Author Identifier

Krista Davies: https://orcid.org/0000-0002-6503-9964

Date of Award

2025

Document Type

Thesis - ECU Access Only

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Engineering

First Supervisor

Stefan Iglauer

Second Supervisor

Alireza Keshavarz

Third Supervisor

Lionel Esteban

Abstract

Hydrogen is increasingly recognised as a viable energy source for decarbonising hard-to-abate sectors, particularly where direct electrification is impractical. However, several key technical uncertainties must be resolved before large-scale deployment can be achieved. Among these, the behaviour of hydrogen in subsurface environments, both in the context of natural hydrogen accumulations and manufactured hydrogen storage, remains poorly understood. This is especially true in near-surface and carbonate-rich settings, where physical transport processes and geochemical reactivity have yet to be fully characterised.

In this study, I investigate the dynamics of natural hydrogen micro-seepage at surface and assess the geochemical reactivity of dolomitic carbonates under subsurface conditions. Field investigations employed autonomous soil gas monitoring systems at known hydrogen seepage sites, generating continuous, high-temporal-resolution datasets. These data capture the influence of environmental conditions such as barometric pressure, rainfall events, and temperature on hydrogen emissions at the surface.

The results indicate that hydrogen seepage is episodic rather than continuous, and is strongly influenced by groundwater levels. Pulsed emissions were strongly modulated by atmospheric pressure gradients and near-surface hydrological conditions. In particular, suppression of hydrogen flux following rainfall events was observed, highlighting the role of water saturation in modulating diffusion of hydrogen gas through the soil substrate.

To address the limitations of conventional soil gas surveys in high groundwater environments, I developed and field-tested a headspace gas analysis protocol that enables effective sampling of trapped gases under water-logged conditions. This approach proved essential where traditional soil gas sampling methods are not viable, demonstrating that hydrogen gas was trapped in groundwater and required agitation to degas the groundwater. High concentrations of hydrogen were observed in this way, but again, the hydrogen concentrations appeared to be episodic rather than constant.

As soil gas sampling is becoming an important natural hydrogen exploration method, with sub-circular depressions as a focal point, understanding the nature and distribution of drilling-induced artifacts is critical. Soil strength and moisture profiling soil type and spatial analysis were used alongside traditional soil gas sampling techniques to differentiate natural hydrogen anomalies from those arising due to drilling-related artifacts. On this basis, I propose a classification framework incorporating dissipation rate and relationship to soil type and strength as diagnostic criteria. Thus, natural hydrogen micro-seepage can be differentiated from drilling induced artifacts.

Laboratory experiments were conducted on dolomitic carbonate core samples to determine the effect of hydrogen exposure at reservoir conditions. Samples were exposed to high-purity hydrogen under controlled pressure, temperature, and brine salinity conditions representative of the subsurface conditions of the origin field. Mineralogical analysis (XRD, SEM-EDS), petrophysical characterisation (porosity, permeability), and mechanical testing revealed that hydrogen exposure can promote dolomite dissolution and localized replacement by ankerite, accompanied by textural reorganisation of the pore network. The extent of these alterations varied as a function of initial porosity, and accessory mineralogy, with reactions ceasing within three months in the high porosity and permeability samples. These observations have direct implications for reservoir integrity and long-term containment under hydrogen injection conditions, and provide indicator mineralogy for hydrogen exposure in the exploration for natural hydrogen.

Field observations and laboratory experiments together offer a novel framework for understanding hydrogen behaviour in both natural and engineered subsurface systems. By combining validated field protocols with environmental diagnostics, we improve not only the detection of near-surface hydrogen seepage but also our capacity to anticipate how reservoirs might respond to hydrogen over time. These results reduce uncertainty in subsurface hydrogen applications and lay the groundwork for practical guidelines and regulatory standards in this fast-evolving area of geoscience.

DOI

10.25958/crxf-kn91

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