Coupled Thermo-Fluid-Mechanics of Thermally Stressed Granite for Hot Dry Rock Geothermal Reservoir Applications

This 3-year self-funded PhD will be based in the School of the Environment, Geography and Geosciences and will be supervised by Dr Philip Benson and Professor Ingo Sass (TU Darmstadt).

Permeability is the most important property of geothermal reservoirs and the subject of numerous studies (e.g. Sass and Götz, 2012; Luviano et al., 2015; Brehme et al., 2016; Bär et al., 2017).

While all rocks contain inherent porosity and permeability, the development of a secondary permeability (fracture related) is gaining renewed interest as a means to develop Enhanced Geothermal  Systems (EGS), by injecting new tensile fracture networks in hot but relatively impermeable rocks as a source of deep sustainable geothermal energy.

The permeability of EGS will be simulated in a controlled laboratory environment to link Acoustic Emission or AE (the laboratory analogue of tectonic seismicity) to field scale geophysical methods, which have seen an increased application for geothermal sciences, and significant promise in this area.

On this project, a suite of fractured granite samples will be prepared by subjecting them to elevated HDR environments, with thermal damage controlled and monitored using a tube furnace equipped with a waveguide system for measuring passive and active seismicity (Acoustic Emission, AE).

Thermal stressing temperature - which generates a primary microfracture fabric via the differential expansion of component minerals in the granite – will be increased stepwise from 100°C to 600°C to induce a network of cracks. To calibrate the method, samples will be scanned pre- and post-treatment using high resolution X-Ray Computed Tomography.

Primary permeability of the thermally treated samples will be determined using high-pressure rock physics equipment capable of measuring active/passive seismicity and permeability at a range of simulated burial conditions to 4 km depth, and to temperatures of 200°C to simulate geothermal reservoir conditions.

Once primary permeability has been established, the equipment will deform and fracture selected samples in both compression and tension to test the associated secondary permeability, and to thus evaluate improvements in permeability and heat flow resulting from secondary stimulation of Hot Dry Rocks.

Finally, to understand the interplay and relationship between permeability and the heat transfer and thermal conductivity of the rock/fluid system, a range of post-test frictional thermo-physics models will be developed to provide new links between laboratory and field scale processes. An additional output of this link will be to better use the natural seismicity as a tool to both monitor and understand fracturing in EGS for risk mitigation and optimisation purposes.

Fees and funding

Visit the research subject area page for fees and funding information for this project.

Funding Availability: Self-funded PhD students only

PhD full-time and part-time courses are eligible for the UK Government Doctoral Loan (UK and EU students only).

How to apply

Please contact Dr Philip Benson (philip.benson@port.ac.uk) to discuss your interest before you apply, quoting the project code.

Please note, to be considered for this self-funded PhD opportunity you must quote project code SEES4830219 when applying.