Dear colleagues,

We are pleased to advertise the PhD project described below. The project is fully funded for students from the UK and other EU member states. Interested candidates with a suitable background are asked to contact Florian Fusseis ([log in to unmask]) for further information. Applications have to be submitted through the School's website. The advertisement remains open until the position is filled.

With best regards,
Florian Fusseis

4-dimensional studies of transport properties in low-grade metamorphic rocks
Florian Fusseis, Ian Butler 
School of Geosciences, The University of Edinburgh

Rationale: Fluids critically affect rock deformation and metamorphic processes in the crust. Fluid migration, which controls where fluids can interact with rocks, relies on the availability of permeable pore space. In metamorphic environments, porosity is formed and destroyed when chemical and physical boundary conditions change. Metamorphic porosity is therefore highly variable in space and time. Yet, our knowledge of the spatiotemporal variability of the resulting transport properties of rocks at elevated pressures and temperatures is surprisingly incomplete. In a metamorphic system, when, and where exactly do pores form due to a given change of pressure, temperature or fluid composition? How much new porosity is formed, and how long does it exist? And, most importantly, what is the effect of the new porosity on permeability and fluid transfer over multiple spatial and temporal scales? These questions are of particular relevance where a fluid is in chemical disequilibrium with a host rock and dissolution/precipitation processes occur. In fact, geothermal energy extraction, geological radioactive waste storage and CO2 sequestration depend on a detailed knowledge of the effects of changes in fluid composition, temperature, the stress state and/or accumulating strain on permeability.

In studies on fluid transport, a direct link between measurable fluctuations in bulk rock properties and the associated process(es) occurring on the grain scale is often missing. As a consequence, it remains difficult to answer the questions asked above. This gap in understanding can be addressed where, in experiments, bulk transport measurements and analyses of a changing fluid geochemistry are combined with in-situ x-ray tomography. This project will adopt such an approach to experimentally investigate dissolution/precipitation processes and corresponding modifications to bulk transport properties in low-grade metamorphic environments. Sample size, scan resolution, and acquisition time of a 3-dimensional tomographic dataset depend on the instrument used and define the quality of the link between measurement and observed processes. To cover fast and slow processes alike, and image both with a sub-micron resolution, this project will combine lab- and Synchrotron-based x-ray micro-tomographs. Experiments use fluid chemistry as a ‘live’ indicator of fluid-rock interaction. The results gained in this project will provide an unprecedented insight into fluid-rock interaction processes. The experiments will return unique data for the benchmarking of numerical THCM and digital rock physics simulations.

The study benefits from two recent technical advances: Ongoing upgrades at the brightest Synchrotron x-ray sources allow for x-ray tomographic data acquisition at very high energies in fractions of a second. The high photon fluxes allow using new portable x-ray transparent experimental setups that enable simulating fluid flow in, and interaction with a host rock from surface- to mid-crustal conditions. In combination, these developments permit time-resolved 3-dimensional studies of metamorphic fluid flow on the micron- to nano-scale.

Methodology: We will conduct both, long- and short-term experiments on a suite of fluid-rock combinations under consideration for hot-dry rock geothermal energy extraction, geological radioactive waste storage and CO2 sequestration. We will use portable x-ray-transparent fluid-rock interaction cells that are linked to hydraulic as well as micro-geochemical analytical instruments. Experiments will be conducted using the School of Geosciences’ micro-tomograph at the University of Edinburgh, as well as at the micro-tomography beam line 2BM at the Advanced Photon Source (Argonne, USA). Experiments and data analysis will involve collaboration with colleagues in Australia, France, Switzerland and the United States. Data analysis will involve the use of large-scale computing facilities in Edinburgh and overseas.

Training: The successful candidate will receive specialist training in the novel experimental field of time-resolved (‘4D’) x-ray tomographic studies. At the school, the student has access to a very experienced team of experimentalists in both x-ray tomography and micro-geochemistry. He/she will be encouraged to engage in a multidisciplinary workflow that involves experiment design, Synchrotron research, data analysis on supercomputers and links to numerical modeling. The cutting edge aspects of this research will provide the student with excellent future employment prospects in industry and research.