Karst Aquifer~a fractured carbonate rock strata......

Dear Doctor

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Review of underground hydrogen storage: Concepts and challenges Hamed Hematpur , Reza Abdollahi , Shahin Rostami , Manouchehr Haghighi , Martin J. Blunt

Advances in Geo-Energy Research, 2023, 7(2): 111-131

"The only viable method for large-scale, long-term storage for national-scale electricity and hydrogen grids involves storing compressed gaseous hydrogen in large, underground geological structures. These structures are comparatively cost effective and have the capability to store the massive volumes required .

The four major underground hydrogen storage types are depleted hydrocarbon reservoirs, aquifers, salt caverns, and (with a small share) hard rock caverns. Each of these storage sites is, to a certain extent, a unique geological structure that has been designed to operate within its functional parameters .

Underground hydrogen storage (UHS) can provide storage in the 100 GWh range (up to 1 EJ = 1018 J) .

Underground hydrogen storage:

Methods for storing hydrogen are chosen based on the stored volume, the duration of storage, the required speed of discharge, and the geographic availability and cost of the various alternatives. Currently, at the small scale, hydrogen is stored as a gas or liquid in tanks for stationary or mobile applications. When handling significant amounts of hydrogen, at the Gt scale, necessary for continuous operations at a national or international scale, pressurized tanks or liquid storage vessels do not suffice: subsurface storage is essential. Natural gas (methane) storage in has been applied for decades. The knowledge gained by this can be easily transferred to hydrogen . The materials required in access wells, the well head and transmission infrastructure are the main differences between hydrogen and natural gas storage . In the case of hydrogen, embrittlement due to long-term diffusion can cause fracturing, followed by leakage, especially in the steel components, which reduces the strength and stresses that can be safely applied to metal components."

Dear Prof. Sundus,

Thanks for this information. Best Regards.

Fredrick Kayusi Wisam Mohammed Abed Alqaraghuli

Some factors:

1. Porosity: A higher porosity allows for greater storage capacity and efficient hydrogen injection and extraction.

2. Permeability: For effective UHS, the reservoir should have sufficient permeability to enable the movement of hydrogen in and out of the storage site. High permeability facilitates efficient injection and withdrawal rates.

3. Caprock Integrity: It should have low permeability and high integrity to minimize the risk of leakage.

4. Geomechanical Stability: Stability is particularly important for long-term storage projects.

5. Compatibility with Hydrogen: Some rock types, such as salt caverns or depleted gas fields, have been successfully used for UHS due to their favorable chemical interactions with hydrogen.

6. Proximity to Demand Centers: This reduces transportation costs and facilitates the efficient distribution of hydrogen to end-users.

7. Environmental Considerations: The site should have minimal environmental impact and be compatible with regulatory requirements.

Hope it helps