The sensitivity of seismic responses to gas hydrates
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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New England Research, Inc., White River Junction, VT (United States)
1992
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ftunivnotexas:info:ark/67531/metadc1188103 2023-05-15T16:37:56+02:00 The sensitivity of seismic responses to gas hydrates Foley, John E. Burns, Daniel R. United States. Department of Energy. 1992-08-01 24 pages Text https://doi.org/10.2172/6982379 https://digital.library.unt.edu/ark:/67531/metadc1188103/ English eng New England Research, Inc., White River Junction, VT (United States) other: DE93000216 rep-no: DOE/MC/28079-3131 grantno: FG21-91MC28079 doi:10.2172/6982379 osti: 6982379 https://digital.library.unt.edu/ark:/67531/metadc1188103/ ark: ark:/67531/metadc1188103 Saturation Geophysical Surveys Progress Report Gas Saturation Document Types Gas Hydrates Data Geologic Deposits Seismic Surveys Sediments 58 Geosciences 03 Natural Gas S Waves Sea Bed Sensitivity Natural Gas Hydrate Deposits Numerical Data Surveys 030200* -- Natural Gas-- Reserves Geology & Exploration Information P Waves Hydrates 580000 -- Geosciences Partial Waves Report 1992 ftunivnotexas https://doi.org/10.2172/6982379 2022-06-04T22:08:02Z 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. Report Ice permafrost University of North Texas: UNT Digital Library |
institution |
Open Polar |
collection |
University of North Texas: UNT Digital Library |
op_collection_id |
ftunivnotexas |
language |
English |
topic |
Saturation Geophysical Surveys Progress Report Gas Saturation Document Types Gas Hydrates Data Geologic Deposits Seismic Surveys Sediments 58 Geosciences 03 Natural Gas S Waves Sea Bed Sensitivity Natural Gas Hydrate Deposits Numerical Data Surveys 030200* -- Natural Gas-- Reserves Geology & Exploration Information P Waves Hydrates 580000 -- Geosciences Partial Waves |
spellingShingle |
Saturation Geophysical Surveys Progress Report Gas Saturation Document Types Gas Hydrates Data Geologic Deposits Seismic Surveys Sediments 58 Geosciences 03 Natural Gas S Waves Sea Bed Sensitivity Natural Gas Hydrate Deposits Numerical Data Surveys 030200* -- Natural Gas-- Reserves Geology & Exploration Information P Waves Hydrates 580000 -- Geosciences Partial Waves Foley, John E. Burns, Daniel R. The sensitivity of seismic responses to gas hydrates |
topic_facet |
Saturation Geophysical Surveys Progress Report Gas Saturation Document Types Gas Hydrates Data Geologic Deposits Seismic Surveys Sediments 58 Geosciences 03 Natural Gas S Waves Sea Bed Sensitivity Natural Gas Hydrate Deposits Numerical Data Surveys 030200* -- Natural Gas-- Reserves Geology & Exploration Information P Waves Hydrates 580000 -- Geosciences Partial Waves |
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. |
author2 |
United States. Department of Energy. |
format |
Report |
author |
Foley, John E. Burns, Daniel R. |
author_facet |
Foley, John E. Burns, Daniel R. |
author_sort |
Foley, John E. |
title |
The sensitivity of seismic responses to gas hydrates |
title_short |
The sensitivity of seismic responses to gas hydrates |
title_full |
The sensitivity of seismic responses to gas hydrates |
title_fullStr |
The sensitivity of seismic responses to gas hydrates |
title_full_unstemmed |
The sensitivity of seismic responses to gas hydrates |
title_sort |
sensitivity of seismic responses to gas hydrates |
publisher |
New England Research, Inc., White River Junction, VT (United States) |
publishDate |
1992 |
url |
https://doi.org/10.2172/6982379 https://digital.library.unt.edu/ark:/67531/metadc1188103/ |
genre |
Ice permafrost |
genre_facet |
Ice permafrost |
op_relation |
other: DE93000216 rep-no: DOE/MC/28079-3131 grantno: FG21-91MC28079 doi:10.2172/6982379 osti: 6982379 https://digital.library.unt.edu/ark:/67531/metadc1188103/ ark: ark:/67531/metadc1188103 |
op_doi |
https://doi.org/10.2172/6982379 |
_version_ |
1766028237645807616 |