Theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore-filling methane hydrate
Theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore-filling methane hydrate
The majority of presently exploitable marine methane hydrate reservoirs are likely to host hydrate in disseminated form in coarse grain sediments. For hydrate concentrations below 25–40%, disseminated or pore-filling hydrate does not increase elastic frame moduli, thus making impotent traditional seismic velocity-based methods. Here, we present a theoretical model to calculate frequency-dependent P and S wave velocity and attenuation of an effective porous medium composed of solid mineral grains, methane hydrate, methane gas, and water. The model considers elastic wave energy losses caused by local viscous flow both (i) between fluid inclusions in hydrate and pores and (ii) between different aspect ratio pores (created when hydrate grows); the inertial motion of the frame with respect to the pore fluid (Biot's type fluid flow); and gas bubble damping. The sole presence of pore-filling hydrate in the sediment reduces the available porosity and intrinsic permeability of the sediment affecting Biot's type attenuation at high frequencies. Our model shows that attenuation maxima due to fluid inclusions in hydrate are possible over the entire frequency range of interest to exploration seismology (1–106 Hz), depending on the aspect ratio of the inclusions, whereas maxima due to different aspect ratio pores occur only at sonic to ultrasound frequencies (104–106 Hz). This frequency response imposes further constraints on possible hydrate saturations able to reproduce broadband elastic measurements of velocity and attenuation. Our results provide a physical basis for detecting the presence and amount of pore-filling hydrate in seafloor sediments using conventional seismic surveys.
elastic wave attenuation, methane hydrate, rock physics modeling
1835–1847
Marín-Moreno, H.
e466cafd-bd5c-47a1-8522-e6938e7086a4
Sahoo, S.K.
6dab0376-36df-44c5-9f36-cb4a29d9b03b
Best, A.I.
f962ede8-2ff2-42b6-baa1-88d93dfb08dd
Marín-Moreno, H.
e466cafd-bd5c-47a1-8522-e6938e7086a4
Sahoo, S.K.
6dab0376-36df-44c5-9f36-cb4a29d9b03b
Best, A.I.
f962ede8-2ff2-42b6-baa1-88d93dfb08dd
Marín-Moreno, H., Sahoo, S.K. and Best, A.I.
(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), .
(doi:10.1002/2016JB013577).
Abstract
The majority of presently exploitable marine methane hydrate reservoirs are likely to host hydrate in disseminated form in coarse grain sediments. For hydrate concentrations below 25–40%, disseminated or pore-filling hydrate does not increase elastic frame moduli, thus making impotent traditional seismic velocity-based methods. Here, we present a theoretical model to calculate frequency-dependent P and S wave velocity and attenuation of an effective porous medium composed of solid mineral grains, methane hydrate, methane gas, and water. The model considers elastic wave energy losses caused by local viscous flow both (i) between fluid inclusions in hydrate and pores and (ii) between different aspect ratio pores (created when hydrate grows); the inertial motion of the frame with respect to the pore fluid (Biot's type fluid flow); and gas bubble damping. The sole presence of pore-filling hydrate in the sediment reduces the available porosity and intrinsic permeability of the sediment affecting Biot's type attenuation at high frequencies. Our model shows that attenuation maxima due to fluid inclusions in hydrate are possible over the entire frequency range of interest to exploration seismology (1–106 Hz), depending on the aspect ratio of the inclusions, whereas maxima due to different aspect ratio pores occur only at sonic to ultrasound frequencies (104–106 Hz). This frequency response imposes further constraints on possible hydrate saturations able to reproduce broadband elastic measurements of velocity and attenuation. Our results provide a physical basis for detecting the presence and amount of pore-filling hydrate in seafloor sediments using conventional seismic surveys.
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Mar-n-Moreno_et_al-2017-Journal_of_Geophysical_Research__Solid_Earth
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Accepted/In Press date: 23 February 2017
e-pub ahead of print date: 15 March 2017
Additional Information:
Funding Information:
We acknowledge funding from the United Kingdom Natural Environment Research Council (NE/J020753/1). The data used are listed in the references, tables, figures, and in an Excel spreadsheet in the supporting information. The references Berryman []; Bishop [], Dvorkin et al. [], Hovem and Ingram []; Ishii and Mishima []; Kuster and Toksöz []; Mahabadi et al. []; Mindlin [], and Reuss [] refer only to the supporting information. We thank Nicola Tisato and an anonymous reviewer for their detailed and constructive comments.
Keywords:
elastic wave attenuation, methane hydrate, rock physics modeling
Organisations:
Geology & Geophysics, Marine Geoscience
Identifiers
Local EPrints ID: 406467
URI: http://eprints.soton.ac.uk/id/eprint/406467
ISSN: 2169-9313
PURE UUID: 0d1f5b6b-5c3b-41d1-9a55-069722e46b4e
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Date deposited: 18 Mar 2017 02:04
Last modified: 16 Mar 2024 05:09
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Contributors
Author:
H. Marín-Moreno
Author:
S.K. Sahoo
Author:
A.I. Best
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