Laboratory observations of frequency-dependent ultrasonic P-wave velocity and attenuation during methane hydrate formation in Berea sandstone
Laboratory observations of frequency-dependent ultrasonic P-wave velocity and attenuation during methane hydrate formation in Berea sandstone
Knowledge of the effect of methane hydrate saturation and morphology on elastic wave attenuation could help reduce ambiguity in seafloor hydrate content estimates. These are needed for seafloor resource and geohazard assessment, as well as to improve predictions of greenhouse gas fluxes into the water column. At low hydrate saturations, measuring attenuation can be particularly useful as the seismic velocity of hydrate-bearing sediments is relatively insensitive to hydrate content. Here, we present laboratory ultrasonic (448-782 kHz) measurements of P-wave velocity and attenuation for successive cycles of methane hydrate formation (maximum hydrate saturation of 26 per cent) in Berea sandstone. We observed systematic and repeatable changes in the velocity and attenuation frequency spectra with hydrate saturation. Attenuation generally increases with hydrate saturation, and with measurement frequency at hydrate saturations below 6 per cent. For hydrate saturations greater than 6 per cent, attenuation decreases with frequency. The results support earlier experimental observations of frequency-dependent attenuation peaks at specific hydrate saturations. We used an effective medium rock-physics model which considers attenuation from gas bubble resonance, inertial fluid flow and squirt flow from both fluid inclusions in hydrate and different aspect ratio pores created during hydrate formation. Using this model, we linked the measured attenuation spectral changes to a decrease in coexisting methane gas bubble radius, and creation of different aspect ratio pores during hydrate formation.
Acoustic properties, Gas and hydrate systems, Seismic attenuation
713-723
Sahoo, Sourav K.
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North, Laurence J.
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Marín-Moreno, Hector
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Minshull, Tim A.
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Best, Angus I.
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1 October 2019
Sahoo, Sourav K.
6dab0376-36df-44c5-9f36-cb4a29d9b03b
North, Laurence J.
086e30f4-b8be-429c-b6a0-5cc0c3902e53
Marín-Moreno, Hector
e466cafd-bd5c-47a1-8522-e6938e7086a4
Minshull, Tim A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Best, Angus I.
f962ede8-2ff2-42b6-baa1-88d93dfb08dd
Sahoo, Sourav K., North, Laurence J., Marín-Moreno, Hector, Minshull, Tim A. and Best, Angus I.
(2019)
Laboratory observations of frequency-dependent ultrasonic P-wave velocity and attenuation during methane hydrate formation in Berea sandstone.
Geophysical Journal International, 219 (1), .
(doi:10.1093/gji/ggz311).
Abstract
Knowledge of the effect of methane hydrate saturation and morphology on elastic wave attenuation could help reduce ambiguity in seafloor hydrate content estimates. These are needed for seafloor resource and geohazard assessment, as well as to improve predictions of greenhouse gas fluxes into the water column. At low hydrate saturations, measuring attenuation can be particularly useful as the seismic velocity of hydrate-bearing sediments is relatively insensitive to hydrate content. Here, we present laboratory ultrasonic (448-782 kHz) measurements of P-wave velocity and attenuation for successive cycles of methane hydrate formation (maximum hydrate saturation of 26 per cent) in Berea sandstone. We observed systematic and repeatable changes in the velocity and attenuation frequency spectra with hydrate saturation. Attenuation generally increases with hydrate saturation, and with measurement frequency at hydrate saturations below 6 per cent. For hydrate saturations greater than 6 per cent, attenuation decreases with frequency. The results support earlier experimental observations of frequency-dependent attenuation peaks at specific hydrate saturations. We used an effective medium rock-physics model which considers attenuation from gas bubble resonance, inertial fluid flow and squirt flow from both fluid inclusions in hydrate and different aspect ratio pores created during hydrate formation. Using this model, we linked the measured attenuation spectral changes to a decrease in coexisting methane gas bubble radius, and creation of different aspect ratio pores during hydrate formation.
Text
ggz311
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Accepted/In Press date: 10 July 2019
e-pub ahead of print date: 17 July 2019
Published date: 1 October 2019
Additional Information:
Publisher Copyright:
© 2019 The Author(s) 2019. Published by Oxford University Press on behalf of The Royal Astronomical Society.
Keywords:
Acoustic properties, Gas and hydrate systems, Seismic attenuation
Identifiers
Local EPrints ID: 433628
URI: http://eprints.soton.ac.uk/id/eprint/433628
ISSN: 0956-540X
PURE UUID: 77f7c2ba-1798-432e-b10d-fa6711e5978d
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Date deposited: 28 Aug 2019 16:30
Last modified: 17 Mar 2024 02:50
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Contributors
Author:
Sourav K. Sahoo
Author:
Laurence J. North
Author:
Hector Marín-Moreno
Author:
Angus I. Best
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