Monday, 31 March 2025/ Edition 52

Welcome to the one-year edition of Core Elements! 🎉 I’ve truly enjoyed my time writing on various geoscience studies and topics and connecting with readers each week. This week’s focus: underground hydrogen storage (UHS).

Hydrogen has long been viewed as clean energy, because when combusted, it produces only heat and water. Moreover, the heating value of hydrogen is twice that of natural gas.

Creating a large-scale “hydrogen economy,” however, will require significant growth around supplies (efficient and clean ways of production) and widespread infrastructure (UHS facilities). Here, I share some recent studies on UHS.

Rasoul Sorkhabi

Editor, Core Elements

Global UHS: A Report

Deemerwha Studio/Shutterstock.com

Duartey and colleagues from the New Mexico Institute of Mining and Technology have published a global survey of UHS projects. 

Hydrogen projects: Worldwide, there are 1,572 projects related to hydrogen with a total investment of $680 billion (as of May 2024).

Europe tops the list of places with the highest investments in hydrogen projects, followed by Latin America, North America, Oceania, the Middle East, China, and India.

Hydrogen storage challenges:

• Because it is the smallest and lightest element, hydrogen is highly fugitive.

• Hydrogen is very reactive and can form harmful gases such as hydrogen sulfide.

• Certain microbes thrive on hydrogen.

Ideally, each UHS project has:

• A suitable reservoir rock type with sufficient porosity and permeability, protected by thick and impermeable cap rock

• Sufficient depth, storage capacity, and above-ground infrastructures

While hydrogen can be stored in surface tanks (in gaseous or liquid form), underground storage systems have a much greater capacity with a longer discharge duration. There are three main types:

1. Salt caverns

   • Pros: Proven sealing and low leakage risk

   • Cons: Limited availability in most regions, high cost, small storage capacity, low withdrawal rate

2.  Depleted gas reservoirs

   • Pros: Geographic abundance, medium or large storage capacity

   • Cons: High risk of leakage 

3. Saline aquifers

   • Pros: Geographic abundance, very large storage capacity, high withdrawal rate

   • Cons: High leakage risk, high seismic risk

UHS facilities need cushion gas along with hydrogen during storage, in addition to operational/maintenance pressures.

Cushion gas and pressure requirements depend on the type of storage:

• Salt caverns: 20–30 percent, with operational pressures of 35-270 bars

• Saline aquifers: 45–80 percent, with operational pressures of 30–315 bars

• Depleted gas reservoirs: 50–60 percent, with operational pressures of 15–286 bars

The costs of each type of storage system are (in U.S. dollars per kilogram of hydrogen stored):

• $0.39–2.41 for salt caverns

• $1.50 for saline aquifers

• $1.42 for depleted gas reservoirs

Go deeper: Read more in MDPI Energies.

Sponsored

Pipeline Design Plays Critical Role in Transboundary CCS

Transboundary CCS plays a key role in decarbonization strategies for countries with a significant number of industrial emitters but limited domestic storage, particularly geographic zones characterized by earthquake epicenters, volcanoes, and tectonic plate boundaries.

UHS Assessment of Salt Caverns in the United States

L_B_Photography/ Shutterstock.com

Salt caverns are increasingly considered promising UHS sites. In a recent article in the International Journal of Hydrogen Energy, Huang and colleagues from Los Alamos National Laboratory have made a techno-economic assessment of U.S. salt caverns.

Researchers considered these design and operational parameters:

• Salt shape (cylindrical, domal, diamond or capsule)

• Height (thickness)

• Diameter

• Top depth (overburden) and bottom depth

• Area

• Cushion gas percentage

• Unit price of electricity in U.S. dollars per kilowatt-hour

• Project cost in dollars per kilogram

They modeled these parameters for 18 selected salt caverns across Arizona, Utah, Colorado, Texas, Louisiana, and Mississippi.

Techno-economic results:

• Working gas capacity of the salt caverns ranged from 0.29 to 7.84 kilotons. Sevier Valley (Utah) has the largest capacity, and Midland (Texas) has the lowest working gas capacity.

• The individual capital cost of UHS in a single salt cavern varies from $12.8 to $117.7 million. Due to their sizes, Sevier Valley is the most expensive, and Midland is the least expensive.

• Total capital cost of UHS in salt caverns range from $17.2 billion to $6.673 trillion. The Michigan Salt Basin has the largest total cost, while the Eagle Valley basin (Colorado) has the lowest, mainly due to their areal extents.

• The levelized cost of UHS in a “single salt cavern” varies from $2.20 to $10.50 per kilogram of hydrogen. Midland has the highest levelized cost, and Sevier Valley has the lowest.

• The levelized “total cost” of UHS in salt caverns are estimated to be $2.20 to $3.50 per kilogram of hydrogen. The multi-salt cavern Appalachian Basin has the largest levelized total cost, and Sevier Valley has the lowest.

Go deeper: Read the full article online.

A Map of UHS Science in China

In a new study, Huang and colleagues discuss a scientific knowledge map of UHS with particular focus on China.

Research growth:

• From 2020 to 2024, UHS-focused publications grew from 16 to 245—a more than fifteen-fold increase.

• Of the 176 articles published on salt caverns during these four years, China accounted for 24 percent, the United States 20 percent, Poland 14 percent, and Germany 13 percent.

• Salt cavern research tended to focus on: UHS, machine learning, bedded salt caverns, hydrogen transport, hydrogen storage, energy storage in general, permeability, microbial loss, the energy transition, and underground energy storage.

UHS research hotspots in Chinese universities and institutions revolve around:

1. Geological conditions (cap rock sealing and storage permeability)

2. Engineering practices (theoretical modeling or data-driven simulation)

3. Thermal coupling effect (injection and production)

4. Microbial activity

5. Economic optimization (techno-economic feasibility)

6. Multi-energy (natural gas, carbon dioxide, and hydrogen) collaboration

Go deeper: Read the full study in MDPI Energies.

👍 If you enjoyed this edition of Core Elements, consider supporting AAPG's brand of newsletters by forwarding to a friend or colleague and signing up for our other newsletters here.

➡️ Was this newsletter forwarded to you? Subscribe to Core Elements here.

✉️ To get in touch with Rasoul, send an email to editorial@aapg.org.