increase in the value of industry (1012 CNY) | >2.0 | 1.5–2.0 | 1.0–1.5 | <1.0 |
| Installed capacity of renewable energy (104 kWh) | >5000 | 2000–5000 | 1500–2000 | <1500 |
| Electricity consumption (108 kWh) | >4000 | 3000–4000 | 1500–3000 | <1500 |
| Heating area (108 m2) | >10 | 6–10 | 2–6 | <2 |
| Total amount of natural gas supplied (108 m3) | >80 | 50–80 | 20–50 | <20 |
| 2031–2035 | ||||
| The increase in the value of transportation (108 CNY) | >4000 | 3000–4000 | 2000–3000 | <2000 |
| The increase in the value of industry (1012 CNY) | >3 | 2–3 | 1–2 | <1 |
| Installed capacity of renewable energy (104 kWh) | >8000 | 4000–8000 | 2000–4000 | <2000 |
| Electricity consumption (108 kWh) | >6000 | 4000–6000 | 2000–4000 | <2000 |
| Heating area (108 m2) | >15 | 10–15 | 5–10 | <5 |
| Total amount of natural gas supplied (108 m3) | >120 | 80–120 | 30–80 | <30 |
3.2.2 Geological factors of the salt mine
1.
Regional tectonic features
If the history of earthquake frequency within the rock salt geological structure is low and faults have not developed, the deposition of the entire area will be stable, which is conducive to the stability and sealing of the cavity. Generally, the storage site should be selected in an area with low historical earthquake frequency and no active faults within 200 m.
2.
Distribution range of rock salt
Larger distribution range of the salt group means that a larger-scale hydrogen storage site can be built. The unit investment will be smaller.
3.
Rock salt thickness
The greater the thickness of the rock salt ore body, the greater the volume of gas storage. The formation thickness of rock salt should be at least 100 m.
4.
Content of NaCl
Higher NaCl content of the rock salt ore body means fewer interlayers and less insoluble matter content in the rock salt, faster cavern building speed, easily controllable salt cavern shape, and better hydrogen storage safety. It is generally believed that the NaCl content of the rock salt ore body for the construction of a hydrogen storage facility cannot be lower than 50%.
5.
Interlayer thickness
The smaller thickness of the interlayer and the smaller volume ratio of the interlayer are more conducive to increasing the cavern building rate and controlling the cavern shape, thereby reducing the likelihood of extensive interlayer collapse or casing deformation damage.
6.
The nature of the interlayer
The properties of the interlayer mainly refer to its solubility and permeability. Normally, the higher the soluble content of the interlayer, the faster the cavern-forming rate and the larger the available volume of the cavity. The smaller the unoccupied interlayer porosity, the better the airtightness of the hydrogen storage.
7.
Buried depth of rock salt roof
The deeper the salt layer buried, the greater the reserves. However, great depth would speed up the creep rate of rock salt, which will not only increase the cost of building a hydrogen storage site but also lead to safety hazards such as surface subsidence. Therefore, it is necessary to consider both cost and safety for storage depth. The best burial depth of the salt roof is between 600 and 1200 m (Jing et al., 2012).
8.
Lithology and thickness of roof and floor
Normally, the rock salt roof and floor must be hard rock or thick clay-like rocks, free of aquifers and seepage layers. There should be no major ground subsidence or brine leakage during mining. The thicker top and bottom salt formation will provide better airtightness, which can effectively reduce the diffusion and leakage of hydrogen. The thickness of the top and bottom formation should be greater than 30 m.
9.
Caprock permeability and breakthrough pressure
Lower permeability of caprock and greater breakthrough pressure will better enable sealing of caprock. The permeability and breakthrough pressure can be qualitatively measured according to the development of fractures in caprock. Normally, low degree of fracture development is indicative of lower permeability of caprock and greater breakthrough pressure.
3.2.3 Hydrological factors of the salt mine
1.
Distribution of groundwater system
If there is water in the salt mine layer connected to the surface water system, there will be a channel for gas leakage, resulting in the failure of airtightness of the salt cavern cavity.
2.
Water resources security
Cavity-building water needs to have sufficient water source guarantee, and for brine, a long-term source for acceptance or treatment is needed. If the distance between the water source and the brine-receiving location is too far, the cavern construction cost will be high.
3.2.4 Ground factors of the salt mine
1.
Surface population density and building density
The location of the hydrogen storage facility should be away from population-dense areas, large buildings, factories, and special areas under environmental protection or military service locations to avoid accidents such as leakage and ground subsidence.
2.
Distance to major users or hydrogen pipelines
For the construction of hydrogen storage facilities, the distance from hydrogen transmission pipelines or major users should be considered, in addition to peak shaving requirements and gas source guarantees. It is suggested that the distance between the construction of hydrogen storage facilities and main users or hydrogen transmission pipelines should be less than 300 km.
3.3 Site selection system evaluation for UHS in salt caverns
Based on the analysis of the site selection factors for UHS in salt caverns, a comprehensive evaluation index method was proposed. Ten experts or engineers with relevant research experience were invited to participate in the rating process. The AHP method was used to calculate the weight of hydrogen storage site selection indexes, and the following scores for site selection indexes were listed (Table 4). Thereby, combined the AHP method with the evaluation index method, a site selection method of UHS in salt caverns was developed. Summing the product of each index score and the corresponding weight value, the comprehensive storage construction level value P was obtained (Table 5). The specific flowchart is illustrated in Figure 3.
 |
 |
| Category | Score P |
|---|---|
| Preferred location | 9 < P ≤ 10 |
| Suitable location | 7 < P ≤ 9 |
| Medium location | 5 < P ≤ 7 |
| Unsuitable location | P ≤ 5 |
3.4 Site selection system applied to the Pingdingshan salt mine
Fourteen to 20 salt groups of the Pingdingshan salt mine have been investigated as potential sites for natural gas storage (Zheng et al., 2020). To apply the developed site selection method for a candidate site, 14–20 salt groups of the Pingdingshan salt mine and the dynamic demands of hydrogen energy in Henan province are evaluated in this section. The salt layer that was evaluated is situated to the south of Pingdingshan City in Henan Province, approximately 50 km from the city's urban area and 140 km from the provincial capital of Zhengzhou City.
3.4.1 Evaluation of dynamic demands of hydrogen energy
Henan is a large province with industrial and energy consumption in China. In 2021, the value added of the transportation and transportation industry in Henan Province was 336.82 billion CNY, the value added of the industry was 1.81 trillion CNY, the installed capacity of renewable energy was 38.13 million kWh, power consumption was 364.7 billion kWh, the heating area was 64 million square meters, and the total natural gas supply was 6.73 billion cubic meters. In August 2022, Henan Province released the “Long-Term Plan for the Development of the Hydrogen Energy Industry in Henan Province (2022–2035) (Henan Provincial People's Government General Office, 2022).” The plan proposed that, by 2025, the annual output value of the hydrogen energy industry will exceed 100 billion CNY, more than 5000 hydrogen fuel cell vehicles will be used, and the terminal price of hydrogen will be reduced to below 30 CNY/kg. By 2035, the application of hydrogen energy in the transportation sector will be basically industrialized, and the comprehensive indicators of key technologies such as hydrogen production, storage, transportation, and addition will reach world-class levels.
3.4.2 Evaluation of geological, hydrological, and ground factors
The historical seismic activity in the area where the salt layer is located is relatively weak. The faults in the block are not developed, and there is no active fault in the vicinity of 1 km. The distribution area of the 14–20 salt group is about 11.98 km2, the total thickness of the formation is about 200–260 m, and the average NaCl content can reach more than 73%. The number of interlayers is small and the thickness is small, ranging from 2 to 8 m, with an average of 5.1 m, and contains a total of eight interlayers. The interlayer is mainly composed of mudstone, with a high average soluble NaCl content, an average pore diameter of 9.669 nm, a relatively dispersed pore distribution, and good sealing conditions. The buried depth of the salt group caprock is 900–1400 m; caprock has few fractures and is dense in lithology, has a breakthrough pressure of 10–12 MPa, and a thickness of 56–118 m. Salt deposits are isolated from the groundwater system. The target area is relatively close to the water source, and the water source and the brine treatment area are within 10 km from the storage site. There are no major buildings nearby, but the surface population distribution is denser (Chen et al., 2016).
3.4.3 Final evaluation
In Table 4, the scores of the indicators of the 14–20 salt groups in the Pingdingshan salt mine in Henan province are shown. The scores of the 20 basic indicators are as follows: 10, 10, 10, 10, 8, 10, 10, 6, 8, 8, 10, 8, 8, 8, 10, 10, 8, 6, 10, and 8. Summing the product of each indicator score and the corresponding weight value, a comprehensive storage construction level value of the storage site: P = 8.779 was obtained. Compared with Table 5, the storage site is suitable, which shows that the Pingdingshan salt mine is a suitable candidate for the construction of a UHS site in China.
4 CONCLUSIONS AND PROSPECTS
4.1 Conclusions
1.
The prominence of hydrogen storage research has been steadily increasing, reaching a centrality measure of 0.21 in salt cavern storage studies. This signifies a shift in salt cavern energy storage research from a theoretical level to an application-oriented approach, underpinning considerations of the dynamic demands for hydrogen energy. Currently, interest in research related to geological, hydrological, and ground factors remains high, as indicated by the frequency of these keywords.
2.
According to China's Five-Year Plan for national economic and social development, the dynamic demands of hydrogen energy are divided into three stages with different index values. Based on this novelty factor and three other factors focused on salt mines, a comprehensive site selection system was developed.
3.
Applying the developed site selection system to evaluate the 14–20 salt groups of the Pingdingshan salt mine and the dynamic demands for hydrogen energy in Henan province, a comprehensive storage construction grade value of the storage site was evaluated as 8.779, indicating that it is a suitable location for UHS in China.
4.2 Limitations and future directions
In this study, a preliminary site selection system was constructed for UHS in salt caverns. However, there are certain limitations. First, the model is geographically constrained, having been specifically designed to suit China's unique national and geological contexts. This may limit the applicability of the research findings to other regions with different geological, hydrological, or surface characteristics. Second, while the study effectively uses AHP, it heavily relies on expert opinions to weight each index, which could potentially introduce bias.
In future work, the methodology of this study could be applied to other potential hydrogen storage locations in different geological environments, verifying its effectiveness and adaptability. Simultaneously, further research could explore the application of alternative or complementary methodologies to AHP and expert survey methods used in this study, which can mitigate potential biases and improve the robustness of the site selection system.
AUTHOR CONTRIBUTIONS
Liangchao Huang: Conceptualization; data curation; formal analysis; writing; methodology; software. Yanli Fang: Writing; conceptualization; methodology. Zhengmeng Hou: Supervision; review; project administration. Yachen Xie: Writing; visualization. Jiashun Luo: Validation; formal analysis. Lin Wu: Validation; investigation. Qichen Wang: Methodology. Yilin Guo: Data curation. Wei Sun: Validation; methodology.
ACKNOWLEDGMENTS
This work was supported by the Henan Institute for Chinese Development Strategy of Engineering & Technology (Grant No. 2022HENZDA02), the Since & Technology Department of Sichuan Province Project (Grant No. 2021YFH0010), and the High-End Foreign Experts Program of the Yunnan Revitalization Talents Support Plan of Yunnan Province.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.
Biographies
Yanli Fang is currently a doctoral candidate and research assistant at the Clausthal University of Technology. She primarily focuses on underground energy storage in salt caverns, with a particular focus on hydrogen storage, compressed air energy storage (CAES), natural gas storage, and liquid fuel storage. Her research contributions include publication of 15 papers indexed in SCI/EI databases, acquisition of one software copyright, and the filing of two patents.
Prof. Zhengmeng Hou is the head of rock mechanics at Clausthal University of Technology as well as an academician of the Academy of Geosciences and Geotechnologies, Germany. He has been engaged in teaching, scientific research, and international cooperation in the fields of unconventional petroleum and geothermal development, hydraulic fracturing, CCUS, carbon neutrality and energy transition, underground storage of natural gas and strategic oil, especially renewable energy coupled with power-to-X, as well as deep rock mechanics. He has published more than 250 papers in SCI/EI, 10 monographs in English and German, and one monograph in Chinese, and edited five international conference proceedings.
