Dr A Best, Dr S Sahoo, Dr Laurence North, Prof T Minshull
No more applications being accepted
Competition Funded PhD Project (European/UK Students Only)
About the Project
Project Rationale:
Globally, seafloor gas hydrates offer a strategic source of natural gas that may be equivalent in size to all known conventional gas reserves. Ice-like hydrates occur in deep water (>300 m) areas on continental margins at relatively shallow sub-seafloor depths (100s m), and are attractive deposits for commercial exploitation. Several nations (e.g. Japan, China and India) have run national seafloor gas hydrates exploration programmes for over 10 years, and are now moving towards full-scale exploitation of these natural gas resources driven by strategic energy demands. Despite this, there are still many technical challenges to overcome to ensure safe and environmentally responsible hydrate reservoir production. Hydrate production involves dissociation of the hydrate into water and natural gas, which can cause mechanical changes to the host sediments forming the reservoir. The sediment composition (generally sands, but with different amounts of clay) influences the mechanical and reservoir properties of the reservoir and hydrate content and distribution hence production efficiency. Environmentally sustainable production will require proper reservoir delineation and characterisation using geophysical (seismic and electrical) and geotechnical methods, and active monitoring during production. This requires improved knowledge of hydrate reservoir geophysical properties under complex solid-fluid phase changes, for in situ geophysical interpretation.
Methodology:
Most geophysical laboratory studies of hydrates have been at ultrasonic frequency, while field measurements are at seismic and sonic frequencies. Elastic properties are frequency dependent, and the student will exploit unique experimental facilities developed at the NOC to make measurements at frequencies more relevant to field data from real reservoirs. The student will use an acoustic-pulse tube for direct propagation velocity and attenuation measurements at 1 – 10 kHz frequency. The same samples will be transferred to another pressure vessel to measure permeability, S-wave properties using a bender element, and to carry out electrical resistivity tomography using a bespoke system that also measures anisotropy. The student will develop techniques for creating synthetic methane/CO2 gas hydrates in sand samples with controlled clay contents, and study their seismic and electrical properties over different hydrate saturations. The results will be analysed for useful relationships between geophysical and reservoir parameters, and compared to theoretical wave propagation models for model validation and further development. The student will use X-ray computer tomography for tracking the evolution of hydrate morphology in different sediment types. The understanding developed will then be applied to specific hydrate reservoir examples in collaboration with NOC research partners from e.g. China.
Training:
All doctoral candidates will enrol in the Graduate School of NOCS (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 200 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas). Specific training will include:
The student will be trained in all pertinent laboratory experimental methods (with dedicated technical support and health and safety training), including acoustic, ultrasonic, electrical resistivity, reservoir properties such as porosity, permeability, sedimentology (mineralogy, grain size), and X-ray CT imaging. Training will be given in the latest signal processing and geophysical analysis methods, including theoretical aspects. The student will join an active, diverse team of researchers working on related topics, with ample opportunity for mutual support, development and the sharing of ideas and knowledge. The student will also have opportunities to participate in the acquisition of geophysical data at sea.
References
Best, A. I., J. A. Priest, C. R. I. Clayton, and E. V. L. Rees (2013), The effect of methane hydrate morphology and water saturation on seismic wave attenuation in sand under shallow sub-seafloor conditions, Earth and Planetary Science Letters, 368, 78-87, doi:10.1016/j.epsl.2013.02.033.
Marin-Moreno, H., S. K. Sahoo, and A. I. Best (2017), Theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore-filling methane hydrate, Journal of Geophysical Research-Solid Earth, 122(3), 1835-1847, doi:10.1002/2016jb013577.
Sahoo, S. K., B. N. Madhusudhan, H. Marin-Moreno, L. J. North, S. Ahmed, I. H. Falcon-Suarez, T. A. MInshull, and A. I. Best (2018), Laboratory insights into the effect of sediment-hosted methane hydrate morphology on elastic wave velocity from time-lapse 4-D synchrotron X-Ray Computed Tomography, Geochemistry, Geophysics, Geosystems, 19, doi:10.1029/2018GC007710.