Dear Colleagues,

Underground storage of energy resources is a promising technology. It offers a large storage capacity for both conventional and unconventional resources. Although subsurface reservoirs have been proposed and utilized as potential storage sites for troublesome gases (e.g., CO₂), the current needs for large-scale storage of energy resources have opened several discussions on their potential use of storing energy resources. In fact, subsurface storage of natural gas in salt caverns has been in use for decades. On the other hand, hydrogen is considered a potential player for net-zero emission energy systems. In order for hydrogen to find a viable contribution to future energy share, it is required that large-scale storage systems of hydrogen are secured. Subsurface reservoirs, including mined salt caverns, depleted reservoirs, or aquifers, can, most effectively, achieve this goal. On the other hand, underground water can be used as a high-capacity thermal energy storage due to the larger heat capacity of water. Furthermore, subsurface thermal energy sources due to the higher temperature of the interior of the Earth, which manifests what is known as geothermal energy, is another venue of the wide variety of possibilities subsurface reservoirs may offer. Other energy resources that can benefit from the large storage capacity of subsurface reservoirs include compressed air, which can be used back and forth when needed. These wide varieties of applications and possibilities suggest the need for comprehensive research and studies on the feasibility of these options to identify frameworks, solutions, benefits and drawbacks. To introduce the latest advancements in theoretical, numerical and experimental research as well as industrial applications of subsurface reservoirs as potential energy storage systems, this Special Issue aims to collect recent developments in this regard. It focuses on, but is not limited to, topics relevant to underground energy storage in mining and tunneling engineering, oil and gas engineering, thermal engineering, etc.

Prof. Dr. Yi Wang
Prof. Dr. Bo Yu
Dr. Amgad Salama
Guest Editors

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• underground natural gas storage
• underground hydrogen storage
• aquifer thermal energy storage
• underground compressed air storage
• hydrogen energy
• geothermal energy
• depleted oil/gas reservoirs
• salt carven
• reservoir simulation
• mathematical modeling
• experiments
• computational algorithms
• case study
• industrial application