Two PhD positions on creep behaviour of rock salt and application to salt caverns (1.0 FTE) (# of pos: 2)

The Department of Earth Sciences of Utrecht University, group Experimental Rock Deformation, invites applications from highly motivated candidates for two PhD positions (preferably) starting on January 1st 2023, within a collaborative research programme titled Multi-scale validation of constitutive models for rock salt creep behaviour and application to field-scale numerical models.
This programme aims to advance the fundamental understanding of rock salt creep behaviour in salt production and salt cavern energy storage applications. The programme is a research collaboration between Utrecht University (UU) and the Netherlands Organization for Applied Scientific Research (TNO).

Salt caverns created for brine production or energy storage tend to converge due to salt creep, which may lead to potential induced seismicity, loss of cavern stability and integrity of the rocks surrounding the caverns and surface subsidence. However, the amount of cavern convergence and subsidence, particularly on the long-term, cannot at present be predicted with confidence, hindering the full assessment of surface effects.

Two PhD positions are available. One is intended to carry out a laboratory-based study to quantify salt creep behaviour at in-situ conditions and derive mechanism-based constitutive laws. The other one is intended for a numerical modeling study focusing on upscaling of experimental results and applying constitutive laws to investigate cavern- and field-scale behaviour in the context of salt production and storage applications.

PhD position 1: Experimental Rock Mechanics and Microphysics Supervisors: S.J.T. Hangx (UU), J.H. ter Heege (TNO), J.H.P. de Bresser (UU, promotor).

The aim of this 4-year PhD project is to:

• experimentally determine the low-stress deformation processes operating in natural rock salt under realistic in-situ conditions, including dynamic recrystallisation and transient creep;
• test existing and new theoretical models for these processes; and
• upscale the results obtained to provide deformation laws (constitutive models) for Dutch Zechstein salt that can be applied in cavern (abandonment) and subsidence modelling via the associated PhD position 2. The approach will involve conventional mm-/cm-scale triaxial deformation experiments, potentially coupled to real-time CT-imaging.

PhD position 2: Numerical Modelling of salt caverns
Supervisors: B.B.T. Wassing (TNO), J.H.P. de Bresser (UU, promotor)

The aim of this 4-year PhD project is to:

• develop 3D numerical modelling tools for single- and multi-cavern systems implementing the (upscaled) constitutive laws developed;
• evaluate model forecasts against field observations; and
• apply the models to field cases and simulate different operational, cavern abandonment and shut-in strategies for both brine production and energy storage caverns. The approach will involve expanding on existing single-cavern numerical models. Field data from salt caverns in the Netherlands will be made available by TNO or cavern operators and used for model evaluation and simulations that include sensitivity analyses and operational scenarios.

Throughout the programme, there will be a close collaboration between the two PhD candidates and the team of researchers and supervisors involved from UU and TNO. The results obtained will be directly usable, by providing the physical basis and numerical tools for realistic, cavern-scale modelling. The main aim is to obtain more accurate predictions of long-term cavern behaviour and associated surface effects. All phases of a cavern life-cycle will be considered, from creation to shut-in and long-term abandonment. The programme contributes towards a safer and more sustainable way of operating production and storage caverns in salt by reducing risks of cavern operations. In a broader context, reducing risks and increasing efficiency of salt cavern usage for energy buffering systems based on hydrogen and compressed air energy storage contributes directly to a transition from high-carbon fossil fuels, such as oil and coal, towards cleaner energy production.

This UU-TNO research collaboration is funded in part by the Ministry of Economic Affairs and Climate (EZK) and TNO. We offer guaranteed funding for each project and a personalised training programme, which reflects the candidates' training needs and career objectives. About 20% of both candidates' time will be dedicated to this training component, which includes training on the job in assisting in the BSc and MSc teaching programmes of the Earth Sciences department at Utrecht University.