Estimation of seismic attenuation of gas hydrate bearing sediments from multi-channel seismic data: A case study from Krishna–Godavari offshore basin

Dewangan, P.; Mandal, Riddhi; Jaiswal, Priyank; Ramprasad, T.; Sriram, G.

doi:10.1016/j.marpetgeo.2014.05.015

Cited by 29 publications

(17 citation statements)

References 33 publications

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“…The Q estimates in the first layer (L1) do not correspond well. Noisy amplitude spectrum near the seafloor (Dewangan et al 2014) and fluctuating SR (Figure 8c) can be the possible reason for the unstable Q estimates from the SR method in the first layer. However, in the context of this analysis, it is important to study relative changes in Q particularly along Q slices throughout the whole volume because these might be related to the type of pore fluid and saturation in a given area or structure.…”

Section: Discussionmentioning

confidence: 99%

“…For example, studies on well-log data Goldberg, 2002, 2005;Matsushima, 2005), vertical seismic profile (VSP) data Bellefleur et al, 2007), and on crosshole seismic data (Pratt et al, 2003;Bauer et al, 2005) indicated an increase in attenuation. Other studies, mainly on surface seismic data (Matsushima, 2006;Rossi et al, 2007;Dewangan et al, 2014) indicated a decrease in attenuation. The increase (Guerin and Goldberg, 2002;Gei and Carcione, 2003;Chand and Minshull, 2004;Lee and Collett, 2006) and decrease (Sain and Singh, 2011;Dewangan et al, 2014) in attenuation have been explained by using different rockphysics models depending on the assumed microstructure of the hydrate and also sediment-hydrate mixtures.…”

Section: Introductionmentioning

confidence: 93%

“…Other studies, mainly on surface seismic data (Matsushima, 2006;Rossi et al, 2007;Dewangan et al, 2014) indicated a decrease in attenuation. The increase (Guerin and Goldberg, 2002;Gei and Carcione, 2003;Chand and Minshull, 2004;Lee and Collett, 2006) and decrease (Sain and Singh, 2011;Dewangan et al, 2014) in attenuation have been explained by using different rockphysics models depending on the assumed microstructure of the hydrate and also sediment-hydrate mixtures. Chand and Minshull (2004) suggest that the amount of attenuation not only changes with hydrate saturation but also with the frequency of the seismic signal.…”

Section: Introductionmentioning

confidence: 93%

“…Because gas hydrate increases the stiffness of the matrix (Jung et al, 2012) and P-wave velocity, it was normally assumed that the sediments saturated with gas hydrates will show lower attenuation (Wood et al, 2000). Unlike P-wave velocity, no unique trend of seismic attenuation in gas hydrates can be observed from the literature; thus, making attenuation characteristic of the gas hydrate bearing sediments a debatable topic (Guerin et al, 1999;Wood et al, 2000;Chand et al, 2004;Rossi et al, 2007;Sain et al, 2009;Sain and Singh, 2011;Jaiswal et al, 2012;Dewangan et al, 2014). Laboratory experiments in hydrate bearing sediments indicated increase of attenuation with hydrate saturation (Priest et al, 2006;Best et al, 2013), whereas attenuation estimates from field experiments on gas hydrates indicated contradicting results.…”

Section: Introductionmentioning

confidence: 99%

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Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

et al. 2016

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We have estimated the seismic attenuation in gas hydrate and free-gas-bearing sediments from high-resolution P-cable 3D seismic data from the Vestnesa Ridge on the Arctic continental margin of Svalbard. P-cable data have a broad bandwidth (20-300 Hz), which is extremely advantageous in estimating seismic attenuation in a medium. The seismic quality factor (Q), the inverse of seismic attenuation, is estimated from the seismic data set using the centroid frequency shift and spectral ratio (SR) methods. The centroid frequency shift method establishes a relationship between the change in the centroid frequency of an amplitude spectrum and the Q value of a medium. The SR method estimates the Q value of a medium by studying the differential decay of different frequencies. The broad bandwidth and short offset characteristics of the P-cable data set are useful to continuously map the Q for different layers throughout the 3D seismic volume. The centroid frequency shift method is found to be relatively more stable than the SR method. Q values estimated using these two methods are in concordance with each other. The Q data document attenuation anomalies in the layers in the gas hydrate stability zone above the bottom-simulating reflection (BSR) and in the free gas zone below. Changes in the attenuation anomalies correlate with small-scale fault systems in the Vestnesa Ridge suggesting a strong structural control on the distribution of free gas and gas hydrates in the region. We argued that high and spatially limited Q anomalies in the layer above the BSR indicate the presence of gas hydrates in marine sediments in this setting. Hence, our workflow to analyze Q using high-resolution P-cable 3D seismic data with a large bandwidth could be a potential technique to detect and directly map the distribution of gas hydrates in marine sediments.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

et al. 2016

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“…In other words, the bulk and shear moduli increase due to the GH matrix-supporting effect within the sedimentary frame (Ecker et al, 1998). Additionally, the presence of GH causes higher attenuation of the seismic waves (Bellefleur et al, 2007;Dewangan et al, 2014) which was in particularly observed for sediments containing dispersed GH in the pore space (Guerin and Goldberg, 2002;Dvorkin and Uden, 2004). This anomalous seismic behavior in terms of increased attenuation and velocities (Guerin and Goldberg, 2002;Dvorkin and Uden, 2004) cannot be fully explained, although wave-induced fluid flow at the microscopic and mesoscopic scales has been speculated to cause them (Priest et al, 2006;Gerner et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Squirt flow due to interfacial water films in hydrate bearing sediments

et al. 2018

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Abstract. Sediments containing gas hydrate dispersed in the pore space are known to show a characteristic seismic anomaly which is a high attenuation along with increasing seismic velocities. Currently, this observation cannot be fully explained albeit squirt-flow type mechanisms on the microscale have been speculated to be the cause. Recent major findings from in situ experiments, using the "gas in excess" and "water in excess" formation method, and coupled with high-resolution synchrotron-based X-ray micro-tomography, have revealed the systematic presence of thin water films between the quartz grains and the encrusting hydrate. The data obtained from these experiments underwent an image processing procedure to quantify the thicknesses and geometries of the aforementioned interfacial water films. Overall, the water films vary from sub-micrometer to a few micrometers in thickness. In addition, some of the water films interconnect through water bridges. This geometrical analysis is used to propose a new conceptual squirt flow model for hydrate bearing sediments. A series of numerical simulations is performed considering variations of the proposed model to study seismic attenuation caused by such thin water films. Our results support previous speculation that squirt flow can explain high attenuation at seismic frequencies in hydrate bearing sediments, but based on a conceptual squirt flow model which is geometrically different than those previously considered.

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Controls on evolution of gas‐hydrate system in the Krishna‐Godavari basin, offshore India

Badesab

Dewangan

Usapkar

et al. 2017

Geochem Geophys Geosyst

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In this study, we integrate environmental magnetic, sedimentological, and geochemical records of sediment core of Hole NGHP-01-10D overlying methane hydrate deposits to decipher the controls on the evolution of fracture-filled gas-hydrate system in the Krishna-Godavari (K-G) basin. Four distinct sedimentary units have been identified, based on the sediment magnetic signatures. An anomalous zone of enhanced magnetic susceptibility (Unit III: 51.9-160.4 mbsf) coinciding with the gas hydrate bearing intervals is due to the presence of magnetite-rich detrital minerals brought-in by the river systems as a result of higher sedimentation events in K-G basin and has no influence over hydrate formation. A strong to moderate correlation between magnetite concentration and chromium reducible sulfur (CRS) content indicates significant influence of sulfidization on the magnetic record and could be further exploited as a proxy to decipher paleo-H 2 S seepage events. Analysis of high-resolution seismic, bathymetry, and subbottom profiler data reveals the existence of a regional fault system in K-G basin. The opening and closing dynamics of the faults facilitated the migration and trapping of required gas concentrations resulting in accumulation of gas hydrates at the studied site. The seismic data provides support to the rock-magnetic interpretations. The observed variations in magnetic and geochemical properties have resulted from the episodic flow of methane and sulfide-enriched fluids through the fracture-filled network formed as a result of shale-tectonism. Our study demonstrated the potential of using an enviro-magnetic approach in combination with other proxies to constrain the evolution of gas-hydrate system in marine environments. Key Points:Magnetic signatures of detrital and diagenetic processes associated with evolution of gas-hydrate system. Changes in magnetic and geochemical properties controlled by underlying gas-hydrates. Magnetic proxy to decipher paleo-H2S seepage events in marine sediments.

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Estimation of seismic attenuation of gas hydrate bearing sediments from multi-channel seismic data: A case study from Krishna–Godavari offshore basin

Cited by 29 publications

References 33 publications

Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

Squirt flow due to interfacial water films in hydrate bearing sediments

Controls on evolution of gas‐hydrate system in the Krishna‐Godavari basin, offshore India

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