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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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) |
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SciTec Connect (Office of Scientific and Technical Information - OSTI, U.S. Department of Energy) |
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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 |
_version_ |
1772815290302726144 |