Acoustics of gas-bearing sediments I. Background

Anderson, A.; Hampton, L. D.

doi:10.1121/1.384453

Cited by 246 publications

(147 citation statements)

References 34 publications

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“…acoustic turbidity, enhanced reflections, acoustic blanking, etc.) because of its influence on the sediment's bulk properties (Judd and Hovland, 1992;Anderson and Hampton, 1980). The exact response to the presence of free gas depends on the frequency of the seismic source (Richardson and Fig.…”

Section: Gas Hydrate and Free Gas Occurrencesmentioning

confidence: 99%

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

et al. 2006

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The Dnepr paleo-delta area in the NW Black Sea is characterized by an abundant presence of methane seeps. During the expeditions of May-June 2003 and within the EU-funded CRIMEA project, detailed multibeam, seismic and hydro-acoustic water-column investigations were carried out to study the relation between the spatial distribution of methane seeps, sea-floor morphology and sub-surface structures.2778 new methane seeps were detected on echosounding records in an area of 1540 km 2 . All seeps are located in the transition zone between the continental shelf and slope, in water depths of 66 to 825 m. The integration of the different geophysical datasets clearly indicates that methane seeps are not randomly distributed in this area, but are concentrated in specific locations.The depth limit for the majority of the detected seeps is 725 m water depth, which corresponds more or less with the stability limit for pure methane hydrate at the ambient bottom temperature (8.9 8C) in this part of the Black Sea. This suggests that, where gas hydrates are stable, they play the role of buffer for the upward migration of methane gas and thus prevent seepage of methane bubbles into the water column.Higher up on the margin, gas seeps are widespread, but accurate mapping illustrates that seeps occur preferentially in association with particular morphological and sub-surface features. On the shelf, the highest concentration of seeps is found in elongated depressions (pockmarks) above the margins of filled channels. On the continental slope where no pockmarks have been observed, seepage occurs along crests of sedimentary ridges. There, seepage is focussed by a parallel-stratified sediment cover that thins out towards the ridge crests. On the slope, seepage also appears in the vicinity of canyons (bottom, flanks and margins) or near the scarps of submarine landslides where mass-wasting breaches the fine-grained sediment cover that acts as a stratigraphic seal. The seismic data show the presence of a distinct bgas front,Q which has been used to map the depth of the free gas within the sea-floor sediments. The depth of this gas front is variable and locally domes up to the sea floor. Where the gas front approaches the seafloor, gas bubbles were detected in the water column. A regional map of the sub-surface depth of the gas front emphasises this bgas front-versus-seepQ relationship. The integration of all data sets indicates that the spatial distribution of methane seeps in the Dnepr paleo-delta is mainly controlled by the gas-hydrate stability zone as well as by stratigraphic and sedimentary factors. D

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Section: Gas Hydrate and Free Gas Occurrencesmentioning

confidence: 99%

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

et al. 2006

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“…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%

“…Anderson andHampton (1980a and1980b) have developed a theory for predicting the Vp through gassy sediments. In their studies, they consider the case in which the gas forms a three-phase medium with the interstitial water and surrounding sediment, and where the gas is in the form of bubbles within the pore water.…”

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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Constraints on a shallow offshore gas environment determined by a multidisciplinary geophysical approach: The Malin Sea, NW Ireland

García

Monteys

Evans

et al. 2014

Geochem. Geophys. Geosyst.

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During the Irish National Seabed Survey (INSS) in 2003, a gas related pockmark field was discovered and extensively mapped in the Malin Shelf region (NW Ireland). In summer 2006, additional complementary data involving core sample analysis, multibeam and single-beam backscatter classification, and a marine controlled-source electromagnetic survey were obtained in specific locations.This multidisciplinary approach allowed us to map the upper 20 m of the seabed in an unprecedented way and to correlate the main geophysical parameters with the geological properties of the seabed. The EM data provide us with information about sediment conductivity, which can be used as a proxy for porosity and also to identify the presence of fluid and fluid migration pathways. We conclude that, as a whole, the central part of the Malin basin is characterized by higher conductivities, which we interpret as a lithological change. Within the basin several areas are characterized by conductive anomalies associated with fluid flow processes and potentially the presence of microbial activity, as suggested by previous work. Pockmark structures show a characteristic electrical signature, with high-conductivity anomalies on the edges and less conductive, homogeneous interiors with several high-conductivity anomalies, potentially associated with gas-driven microbial activity.

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Acoustics of gas-bearing sediments I. Background

Cited by 246 publications

References 34 publications

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

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

Constraints on a shallow offshore gas environment determined by a multidisciplinary geophysical approach: The Malin Sea, NW Ireland

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