Coupled Thermal-Hydro-Mechanical and Chemical (THMC) processes in salt formations for disposal and storage applications

This PhD project aims to: 1) improve the conceptual understanding of the physicochemical processes and mechanisms that govern the migration of gases and brine in rock salt formations under the influence of a thermal gradient; 2) Develop a novel and efficient THMC numerical framework that will be validated against experimental data collected by international research programmes.

Requirements/eligibility: We seek a highly motivated and numerate graduate who is willing to work in the area of mathematical modelling of coupled processes in porous media, specifically nuclear waste disposal in salt caverns. Applicants should have or expect to achieve at least a 2.1 honours degree (or equivalent), in Applied Mathematics, Physics, Engineering, Environmental Science, Computer Science, or a related discipline. Successful candidates will join the Subsurface Energy Engineering group and PhD programme of the Department of Chemical Engineering at the University of Manchester. This is a joint programme between the University of Manchester and the National Nuclear Laboratory. Moreover, additional support and technical advice will be offered by the Rock Deformation Lab of the University of Liverpool (namely Prof. Dan Faulkner, Dr John Wheeler and Dr John Bedford).

Context:

Salt characterisation and evolution plays an important role across multiple parts of the energy sector due to it’s impermeable nature and influence on heat transfer. For example, salt tectonics provides structural and stratigraphic traps in prolific hydrocarbon basins (e.g., UK Central North Sea and US Gulf of Mexico). The ability of salt to move in the subsurface also provides the potential for any temporary fluid flow conduits (e.g., joints or fractures) to close and self-seal over relatively short timescales (10’s of years). As a result, salt has long been considered as a potential storage site for hydrogen and disposal concept for radioactive waste. 

Geological disposal is recognised internationally as the safest long-term solution for higher-activity radioactive waste. It involves the construction of a geological disposal facility (GDF) deep underground, that consists of a series of tunnels and vaults in which the radioactive waste is placed. This solution is based on the multibarrier concept provided by the geosphere, which includes the host rock and the surrounding geological environment, and the engineered barrier system that includes waste form, waste containers, buffers and backfill.

Geological disposal is also the UK Government’s policy, for disposing of higher-activity radioactive wastes. The selection of a site for a GDF in the UK is a voluntary process requiring a suitable site and a willing community to host a GDF. Currently, the geological setting for both potential sites under consideration is Lower Strength Sedimentary Rocks (i.e., Ancholme Group and Mercia Mudstone Group). However, the Mercia Mudstone Group (MMG) demonstrates more complex geology, that also includes evaporitic (e.g., halite, anhydrite, and gypsum) strata. As such, the safety case for the UK’s radioactive disposal programme, also needs to be underpinned by a thorough understanding of the long-term THMC evolution of MMG’s evaporitic strata.

In the vicinity of the disposal facility, the heat produced by the decay of the radioactive waste is expected to induce changes in the rock salt formations. For example, changes in the temperature field may enhance salt creep, and induce the thermal expansion of both solid and fluid phases (i.e., locally elevated stress and fluid pressure) which may affect the migration of brine but also locally increase the rock’s hydraulic conductivity. Furthermore, high-temperature gradients will alter the rock solubility and the dissolution and precipitation of salt due to evaporation and condensation of water vapour. In particular, for gypsum it is known that the heating induced, dehydration process is a metamorphic reaction that can lead to anhydrite formation which is associated with a  decrease in rock volume and the formation of new pore space (i.e., potential fluid pathways).   

This programme will focus on describing these ongoing and interdependent physicochemical processes. In particular, the two main tasks of this PhD project are:

·       Task 1: The development and implementation of mathematical models that capture these coupled processes phenomena.

·       Task 2: The validation of the numerical models against experimental data.

Impact: This project will aim to develop novel mathematical models to quantify the long-term thermal-hydraulic-mechanical and chemical evolution of MMG’s evaporitic strata. Output of this work will support the safety assessment for rock salt disposal of radioactive waste.

Training: Full training in the usage of modelling software that may include (PFLOTRAN, TOUGH, COMSOL Multiphysics, OpenGeoSys, FLAC3D, and Code_Bright), will be provided. Further, this PhD offers the opportunity for the student to be involved in experimental work and closely collaborate with with Academic group of the Rock Deformation Lab at the University of Liverpool.  In addition  as  part of this program the student will be given the option to undertake a short placement at NNL to gain valuable industry insights and obtain specialist training.

Careers: This PhD presents a great opportunity to extend your expertise in the fields of dynamics of fluids in porous media, mathematical and numerical modelling, geomechanics, geochemistry, and to gain proficiency in the usage of multiple state-of the art modelling platforms and.

The knowledge and skills gained within this PhD programme are in high-demand, and offer a wide range of excellent career pathways, in the nuclear and CCS sectors (e.g., storage of industrial gases such as hydrogen and hydrocarbons), and the mining industry (salt and potash).

How to apply:

You will need to submit an online application through our website here: https://uom.link/pgr-apply

Enquiries about this project can be sent to Dr Masoud Babaei – [email protected] as the lead project supervisor. If you have any queries regarding making an application please contact our admissions team [email protected]

Equality, diversity and inclusion is fundamental to the success of The University of Manchester, and is at the heart of all of our activities. We know that diversity strengthens our research community, leading to enhanced research creativity, productivity and quality, and societal and economic impact. We actively encourage applicants from diverse career paths and backgrounds and from all sections of the community, regardless of age, disability, ethnicity, gender, gender expression, sexual orientation and transgender status.