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Title: Faults as episodic conduits for hydrocarbons, CO2 and groundwater in sandstones
Author: Heather-Cooley, Megan Elizabeth
ISNI:       0000 0004 6422 5882
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2017
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Constraining the dynamic feedback between deforming porous media and fluid is crucial for understanding hydrocarbon reservoirs, CO2 storage sites and other evolving porous media. In particular, predicting complex fault architecture at depth, currently relies on deterministic algorithms, that do not take account of these dynamic coupling. For instance, creation of permeability due to fracturing may permit fluid flow to enter a fault zone, resulting in cementation (strengthening) or alteration (weakening) of the fault and host rocks. The resulting changes in rock strength may enhance or retard further fracturing and may even result in a switch of deformation mechanism. Temporal and spatial evolution of fluid flow through faulted porous rocks has been studied in a field site in SE Utah, USA. The field area presents a well-exposed fault system that contains evidence for flow of multiple phases of groundwater with varying chemistries and flow of hydrocarbons. By detailed field mapping and microstructural observations of the fault rocks and of the evidence for fluid flow (e.g. bleaching and hydrocarbon staining) the fluid flow history and evolving flow properties of the rocks has been unravelled. The 6km long fault presents an erosional scarp of up to 20m high at its centre. This scarp is dissected with canyons that permit cross-sectional views of the fault and associated alteration which has been mapped. The field area contains two general classes of lithology. In porous sandstones, deformation is accommodated by deformation bands and fractures. In tight limestones and siltstones deformation is accommodated by fracturing and the formation of clay-rich fault rocks. Evidence for multiple fluid flow events can be observed. Hydrocarbon staining is confined to the coarsest grained layers in the sandstones, and to fractures in all lithologies. Bleaching surrounds fractures in the fault damage zone and along bedding in the fault zone. This thesis presents evidence for a reduction in porosity due to increased burial and cementation to be the biggest influence on deformation mechanisms for fault growth and evolution. Evidence of the evolving structural and hydrogeological properties of the fault zone are explored. This thesis discusses how such data can be used to improve the predictive capability of fault zone properties at depth where the faults have accommodated post-faulting fluid flow.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral