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Underground Hydrogen Storage (UHS)

UHS technology is still in its infancy. We can provide expert advise . . . starting from focused research studies and demonstration pilots to planning for full scale UHS Hub.

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Types of Underground Hydrogen Storage (Geological)

UHS or geological storage options are of two types 

  1. Conventional Storage Option

    1. Salt Caverns

    2. Depleted Oil & Gas (DOG) Field 

    3. Saline Aquifers

  2. Unconventional Storage Options

    1. Abandoned Coal Mines

    2. Lined Hard Rock Caverns

    3. Refrigerated Mined Caverns


Salt Caverns

Salt caverns are located in thick halite formations. They are artificial chambers made by pumping fresh water down a borehole into the salt layer to dissolve the salt and circulate the saline solution to the surface. The process is called 'Solution Mining' This process continues until the required size of cavern is reached. 

Hydrocarbon liquid or gas storage technology in salt caverns is well understood and can be be an analogue for underground hydrogen Storage (UHS). For example, the US Strategic Petroleum Reserve (SPR), which is the world's largest supply of emergency crude oil, is stored in salt caverns at four sites along the Gulf of Mexico coastline. 

Caverns are often regarded as the best option for UHS due to their low gas permeability, good rheology — which contributes to excellent sealing strength, and ability to redistribute stresses via viscous-plastic deformation (Lemieux et al., 2019). Because of the sealing nature of evaporite (such as anhydrite, gypsum, and rock salts) and the mechanical stability of salt caverns, the injection and withdrawal process is suitable for medium and short-term storage

Operational H2 Storage - Salt Caverns

There are three-salt cavern reported in the UK in 1972, three salt caverns in the US in 1983, and the Kiel town gas project in Germany are all examples of successful H2 storage. All  three salt cavern storage projects operational in US are located in Texas (Spindle top, Clemens Dome and Moss Bluff)


Ideal Usage

The projects’ experience suggests that H2 may be stored in salt caverns for a long time

EXAMPLE PROJECT (Hub Type Development)

HyPSTER Project France - First Underground Hydrogen Storage (UHS)  demonstration project for Green hydrogen HyPSTER stands for Hydrogen Pilot STorage for large Ecosystem Replication

Depleted Oil & Gas (DOG) Fields 

To date, the depleted reservoir is the conventional storage means and proven technology for natural gas. They are characterized as porous and permeable hydrocarbon reservoirs located thousands of feet be- neath the subsurface with almost all the recoverable products being extracted.  DOGF can be an analogue for Underground Hydrogen Storage (UHS).

Depleted oil and gas fields are part of saline aquifers where oil and gas fields have been deposited over time. Generally, they are easy to develop, operate and maintain due to the already existing infrastructure with proven integrity. DOG field have proven credence since;

  • They have previously trapped hydrocarbon that migrated from the underlying source rocks

  • Has a well-identified geological structure (anticline or stratigraphic)

  • They serve as a suitable storage container, with suffi- cient permeability to meet the operational flow and a successful trapping system to prevent fluid migration via leaking.


Current Status

Currently, no H2 storage has been successfully achieved in depleted fields. 

Ideal Usage

  • In comparison to aquifer UHS options, depleted gas reservoirs are more advantageous in that the existence of the remaining gas serves as a benefit to prevent a massive amount of cushion gas required for pressure maintenance during operations. 

  • The best choices for seasonal gas storage due to their flexibility of cycling 


In the absence of caverns and depleted hydrocarbon reservoirs, aquifers are primarily utilized for UHS. They present better UHS options since they are commonly found in all sedimentary basins around the world. The storage mechanism for aquifer and depleted hydrocarbon reservoirs are similar since they are both characterized as porous and permeable. 

Site characterization and geological assessment is essential. This includes:

  1. The host rock for injection has good reservoir properties,

  2. The host rock for injection has good qualities to prevent the migration of the stored gas.

  3. An impermeable seal for preventing vertical migration due to buoyancy and an anticline trap to prevent lateral migration of H2 away from the well for effective plume build-up, 

Current Status

Currently, no pure 100% H2 storage has been successfully achieved in aquifers. However, the town gas project (produced by gasification of coal which contains notable amounts of H2 and other components) has been documented as the few storage aquifer project in Europe.These aquifers reported are Ketzin in Germany, Lobodice in the Czech Republic, and Beynes in France.

Ideal Usage

Both aquifer and depleted hydrocarbon storage options however are the best choices for seasonal gas storage due to their flexibility of cycling 

Types of H2 Storage - By Way H2 is Stored


  1. Underground Storage of Pure Hydrogen 

  2. Underground storage of a mixture with natural gas in H2

  3. Underground Storage of Rich H2 mixture with CO, CH4 and CO2 (syngas or Town gas)

  4. Underground Methanation Reactor (UMR)

  1. Underground Storage of Pure Hydrogen 

Only the pure form of H is stored under- 2ground, and the destination of the final form of the pure H2 is fuel-cell application in vehicles. Salt caverns, with a high degree of purity characterized by a very low risk of potential gas contamination by impurities, are the most convenient storage sites for ultra-pure H2.The pure H2 is mainly produced through chemical or thermal electrolysis from the excess renewable electricity (e.g., windmills, solar cells) or from the nuclear plant


2- Underground storage of a mixture with natural gas in H2

Pure H2 in this case, is produced through water electrolysis before injecting into an underground site containing natural gas for transportation.  This form of H2 storage is applied for transportation purposes, especially when a long dis- tance between the production site of the CH4 gas and consumer market is less than 2000 km.Different separation techniques, including pressure-swing adsorption (operates at < 20% H2 concentration), membrane separation (at relatively higher H2 concentration), and electrochemical H2 separation, are used to separate the blended H2 and CH4 before consumption 


3-Underground storage of rich H2 mixture with CO, CH4 and CO2 (syngas or town gas)

Syngas is produced through the mixture of H2 (20%–40%) with CO whereas town gas is the mixture of H2 (50%–60%) with CO and CH4. This type of mixture is formed through superfi- cial or underground coal gasification, which involves introducing vapor at 1073 K together with O2 to represent coal combustion. It is reported that the latest version of this technology (coal gasification) allows about 70% H2 for the mixture and it can be consumed in two forms namely (i) as electricity in gas turbines via thermo-mechanical conversion and (ii) as fuel for lighting and heating especially in the case of town gas

4-Underground methanation reactor (UMR))

UMR represents an H2 mixture with CO2 in the presence of methanogenic bacteria. The key key mechanism to note is UMR enriches the energy potential of the gas by transforming the mixture of H2 and CO2 into CH4, and it is often found in porous media UHS sites (aquifer and depleted gas reservoir).


Furthermore, the CO2 proportion injected is completely converted to CH4; thus, UMR resulting gas is injected into a grid of natural gas and is used as fuel, whereas syngas or town gas proportions of the various components are not controlled, and the resulting gas is converted to electricity.

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