Risk Reduction Projects

Offshore wind-farm construction, as well as the laying of cables and boring of tunnels, requires a detailed understanding of the geology immediately beneath the seabed. Conventional 2D seismic reflection data is typically used to image subsurface geology for offshore construction, but its 5-10 m resolution often limits its applicability. Ultra-high resolution P-cable reflection seismology is a relatively new technique that can image shallow geology at resolutions of ~1 m. This new technology could thus prove critical for generating higher resolution and 3D ground models, ultimately improving the placement of seabed infrastructure, enhancing economics and lifespans, and reducing risk. Despite the potential of P-cable technology for the growing offshore construction industry and the transition to renewable energy sources, it has received little attention.

This project will use several P-cable datasets and, alongside borehole data, to define the survey area’s shallow subsurface and build 3D geological models of it. The three key objectives of the seismic interpretation are: (1) map sedimentary packages; (2) quantify shallow fault displacement patterns to unravel when they were active; and (3) identify the age and locations of mass transport complexes. With this information and the resulting 3D geological model you will take standard wind farm configurations and test their placement in each area, assessing their safety and lifespan (e.g., would standard wind-farm configurations place turbines above active faults?). You could augment seismic interpretation with attribute analysis (e.g., spectral decomposition), and use seismic forward modelling determine the uplift in resolution from conventional seismic to P-cable reflection data (i.e. assessing what information is missed in the conventional seismic dataset).

Overall, these objectives will allow you to demonstrate the use of P-cable data to understanding the shallow subsurface geology in 3D and through distribution of your findings, you will help bring the technology to the attention of relevant companies.

Academic lead – Dr Craig Magee

The Corbetti caldera in the Main Ethiopian Rift (MER) is planned to become the site of Ethiopia’s second and largest geothermal power plant, potentially producing > 1 GW of zero-carbon electricity . Like most ‘high-enthalpy’ geothermal sites, the source of heat is magma injected into the crust, and the heat is transported to the surface along fractures via water-rich fluids. When exploiting such a system, it is critically important to understand the distribution of heat sources and pathways, but there remain significant sources of uncertainty. Reducing uncertainty and quantifying risk in developing geothermal resources is likewise critical. In this project, you will use seismic data to help improve our understanding of the processes at play beneath Corbetti and better image its interior.

Together with your advisors, you will use existing seismic recordings of microearthquakes and make new measurements of surface wave velocities on a network of stations at the caldera. You will then invert these data using new probabilistic methods (Zhang et al., 2020) to reveal the velocity structure of Corbetti, which importantly will include error bounds. You will then integrate this new model with existing geochemical and geophysical models (e.g., Gíslason et al., 2015; Lloyd et al., 2018) to better understand the processes occurring at this volcano, and better constrain the source and pathways for heated fluids. Your work will also help understand other systems in the MER and the structure of volcanoes in general.

References:
Gíslason, G., Eysteinsson, H., Björnsson, G., Harðardóttir, V., 2015. Results of Surface Exploration in the Corbetti Geothermal Area, Ethiopia, in: Proceedings, World Geothermal Congress, p. 10.
Lloyd, R., Biggs, J., Wilks, M., Nowacki, A., Kendall, J.-M., Ayele, A., Lewi, E., Eysteinsson, H., 2018. Evidence for cross rift structural controls on deformation and seismicity at a continental rift caldera. Earth and Planetary Science Letters 487, 190–200. https://doi.org/10.1016/j.epsl.2018.01.037
Zhang, X., Roy, C., Curtis, A., Nowacki, A., Baptie, B., 2020. Imaging the subsurface using induced seismicity and ambient noise: 3D Tomographic Monte Carlo joint inversion of earthquake body wave travel times and surface wave dispersion. Geophysical Journal International 222, 1639–1655. https://doi.org/10.1093/gji/ggaa230

Academic lead – Dr Andy Nowacki

This project will determine the suitability of giant subsurface saline aquifers for the safe and long-term storage of CO2. Very large storage volumes within unclosed Triassic saline aquifers of the UK have the potential to contribute significantly to the solution of what is the most pressing problem faced by the world today: how to dramatically reduce emissions of greenhouse gas to the atmosphere. The successful candidate will use techniques in sedimentary facies analysis, structural geology, basin analysis, petrophysics and reservoir modelling to investigate the role of lithological heterogeneity in determining injectivity of CO2 into aquifers and the ability of low-permeability seal units to act as barriers to the upward movement of CO2. Although depleted UK oil and gas reservoirs are attractive short-term targets for CO2 storage because their geological character is known, their storage capacities are limited. Much larger saline aquifers must additionally be utilised if the majority of carbon produced by the UK’s large point source emitters (e.g., cities, power stations) is to be sequestered effectively over coming decades. Triassic saline aquifers of the UK Southern North Sea, East Irish Sea Basin and adjacent onshore areas, with their favourable porosity and permeability character and their stratigraphical juxtaposition to seals, can potentially store significantly more CO2 than the combined capacity of the regions’ depleted hydrocarbon fields. This project will undertake a combined outcrop and subsurface characterisation of the Triassic Bunter and Ormskirk Sandstone formations (and lateral equivalents), two of the largest UK saline aquifers considered as potentially suitable for long-term CO2 storage. The size, shape, frequency and degree of interconnectivity of sedimentary geobodies will be characterised. Results will quantify net CO2 storage potential, will predict injectivity within different sedimentary successions, will predict flow migration pathways, and will assess the ability of aquifers to retain CO2 over long time scales. Fluvial, Eolian & Shallow-Marine Research Group (http://frg.leeds.ac.uk/)

Academic lead - Professor Nigel Mountney