Impact of Geochemical Weathering on Fault Zone Architecture

Cross-fault flow properties of fault zones have long been studied to constrain their ability to hold a hydrocarbon column. However flow within fault zones can lead them to act as sub-vertical conduits. Faults can act as seal bypass systems, permitting linkage of compartments in conventional hydrocarbon systems. Faults can also provide conduits for gas flow out of unconventional reservoirs, reducing the economic gas in place; or provide pathways for water into unconventional wells, increasing water production and the consequent environmental impacts. There is therefore an urgent need to develop new workflows and tools for quantifying the risk of within-fault flow for a given subsurface fault.
The risk of flow within fault zones is affected by the internal structural architecture of the fault, the petrophysical properties of the fault rocks and the interplay of mechanical and chemical processes within the fault zone (fault zone diagenesis). The latter is the least-studied aspect of within-fault flow.
The Little Grand Wash and Iron Wash faults, Utah, provide surface analogues for faults in unconventional and conventional reservoirs respectively. The sites represent excellent natural labs for characterising the processes that constrain within-fault flow: the research team have collected unparalleled data at both sites from surface exposures and wells (both scientific and industry) and have extensive datasets of fault zone structure subsurface samples of fault rocks. Subsurface samples allow exploration of the appropriate ways to correct for the effect of weathering on surface analogues. The PhD student will collect new field data to investigate the effect of geochemical reactions on both the mechanical response of the fault rocks and the hydraulic properties of the fault rocks. They will constrain the fault zone diagenesis using petrological,SEM techniques and whole-rock chemical and isotopic analyses; use state of the art flow modelling developed at Strathclyde to investigate the range of likely within-fault flow scenarios; collect new mechanical data in Strathclyde geo-mechanics labs; and develop a predictive workflow/tool for within-fault flow. Finally they will validate this tool against industry datasets both in the literature and provided by NERC CDT partners.