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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New England Research, Inc., White River Junction, VT (United States)
1992
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ftunivnotexas:info:ark/67531/metadc1400277 2023-05-15T16:37:55+02:00 The sensitivity of seismic responses to gas hydrates. Final report Foley, J. E. Burns, D. R. United States. Department of Energy. 1992-08-01 24 p. Text https://doi.org/10.2172/10180822 https://digital.library.unt.edu/ark:/67531/metadc1400277/ English eng New England Research, Inc., White River Junction, VT (United States) other: DE93000216 rep-no: DOE/MC/28079--3131 grantno: FG21-91MC28079 doi:10.2172/10180822 osti: 10180822 https://digital.library.unt.edu/ark:/67531/metadc1400277/ ark: ark:/67531/metadc1400277 Other Information: PBD: Aug 1992 S Waves Sensitivity Sea Bed Seismic Surveys P Waves Progress Report 58 Geosciences Natural Gas Hydrate Deposits 580000 Gas Hydrates Gas Saturation Numerical Data 03 Natural Gas Geosciences Reserves Geology And Exploration Sediments 030200 Report 1992 ftunivnotexas https://doi.org/10.2172/10180822 2019-04-06T22:08:48Z 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 |
S Waves Sensitivity Sea Bed Seismic Surveys P Waves Progress Report 58 Geosciences Natural Gas Hydrate Deposits 580000 Gas Hydrates Gas Saturation Numerical Data 03 Natural Gas Geosciences Reserves Geology And Exploration Sediments 030200 |
spellingShingle |
S Waves Sensitivity Sea Bed Seismic Surveys P Waves Progress Report 58 Geosciences Natural Gas Hydrate Deposits 580000 Gas Hydrates Gas Saturation Numerical Data 03 Natural Gas Geosciences Reserves Geology And Exploration Sediments 030200 Foley, J. E. Burns, D. R. The sensitivity of seismic responses to gas hydrates. Final report |
topic_facet |
S Waves Sensitivity Sea Bed Seismic Surveys P Waves Progress Report 58 Geosciences Natural Gas Hydrate Deposits 580000 Gas Hydrates Gas Saturation Numerical Data 03 Natural Gas Geosciences Reserves Geology And Exploration Sediments 030200 |
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, 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 |
publisher |
New England Research, Inc., White River Junction, VT (United States) |
publishDate |
1992 |
url |
https://doi.org/10.2172/10180822 https://digital.library.unt.edu/ark:/67531/metadc1400277/ |
genre |
Ice permafrost |
genre_facet |
Ice permafrost |
op_source |
Other Information: PBD: Aug 1992 |
op_relation |
other: DE93000216 rep-no: DOE/MC/28079--3131 grantno: FG21-91MC28079 doi:10.2172/10180822 osti: 10180822 https://digital.library.unt.edu/ark:/67531/metadc1400277/ ark: ark:/67531/metadc1400277 |
op_doi |
https://doi.org/10.2172/10180822 |
_version_ |
1766028211885441024 |