Hydrogen is expected to become essential in the future Dutch energy system as a clean energy carrier. In 2030 the storage demand will be relatively small and could be accommodated in 1-4 salt caverns. But between 2030 and 2050 this storage need will increase drastically. Up to now there are no UHS sites in The Netherlands, but the first tests with cyclic hydrogen injection in a salt cavern are being executed. The KEM-28 research question has as objective to a) assess the long-term durability of rocks and well materials when subjected to hydrogen under an alternating pressure regime that causes mechanical and thermal stresses, and to b) understand if this behaviour can interfere with nearby underground storage and/or production locations, such as producing gas fields, conglomerates of large numbers of salt caverns for hydrogen storage, salt caverns for compressed air energy storage (CAES) and gas fields used for CO2 storage.
The project is commisioned in 2022 to the the H2 Cavern Conglomerate Consortium, composed of smartTectonics GmbH, Germany; Brouard Consulting, France; MaP – Microstructures and Pores GmbH, Germany: Pondera Geo Energy, Netherlands; and GeoStructures Consultancy for Structural Geology and Geomechanics, Netherlands. The project finished end of 2023.
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Hydrogen is expected to become essential in the future Dutch energy system as a clean energy carrier by assisting the integration of renewable energies and decarbonizing specific applications in hard to abate sectors, such as industry, mobility and the residential sector. For large- scale energy storage in the order of TWh, underground hydrogen storage (UHS) in salt caverns and porous reservoirs will be needed. In 2030 the storage demand will be relatively small and could be accommodated in 1-4 salt caverns. But between 2030 and 2050 this storage need will increase drastically and could require up to 60 salt caverns and/or storage in several gas fields. Up to now there are no UHS sites in The Netherlands, but the first tests with cyclic hydrogen injection in a salt cavern are being executed.
The KEM-28 research question has as objective to a) assess the long-term durability of rocks and well materials when subjected to hydrogen under an alternating pressure regime that causes mechanical and thermal stresses, and to b) understand if this behaviour can interfere with nearby underground storage and/or production locations, such as producing gas fields, conglomerates of large numbers of salt caverns for hydrogen storage, salt caverns for compressed air energy storage (CAES) and gas fields used for CO2 storage. It is thus crucial for assessing the specific risks associated with UHS in salt caverns and to develop strategies for how to manage and mitigate them, as well as better understand interference with other means of underground storage and/or production sites in the Netherlands that can be expected. Additionally specific research questions should be answered focused on the use of underground hydrogen storage in salt caverns as part of the Dutch energy transition.
The work consisted of four main tasks:
i) A literature review on hazard and risks for UHS in conglomerates of salt caverns in the Northern and North-eastern Netherlands (focusing on the Zechstein salt layer).
ii) A geomechanical study on the stability of the cavern field, seismicity and induced seismicity assuming that a conglomerate of salt caverns are used for storage of hydrogen and other underground storages.
iii) A generic risk analysis (semi-quantitative) in terms of health, safety and environment, related to UHS in conglomerates of salt caverns in the Zechstein salt of the Northern Netherlands including biotic and abiotic geochemical processes in salt caverns and recommendations for further research.
iv) A recommended strategy for a quantitative risk analysis, in terms of health, safety and environment, related to UHS in conglomerates of salt caverns in the Zechstein salt of the Northern Netherlands, as well as risk management and mitigation of conglomerates of UHS in salt caverns .
KEM PROJECT FINAL REPORT
The deliverables were presented in a final report of 791 pages, that included the phase 1literature review report and reports on the other three tasks. The results of Task 1 is reported in Part 1 of the report, the results of Task 2 in Part 2 of the report and the results of Tasks 3 and 4 in a combined “Part 3&4” of the report.
This research has been about the feasibility of underground storage of hydrogen (UHS) in a conglomerate of salt caverns onshore in the Netherlands, analysing potential failure scenarios and quantifying and ranking the corresponding risks, and identifying measures to mitigate those risks. General guidelines and design factors for a conglomerate of nine identical salt caverns are determined and described. The results and conclusions of this study provide the basis for integrating the creep of a highly heterogeneous multi-phase rock salt into thermomechanical simulations, which ultimately supports the risk assessments of UHS in salt caverns. Based on this study, the following is established:
- Hydrogen storage in a conglomerate of salt caverns in the Netherlands is technically feasible. However, many preventive and corrective measures have to be implemented and additional site-specific research have to be performed to minimize risks.
- Use of old wells and caverns for storage should be avoided as they are not made of H2- and H2S-certified material. One should preferably start with new caverns.
- It is better to start with a relatively small design with low frequency operation. This should be accompanied with monitoring and performing additional research, and continuous evaluation.
- The best location for creating a cavern conglomerate is in the centre of the dome; this will have the least impact on the brittle deformation in the overburden.
- The cavern field should not be placed close to the salt-sediment interface and in the immediate vicinity of faults as it may result in induced brittle deformation in the pre-existing fault zones. This depends on the general dome dynamics.
- The stress field within a few hundred meters of a salt cavern will be significantly disturbed. The disturbance depends on the creep rheology of the rock salt and the dome internal stratigraphy.
- The development of a self-propagating damage zone in the salt rock of a hydrogen cavern is a real possibility. Such events may be caused by an interplay of stress changes due to cavern pressure, creation and destruction of porosity by microcracking, recrystallization, fracture healing, and salt deformation due to effective pressure changes and gas pressure gradients. The extent of these effects depends on the presence of heterogeneities (like anhydrite) and the nature of Kristallbrockensalz, and need to be determined by site-specific investigations and modelling.
- The presence of heterogeneities will not have a significant effect on the creep properties of the rock salt if their volume fraction is less than 20%.
- If the volume fraction of heterogeneities is 60 % or more, they will dominate the effective creep behaviour of the rock salt; a behaviour that is less predictable and follows the individual and (uncertain) creep properties of the mega grains and anhydrite impurities.
- Dissolution of hydrogen gas in the brine leads to the formation of hydrogen sulphide which interacts with the surrounding rock salt and second phase lithologies, and thereby alters the composition of the stored gas. Also, changes in geometry and porosity may occur leading to the connectivity and permeability of the insoluble or low-soluble layers.
- Site-specific research must be carried out for each location for a thorough risk analysis. This includes: detailed geochemical studies and modelling, characterization of subsurface geologic conditions with sufficient spatial resolution to identify critical lithologies, and supplementary laboratory and in-situ testing. In particular, mineralogical, chemical, physical, and microbiological conditions of the site before injecting hydrogen into a cavern and during storage must be investigated and monitored. Analysis of the surface effects of a blowout (jet fire, flash fire and unconfined vapor explosion), evolution of the hydrogen plume formed by a leak for several atmospheric conditions, and calculation of the distance of effects for several scenarios.
- Risk measures should be evaluated and reported to all relevant stakeholders and the risk analyses should be updated during various stages of storage.
Also, the following preventive and corrective measures must be considered:
Main preventive measures: selecting the best shape, depth, and location for caverns; determining methods of prevention of micro annuli at the casing / cement / rock interfaces, generic research on interaction of materials with hydrogen and/or H2S and using H2- and H2S-certified material; establishing minimum preconditions for H2 storage caverns (regular cavern and well tests, sonar measurements, high-quality Mechanical Integrity Tests including clear success criteria, cement bonding log, safety valve tests); open, pro-active communication with stakeholders (public, politics, and press) and other operators; implementing strict regulations (e.g., with respect to stacked mining) and strengthening the role of regulator.
Main corrective measures: developing and implementing a rapid response plan; adaptation of the storage properties (e.g., pressures (min/max), max. yield); treatment of micro-annuli and other parts with special materials (resins, silicates, etc.) and biological treatment); controlled production and/or flaring of H2; open communication with stakeholders (public, politics and press) and other operators.The significance and consequences of these effects must be studied specifically for each storage site.
The project has been evaluated by the KEM scientific expert panel. The evaluation (the revised version) can be opened using the next link.
The overall objectives of this project were the development of guidelines and delineation of strategies for risk analysis, risk management and risk mitigation in relation to the underground storage of hydrogen (UHS) in a conglomerate of salt caverns onshore in the Netherlands. In particular, the research had to aim at quantifying and ranking the risks based on different failure scenarios, taking into account the likelihood of their occurrence and effects, and identifying measures to mitigate those risks.
The following conclusions and recommendations can be formulated:
- Hydrogen storage in a conglomerate of salt caverns in the Netherlands is technically feasible. However, many preventive and corrective measures have to be implemented and additional site-specific research have to be performed to minimize risks.
- Use of old wells and caverns for storage should be avoided as they are not made of H2- and H2S-certified material. One should preferably start with new caverns.
- It is better to start with a relatively small design with low frequency operation. This should be accompanied with monitoring and performing additional research, and continuous evaluation.
- The best location for creating a cavern conglomerate is in the centre of the dome; this will have the least impact on the brittle deformation in the overburden.
- The cavern field should not be placed close to the salt-sediment interface and in the immediate vicinity of faults as it may result in induced brittle deformation in the pre-existing fault zones. This depends on the general dome dynamics.
- The stress field within a few hundred meters of a salt cavern will be significantly disturbed. The disturbance depends on the creep rheology of the rock salt and the dome internal stratigraphy.
- The development of a self-propagating damage zone in the salt rock of a hydrogen cavern is a real possibility. Such events may be caused by an interplay of stress changes due to cavern pressure, creation and destruction of porosity by microcracking, recrystallization, fracture healing, and salt deformation due to effective pressure changes and gas pressure gradients. The extent of these effects depends on the presence of heterogeneities (like anhydrite) and the nature of Kristallbrockensalz, and need to be determined by site-specific investigations and modelling.
- The presence of heterogeneities will not have a significant effect on the creep properties of the rock salt if their volume fraction is less than 20%.
- If the volume fraction of heterogeneities is 60 % or more, they will dominate the effective creep behaviour of the rock salt; a behaviour that is less predictable and follows the individual and (uncertain) creep properties of the mega grains and anhydrite impurities.
- Dissolution of hydrogen gas in the brine leads to the formation of hydrogen sulphide which interacts with the surrounding rock salt and second phase lithologies, and thereby alters the composition of the stored gas. Also, changes in geometry and porosity may occur leading to the connectivity and permeability of the insoluble or low soluble layers. The significance and consequences of these effects must be studied specifically for each storage site.
- Site-specific research must be carried out for each location for a thorough risk analysis. This includes: detailed geochemical studies and modelling, characterization of subsurface geologic conditions with sufficient spatial resolution to identify critical lithologies, and supplementary laboratory and in-situ testing. In particular, mineralogical, chemical, physical, and microbiological conditions of the site before injecting hydrogen into a cavern and during storage must be investigated and monitored. Analysis of the surface effects of a blowout (jet fire, flash fire and unconfined vapor explosion), evolution of the hydrogen plume formed by a leak for several atmospheric conditions, and calculation of the distance of effects for several scenarios.
- Risk measures should be evaluated and reported to all relevant stakeholders and the risk analyses should be updated during various stages of storage. Also, the following preventive and corrective measures must be considered:
Main preventive measures: selecting the best shape, depth, and location for caverns; determining methods of prevention of micro annuli at the casing / cement / rock interfaces, generic research on interaction of materials with hydrogen and/or H2S and using H2- and H2S-certified material; establishing minimum preconditions for H2 storage caverns (regular cavern and well tests, sonar measurements, high-quality Mechanical Integrity Tests including clear success criteria, cement bonding log, safety valve tests); open, pro-active communication with stakeholders (public, politics, and press) and other operators; implementing strict regulations (e.g., with respect to stacked mining) and strengthening the role of regulator.
Main corrective measures: developing and implementing a rapid response plan; adaptation of the storage properties (e.g., pressures (min/max), max. yield); treatment of micro-annuli and other parts with special materials (resins, silicates, etc.) and biological treatment); controlled production and/or flaring of H2; open communication with stakeholders (public, politics and press) and other operators.
The Project has delivered good quality work on many relevant issues and results of this project and its recommendations are useful to the government and the regulators in formulating policies and informing the public, and companies that are involved in subsurface production or storage activities in the Netherlands. It is, however, important that more research, development and validation is done to establish appropriate simulation models for quantitative predictions, risk assessment and uncertainty quantifications.
Overall, social acceptance of hydrogen storage is an important part of the success or failure of hydrogen storage and should receive attention from the government.