A fully funded 4-year PhD project at the Dublin Institute for Advanced Studies.

Project background:

Studying underground fluid-flow behaviours is relevant for a range of applications, such as understanding fluid movements in aquifers, volcanoes, geothermal injection, and microseismic experiments. Describing the fluid-flow regime is generally complex as it depends on a series of case-dependent parameters, including fluid properties (velocity, viscosity, and the presence of two or three phases) and fracture characteristics (geometry, roughness). However, it has important implications, as fluids can generate a variety of seismic responses, which are crucial for natural hazard assessment and monitoring.

Following pre-existing models, some seismic signals are widely used to locate fluid movements, and provide fracture sizes and fluid compositions. In particular, there are diverse models explaining how long-standing vibrations, such as resonances, are generated. Most of these models require either the presence of a resonating body, such as a fracture or a cavity, or the movement of fluids, or both. While all these models have pros and cons, they usually assume certain fluid-flow regimes, conditions and contributions. For example, fluid pressure variations could trigger Krauklis waves propagation on the fracture walls, leading to its resonance, but this occurs only for a range of fluid viscosities and fracture widths (i.e, thick-fracture regime). Fluids could also generate resonances themselves through periodic fluid-flow instabilities such as vortex shedding or Kelvin-Helmholtz instabilities.

Even though these models provide important estimates to interpret observations, many important assumptions and uncertainties remain about them. For this project, the student will first focus on modelling the fluid movements inside a fracture using existing software, considering a range of fluid properties and fracture characteristics. The modelling will involve an unstable fluid-flow regime at high Reynolds numbers, and the influence on the resulting flow of key characteristics will be evaluated: i) a simplified version of a realistic 3D fracture with different thicknesses, lengths, shapes and roughness; ii) fluid properties (e.g., fluid velocity and viscosity, multi-phase flow). Realistic fluid properties encountered at volcanoes, underground water flow and fluid injections will be considered. These results will then provide the complex fluid excitation to model the seismic response of the fracture via wave propagation modelling. Finally, the modelling results will be compared to real data acquired during passive seismic monitoring of water reservoirs and/or volcanoes.

The general goal is to better understand how fluid and fracture characteristics relate to observed seismic responses, and provide quantitative estimates to improve the interpretation of signals used for monitoring and natural hazard assessment purposes.

Main tasks:

• Define realistic fracture and fluid properties for different simulations
• Design 3D fracture models for Computational Fluid Dynamics modelling and simulate fluid-flow behaviours for these models
• Compute the wavefield corresponding to these fluid-fracture systems
• Analyse continuous seismological data
• Present results at national and international conferences as well as in peer-reviewed publications

Duration: The PhD position is funded for 4 years

Scholarship: €19,000 tax-free annual stipend (currently under review for increase in 2024), a budget for travel, laptop and other research materials, as well as an annual contribution towards fees.

Start date: January, 2024, or as soon as possible thereafter

Applicant requirements:

• Must have a Masters in one of the following fields: Geosciences, Geophysics, or Physics
• Solid background in computational methods, signal processing, seismology and geophysical fluid dynamics is advantageous
• Requires the ability to work both independently and with a team of people from diverse backgrounds
• Evidence of strong oral and scientific English writing proficiency

Application details:

Send a PDF copy of their transcript of records, a CV and a cover letter including motivation for applying, research interests and experience and the names and contact of two academic references in one PDF file to Prof. Jean-Baptiste Tary at tary@cp.dias.ie. For full consideration, application materials must be received by October 29, 2023. Applications will continue to be accepted after this until the position is filled. Selected candidates will then be contacted for an online interview. Please apply using this link: https://dias.ie/phdscholar

At DIAS, we are committed to building an inclusive scientific community, distinguished by scientific excellence, gender balance, and diversity.