The sensitivity of seismic responses to gas hydrates. Final report

The sensitivity of seismic reflection coefficients and amplitudes, and their variations with changing incidence angles and offsets, was determined with respect to changes in the parameters which characterize marine sediments containing gas hydrates. Using the results of studies of ice saturation eff...

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Main Authors: Foley, J.E., Burns, D.R.
Language:unknown
Published: 2008
Subjects:
Ice
Online Access:http://www.osti.gov/servlets/purl/10180822
https://www.osti.gov/biblio/10180822
https://doi.org/10.2172/10180822
id ftosti:oai:osti.gov:10180822
record_format openpolar
spelling ftosti:oai:osti.gov:10180822 2023-07-30T04:04:06+02:00 The sensitivity of seismic responses to gas hydrates. Final report Foley, J.E. Burns, D.R. 2008-06-19 application/pdf http://www.osti.gov/servlets/purl/10180822 https://www.osti.gov/biblio/10180822 https://doi.org/10.2172/10180822 unknown http://www.osti.gov/servlets/purl/10180822 https://www.osti.gov/biblio/10180822 https://doi.org/10.2172/10180822 doi:10.2172/10180822 03 NATURAL GAS 58 GEOSCIENCES NATURAL GAS HYDRATE DEPOSITS SEISMIC SURVEYS PROGRESS REPORT GAS HYDRATES GAS SATURATION P WAVES S WAVES SENSITIVITY NUMERICAL DATA SEA BED SEDIMENTS 2008 ftosti https://doi.org/10.2172/10180822 2023-07-11T11:01:28Z The sensitivity of seismic reflection coefficients and amplitudes, and their variations with changing incidence angles and offsets, was determined with respect to changes in the parameters which characterize marine sediments containing gas hydrates. Using the results of studies of ice saturation effects in permafrost soils, we have introduced rheological effects of hydrate saturation. The replacement of pore fluids in highly porous and unconsolidated marine sediments with crystalline gas hydrates, increases the rigidity of the sediments, and alters the ratio of compressional/shear strength ratio. This causes Vp/Vs ratio variations which have an effect on the amplitudes of P-wave and S-wave reflections. Analysis of reflection coefficient functions has revealed that amplitudes are very sensitive to porosity estimates, and errors in the assumed model porosity can effect the estimates of hydrate saturation. Additionally, we see that the level of free gas saturation is difficult to determine. A review of the effects of free gas and hydrate saturation on shear wave arrivals indicates that far-offset P to S wave converted arrivals may provide a means of characterizing hydrate saturations. Complications in reflection coefficient and amplitude modelling can arise from gradients in hydrate saturation levels and from rough sea floor topography. An increase in hydrate saturation with depth in marine sediments causes rays to bend towards horizontal and increases the reflection incidence angles and subsequent amplitudes. This effect is strongly accentuated when the vertical separation between the source and the hydrate reflection horizon is reduced. The effect on amplitude variations with offset due to a rough sea floor was determined through finite difference wavefield modelling. Strong diffractions in the waveforms add noise to the amplitude versus offset functions. Other/Unknown Material Ice permafrost SciTec Connect (Office of Scientific and Technical Information - OSTI, U.S. Department of Energy)
institution Open Polar
collection SciTec Connect (Office of Scientific and Technical Information - OSTI, U.S. Department of Energy)
op_collection_id ftosti
language unknown
topic 03 NATURAL GAS
58 GEOSCIENCES
NATURAL GAS HYDRATE DEPOSITS
SEISMIC SURVEYS
PROGRESS REPORT
GAS HYDRATES
GAS SATURATION
P WAVES
S WAVES
SENSITIVITY
NUMERICAL DATA
SEA BED
SEDIMENTS
spellingShingle 03 NATURAL GAS
58 GEOSCIENCES
NATURAL GAS HYDRATE DEPOSITS
SEISMIC SURVEYS
PROGRESS REPORT
GAS HYDRATES
GAS SATURATION
P WAVES
S WAVES
SENSITIVITY
NUMERICAL DATA
SEA BED
SEDIMENTS
Foley, J.E.
Burns, D.R.
The sensitivity of seismic responses to gas hydrates. Final report
topic_facet 03 NATURAL GAS
58 GEOSCIENCES
NATURAL GAS HYDRATE DEPOSITS
SEISMIC SURVEYS
PROGRESS REPORT
GAS HYDRATES
GAS SATURATION
P WAVES
S WAVES
SENSITIVITY
NUMERICAL DATA
SEA BED
SEDIMENTS
description The sensitivity of seismic reflection coefficients and amplitudes, and their variations with changing incidence angles and offsets, was determined with respect to changes in the parameters which characterize marine sediments containing gas hydrates. Using the results of studies of ice saturation effects in permafrost soils, we have introduced rheological effects of hydrate saturation. The replacement of pore fluids in highly porous and unconsolidated marine sediments with crystalline gas hydrates, increases the rigidity of the sediments, and alters the ratio of compressional/shear strength ratio. This causes Vp/Vs ratio variations which have an effect on the amplitudes of P-wave and S-wave reflections. Analysis of reflection coefficient functions has revealed that amplitudes are very sensitive to porosity estimates, and errors in the assumed model porosity can effect the estimates of hydrate saturation. Additionally, we see that the level of free gas saturation is difficult to determine. A review of the effects of free gas and hydrate saturation on shear wave arrivals indicates that far-offset P to S wave converted arrivals may provide a means of characterizing hydrate saturations. Complications in reflection coefficient and amplitude modelling can arise from gradients in hydrate saturation levels and from rough sea floor topography. An increase in hydrate saturation with depth in marine sediments causes rays to bend towards horizontal and increases the reflection incidence angles and subsequent amplitudes. This effect is strongly accentuated when the vertical separation between the source and the hydrate reflection horizon is reduced. The effect on amplitude variations with offset due to a rough sea floor was determined through finite difference wavefield modelling. Strong diffractions in the waveforms add noise to the amplitude versus offset functions.
author Foley, J.E.
Burns, D.R.
author_facet Foley, J.E.
Burns, D.R.
author_sort Foley, J.E.
title The sensitivity of seismic responses to gas hydrates. Final report
title_short The sensitivity of seismic responses to gas hydrates. Final report
title_full The sensitivity of seismic responses to gas hydrates. Final report
title_fullStr The sensitivity of seismic responses to gas hydrates. Final report
title_full_unstemmed The sensitivity of seismic responses to gas hydrates. Final report
title_sort sensitivity of seismic responses to gas hydrates. final report
publishDate 2008
url http://www.osti.gov/servlets/purl/10180822
https://www.osti.gov/biblio/10180822
https://doi.org/10.2172/10180822
genre Ice
permafrost
genre_facet Ice
permafrost
op_relation http://www.osti.gov/servlets/purl/10180822
https://www.osti.gov/biblio/10180822
https://doi.org/10.2172/10180822
doi:10.2172/10180822
op_doi https://doi.org/10.2172/10180822
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