Acoustics of gas-bearing sediments. II. Measurements and models

Anderson, A.; Hampton, L. D.

doi:10.1121/1.384454

Cited by 102 publications

(104 citation statements)

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“…The bulk of the dispersion occurs between the 1-kHz and 3-kHz data sets; the 3-, 5-, and 7-kHz data sets all tend to have similar velocities. The observed dispersion does not fit the theoretical models of Anderson and Hampton (1980b); this discrepancy is believed to be caused by experimental error.…”

Section: Velocity Tomographymentioning

confidence: 62%

“…Empirical relationships between the dynamic frame bulk modulus and sediment porosity (Hamilton, 1971) and the dynamic rigidity modulus and grain size (Anderson and Hampton, 1980b) were used to determine values for these moduli (Kd.15 dyn/cm2 and W . 2 5 dyn/cm2).…”

Section: Discussionmentioning

confidence: 99%

“…Combined attenuation and velocity modeling using theories presented by Hampton (1980a and1980b) indicate that, for a silt-clay sediment model, gas concentrations of 25% to 35% of the pore space are required. The attenuation data also indicate that the dominant gas bubble size must be about 1 mm in diameter.…”

Section: Discussionmentioning

confidence: 99%

“…The presence of gas complicates this relationship by introducing energy losses associated with resonance of interstitial gas bubbles Hampton, 1980a and1980b). The acoustic effects of gas bubbles in liquids was first addressed by Minnaert (1933), who developed a fundamental relationship describing bubble pulsation on the basis of energy considerations.…”

Section: Compressional Wave Dispersion and Attenuationmentioning

confidence: 99%

“…The acoustic effects of gas bubbles in liquids was first addressed by Minnaert (1933), who developed a fundamental relationship describing bubble pulsation on the basis of energy considerations. Hampton (1980a and1980b) extended this theory by modifying the equations to fit a gassy, unconsolidated sediment case.…”

Section: Compressional Wave Dispersion and Attenuationmentioning

confidence: 99%

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Compressional Wave Character in Gassy, Near‐Surface Sediments in Southern Louisiana Determined from Variable Frequency Cross‐Well, Borehole Logging, and Surface Seismic Measurements

Thompson¹,

McGinnis²,

Wilkey³

et al. 1995

Symposium on the Application of Geophysics to Engineering and Environmental Problems 1995

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DISCLAIMERThe submitted manuscript has been authored by a contractor of the U.S. Government under contract No. W-31-1WENG-38. Accordingly, the U. S. Government retains a nonexclusive, royalty.free licensn to pvblish or reproduce the published form of this contribution. or allow others to do so, for U. S. Government purposes.This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recorn- ABSTRACTVelocity and attenuation data were used to test theoretical equations describing the frequency dependence of compressional wave velocity and attenuation through gas-rich sediments in coastal Louisiana. The cross-well data (obtained from a variable-frequency, cross-well seismic experiment using source frequencies of 1, 3, 5, and 7 kHz) were augmented with velocities derived from a nearby seismic refraction station using a lowfrequency (QO Hz) source. Velocities obtained h m the borehole-sonic tool (18 kHz)were not used, because it is unclear at this time what signal phase was being detected. Energy at 1 and 3 kJ3z was successfully transmitted over distances from 3.69 to 30 m; the 5-and 7-lcHz data were obtained only at distances up to 20 m.Velocity tomograms were constructed for one borehole pair and covered a depth interval of 10-50 m. Results from the tomographic modeling indicate that gas-induced low velocities are present to depths of greater than 4-0 m. Analysis of the velocity dispersion suggests that gas-bubble resonance must be greater than 7 kHz, which is above the range of frequencies used in the experiment. Washout of the boreholes at depths above 15 m resulted in a degassed zone containing velocities higher than those indicated in both nearby reitaction and reflection surveys. Velocity and attenuation information were obtained for a low-velocity zone centered at a depth of approximately 18 m. Measured attenuations of 1.57,2.95, and 3.24 dB/m for the 3-, 5-, and 7-m~ signals, respectively, were modeled along with the velocity data using a silt-clay sediment type, Density and porosity data for the model were obtained from the geophysical logs; the bulk and shear moduli were estimated from published relationships. Modeling results indicate that gas bubbles measuring 1 mm in diameter occupy at least 25% to 35% of the pore space.

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Section: Velocity Tomographymentioning

confidence: 62%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Compressional Wave Dispersion and Attenuationmentioning

confidence: 99%

Section: Compressional Wave Dispersion and Attenuationmentioning

confidence: 99%

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Compressional Wave Character in Gassy, Near‐Surface Sediments in Southern Louisiana Determined from Variable Frequency Cross‐Well, Borehole Logging, and Surface Seismic Measurements

Thompson¹,

McGinnis²,

Wilkey³

et al. 1995

Symposium on the Application of Geophysics to Engineering and Environmental Problems 1995

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Estimating the free gas content in Baltic Sea sediments using compressional wave velocity from marine seismic data

et al. 2014

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A 2‐D high‐resolution velocity field was obtained from marine seismic data to quantify free gas content in shallow muddy sediments at in situ pressure and temperature. The velocities were acquired applying Migration Velocity Analysis on prestack time‐migrated data. Compressional wave velocities are highly sensitive to free gas as very small amounts of gas can cause a significant decrease in the medium velocity. The analyzed profile crosses a depression filled with organic‐rich Holocene mud in the Bornholm Basin, Baltic Sea. The interval velocity field reveals two low‐velocity patches, which extend from the reversed polarity reflections marking the top of the gassy sediment layer down to the base of the Holocene mud. Average interval velocities within the gassy mud are lower than the seafloor migration velocity by up to ∼500 m/s. This decrease, using a geoacoustic model, is caused by an average 0.046% gas volume fraction. The interval velocities in individual cells of the velocity field are reduced to ∼200 m/s predicting up to 3.4% gas content. The velocity field is limited in resolution due to velocity determination at and between reflections; however, together with the stratigraphic interpretation, geological units containing free gas could be identified. Shallow gas occurs vertically throughout most of the Holocene mud in the gassy area. Comparison with biogeochemical studies at other Baltic Sea sites suggests that the distribution of free gas is likely to be patchy in the sediment, but the gas concentration may peak below the sulfate‐methane transition zone and gradually decrease below.

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Frequency dependence in seismoacoustic imaging of shallow free gas due to gas bubble resonance

2015

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Shallow free gas is investigated in seismoacoustic data in 10 frequency bands covering a frequency range between 0.2 and 43 kHz. At the edge of a gassy patch in the Bornholm Basin (Baltic Sea), compressional wave attenuation caused by free gas is estimated from reflection amplitudes beneath the gassy sediment layer. Imaging of shallow free gas is considerably influenced by gas bubble resonance, because in the resonance frequency range attenuation is significantly increased. At the resonance frequency of the largest bubbles between 3 and 5 kHz, high scattering causes complete acoustic blanking beneath the top of the gassy sediment layer. In the wider resonance frequency range between 3 and 15 kHz, the effect of smaller bubbles becomes dominant and the attenuation slightly decreases. This allows acoustic waves to be transmitted and reflections can be observed beneath the gassy sediment layer for higher frequencies. Above resonance beginning at ∼19 kHz, attenuation is low and the presence of free gas can be inferred from the decreased reflection amplitudes beneath the gassy layer. Below the resonance frequency range (<1 kHz), attenuation is generally very low and not dependent on frequency. Using the geoacoustic model of Anderson and Hampton, the observed frequency boundaries suggest gas bubble sizes between 1 and 4–6 mm, and gas volume fractions up to 0.02% in a ∼2 m thick sediment layer, whose upper boundary is the gas front. With the multifrequency acoustic approach and the Anderson and Hampton model, quantification of free gas in shallow marine environments is possible if the measurement frequency range allows the identification of the resonance frequency peak. The method presented is limited to places with only moderate attenuation, where the amplitudes of a reflection can be analyzed beneath the gassy sediment layer.

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Acoustics of gas-bearing sediments. II. Measurements and models

Cited by 102 publications

References 3 publications

Compressional Wave Character in Gassy, Near‐Surface Sediments in Southern Louisiana Determined from Variable Frequency Cross‐Well, Borehole Logging, and Surface Seismic Measurements

Compressional Wave Character in Gassy, Near‐Surface Sediments in Southern Louisiana Determined from Variable Frequency Cross‐Well, Borehole Logging, and Surface Seismic Measurements

Estimating the free gas content in Baltic Sea sediments using compressional wave velocity from marine seismic data

Frequency dependence in seismoacoustic imaging of shallow free gas due to gas bubble resonance

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