Imaging the fine-scale velocity structure, the physical properties and the sedimentary faulting that controls the fluid flow within the gas-charged sediments of northern North Sea.

Programme website: http://inspire-dtp.ac.uk

Project Rationale:
Carbon Capture and Storage is a low carbon technology which captures the CO2 emitted during power generation, to securely and permanently store underground, for example within depleted oil and gas fields. Securely storing the CO2 within a reservoir requires a good knowledge of the physical properties of the overburden and the associated fluid pathways. During burial of sediments, the porosity of sediments decreases and fluids migrate vertically through chimney and pipe structures created by hydro-fracturing. In order to assess the leakage potential of a CO2 storage reservoir, it is critical to develop an understanding of the formation mechanisms and the longevity of these chimney and pipe structures. Seabed craters caused by erupting fluids, called pockmarks, provide natural analogues for studying the fluid pathways and the physical properties of chimney and pipe structures.

In 2017, a state of the art ocean bottom seismic survey was acquired around a natural gas escape zone, Scanner Pockmark, North Sea to gain knowledge about the physical processes related to gas escape from shallow sediments. The aim of this project is to determine the fine-scale velocity structure, and the physical properties of thin gas-charged layers and the sedimentary faulting that controls the fluid-flow.

Methodology:
The student will have access to the three-dimensional, multi-source (Bolt airguns, GI-guns and three different sparker sources), full azimuth ocean bottom seismic dataset acquired as part of NERC-funded CHIMNEY, and European Union funded STEMM-CCS projects, and a three-dimensional anisotropic velocity model based on travel-time tomography. The project will involve:
i) Deriving a fine-scale velocity model via full-waveform inversion (FWI), by minimizing the difference between the observed waveforms and those modelled through the initial model that accounts for the directional changes in the subsurface wave velocities.
ii) Application of mirror imaging techniques that use the seismic energy that reflects from sea-surface, instead of the primary seismic energy created by the seismic source in order to improve the resolution at the shallower parts of the study region.
iii) Estimation of seismic attributes using the seismic image obtained by mirror imaging and comparison with the seismic attributes from multi-channel seismic profiles.
The high resolution velocity model, the seismic attributes and the distribution of shallow faulting will be analyzed jointly in order to extend our knowledge about hydro-fracturing and vertical fluid migration pathways.

Training:
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre. Specific training will include:

i) Seismic data processing, analysis and visualization;
ii) Scientific computational skills that can be transferred easily to a range of fields after graduation;
iii) Continuum mechanics and physical properties of sedimentary rocks

The student will be part of a wide project that already hosts a number of associated PhD students at different stages. They will have the opportunity to present their results to academic, government-funded and industrial specialists, and will be thoroughly coached in the skillful delivery of their methods and results to these audiences in both verbal and written form. The student will be rigorously trained in the art of scientific communication in the form of academic papers in international journals, and will have the opportunity to participate in seagoing scientific surveys.