Thesis

The architecture and fluid flow properties of shallow fault systems : implications for environmental monitoring of subsurface technologies

Creator
Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T17059
Person Identifier (Local)
  • 201992634
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • Action and solutions to combat the challenges of changing climate is needed. To meet global climate targets, there is an anticipation that there must be a scaling up of existing and emerging subsurface technologies (e.g. geological carbon dioxide (CO2) storage, energy storage (e.g., hydrogen) and geothermal energy). Many of these emerging technologies involve some element of subsurface fluid injection, storage, and withdrawal. Therefore key to secure and safe operation is robust site selection criteria, appropriate measuring, monitoring, and verification (MMV) systems and remediation procedures. Understanding the architecture of shallow fault zones (<1 km depth in the Earth’s crust) and implications for subsurface fluid flow is important to inform these criteria, systems and approaches. Yet, shallow fault zones are less well studied and modelled compared with deeper faulting (i.e. reservoir depths). To enhance current understanding of shallow fault systems, this thesis presents a comprehensive study of two field sites which have injected CO2 into shallow fault zones: the In-Situ Lab (Harvey, Western Australia) and the Otway International Test Centre (Otway, Victoria). Data collected at the field sites are examined, rock core is observed at different scales and sampled, and fieldwork is undertaken to understand the regional structural setting. By synthesising these data, research findings show that shallow fault zones often do not exhibit “classic” fault architectures, which are based on deformation in the brittle regime, and instead the dominant deformation style in shallower fault zones is particulate flow, which is only observed through using methods of study across a range of scales. The resulting variability in deformation styles influences the hydraulic properties of the rock. Furthermore, fault rock and surrounding host rock can often be weak in shallow fault zones meaning the methods used for analysis need to be suitable for use on lower strength sedimentary rocks. Shallow fault zones present new challenges in effectively designing suitable geological modelling approaches due to increased uncertainties in shallow stress magnitudes and the characteristics of shallow fault architecture – meaning it is not reasonable to use standard fault or stress analysis tools. Separately, a global study of natural hydrogen seepage sites is presented which provides insights into variations in surface seepage expression and controls on the production, consumption and transformation of hydrogen in the subsurface, with implications for environmental monitoring.
Advisor / supervisor
  • Johnson, Gareth
  • Roberts, Jennifer J.
  • Shipton, Zoe Kai
Resource Type
DOI

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