Inside FrHyGe: Expert voices on hydrogen storage and safety

In this second edition, Hippolyte Djizanne, Geomechanics research scientist at Ineris, and Arnaud Réveillère, Head of Department Salt and Porous Media at Geostock, explain how their work in FrHyGe combines advanced research, demonstrator design, and safety assessment to enable underground hydrogen storage across Europe. By integrating the technical developments of the Manosque demonstrator with risk-based safety and regulatory strategies, they illustrate how a collaborative, multi-expertise approach is shaping a scalable and secure model for future industrial projects.

  1. What’s your role in the FrHyGe project and which key experiences prepared you to lead your respective work packages ?

H. Djizanne: As leader of Work Package 5, I am responsible for the environmental, safety, and regulatory assessment of the FrHyGe project. My role is to ensure that underground hydrogen storage operations are developed within a robust safety framework, anticipating potential risks and ensuring compliance with national and EU regulations. I previously led risk analysis for the HyPSTER project, the first European demonstrator of hydrogen storage in salt caverns, which provided extensive experience in safety assessments and hydrogen-specific risk scenarios. My background in geomechanics, underground storage risk analysis, and project management, especially within European R&D frameworks, helps bridge scientific rigor with regulatory relevance

A. Réveillère: I lead Work Package 2, which includes defining the Manosque demonstrator’s objectives and the technological/scientific developments relevant to underground hydrogen storage. My preparation for this role comes from two key experiences. First, in 2021, while working with Storengy for Géométhane, I proposed cycling between GA and GB caverns to demonstrate the feasibility of multiple hydrogen cycles without needing a lot of hydrogen or venting it. This idea was ready for deployment when the European Clean Hydrogen Partnership (CHP) call for projects was released. Second, I led the CHP-funded research project Hystories from 2021 to 2023 and served on the Solution Mining Research Institute (SMRI) Research/Executive Committees (together with Hippolyte Djizanne and with Yvan Charnavel from Storengy, also involved in the proposal). These roles, along with collaboration with key researchers from Mines Paris -PSL, IFPEN, Ineris and others, kept me well-informed of the state of the art, its gaps and the researchers able to address them. These experiences enabled me to lead WP2 during its construction and now its implementation.

  1. How does your technical focus (research task) contribute to the overall goals of underground hydrogen storage in salt caverns?

H. Djizanne: WP5 is essential to FrHyGe mission to pave the way toward safe, permitted, and replicable large-scale hydrogen storage in salt caverns. It delivers a comprehensive risk assessment, a robust safety plan, and a complete permitting strategy, all grounded in regulatory and technical rigor. We analyze worst-case scenarios, including blowouts, seismic-induced instabilities, earthquake hazards, salt permeation, ecological issues, and external hazards such as forest fires. We also assess environmental impacts, including greenhouse gas emissions, through dynamic life-cycle analysis. These efforts help ensure the Manosque demonstrator and future replicators meet both safety expectations and public trust.

A. Réveillère: In publicly funded research projects, researchers bring their active topics and ideas to advance them. We need individuals with innovative ideas and the capacity to develop them. The challenge is to align these individual research goals with the broader objective of industrial H2 storage deployment. By integrating the Manosque demonstrator’s conceptual design and R&D efforts into the same WP2, we make these research ideas address the challenges of at-scale applications, while also enabling them to be validated with field data observations. Replication studies at industrial scale in Harsefeld (Germany) and Manosque ensure that these technical and scientific findings are applied in the European hydrogen storage industry.

  1. FrHyGe’s success relies on close collaboration between work packages. Could you explain how WP2 and WP5 interact? What joint activities or interfaces ensure the demonstrator design, scientific developments, and environmental safety assessments advance together?

H. Djizanne: WP2 and WP5 are deeply interdependent. WP2 defines the demonstrator design and operations, while WP5 evaluates the safety and environmental implications of these designs. For instance, the WP2 conceptual design of the subsurface and surface facilities directly informs our hazard identification and scenario modeling. We jointly define representative operating conditions to test hydrogen-specific risks under realistic constraints. Moreover, WP5 provides safety inputs for WP2 equipment choices (such as vent sizing, safety distances, or hydrogen quality control) before implementation, and supports the permitting strategy, ensuring design compliance with French and European regulations. Our coordination through regular meetings and shared modeling approaches ensures that scientific developments inform risk-based design and vice versa.

A. Réveillère: I would add that WP3, which hosts the implementation of the demonstrator, is also fully integrated into this interaction since hazard studies and permitting, both part of WP5, are required for this implementation. No work package can fully advance alone.

  1. Arnaud, could you explain the purpose and expected benefits of the work on the gas treatment skid unit concept, the Surface Conceptual Design, as well as gas-quality measurement discussions with NaTran and Storengy ?

Underground gas storage facilities are large-scale infrastructures that inject gas from a European-wide transportation grid and return it when needed. The returned gas must meet grid specifications, including limited water content (“dry gas”) and impurities like sulfates. However, brine is always present at the bottom of salt caverns, causing water vapor to mix into the gas phase when dry gas is injected. Additionally, hydrogen can fuel microorganisms that produce H2S. Although microbial activity is limited in harsh NaCl-saturated conditions, should H2S be detected, we wanted to demonstrate it can be treated.

To address these challenges, Storengy is developing surface facilities, including a compressor, and collaborating with Axens on the gas treatment process. NaTran is working on gas quality analyses. These components are the main bricks of underground storage surface facilities, and we aim to demonstrate their effectiveness with hydrogen.

  1. Hippolyte, could you briefly describe the major hazard risk assessment process carried out as part of the environmental, safety, and regulatory assessment, and how it addresses scenarios such as hydrogen well blowouts, seismic-induced cavern instability, and hydrogen permeation through salt?

The WP5 risk assessment combines structured HAZID workshops, scenario selection, and advanced modeling. We evaluate hazards throughout the demonstrator’s lifecycle and model four worst-case scenarios: (1) a hydrogen well blowout, extending the modeling work initiated in HyPSTER; (2) cavern instability under seismic loading, using local historical earthquake data; (3) loss of cavern seal through hydrogen permeation, assessing how geomechanical degradation could trigger leaks; and (4) forest fire impacts on hydrogen infrastructure, especially relevant in the wooded Manosque region. Each scenario is assessed using quantitative tools (e.g., dispersion models, explosion models, rock salt models) and categorized in the risk matrix. When risks are deemed unacceptable, we define additional safety barriers and emergency measures.

  1. Arnaud, you recently presented at the SMRI Spring 2025 Conference in Wilhelmshaven on the modeling of flow through hypothetical leak paths using various gases and models. Could you share more insights into the key findings and their implications for H₂ cavern tightness testing ?

I worked with an intern and then with colleagues Vincent Barrère and Mehdi Karimi-Jafari on modeling the flow of N₂, H₂, and CH₄ through a hypothetical leak path. Vincent presented our findings at the SMRI conference, which had about 250 attendees, including regulators, researchers, consultants, operators, and contractors. This platform allowed us to disseminate our research and receive valuable feedback.

Our key finding was that, if a leak path exists, the volumetric flow with H₂ is 2.6 times higher than with N₂, while the mass flow is five times lower. This is due to the differences in viscosity and density between the gases. Although this was expected, this quantitative estimation was new. We used this modeling approach because we cannot rely on the Manosque demonstrator, where no leaks are expected for either gas.

N₂-based tests are standard for “Mechanical Integrity Tests” of natural gas caverns. Why wouldn’t it be the same for hydrogen storage caverns ? This work does not aim at answering, nor at being a new standard. Standards need these kinds of technical developments, but also feedback from the industry, time and consensus.

7. Hippolyte, you spoke at the SMRI Spring 2025 Conference in Wilhelmshaven on the topic ‘Thermomechanical Analysis of Wall Spalling in Salt Caverns for Gas Storage: Insights from DISROC Fracture Modeling. In that context, which aspects of Ineris’ work within the FrHyGe project did you highlight during your presentation?

You are probably referring to the brilliant presentation by my PhD student Hajar Habbani last month in Wilhelmshaven. Her research focused on fracture risk due to cyclic hydrogen operations, such as simulating spalling at cavern walls under coupled thermo-mechanical loads. These modeling efforts help evaluate the integrity of the cavern walls and completion, particularly under extreme scenarios. The study helps define operational limits and supports WP2 in refining cavern design for durability and safety. I also highlighted how this work contributes to closing key safety knowledge gaps, aligning with FrHyGe’s broader aim of establishing a replicable and secure model for hydrogen storage across Europe.