Salt Cavern Storage Research Articles

Safety of Hydrogen Storage Technologies

While hydrogen is regularly discussed as a possible option for storing regenerative energies, its low minimum ignition energy and broad range of explosive concentrations pose safety challenges regarding hydrogen storage, and there are also challenges related to hydrogen production and transport and at the point of use. A risk assessment of the whole hydrogen energy system is necessary to develop hydrogen utilization further. Here, we concentrate on the most important hydrogen storage technologies, especially high-pressure storage, liquid hydrogen in cryogenic tanks, methanol storage, and salt cavern storage. This review aims to study the most recent research results related to these storage techniques by describing typical sensors and explosion protection measures, thus allowing for a risk assessment of hydrogen storage through these technologies.

Effect of a gunite lining on the stability of salt caverns in bedded formations for hydrogen storage

In this paper, a novel methodology to improve the structural behaviour and durability of bedded salt caverns for hydrogen storage is proposed. The suggested technology consists in applying a gunite lining over the whole cavern surface by means of a pneumatic air blowing. This continuous flow projected at high speed onto the cavern surface produces a self-compacted gunite facing. The effect of adding a gunite lining on the structural performance of a bedded salt cavern is analysed. The nonlinear finite element method is then applied to solve the inherent nonlinear solid mechanics problem. It is shown that reinforcing salt caverns with a gunite lining improves the cavern behaviour, specially in the case of caverns located within a horizontal salt stratum confined between other strata. When dealing with these salt formations, the stratum geometry limits the cavern height. In general, wider caverns that exhibit larger displacements are required to achieve a huge storage capacity. Moreover, these caverns can be located at a considerable depth, where the temperature has an important role on the creep deformation process. Therefore, the proposition of stabilization techniques is required to ensure both their structural integrity and the ground subsidence. This technology allows the safe exploitation of salt caverns located at bedded-type stratified horizontal salt formations.

Selection decision of optimal hydrogen storage salt cavern based on combination weight and cumulative prospect theory

With the background of ' energy revolution ' and ' double carbon ', clean energy has gradually become a global research hotspot, and hydrogen is the key to affect the future energy pattern. With the continuous expansion of the field of energy storage, underground hydrogen storage is widely considered to be an effective way to solve large-capacity long-term storage, in which salt caverns are considered because of their unique advantages. At present, most of the research on salt cavern selection starts from the salt cavern itself and ignores the environment and social groups, and the discussion is too one-sided. This paper evaluates the criteria from both subjective and objective aspects, and constructs a multi-criteria decision-making model for selecting salt caverns based on prospect theory. It aims to select the most suitable hydrogen storage salt caverns from the overall impact of society, environment, salt cavern characteristics and supply and demand sides. Taking Jintan area of Jiangsu Province in China as an example, this paper selects an optimal salt cavern and an alternative salt cavern from five salt caverns, and carries out double verification of sensitivity analysis and comparative analysis. This study will provide some reference for the field of underground hydrogen energy storage, and provide reference for relevant areas suitable for hydrogen storage.

Combined cycle gas turbine (CCGT) plants utilizing methane-hydrogen blends represent a significant element in Australia’s journey toward achieving net-zero emissions

To deliver 570 TWh of dispatchable electricity to the grid in Australia, it is necessary to build up wind and solar photovoltaic power plants generating capacity of 325 GW, and a long-term hydrogen energy storage system comprising 50–150 GW of electrolyzers, 50 TWh of hydrogen storage, and 165 GW of hydrogen power generation. While the addition of other renewable energy producers and energy storage technologies effective on shorter scales are certainly welcome and positively impact the above demand, the inclusion of inter-annual variability and safety negatively impacts these numbers. Fuel cells are currently less advanced compared to electrolyzers and hydrogen storage in salt caverns. Expanding hydrogen power generation will require exploring additional opportunities. Here we advocate for methane-hydrogen Combined Cycle Gas Turbine (CCGT) plants. Their adaptability to effortlessly integrate methane and green hydrogen mixtures positions them as a key player in the evolution toward net zero. This transition will be complete once a fully established wind and solar photovoltaic generation, coupled with an efficient hydrogen energy storage system, is in place. Notably, these CCGT plants consistently yield the lowest Life Cycle Analysis (LCA) carbon dioxide (CO2) emissions during the grid’s progression toward net zero.

Feasibility analysis on the debrining for compressed air energy storage salt cavern with sediment

Using the sediment void to store gas is a promising solution for the construction of compressed air energy storage (CAES) salt cavern with high impurity. However, it remains debatable whether the pressure loss of brine in the sediment can notably affect debrining. In this paper, the in-situ sediments are obtained, and their porosity, moisture content after debrining and permeability are measured. A model of debrining in salt cavern with sediment is built. The model prediction error of injection gas pressure is less than 0.34 %. A criterion for the feasibility evaluation of debrining for CAES salt cavern with sediment is proposed. The results show that the porosity of the in-situ sediment is 47.9 %. When the sediment volume reaches 98 % of the cavern volume, the pressure loss of brine in the sediment and the maximum gas pressure are less than 3.1 MPa and 17 MPa, respectively. The sediment has good permeability, it is feasible to debrine in salt cavern with sediment. It is suggested that the debrining rate and the tubing diameter increase to more than 120 m3/h and 0.14 m, respectively. This study provides valuable guidance for the debrining in salt caverns with sediment.

Research on the Stability of Salt Cavern Hydrogen Storage and Natural Gas Storage under Long-Term Storage Conditions

The stability of salt cavern storage during prolonged operation is a crucial indicator of its safety. This study focuses on an operational underground gas storage facility, conducting comparative numerical simulations for the storage of natural gas and hydrogen. We investigated the evolution of stability for natural gas and hydrogen storage under long-term storage conditions. The main conclusions are as follows: (1) A new equation for stress equilibrium and constitutive relations are derived. (2) At the same storage pressure, the effective stress at the same position in the interlayer is greater for hydrogen storage compared to natural gas storage, signifying a higher level of danger. (3) At the same storage pressure, the displacement at the cavity top for hydrogen storage is greater than that for natural gas storage. The displacement difference between the two is greatest at 9 MPa, amounting to 0.026 m. (4) Due to hydrogen’s lower dynamic viscosity and higher permeability, the depth and extent of the plastic zones within the interlayers are greater compared to natural gas. When the storage pressure is 15 MPa, the depth of the plastic zone within the interlayer can be up to 2.1 m greater than when storing natural gas, occurring in the third interlayer from the top. These research findings may serve as a valuable reference for determining the operational parameters of on-site salt cavern hydrogen storage facilities.

Study on salt crystals fouling on the tubing surface for energy storage salt cavern during debrining

Salt crystals fouling may lead to the blockage of debrining inner tubing(DIT) for underground gas storage(UGS) salt cavern. In this paper, the components of salt crystals are analyzed, and a model for calculating the salt crystals fouling is established, which considers the coupling effects of flow-thermal-chemical. This model is verified by comparing monitoring data of an actual salt cavern debrining. The influences of salt cavern depth, DIT size and heat conductivity on salt crystals fouling rate are analyzed. When the salt cavern depth is increased from 1000 to 2000 m, the salt crystals fouling rate increases from 3.61 to 32.17 mm/day. The influences of the DIT size on the salt crystals fouling rate are minor. When the heat conductivity of tubing decreases from 4 to 0.4 W/(m·℃), the salt crystals fouling rate reduces by 30.37 %. This study could help formulate a debrining scheme to prevent the DIT clogging.

Research of interlayer dip angle effect on stability of salt cavern energy and carbon storages in bedded salt rock

In order to clean and decarbonize energy, large-scale underground energy storage in salt caverns can be utilized. The construction and safety evaluations for these caverns are crucial, especially for salt caverns with significant interlayer dip angles. Aimed at the bedded salt rocks for energy and carbon storage, this study focuses on the impact of different interlayer dip angles on the stability of underground energy and carbon storage caverns in bedded salt rock formations in China. Four salt caverns with varying interlayer dip angles of 0–30° were established for stability comparison. Numerical simulations reveal that caverns with high interlayer dip angles demonstrate low volume shrinkage, general deformation resistance and small equivalent strain, while exhibiting a larger volume of plastic zones compared to caverns with lower interlayer dip angles. It is important to consider the deformation of the cavern wall rock in the down-dip direction for caverns with high interlayer dip angles. The presence of inclined interlayers affects the symmetry of the contour distribution of deformation, safety factor and equivalent strain. Furthermore, recommendations are provided for the construction of salt caverns in salt rock formations with high interlayer dip angles.

Experimental investigation on the oil extraction process for a novel underground oil storage method: Oil storage in salt cavern insoluble sediment voids

Large-scale underground oil storage is vital for addressing the energy crisis. Leveraging the insoluble sediment space at the bottoms of salt caverns for oil storage is particularly effective in high-impurity salt mines, enhancing oil storage capacity. The process of extracting oil from the sediment void is essential for utilizing this resource. Three experimental devices were developed to investigate this extraction process. We conducted experiments on oil extraction processes and rates for various oil types, analyzing weight changes and influencing factors. The sediment and water content in the extracted oil were also evaluated. Results indicated that extracting oil from the sediment void is feasible, yielding average recovery rates over 90.0 %. High-viscosity oil at 50 °C exhibited three stages: initial stability, a rapid rise, and final stability. Low-viscosity oil correlated with brine injection rates, displaying a rapid rise, stable phase, and subsequent decline. Petrolatum extraction was easier than diesel extraction, and ground temperature improved recovery rates. Changes in water and sediment content had minimal impact on oil quality. This research provides insights for large-scale underground energy storage.

Microstructural evolution and mechanical behaviors of rock salt in energy storage: A molecular dynamics approach

The microstructure of rock salt significantly influences its macroscopic mechanical behaviors and deformation phenomena. Understanding the deformation and failure characteristics of rock salt at multiple scales is crucial for the secure and efficient functioning of energy storage in salt caverns. Although the macroscopic behaviors of rock salt are well understood, the microstructural changes occurring under uniaxial compression have not been thoroughly investigated. This study aims to investigate the evolving laws of rock salt microstructure and mechanical properties during the damage process, thereby providing a fundamental understanding of the underlying mechanism. To achieve this, a series of characterization tests on rock salt were conducted to study its microstructure and defects. Building on this, molecular dynamics simulations were utilized in rock mechanics to elucidate the mechanical behaviors, structural evolutions, and dislocation motions of rock salt during the damage process. The rock salt obtained from Qianjiang, China, is a polycrystalline material with an average subgrain size of 46 nm and an average dislocation density of 4.76 × 10−6 1/Å2. Uniaxial compression of single crystal NaCl exhibits three stages: elastic compression, rapid dislocation multiplication, and forest hardening. Scattered dislocations and isolated dislocation tangles trigger further plastic slippage, leading to decreased strength. Later, the formation of a dislocation cell network hinders further slip and reinforces the strength of rock salt. Plastic deformation is found to be a dominant factor in grain refinement and the formation of polycrystalline structures. Intergranular cracking results from cross-patterned dislocation lines on grain boundaries, which become vulnerable areas of the structure. This study describes the evolutionary process of rock salt microstructures and mechanical properties, identifies the micro-destruction mechanisms during the damage process at the ionic level, and provides insights into the micro-mechanical behavior of rock salt and for the design and stability assessment of underground energy storage facilities.

Overview of Salt Cavern Oil Storage Development and Site Suitability Analysis

Salt cavern storage, characterized by its safety, stability, large scale, economic viability, and efficiency, stands out as a cost-effective and relatively secure method for large-scale petroleum reserves. This paper provides an overview of the current development status of salt cavern storage technologies both domestically and internationally, analyzes the advantageous conditions and numerous challenges faced by salt cavern Strategic Petroleum Reserve (SPR) storage in China, and forecasts the development trends of this technology. The conclusions indicate that China possesses all of the necessary conditions for the development of salt cavern storage. Moreover, utilizing the Analytical Hierarchy Process (AHP), a macro suitability hierarchical evaluation system is constructed for the site selection and construction of salt cavern storage facilities. This system quantifies various site selection indicators, integrating expert opinions and findings from relevant theoretical research to establish grading standards for the suitability indices of salt cavern storage construction. Applied to the site evaluation of salt cavern storage at the Jintan Salt Mine in Jiangsu, the results indicate its high suitability for storage construction, making it an ideal location for establishing such facilities. The evaluation results are consistent with expert opinions, demonstrating the rationality of this method.

Gas tightness around salt cavern gas storage in bedded salt formations

Underground salt cavern storage has become the preferred medium for storing gas energy and strategic substances. Salt caverns are suitable for storing small molecular gases due to the low porosity and permeability of salt rocks. This paper comprehensively analyzes the physical properties of four gases - hydrogen, helium, methane, and carbon dioxide - under subsurface temperature and pressure conditions. It categorizes the flow regimes of these gases in salt rocks under geological pressure conditions based on the Knudsen number. In a typical 1000 m salt cavern, the predominant permeation flow regime of four gases in the surrounding rock is Klinkenberg flow, with helium potentially undergoing transitional flow at low operation pressures. A 3D numerical model is established for an actual salt cavern to compare the permeation and leakage characteristics of these gases within salt rock formations. Results indicate that, under identical operation conditions, the permeation range of the gases decreases in the following order: hydrogen > methane > helium > carbon dioxide. Under the cyclic operation pressures, the cumulative leakage amount of hydrogen, helium, and methane increases over time, while that of carbon dioxide initially rises and then decreases. This behavior is attributed to the fact that the reverse-permeation rate of carbon dioxide at low pressures exceeds its permeation rate at high pressures. Over 30 years cyclic operation, the leakage ratios of the gases are as follows: hydrogen (13.29 %), methane (9.34 %), helium (7.47 %), and carbon dioxide (0.93 %), with hydrogen exhibiting the highest and carbon dioxide the lowest leakage ratios. Larger permeability results in a larger permeation range, while larger porosity leads to a smaller permeation range. When the permeability of salt layer is greater than 1e-20 m2, the permeation range of hydrogen significantly increases. Gas leakage ratios increase with permeability nonlinearly and increase with porosity linearly. The impact of salt layer permeability on leakage ratios is greater than that of porosity. This study provides crucial guidance for the selection of geological formations for storing hydrogen, helium, methane, and carbon dioxide in salt caverns, as well as the investigation of gas permeation characteristics in salt layers.

Geometry prediction and design for energy storage salt caverns using artificial neural network

Salt cavern is one of the best storage for hydrogen, compressed air, and natural gas. However, the current physical/numerical simulation-based construction design cannot yield optimal solutions due to the complex correlation of multiple construction parameters. This paper proposes a novel machine-learning-enabled method for the geometry prediction and design optimization during salt cavern construction. A dataset of 1197 simulations of salt cavern construction is collected using our previously developed program. Construction parameters are included as inputs, and the simulated cavern geometries as outputs. A Gated Recurrent Unit model is selected and well-trained from 600 artificial neural network models. The model achieves a mean absolute error of 1.6m in the test dataset and of 2.83m for the geometric prediction of cavern JT52 in Jintan, meeting the field design requirements. Furthermore, an optimized construction design method is proposed by looping generating construction parameters, shape prediction, and deviation calculation until the deviation meets requirements. It succeed in designing an ideal ellipsoid cavern in approximately 51 min, with a capacity ratio fc 31 % larger than those of the field caverns. This approach demonstrates the potential for machine learning methods to serve as the third generation of construction design methods after physical and numerical modeling.

Integrating 1D and 3D geomechanical modeling to ensure safe hydrogen storage in bedded salt caverns: A comprehensive case study in canning salt, Western Australia

The viability of hydrogen storage in bedded salt caverns hinges on understanding the geomechanical challenges posed by the anisotropic stress states and complex geology of such environments. This study presents a comprehensive geomechanical analysis focusing on a proposed cavern within the Carribuddy Formation in Western Australia, characterized by its interbedded salt layers. This paper introduces a new geomechanical workflow, encompassing 1D and 3D modeling techniques to provide detailed changes of mechanical properties and stress state in interbedded salt formation allowing to identify the initial optimal operational pressures for underground hydrogen storage. Initial 1D models evaluated mechanical properties and in-situ stresses, while subsequent 3D simulations, enriched by data from neighboring wells, detailed the stress, strain, and displacement responses of the cavern walls to internal pressure changes. The analysis pinpointed an initial safe gas pressure range between 3000 and 4000 psi, attributing this margin to the robust characterization of the mechanical and in-situ stress of the formation. Our findings underscore the significance of high-resolution geomechanical modeling in identifying initial optimal operational pressures for hydrogen storage in salt caverns, ensuring both safety and structural integrity.

Opportunities and constraints of hydrogen energy storage systems

Abstract In contrast to battery storage systems, power-to-hydrogen-to-power (P-H2-P) storage systems provide opportunities to separately optimize the costs and efficiency of the system’s charging, storage, and discharging components. The value of capital cost reduction relative to round-trip efficiency improvements of P-H2-P systems is not well understood in electricity systems with abundant curtailed power. Here, we used a macro-energy model to evaluate the sensitivity of system costs to techno-economic characteristics of P-H2-P systems in stylized wind-solar-battery electricity systems with restricted natural gas generation. Assuming current costs and current round-trip P-H2-P efficiencies, least-cost wind and solar electricity systems had large amounts of excess variable renewable generation capacity. These systems included P-H2-P in the least-cost solution, despite its low round-trip efficiency and relatively high P-H2-P power discharge costs. These electricity system costs were not highly sensitive to the efficient use of otherwise-curtailed power, but were sensitive to the capital cost of the P-H2-P power discharge component. If the capital costs of the charging and discharging components were decreased relative to generation costs, curtailment would decrease, and electricity system costs would become increasingly sensitive to improvements in the P-H2-P round-trip efficiency. These results suggest that capital cost reductions, especially in the discharge component, provide a key opportunity for innovation in P-H2-P systems for applications in electricity systems dominated by wind and solar generation. Analysis of underground salt cavern storage constraints in U.S.-based wind and solar scenarios suggests that ample hydrogen storage capacity could be obtained by repurposing the depleted natural gas reservoirs that are currently used for seasonal natural gas storage.

Well Integrity in Salt Cavern Hydrogen Storage

Underground hydrogen storage (UHS) in salt caverns is a sustainable energy solution to reduce global warming. Salt rocks provide an exceptional insulator to store natural hydrogen, as they have low porosity and permeability. Nevertheless, the salt creeping nature and hydrogen-induced impact on the operational infrastructure threaten the integrity of the injection/production wells. Furthermore, the scarcity of global UHS initiatives indicates that investigations on well integrity remain insufficient. This study strives to profoundly detect the research gap and imperative considerations for well integrity preservation in UHS projects. The research integrates the salt critical characteristics, the geomechanical and geochemical risks, and the necessary measurements to maintain well integrity. The casing mechanical failure was found as the most challenging threat. Furthermore, the corrosive and erosive effects of hydrogen atoms on cement and casing may critically put the well integrity at risk. The research also indicated that the simultaneous impact of temperature on the salt creep behavior and hydrogen-induced corrosion is an unexplored area that has scope for further research. This inclusive research is an up-to-date source for analysis of the previous advancements, current shortcomings, and future requirements to preserve well integrity in UHS initiatives implemented within salt caverns.

Mechanical Properties of Rock Salt from the Kłodawa Salt Dome-A Statistical Analysis of Geomechanical Data.

Rock salt is a potential medium for underground storage of energy resources and radioactive substances due to its physical and mechanical properties, distinguishing it from other rock media. Designing storage facilities that ensure stability, tightness, and safety requires understanding the geomechanical properties of rock salt. Despite numerous research efforts on the behaviour of rock salt mass, many cases still show unfavourable phenomena occurring within it. Therefore, the formulation of strength criteria in a three-dimensional stress state and the prediction of deformation processes significantly impact the functionality of storage in salt caverns. This article presents rock salt's mechanical properties from the Kłodawa salt dome and a statistical analysis of the determined geomechanical data. The analysis is divided into individual mining fields (Fields 1-6). The analysis of numerical parameter values obtained in uniaxial compression tests for rock salt from mining Fields 1-6 indicates an average variation in their strength and deformation properties. Upon comparing the results of Young's modulus (E) with uniaxial compressive strength (UCS), its value was observed with a decrease in uniaxial compressive strength (E = 4.19968·UCS2, R-square = -0.61). The tensile strength of rock salt from mining Fields 1-6 also exhibits moderate variability. An increasing trend in tensile strength was observed with increased bulk density (σt = 0.0027697·ρ - 4.5892, r = 0.60). However, the results of triaxial tests indicated that within the entire range of normal stresses, the process of increasing maximum shear stresses occurs linearly ((σ1 - σ3)/2 = ((σ1 + σ3)/2)·0.610676 + 2.28335, r = 0.92). A linear relationship was also obtained for failure stresses as a function of radial stresses (σ1 = σ3·2.51861 + 32.9488, r = 0.73). Based on the results, the most homogeneous rock salt was from Field 2 and Field 6, while the most variable rock salt was from Field 3.

Artificial intelligence-driven assessment of salt caverns for underground hydrogen storage in Poland

This study explores the feasibility of utilizing bedded salt deposits as sites for underground hydrogen storage. We introduce an innovative artificial intelligence framework that applies multi-criteria decision-making and spatial data analysis to identify the most suitable locations for storing hydrogen in salt caverns. Our approach integrates a unified platform with eight distinct machine-learning algorithms—KNN, SVM, LightGBM, XGBoost, MLP, CatBoost, GBR, and MLR—creating rock salt deposit suitability maps for hydrogen storage. The performance of these algorithms was evaluated using various metrics, including Mean Squared Error (MSE), Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), Root Mean Square Error (RMSE), and Correlation Coefficient (R2), compared against an actual dataset. The CatBoost model demonstrated exceptional performance, achieving an R2 of 0.88, MSE of 0.0816, MAE of 0.1994, RMSE of 0.2833, and MAPE of 0.0163. The novel methodology, leveraging advanced machine learning techniques, offers a unique perspective in assessing the potential of underground hydrogen storage. This approach is a valuable asset for various stakeholders, including government bodies, geological services, renewable energy facilities, and the chemical/petrochemical industry, aiding them in identifying optimal locations for hydrogen storage.

Volume-of-fluid-based method for three-dimensional shape prediction during the construction of horizontal salt caverns energy storage

Construction prediction is the key for the shape control of energy storage salt caverns, which benefits with the storage capacity and long-term operational safety. However, the conventional grid discretization methods using elastic grid could not accurately tracking the three-dimensional boundary movements of salt cavern. This paper introduced a novel construction prediction model of salt cavern using a Volume-of-fluid based method. The tracking of the salt caverns’ dissolving boundary is successfully reconstructed and tracked by the fluid volume fractions (0-1) in structural grids. The model was validated by indoor experiment and field data. In the simulation of indoor experiment, the lateral expansion, which was difficult to reproduce in previous models, is successfully simulated. The volume of the simulation chamber is 392.8 ml with an error of 1.9 %. During the simulation of Volgograd horizontal cavern construction, the simulated cavern shape is close to the sonar detection, with an average error in radius about 3.6 %. And the brine-discharge concentration is consistent with the site monitoring, with an average error about 4.5 %. These results validate the capability of the proposed method in three-dimensional dynamic boundary tracking and shape prediction of salt cavern.

The role of salt basins in the race to net zero: a focus on Australian basins and key research topics

Globally, many salt basins host highly productive fossil fuel resources and provide excellent opportunities for developing economically viable clean energy systems such as (1) energy storage in salt caverns, including hydrogen, helium, natural gas, and other economic gases; (2) permanent sequestration of carbon dioxide; (3) development of geothermal energy; (4) critical mineral exploration and extraction, and (5) natural hydrogen production. Despite the high potential to deploy financially viable clean energy solutions related to the formation and evolution of salt basins, our current knowledge regarding critical aspects of salt basin characterisation in Australia is limited. New research is necessary to develop these sustainable energy systems and achieve net zero emissions; therefore, it is critical to re-evaluate the geology of salt basins. Key research areas to enable these opportunities relate to the precipitation, deposition, and deformation of salt basins. This paper reviews the potential for a range of energy systems within salt basins, outlines emerging research topics, and demonstrates the value of Australian salt basin outcrop analogues for improved subsurface interpretation globally.