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Journal ArticleDOI

Anisotropic amplitude variation of the bottom-simulating reflector beneath fracture-filled gas hydrate deposit

01 May 2013-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 118, Iss: 5, pp 2258-2274
TL;DR: In this article, the amplitude variation with angle (AVA) pattern of bottom-simulating reflectors (BSRs) under fracture-filled gas hydrate deposits when the effective medium is anisotropic is reported.
Abstract: [1] For the first time, we report the amplitude variation with angle (AVA) pattern of bottom-simulating reflectors (BSRs) beneath fracture-filled gas hydrate deposits when the effective medium is anisotropic. The common depth point (CDP) gathers of two mutually perpendicular multichannel seismic profiles, located in the vicinity of Site NGHP-01-10, are appropriately processed such that they are fit for AVA analysis. AVA analysis of the BSR shows normal-incidence reflection coefficients of −0.04 to −0.11 with positive gradients of 0.04 to 0.31 indicating class IV pattern. The acoustic properties from isotropic rock physics model predict class III AVA pattern which cannot explain the observed class IV AVA pattern in Krishna-Godavari basin due to the anisotropic nature of fracture-filled gas hydrate deposits. We modeled the observed class IV AVA of the BSR by assuming that the gas hydrate bearing sediment can be represented by horizontally transversely isotropic (HTI) medium after accounting for anisotropic wave propagation effects on BSR amplitudes. The effective medium properties are estimated using Backus averaging technique, and the AVA pattern of BSRs is modeled using the properties of overlying HTI and underlying isotropy/HTI media with or without free gas. Anisotropic AVA analysis of the BSR from the inline seismic profile shows 5–30% gas hydrate concentration (equivalent to fracture density) and the azimuth of fracture system (fracture orientation) with respect to the seismic profile is close to 45°. Free gas below the base of gas hydrate stability zone is interpreted in the vicinity of fault system (F1).
Citations
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Journal ArticleDOI
TL;DR: This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade.
Abstract: Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade Challenges, limitations, and future perspectives of each field are briefly discussed The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field

349 citations

Journal ArticleDOI
TL;DR: The occurrence of methane gas hydrates at very shallow depths at some of the seep-sites is attributed to high methane flux and conducive P–T conditions, necessary for the stability of methane hydrate.
Abstract: Here we report the discovery of cold-seep ecosystem and shallow methane hydrates (2–3 mbsf) associated with methane gas flares in the water column from the Indian EEZ for the first time. The seep-sites are located in the Krishna–Godavari (K–G) basin at water depths of 900–1800 m and are characterized by gas flares in the water-column images. The occurrence of methane gas hydrates at very shallow depths (2–3 mbsf) at some of the seep-sites is attributed to high methane flux and conducive P–T conditions, necessary for the stability of methane hydrate. Chemosymbiont bearing Bivalves (Vesicomidae, Mytilidae, Thyasiridae and Solemyidae families); Polychaetes (Siboglinidae family) and Gastropods (Provannidae family) are also identified from seep-sites.

28 citations

Journal ArticleDOI
TL;DR: In this paper, the amplitude with offset (AVO) analysis was performed on multichannel seismic data in the vicinity of Site NGHP-01-10, where thick fracture-filled gas hydrate is reported.

28 citations

Journal ArticleDOI
TL;DR: In this article, a joint analysis of P-wave velocity and resistivity is proposed to identify hydrate morphology and estimate hydrate saturation in a continuous depth profile, and the results demonstrate that, in the case of identical hydrate concentration, fracture-filling gas hydrate-bearing sediments typically exhibit higher resistivity but lower P wave velocity than those of porefilling GHBS, while the cross plots between these two properties are strikingly different for the two types of GHBS.

27 citations

Journal ArticleDOI
TL;DR: In this article, a friction-dependent effective medium model (EMM) was proposed to understand the interaction between the sediment grains of unconsolidated marine sediments as well as with hydrate.

24 citations


Cites background from "Anisotropic amplitude variation of ..."

  • ...The study of amplitude variation of BSR with incidence angle in the vicinity of site NGHP–01–10 also suggests that the medium is anisotropic and realistic gas hydrate saturation as well as fracture azimuth can be estimated assuming the anisotropic rock physics model (Sriram et al., 2013)....

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References
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Book
01 Jan 1990
TL;DR: In this paper, the authors compared the properties of hydrates and ice with those of natural gas and showed the effect of thermodynamic inhibitors on the formation of hydrate formation and dissolution process.
Abstract: PREFACE Overview and Historical Perspective Hydrates as a Laboratory Curiosity Hydrates in the Natural Gas Industry Hydrates as an Energy Resource Environmental Aspects of Hydrates Safety Aspects of Hydrates Relationship of This Chapter to Those That Follow Molecular Structures and Similarities to Ice Crystal Structures of Ice Ih and Natural Gas Hydrates Comparison of Properties of Hydrates and Ice The What and the How of Hydrate Structures Hydrate Formation and Dissociation Processes Hydrate Nucleation Hydrate Growth Hydrate Dissociation Estimation Techniques for Phase Equilibria of Natural Gas Hydrates Hydrate Phase Diagrams for Water + Hydrocarbon Systems Three-Phase (LW-H-V) Equilibrium Calculations Quadruple Points and Equilibrium of Three Condensed Phases (LW-H-LHC) Effect of Thermodynamic Inhibitors on Hydrate Formation Two-Phase Equilibrium: Hydrates with One Other Phase Hydrate Enthalpy and Hydration Number from Phase Equilibrium Summary and Relationship to Chapters Which Follow A Statistical Thermodynamic Approach to Hydrate Phase Equilibria Statistical Thermodynamics of Hydrate Equilibria Application of the Method to Analyze Systems of Methane + Ethane + Propane Computer Simulation: Another Microscopic-Macroscopic Bridge Summary Experimental Methods and Measurements of Hydrate Properties Experimental Apparatuses and Methods for Macroscopic Measurements Measurements of the Hydrate Phase Data for Natural Gas Hydrate Phase Equilibria and Thermal Properties Summary and Relationship to Chapters that Follow References Hydrates in the Earth The Paradigm Is Changing from Assessment of Amount to Production of Gas Sediments with Hydrates Typically Have Low Contents of Biogenic Methane Sediment Lithology and Fluid Flow Are Major Controls on Hydrate Deposition Remote Methods Enable an Estimation of the Extent of a Hydrated Reservoir Drilling Logs and/or Coring Provide Improved Assessments of Hydrated Gas Amounts Hydrate Reservoir Models Indicate Key Variables for Methane Production Future Hydrated Gas Production Trends Are from the Permafrost to the Ocean Hydrates Play a Part in Climate Change and Geohazards Summary Hydrates in Production, Processing, and Transportation How Do Hydrate Plugs Form in Industrial Equipment? How Are Hydrate Plug Formations Prevented? How Is a Hydrate Plug Dissociated? Safety and Hydrate Plug Removal Applications to Gas Transport and Storage Summary of Hydrates in Flow Assurance and Transportation APPENDICES INDEX

6,037 citations


"Anisotropic amplitude variation of ..." refers background in this paper

  • ...It is stable under high pressure and low temperature conditions within zones referred to as gas hydrate stability zone (GHSZ) [Sloan, 1990]....

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Journal ArticleDOI
TL;DR: The equations governing weak anisotropy are much simpler than those governing strong anisotropic, and they are much easier to grasp intuitively as discussed by the authors, which is why they are easier to understand intuitively.
Abstract: Most bulk elastic media are weakly anisotropic. -The equations governing weak anisotropy are much simpler than those governing strong anisotropy, and they are much easier to grasp intuitively. These equations indicate that a certain anisotropic parameter (denoted 6) controls most anisotropic phenomena of importance in exploration geophysics. some of which are nonnegligible even when the anisotropy is weak. The critical parameter 6 is an awkward combination of elastic parameters, a combination which is totally independent of horizontal velocity and which may be either positive or negative in natural contexts.

3,787 citations


"Anisotropic amplitude variation of ..." refers background in this paper

  • ...The parameter e represents the fractional difference between the horizontal and vertical P-wave velocities, and d represents the normalized second derivative of P-wave phase velocity at vertical incidence [Thomsen, 1986]....

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Journal ArticleDOI
TL;DR: In this article, a horizontally layered inhomogeneous medium is considered, whose properties are constant or nearly so when averaged over some vertical height l′, and conditions on the five elastic coefficients of a homogeneous transversely isotropic medium are derived which are necessary and sufficient for the medium to be "long-wave equivalent" to a horizontally-layered inhomogenous medium.
Abstract: A horizontally layered inhomogeneous medium, isotropic or transversely isotropic, is considered, whose properties are constant or nearly so when averaged over some vertical height l′. For waves longer than l′ the medium is shown to behave like a homogeneous, or nearly homogeneous, transversely isotropic medium whose density is the average density and whose elastic coefficients are algebraic combinations of averages of algebraic combinations of the elastic coefficients of the original medium. The nearly homogeneous medium is said to be ‘long-wave equivalent’ to the original medium. Conditions on the five elastic coefficients of a homogeneous transversely isotropic medium are derived which are necessary and sufficient for the medium to be ‘long-wave equivalent’ to a horizontally layered isotropic medium. Further conditions are also derived which are necessary and sufficient for the homogeneous medium to be ‘long-wave equivalent’ to a horizontally layered isotropic medium consisting of only two different homogeneous isotropic materials. Except in singular cases, if the latter two-layered medium exists at all, its proportions and elastic coefficients are uniquely determined by the elastic coefficients of the homogeneous transversely isotropic medium. The observed variations in crustal P-wave velocity with depth, obtained from well logs, are shown to be large enough to explain some of the observed crustal anisotropies as due to layering of isotropic material.

1,585 citations


"Anisotropic amplitude variation of ..." refers background or methods in this paper

  • ...Similar to modeling of fracture-filled gas hydrate layer, the Backus average [Backus, 1962] is used to estimate the effective medium properties of fracture-filled free gas bearing sediment which depend on the properties of free gas bearing sediments with saturations 0–10%, the properties of…...

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  • ...Therefore, we follow Lee and Collett [2009] to estimate the effective medium properties of the gas hydrate bearing sediment in the KG offshore basin using the Backus averaging technique [Backus, 1962; section C]....

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  • ...It is valid when the thicknesses of the stratified layers are less than the seismic wavelength [Backus, 1962]....

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  • ...When the layer thicknesses are much smaller than the seismic wavelength, the effective medium behaves as transversely isotropic with symmetry axis oriented normal to the layering [Backus, 1962; White, 1965]....

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  • ...Similar to modeling of fracture-filled gas hydrate layer, the Backus average [Backus, 1962] is used to estimate the effective medium properties of fracture-filled free gas bearing sediment which depend on the properties of free gas bearing sediments with saturations 0–10%, the properties of water-saturated sediments and the volume fraction of free gas bearing sediment (fracture density)....

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Journal ArticleDOI
TL;DR: In this paper, the compressional wave reflection coefficient R(θ) given by the Zoeppritz equations is simplified to the following: R0+[A0R0+Δσ(1-σ)2]sin2θ+1/2ΔVpVp(tan 2θ-sin2
Abstract: The compressional wave reflection coefficient R(θ) given by the Zoeppritz equations is simplified to the following: R(θ)=R0+[A0R0+Δσ(1-σ)2]sin2θ+1/2ΔVpVp(tan2θ-sin2θ). The first term gives the amplitude at normal incidence (θ = 0), the second term characterizes R(θ) at intermediate angles, and the third term describes the approach to critical angle. The coefficient of the second term is that combination of elastic properties which can be determined by analyzing the offset dependence of event amplitude in conventional multichannel reflection data. If the event amplitude is normalized to its value for normal incidence, then the quantity determined is A=A0+1(1-σ)2ΔσR0. A0 specifies the normal, gradual decrease of amplitude with offset; its value is constrained well enough that the main information conveyed is Δσ/R0, where Δσ is the contrast in Poisson’s ratio at the reflecting interface and R0 is the amplitude at normal incidence. This simplified formula for R(θ) accounts for all of the relations between R(θ...

1,115 citations


"Anisotropic amplitude variation of ..." refers methods in this paper

  • ...The intercept (A) and the gradient (B) of the BSR reflection coefficients are estimated by fitting the data with the three-term Shuey’s approximation Rpp(θ) =A+B sin 2(θ) +C sin 2(θ)tan 2(θ) to the Zoeppritz equations [Shuey, 1985]....

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Journal ArticleDOI
TL;DR: In this article, a unified theoretical framework for three P-wave attenuation mechanisms in sedimentary rocks is given, and the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus, crack porosity, and/or frequency is reduced to zero.
Abstract: Analytical expressions for three P-wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework. Two of the models concern wave-induced flow due to heterogeneity in the elastic moduli at mesoscopic scales (scales greater than grain sizes but smaller than wavelengths). In the first model, the heterogeneity is due to lithological variations (e.g., mixtures of sands and clays) with a single fluid saturating all the pores. In the second model, a single uniform lithology is saturated in mesoscopic ''patches'' by two immiscible fluids (e.g., air and water). In the third model, the heterogeneity is at ''microscopic'' grain scales (broken grain contacts and/or micro-cracks in the grains) and the associated fluid response corresponds to ''squirt flow''. The model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus, crack porosity, and/or frequency is reduced to zero. It is shown that squirt flow is incapable of explaining the measured level of loss (10{sup -2} < Q{sup -1} < 10{sup -1}) within the seismic band of frequencies (1 to 10{sup 4} Hz); however, either of the two mesoscopic scale models easily produce enough attenuation to explain the field data.

728 citations


"Anisotropic amplitude variation of ..." refers background or methods in this paper

  • ...[42] The variable a represents the consolidation parameter [Pride et al., 2004], and the subscripts ma, w, and h refer to sediment grain, water and gas hydrate, respectively....

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  • ...The TPBE model (section A) is defined for the consolidated marine sediments based on the empirical relation between the dry frame moduli and the matrix moduli [Pride, 2003; Pride et al., 2004]....

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  • ...…b2ð Þ; where 1 Kav ¼ b1 fð Þ kma þ fw kw þ fh kh ; b1 ¼ fas 1þ að Þ 1þ afasð Þ ;b2 ¼ fas 1þ gað Þ 1þ gafasð Þ ; and g ¼ 1þ 2a 1þ a : [42] The variable a represents the consolidation parameter [Pride et al., 2004], and the subscripts ma, w, and h refer to sediment grain, water and gas hydrate,…...

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  • ...[41] The TPBE model is defined for unconsolidated marine sediments based on the empirical relation between the frame andmatrixmoduli [Pride, 2003; Pride et al., 2004]....

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  • ...[Lee and Waite, 2008] [41] The TPBE model is defined for unconsolidated marine sediments based on the empirical relation between the frame andmatrixmoduli [Pride, 2003; Pride et al., 2004]....

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