Introduction to Salt Caverns

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.

Safe Underground Gas Storage (UGS) can be achieved in artificial, salt caverns to meet fluctuations in energy demand by providing adequate knowledge on rock salt when subjected to similar cyclic conditions.

Current operational subsurface energy facilities use salt caverns for storage and air as the working gas.

Compressed air energy storage (CAES) represents such a storage option, with three commercial facilities using salt caverns for storage operational in Germany, the US, and Canada, with CAES now being actively considered in many countries.

The storage of natural gas in geological structures such as depleted fields, aquifers and salt caverns plays an important role in a gas supply system as it balances the fluctuation of gas demand and price.

Hence, the idea of blending hydrogen with methane and use underground mine excavations to increase the storage capacity, apart from salt caverns.

Depleted oil or natural gas fields, aquifers, mines, and salt caverns are geological formations that can be used to store natural gas.

Most of them were caused by volume shrinkage of salt caverns.

In the energy transition context, salt caverns are probably the most promising storage solution that promotes the development of intermittent renewable energies, due to their flexible and high deliverability.

To better understand the creep mechanical behavior of salt rock under very long-term tests and more accurately predict the long-term deformation of the salt caverns , a series of long-term uniaxial creep tests lasting for 21000 h (875 days) were carried out.

Underground salt caverns seem to be promising.

Salt caverns should be mainly used for hydrogen storage due to the tightness of rock salt.

Electricity can be partially converted into hydrogen, which can be transported via pipelines, stored in large quantities in underground salt caverns to overcome seasonal effects and used as electricity storage or as a clean fuel for transport.

Small-spacing twin-well (SSTW) salt caverns have an extensive application prospect in thin or bedded rock salt formations due to their good performance, while they are rarely used in ultra-deep formations.

To enable a fast transition of the global energy sector towards operation with 100% renewable and clean energy technology, the geological storage of hydrogen in depleted gas fields or salt caverns has been considered as a strong candidate for the future energy storage required for limiting global warming to well below 2 °C, as agreed under the Paris Agreement.

For this purpose, underground gas storage (UGS) in salt caverns, deep aquifers and oil-/gas reservoirs has been proposed, which are environments with potentially high microbial abundance and activity.

In previous works, the analysis of stability and tightness of salt caverns were mostly carried out independently, and few studies have considered the interaction between them.

Analytical assessments have been conducted on the potential of natural underground containments such as salt caverns, deep saline aquifers, depleted hydrocarbon reservoirs, and coal mines, to store electricity in the form of electrolytically produced hydrogen.

Salt caverns are accepted as an ideal solution for high-pressure hydrogen storage.

The minimum internal pressure obtained by the large deformation solutions was lower than that obtained by the small deformation solutions, which can help to reduce the cushion gas in salt caverns.

, hydrogen) is in subsurface rock salt caverns.

The approach used in this study provides an improved method for the stability evaluation and optimal operation parameters for salt caverns.

Rock salt caverns have been extensively used as reliable repositories for hazardous waste such as nuclear waste, oil or compressed gases.

The extent of dilatancy in this disturbed zone, as well as the impact of dilatancy on the transport properties, are important for assessing the safety of radio-active waste disposal as well as the integrity of salt caverns and boreholes in the context of energy storage, brine cavern abandonment and gas well abandonment.

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.

</p><p>Hydrogen has been stored in small volumes (<25GWh) in salt caverns at various locations onshore in the United Kingdom since 1959.

Underground storage in salt caverns is a preferred method for the intermediate storage of natural gas to cover seasonal fluctuation in consumption and commercial gas storage.

The crude oil price has been keeping at a low level in recent years, which made China's government put more efforts in the development of underground oil storages in depleted salt caverns.

to balance the intermittent of renewable power, large-scale energy storage in underground salt caverns can be utilized.

The analysis reveals up to 725 GWh of ready-to-use capacity by utilising existing underground salt caverns in the UK.

Compressed air energy storage (CAES) is a promising energy conversion storage technology and underground salt caverns are recognized as the appropriate storage places for it.

The article presents a method of forecasting the deformation of the land surface over large fields of underground gas storage facilities located in salt caverns.

Stability analysis of salt caverns is a very complicated subject due to the coupled time-dependent thermo-mechanical behavior of salt during leaching and operational phase of the gas storage subjected to the cyclic loading.

Overall, combining electrolysis-generated hydrogen with hydrogen storage in underground porous media such as geological reservoirs and salt caverns is well suited for shifting excess off-peak energy to meet dispatchable on-peak demand.

The technical aspects and economics of bulk hydrogen storage in underground pipes, lined rock caverns (LRC) and salt caverns are analyzed.

Many insoluble sediments accumulate at cavern bottoms during the construction of salt caverns located in highly insoluble salt formations.

Based on this study, it is found that ignoring the principal stress rotation may overrate the stability and tightness of underground storage in bedded rock salt caverns.

In some of salt caverns, natural gas is currently stored.

Twelve incidents involving well casing and/or cement leaks in the salt caverns storage industry are described.

Although the storage of gaseous hydrogen in salt caverns already is used on a full industrial scale, the approach is not applicable in all regions due to varying geological conditions.

This knowhow allowed the stability analysis of several salt caverns for brine production at the State of Alagoas in Brazil and to the drilling through stratified thick layers of salt of the pre-salt reservoirs in Santos Basin.

Underground salt caverns are used globally for large-scale energy storage.

These results are valuable in evaluating rock damage and guiding the operation of underground salt caverns.

On other hand it deforms under even low deviatoric stress which threatens the structural stability of salt caverns.

Large scale CAES requires underground storage caverns, such as the salt caverns situated in the Cheshire Basin, UK.

To investigate the gypsum-salt interbedded roof collapse, the failure mechanism and the control methods of Dainan siltstone, which is the indirect roof of the horizontal salt caverns in Zhaoji Salt Mine, were thoroughly investigated.

The results show that salt caverns, as well as transmission pipelines, are key technologies for future hydrogen infrastructure systems.

Thus, bringing down the cost of H2 storage and building more salt caverns will be imperative for P2H, whereas reducing the cost of carbon capture should be a key priority for accelerating the deployment of power-to-methane (P2M) technologies.

During the construction of energy storage salt caverns in bedded salt, the unpredictable failure of interlayers results in irregularly shaped caverns with lower storage capacity and with potential safety hazards.

The salt caverns are able to store the large quantities of hydrogen at elevated pressures for seasonal period of time.

When used as compressive air energy storages, underground salt caverns are often subjected to discontinuous cyclic force, characterized by low-stress time intervals (LSIs).

This work presents a comprehensive review of salt caverns history and fundamentals of their mechanical behavior.

The use of salt caverns as a storage facility play a key role in this.

In some of salt caverns, natural gas is currently stored.

Several aspects of the thermodynamic behavior of salt caverns containing brine, oil, natural gas, air or hydrogen are discussed.

UGS is possible in different methods including storage of gas in depleted hydrocarbon reservoirs, aquifers, abandoned mines, and salt caverns.

In this context, hydraulic fracturing tests are implemented on the target formation for the UGS construction of Jintan salt caverns, China, in order to obtain the minimum principal in situ stress and the fracture breakdown pressure.

A plan to create solution-mined salt caverns for natural gas storage by discharging brine into the Shubenacadie River estuary poses a potential risk to an “endangered” stock of striped bass.

In this study underground hydrogen storage in various storage types (aquifers, depleted deposits of natural gas and oil, salt caverns) is examined.

In this work, the potential of using a hydrogen compressor and large-scale underground hydrogen gas storage using either salt caverns or lined rock caverns has been assessed for a number of magnesium- and sodium-based hydrides: MgH2, Mg2FeH6, NaMgH3, NaMgH2F and NaH.

Doing so, these modules can be combined with any compressed air storage volume and thus not only salt caverns, but also decentralized storage units such as pipe storage or LRC can be used.

Salt caverns from solution mining in bedded or domal saline structures are of increasing importance as temporary subsurface storage space to buffer fluctuating renewables and secure a stable energy supply.

In the current energy transition context, one of the most promising technological solutions to the main complication of the Power-to-Gas process, namely, the supply of carbon dioxide, is to temporarily store carbon dioxide in underground facilities such as salt caverns.

Battery, hydrogen vessels and salt caverns are considered as potential storage technologies.

Storage tanks (pressure vessels) must be utilised if geological alternatives, such as solution mined salt caverns, are not available or cannot be excavated in a particular deployment.

In the current energy transition context, salt caverns are promising for massive energy storage but their design methodology needs to be updated to face the challenge of new operating scenarios.

58 TWh) in salt caverns.

CAES technology is often only considered for large scale applications because underground salt caverns are only cost-effective for capacities in the order of hundreds of MWh.

Based on the arch pressure theory the vertical stress in the roof of salt caverns was established.

Early target for detailed studies are the existing salt caverns and an abandoned salt mine in the Lusitanian Basin.

This paper focuses on the mechanical behavior of boreholes or elongated cylindrical salt caverns.

The associated technology pathways consist of electrolyzers, salt caverns, hydrogen pipelines, power cables, and various technologies for reconversion into electricity.