Salt deposits of significant size have the potential to serve as reservoirs for hydrogen storage. They can also facilitate thermal energy transfer to geothermal power stations and impact carbon dioxide sequestration.
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Industries possessing pre-existing knowledge and experience in salt-related processes, such as salt and solution mining and oil and gas exploration, can significantly incorporate this common substance as a fundamental element in the ongoing energy transition.
Salt deposits could play a pivotal role in establishing a sustainable hydrogen economy, provided we deepen our understanding of their behavior and optimize their use across various energy transition applications. This article explores this further.
Properties of Salt
Salt exhibits high thermal conductivity, facilitating efficient heat dissipation from underlying source rocks. This characteristic enables the source rocks situated below the conventional oil window to sustain their productivity even in extremely deep traps.
With its ability to self-heal and crystallize, salt often produces a perfect seal since it is impenetrable to pore water, hydrocarbons, and gases. A total of 14 of the 25 biggest oil fields in the world are sealed with salt.
The sealing properties of salt have been employed for the underground storage of oil, gases, and wastes in salt caverns.
Strategies for Low Carbon Energy Transition
Several technological solutions could facilitate the transition toward a secure, sustainable, low-emission energy system.
The proposed solutions involve the extensive implementation of carbon capture technology in industrial operations, followed by the sequestration of captured carbon in subsurface reservoirs.
The expansion of hydrogen production and utilization necessitates the development of subsurface hydrogen storage facilities. Furthermore, adopting geothermal energy on a larger scale is also recommended.
The Potential of Salt in Energy Transition Technologies
The salient characteristics of salt that render it a highly prized constituent in the domain of oil and gas exploration are equally significant to the field of energy transition technologies.
A comprehensive understanding of the properties and behavior of salt is of the utmost significance for the efficient and effective sub-surface storage of hydrogen, hydrocarbons, and compressed air on a seasonal or strategic basis.
The storage of substances, such as hydrogen or hydrocarbons, can occur within the salt itself, such as in salt caverns or intra-salt repositories, or in the sediments surrounding the salt, where traps are formed due to salt tectonics.
Understanding the thermal properties of salt is crucial, as salt-rich basins could offer promising potential for developing geothermal power generation.
Utilization of Hydrogen for Energy Storage
Using hydrogen (H2) as energy transportation and storage is a viable and straightforward solution for addressing the intermittent supply and demand discrepancies on a significant scale.
Where wind or solar energy production exceeds demand, surplus power can be utilized for water electrolysis to generate sustainable hydrogen.
The production of hydrogen can be achieved through either steam methane reforming or auto-thermal reforming of natural gas. If carbon dioxide sequestration occurs simultaneously, it is referred to as 'blue' hydrogen, whereas if it does not, it is known as 'grey' hydrogen. The hydrogen generated by these techniques can be stored and utilized for future energy production or as a chemical feedstock.
Current Limitations in Hydrogen Energy Storage
Hydrogen has a low density of 0.089 kg/m3 at standard temperature and pressure and lower energy potential per unit volume than natural gas.
This necessitates the utilization of large volumes of hydrogen and a substantial expansion of subsurface storage capacity to store energy at a magnitude that satisfies the requisite demands, which are in the terawatt-hour range.
Role of Salt Deposits in Hydrogen Storage
Salt deposits have been utilized for many years as storage sites for diverse fluids, including hydrocarbons, hydrogen, and waste materials. Currently, there is a critical imperative to decarbonize our energy systems. Therefore, salt deposits are poised to assume a significant function in establishing a sustainable hydrogen economy.
Various subsurface formations, such as salt deposits, saline aquifers, depleted reservoirs, or hard rock-lined deposits, have been identified as potential sites for large-scale hydrogen storage.
Salt deposits represent the sole established alternative among the available options. Hydrogen can be securely stored for extended periods in salt deposits.
Salt deposits possess beneficial features for hydrogen storage, as they allow around 10 cycles of injection and withdrawal per annum at rapid rates, rendering them suitable for short- and medium-term storage. Salt deposits exhibit long-term stability.
The estimated hydrogen loss through leakage is negligible owing to the sealing properties of evaporites, which exhibit low gas permeability. However, this may vary depending on the particular characteristics of the salt formation.
The complex multiphase flow phenomena do not strongly influence the hydrogen injection rate in salt deposits. Salt is generally unreactive toward hydrogen, although it is possible that impurities present in salt may not be inert and require additional investigation. The transformation of water into brine also diminishes the probability of bacterial growth.
The injection rate of hydrogen into salt deposits is not strongly dependent on complex multiphase flow phenomena. Salt is typically inert to hydrogen (although impurities in salt may not be, and this aspect needs further research), and conversion of any water to brine reduces the potential for bacterial activity.
The amount of cushion gas needed in salt deposits is relatively moderate in comparison to the storage capacity of the reservoir.
Utilizing salt deposits as reservoirs for hydrogen storage, intended for energy generation, is a practical option. Furthermore, the permeable geological formations encompassing these structures could serve as a long-term storage solution for carbon dioxide emissions.
Current Limitations in Usage of Salt Deposits for Hydrogen Storage
One of the main limitations associated with salt deposit storage is identifying a cost-effective and environmentally sustainable approach for managing the brines extracted during leaching.
Potential applications for brine utilization encompass salt (NaCl) extraction, geothermal and hydrocarbon industries, and lithium recovery. This presents a compelling prospect in light of the increasing need for electric vehicle batteries.
The feasibility of utilizing salt caverns for hydrogen storage has been demonstrated on a limited scale through technological advancements. However, significant technology scaling will be necessary to utilize this method as a foundation for energy transition.
According to a projection, global hydrogen consumption could reach 700 million metric tons by 2050, contingent upon implementing robust climate policies to constrain global warming to 1.5 °C.
The storage of 20% of the yearly hydrogen demand would necessitate the creation of approximately 14,000 salt caverns, incurring a total expense of $637 billion.
Using knowledge and data from extensive research, hydrocarbon exploration, and salt deposit mining presents a promising opportunity for advancing energy transition technologies.
Salt deposits have considerable potential in facilitating the development of a sustainable hydrogen economy. Understanding salt's behavior can aid in optimizing design, mitigating risk, and enhancing efficiency across various energy transition technologies.
Read More: Can Salt Water Help Produce Green Hydrogen?
References and Further Reading
Duffy, O. B., Hudec, M., Peel, F., Apps, G., Bump, A., Moscardelli, & Shuster, M. (2022) The Role Of Salt Tectonics in the Energy Transition: An Overview and Future Challenges. EarthArXiv. https://eartharxiv.org/repository/view/3452
Bünger, U., Michalski, J., Crotogino, F., & Kruck, O. (2016) Large-Scale Underground Storage of Hydrogen For the Grid Integration of Renewable Energy and Other Applications. Compendium of Hydrogen Energy (pp. 133-163). https://www.sciencedirect.com/science/article/abs/pii/B9781782423645000075
Ozarslan, A. (2012). Large-Scale Hydrogen Energy Storage in Salt Caverns. International Journal of Hydrogen Energy, 37(19), 14265-14277. https://www.sciencedirect.com/science/article/abs/pii/S0360319912017417