Quantifying variability within the medial zone of modern distributive fluvial systems: implications for reservoir characterisation

Williams, Rachel Elizabeth (2023) Quantifying variability within the medial zone of modern distributive fluvial systems: implications for reservoir characterisation. MRes thesis, University of Glasgow.

Abstract

Distributive fluvial systems (DFS) are important reservoirs for hydrocarbons, groundwater, geothermal energy, carbon capture and hydrogen storage through the preservation of channel belt deposits. The study of these systems is important for understanding fluid flow and connectivity. However, previous studies have observed variability in channel characteristics within the rock record (e.g. storey and channel body thicknesses, channel: floodplain), predominantly within the medial zone of these systems. The first part of this study aimed to constrain the downstream position of the three DFS zones (proximal, medial, and distal) using a defined set of criteria, including channel belt width, active channel width, and channel planform. The percentage downstream for the proximal – medial transition, and the medial –distal transition have been identified to fall at approximately 25 – 35% and 65 – 75% downstream, with variation from this trend attributed to high sediment loads. Following this, the second part of the study used quantitative methods, including active channel and channel belt widths, active channel: channel belt: overbank, to characterise variability in the medial zone of modern DFS, in order to understand how the contemporary processes translate to ancient DFS deposits, and drive the observed variability. Analysis of downstream trends within the medial zone identified a downstream decrease in active channel and channel belt widths, related to the downstream decrease in sediment supply and discharge seen on system-wide DFS studies, however no trend is associated with the ratio of active channel width to channel belt width. In some systems there is a downstream decrease in the percentages of active channel and channel belt as overbank proportion increases, however this is directly influenced by the sweep angle of the DFS. Thus, DFS were further categorised as a wide, moderate, or narrow sweep angle DFS. Systems with a wide to moderate sweep angle are characterised by an increase in overbank deposits downstream, which therefore drives a downstream decrease in the percentage of channel belt deposits. However, in systems with a narrow sweep angle, confined by neighbouring systems or topography, the proportions of overbank, channel belt and active channel remain generally constant. Variability in the medial zone is seen through downstream trends between and within systems, and in the measured characteristics between systems, e.g. active channel and channel belt widths etc. The dataset of systems was grouped by climate type, catchment area (a proxy for sediment supply and discharge) and channel planform (a proxy for sediment concentrations and grain size), to identify any clear factors that cause variability between systems. Thus, it can be proposed that variability in the medial zone arises due to a combination of factors but is ultimately driven by variation in sediment concentrations and discharge. Further work may involve quantifying some of these factors of variability, or by using numerical models to infer how medial characteristics of modern DFS appear in the rock record.

• Item Type: Thesis (MRes)
• Qualification Level: Masters
• Subjects: G Geography. Anthropology. Recreation > G Geography (General); G Geography. Anthropology. Recreation > GE Environmental Sciences
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Supervisor's Name: Owen, Dr. Amanda and Williams, Professor Richard
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83893
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Oct 2023 15:19
• Last Modified: 28 Nov 2025 14:03
• Thesis DOI: 10.5525/gla.thesis.83893
• URI: https://theses.gla.ac.uk/id/eprint/83893