PhD (M/F) : Exploring the link between sub-circular depressions and hydrogen concentration

Job Description

Thesis Subject

Pre-proposal context and positioning
Hydrogen is expected to play a central role in the global energy transition, yet most current hydrogen production comes from the energy intensive, and often CO2 emitting, conversion of water or hydrocarbons. Natural hydrogen is generated in the subsurface through several well-documented geological mechanisms, principally water–rock reactions such as serpentinization of Fe-rich minerals and radiolysis of water in crystalline rocks (e.g., Sleep et al., 2004; Lollar et al., 2014; Klein et al., 2020). These processes can produce natural (geologic) hydrogen continuously over geological timescales, after which the gas may migrate or accumulate along permeable structures such as faults, fracture networks and sedimentary traps. Natural hydrogen therefore represents a potentially vast, low-carbon energy resource. Recent assessments suggest that significant quantities could exist worldwide (e.g., Ellis and Gelman, 2024), but their distribution, migration pathways and accessibility remain poorly constrained.
Exploration strategies for natural hydrogen are still at an early stage and largely rely on near-surface geochemical surveys in soils, springs and boreholes. As in the early stages of hydrocarbon exploration, such approaches provide valuable first-order information but do not directly predict subsurface accumulations. One surface expression has nevertheless emerged as particularly promising indicators of deep natural hydrogen migration: sub circular depressions (SCDs) reported in diverse geological settings worldwide (e.g., Russia: Larin et al., 2015; North Carolina: Zgonnik et al., 2015; Namibia: Moretti et al., 2022; Roche et al., 2024). These features have locally been associated with anomalous natural hydrogen concentrations reaching several thousand ppm, suggesting ongoing degassing from depth. Because they can be identified from satellite imagery, they offer a unique, non-invasive entry point for regional-scale exploration.

Objectives
This project aims to determine how reliably SCDs reflect subsurface natural hydrogen migration, with a specific focus on the Bray-Bristol channel fault system, which extends from the Paris Basin in France to the Bristol Channel in the UK. We will integrate satellite observations and remote sensing data, artificial intelligence and field-based geochemical and structural investigations to (i) detect and map potential seepage structures, (ii) validate them on the ground, and (iii) understand the geological controls on gas transport. We will also investigate the generation through gas analyses and reservoir modelling. Ultimately, the project will deliver new exploration tools and conceptual models to support the development of low-carbon natural hydrogen resources.

Methodology and project organization

Research Axis 1: Remote sensing and AI-based mapping of SCDs
The first axis will develop spatial constraints on potential natural hydrogen seepage structures using high-resolution optical, multispectral and radar satellite data combined with automated and AI-driven image analysis. Our team has already trained deep-learning models on a unique dataset of confirmed natural hydrogen-emitting SCDs from five different countries (Ginzburg et al., 2025; Roche et al., 2025). For example, in Namibia, the algorithm successfully highlighted depressions exactly where in situ measurements confirmed natural hydrogen emissions. Thanks to the diversity of this training set, the model is transferable at a global scale using Google Earth imagery. Additional blind tests in Kazakhstan and South Africa revealed more than a thousand new candidate structures. This axis will build on top of existing approached while including the AI expertise of researchers from Imperial and the Computer Science Laboratory in Le Mans to scale up the processing, propose new methodology, frameworks and models for the targeted tasks. Actions in this first axis are three-fold:
- Systematically map SCDs across France and the UK, with priority given to the Bray-Bristol corridor;
- Characterize their morphology, spatial organization and relationship to lithology and tectonic settings;
- Investigate the temporal evolution of SDCs using remote-sensing archives to assess whether these features are stable, episodic or actively evolving.

Research Axis 2: Field validation, geophysical investigation and seepage modelling
The second axis will ground-truth the remote observations and investigate the mechanisms of gas migration. It pursues two main objectives:
i) Validation of AI predictions
- On-site verification of automatically detected depressions;
- High-resolution soil-gas surveys through spot sampling to quantify natural hydrogen concentrations;
- Outputs of this task will serve as feedback for the first axis to improve model performance.
ii) Understanding gas origin and migration
- Multi-gas analyses (H2, CO2, CH4, He) coupled with isotopic gas tracers;
- Surface geophysical acquisition through selected depressions.
- Seepage modelling: build a simplified integrated model combining AI-derived features, geological and geophysical information, and field gas measurements to simulate hydrogen migration, and support predictive mapping of potential seepage.

Several field campaigns are planned in France and the UK. Initial surveys in the Paris Basin have already revealed natural hydrogen anomalies concentrated in depressions. Because the same tectonic system continues into the Bristol Channel in the UK, we will extend measurements across this area to evaluate cross-border continuity and controls. Comparative studies between multiple sites will allow us to determine the respective roles of depressions in focusing natural hydrogen gas flow.

Scientific and Technical Skills Required for the Candidate
- A Master's degree in Earth Sciences is required.
- Proficiency in remote sensing tools and techniques.
- Skills in machine learning, programming, and deep learning.
- General knowledge of natural hydrogen systems.
- Broad knowledge of geophysics and geology (including geomorphology and geochemistry), with a strong interest in interdisciplinary approaches.
- Good command of English, both written and spoken.
- A valid driver's license (Category B) is recommended.

Application Documents Required
Applicants must submit:
- A PDF file containing a complete and up-to-date curriculum vitae (CV).
- A second PDF file including the following documents:
A cover letter.
One or two letters of recommendation, including at least one from the supervisor of the applicant's Master's thesis.
Official academic transcripts documenting the applicant's academic record.

Your Work Environment

The Laboratory of Planetology and Geosciences (LPG – UMR 6112) is a multidisciplinary research unit established in 2000 and distributed across three sites: Nantes Université, the University of Angers, and Le Mans University. LPG is a major national and international player in the field of Earth and Planetary Sciences. The laboratory's research covers a broad range of disciplines, currently organized into three main thematic areas.
Its activities are closely linked to past, ongoing, and planned international space missions exploring both terrestrial and icy bodies of the Solar System. On Earth, research encompasses geosciences in the broadest sense, ranging from the Earth's interior and surface (through imaging, observations, analyses, and modelling in geophysics, geochemistry, and digital sciences) to environmental and paleoenvironmental studies. These investigations rely on laboratory-based experimental approaches as well as numerous field campaigns conducted on land and at sea.
The PhD position will be based at the Le Mans site of LPG. This site hosts approximately 13 staff members (compared with 85 at the Nantes site), within a research unit comprising around 140 personnel in total. The PhD candidate will join the "EARTH" research theme of LPG and will work closely with the various LPG researchers involved in the MITI-Hydrogen project. In addition, strong interactions will be required with researchers from Imperial College.
Furthermore, the hydrogen (H₂) research theme is currently experiencing significant growth within LPG, supported by two ongoing PhD projects that are helping to structure and strengthen this scientific activity. Several additional projects are currently under development or awaiting funding and are expected to further enhance this research area in the coming years by consolidating expertise, fostering collaborations, and increasing the laboratory's visibility in the field of natural hydrogen research.

Constraints and risks

There are no specific risks associated with this position. However, an interest in fieldwork and outdoor activities is essential.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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