The effects of fluid flow on the transport properties of faults in Enhanced Geothermal Systems

Successful operation of Enhanced Geothermal Systems (EGSs) requires easy flow of geothermal fluids. Pre-existing faults often provide low permeability pathways for fluid flow. However, such faults may be reactivated during geothermal operations, potentially leading to induced seismicity. Whether or not fault movement leads to induced seismicity depends on the fault frictional properties, which is affected by a range of factors, including the fault rock composition. Both permeability and frictional properties can be affected by the flow-through of the undersaturated solutions involved in geothermal operations, which can lead to mineral dissolution and precipitation, as such changing the (connected) porosity and the fault rock composition. This project aims to quantify how flow-through of undersaturated solutions affects the composition and transport properties of fault materials typical for EGSs, and what the implications are for the frictional properties and thus induced seismicity. The approach adopted involves experimental work, microstructural investigations and microphysical modelling. In addition, the student may be able to work with an industry reactive transport modelling code.

The project contributes to a better understanding of the processes active in EGSs, including fault frictional properties and induced seismicity. It is anticipated to result in experimental data on and model predictions of the evolution of fault rock composition and permeability during flow-through of geothermal fluids under a range of conditions with trends identified and quantified. These results can be used as input for studies addressing the evolution of the transport properties of typical fault rocks found in EGCs and the risk of induced seismicity in such systems. This project is directly linked to the successful NERC highlight Topics "Geothermal Power Generated from UK Granites (GWatt)" project, on which the primary supervisor is PI for HWU.

The PhD student will learn to: design an experimental program; perform rock deformation experiments; analyse data; perform microstructural analysis, use optical and electron microscopes; formulate microphysical and potentially numerical models; and write scientific papers. Finally, there may be the possibility for an internship with an industrial partner.