Sahoo, Sourav K., Madhusudhan, B.N., Marin-Moreno, H., North, Laurence J, Ahmed, Sharif, Falcon-Suarez, Ismael, Minshull, Timothy and Best, Angus (2018) Laboratory insights into the effect of sediment‐hosted methane hydrate morphology on elastic wave velocity from time‐lapse 4D synchrotron X‐ray computed tomography. Geochemistry, Geophysics, Geosystems, 19 (11), 4502-4521. (doi:10.1029/2018GC007710).
Abstract
A better understanding of the effect of methane hydrate morphology and saturation on elastic wave velocity of hydrate bearing sediments is needed for improved seafloor hydrate resource and geohazard assessment. We conducted X‐ray synchrotron time‐lapse 4D imaging of methane hydrate evolution in Leighton Buzzard sand, and compared the results to analogous hydrate formation and dissociation experiments in Berea sandstone, on which we measured ultrasonic P‐ and S‐wave velocity, and electrical resistivity. The imaging experiment showed that initially hydrate envelops gas bubbles and methane escapes from these bubbles via rupture of hydrate shells, leading to smaller bubbles. This process leads to a transition from pore‐floating to pore‐bridging hydrate morphology. Finally, pore‐bridging hydrate coalesces with that from adjacent pores creating an inter‐pore hydrate framework that interlocks the sand grains. We also observed isolated pockets of gas within hydrate. We observed distinct changes in gradient of P‐ and S‐wave velocity increase with hydrate saturation. Informed by a theoretical model of idealized hydrate morphology and its influence on elastic wave velocity, we were able to link velocity changes to hydrate morphology progression from initial pore‐floating, then pore‐bridging, to an inter‐pore hydrate framework. The latter observation is the first evidence of this type of hydrate morphology, and its measurable effect on velocity. We found anomalously low S‐wave velocity compared to the effective medium model, probably caused by the presence of a water film between hydrate and mineral grains.
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- Faculties (pre 2018 reorg) > Faculty of Engineering and the Environment (pre 2018 reorg) > Southampton Marine & Maritime Institute (pre 2018 reorg)
- Faculties (pre 2018 reorg) > Faculty of Natural and Environmental Sciences (pre 2018 reorg) > National Oceanography Centre (pre 2018 reorg)
- Current Faculties > Faculty of Environmental and Life Sciences > School of Ocean and Earth Science > Geology and Geophysics
School of Ocean and Earth Science > Geology and Geophysics - Current Faculties > Faculty of Engineering and Physical Sciences > School of Engineering > Civil, Maritime and Environmental Engineering
Civil, Maritime and Environmental Engineering
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