Seismic velocities for hydrate‐bearing sediments using weighted equation

Lee, M.W.; Hutchinson, Deborah R.; Collett, Timothy S.; Dillon, William P.

doi:10.1029/96jb01886

Cited by 259 publications

(164 citation statements)

References 32 publications

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“…Although the exact nature of the interaction between grains and hydrate is still subject to some debate, all observations and models agree that the occurrence of hydrate increases the compressional velocity of the formation [Lee et al, 1996;Ecker et al, 1998]. Fundamentally, the increase in V p can be explained by the indurating effect of ice-like particles replacing water in open pore space.…”

Section: Discussionmentioning

confidence: 99%

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

2002

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[1] The Mallik 2L-38 research well was drilled to 1150 m under the Mackenzie Delta, Canada, and penetrated a subpermafrost interval where methane hydrate occupies up to 80% of the pore space. A suite of high-quality downhole logs was acquired to measure in situ the physical properties of these hydrate-bearing sediments. Similar to other hydrate deposits, resistivity and compressional and shear sonic velocity data increase with higher hydrate saturation owing to electrical insulation of the pore space and stiffening of the sediment framework. In addition, sonic waveforms show strong amplitude losses of both compressional and shear waves in intervals where methane hydrate is observed. We use monopole and dipole waveforms to estimate compressional and shear attenuation. Comparing with hydrate saturation values derived from the resistivity log, we observe a linear increase in both attenuation measurements with increasing hydrate saturation, which is not intuitive for stiffening sediments. Numerical modeling of the waveforms allows us to reproduce the recorded waveforms and illustrate these results. We also use a model for wave propagation in frozen porous media to explain qualitatively the loss of sonic waveform amplitude in hydratebearing sediments. We suggest that this model can be improved and extended, allowing hydrate saturation to be quantified from attenuation measurements in similar environments and providing new insight into how hydrate and its sediment host interact.

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Section: Discussionmentioning

confidence: 99%

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

2002

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“…Results of the K-T model are even higher. Lee et al [1996] also concluded that the K-T model overestimates hydrate concentrations, and they proposed a weighted equation as a more accurate and versatile alternative. We interpret the high estimates of the K-T model to be a consequence of its statistical treatment of elastic waves propagation which does not account for the interactions between inclusions [Kuster and ToksOz, 1974].…”

Section: Determination Of the Free Gas Concentrationmentioning

confidence: 99%

Characterization of in situ elastic properties of gas hydrate‐bearing sediments on the Blake Ridge

Guèrin¹,

Goldberg²,

Meltser³

1999

J. Geophys. Res.

183

149

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Abstract. During Ocean Drilling Program Leg 164, shear sonic velocity and other geophysical logs were acquired in gas hydrate-bearing sediments on the Blake Ridge to characterize the very distinct seismic signature of such formations: anomalous low amplitudes overlying a strong bottomsimulating reflector (BSR). A comparison of the bulk moduli derived from the logs to standard elastic consolidation models shows that the sediments are overconsolidated above the BSR at 440 meters below seafloor (mbsf) because of the presence of hydrates. Below the bottom of the thermodynamic hydrate stability zone at -520 mbsf, the high compressibility of the formation and the attenuation of the monopole sonic waveforms are typical of sediments partially saturated with free gas. Between these two depths, gas hydrate and free gas seem to coexist. Within the Gas hydrate stability zone, we estimate the amount of gas hydrates using different models based on theories for wave scattering in multiphase media and for grain cementation. In close agreement with measurements made on discrete in situ samples, the latter describes most accurately the interactions between the matrix, the pore fluids, and the hydrates. This model indicates that 5 to 10% of the pore space is occupied by hydrates deposited uniformly on the surface of the grains. The comparison with Gassmann's model also show that the amount of free gas below the BSR never exceeds 5 % of the pore space but is high enough to generate the BSR. The coexistence of free gas and gas hydrates below the BSR may be explained by capillary effects in the smaller pores or by remaining crystalline structures after partial hydrate decomposition.

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“…Two differing approaches have been made to relate the hydrate fraction (or hydrate saturation) and velocity in ocean sediments. In the first, empirical methods use versions of Wyllie's time average or Wood's equation calibrated with laboratory data [Lee et al, 1996] which are not representative of those found in the hydrate stability region ]. The second approach has been to use theoretical effective medium models to predict the physical properties of bulk sediment from the elastic properties of individual constituents.…”

Section: Hydrate Quantificationmentioning

confidence: 99%

A laboratory investigation into the seismic velocities of methane gas hydrate‐bearing sand

2005

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[1] Remote seismic methods, which measure the compressional wave (P wave) velocity (V p ) and shear wave (S wave) velocity (V s ), can be used to assess the distribution and concentration of marine gas hydrates in situ. However, interpreting seismic data requires an understanding of the seismic properties of hydrate-bearing sediments, which has proved problematic because of difficulties in recovering intact hydrate-bearing sediment samples and in performing valid laboratory tests. Therefore a dedicated gas hydrate resonant column (GHRC) was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both V p and V s made at frequencies and strains relevant to marine seismic investigations. Thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested. The results show a bipartite relationship between velocities and hydrate pore saturation, with a marked transition between 3 and 5% hydrate pore saturation for both V p and V s . This suggests that methane hydrate initially cements sand grain contacts then infills the pore space. These results show in detail for the first time, using a resonant column, how hydrate cementation affects elastic wave properties in quartz sand. This information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation.Citation: Priest, J. A., A. I. Best, and C. R. I. Clayton (2005), A laboratory investigation into the seismic velocities of methane gas hydrate-bearing sand,

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Seismic velocities for hydrate‐bearing sediments using weighted equation

Cited by 259 publications

References 32 publications

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

Characterization of in situ elastic properties of gas hydrate‐bearing sediments on the Blake Ridge

A laboratory investigation into the seismic velocities of methane gas hydrate‐bearing sand

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