Rock physics characterization of hydrate-bearing deepwater sediments

Sava, Diana; Hardage, Bob A.

doi:10.1190/1.2202666

Cited by 29 publications

(10 citation statements)

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“…Prediction of effective bulk moduli following the Hertz-Mindlin (HM;Hertz 1882;Mindlin 1949) or Walton (1987) models has been found to be in good agreement with both laboratory data (Dutta, Mavko and Mukerji 2010;Saul, Lumley and Shragge 2013) and numerical simulations (Makse et al 1999;Sain 2010). Even though a few studies show that Walton's smooth model (total slippage) fits better with the laboratory data on dry sands (Zadeh, Mondol and Jahren 2016) and gas-hydrate bearing sediments (Sava and Hardage 2006), the majority of the published literature on this topic, including the data from Winkler (1983) and Goddard (1990), reports that effective shear modulus is largely over-predicted by the HM and Walton no-slip model. Unconsolidated sand, having no adhesive bonding by cements, is much more likely to have a situation in between the two extreme cases as modelled by Walton (1987).…”

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confidence: 61%

Elastic properties of sands, Part 2: Implementation of contact‐based model to determine the elasticity of the grains from ultrasonic measurements

Ahmed

Lebedev

2019

Geophysical Prospecting

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The prediction of effective elastic properties of a granular medium using ultrasonic data based on contact models has been studied widely in both laboratory experiments and numerical simulations. In contrast, a calculation of the elastic properties of the constituent grains using similar data by inverting the equations from those models is a rather new concept. To do so, we have developed a controlled experiment technique that includes a uniaxial compaction test and measures ultrasonic velocities of four unconsolidated quartz sand samples with different sorting and grain shapes. We observe that both P‐ and S‐wave velocities are significantly influenced by the microstructure or internal arrangement of the grains. Well sorted and more spherical and rounded samples show higher velocities than the poorly sorted and less spherical and rounded samples. A microstructural parameter – namely coordination number – we have calculated from high resolution micro computed tomography images provides a good match between the model and dynamic effective bulk moduli of the sand pack. Combining this coordination number with a frictional parameter calculated from the measured velocity ratios has been very effective to fit the model with the dynamic effective shear moduli. Using these two key parameters along with the experiment results in the contact model we have been able to obtain the elastic parameters of the quartz sand grains in the sample. Elastic parameters obtained thus are very close to the actual values of the quartz grains found in the literature. This technique can be useful in hard rock mineral exploration where missing core samples or an absence of well logs can be replaced by laboratory measurements of powders to find the elasticity or velocities of the rocks. Moreover, the elastic properties of the solid phase calculated using this technique can be used as input parameters for the fluid substitution and rock physics characterization of unconsolidated reservoir sands.

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confidence: 61%

Elastic properties of sands, Part 2: Implementation of contact‐based model to determine the elasticity of the grains from ultrasonic measurements

Ahmed

Lebedev

2019

Geophysical Prospecting

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“…The AVA of BSRs is computed using the Zoeppritz equations [ Zoeppritz , ] with the elastic parameters estimated from the TPBE model for different gas hydrate saturations (Figure b). The presence of free gas below the BSR yields a large normal‐incidence reflection coefficient with class III AVA rather than class IV AVA [ Carcione and Tinivella , ; Sava and Hardage , ]; therefore, no free gas is assumed below the BSR for the TPBE model. The magnitude of the normal‐incidence reflection coefficient increases with hydrate saturation as the velocities of hydrate bearing sediments increase with hydrate saturation (Figure b).…”

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confidence: 99%

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

et al. 2013

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[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 À0.04 to À0.11 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).Citation: Sriram, G., P. Dewangan, T. Ramprasad, and P. Rama Rao (2013), Anisotropic amplitude variation of the bottomsimulating reflector beneath fracture-filled gas hydrate deposit,

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“…They have also been observed in cores to exist as laminae along specific horizons apparently controlled by bedding porosity and in massive deposits as fracture fill [18,19]. Hydrate accumulations have also been subdivided into four (4) basic classes based on simple geological features [5,20]: Class 1 accumulations consist of a hydrate zone with an underlying fluid zone consisting of gas and liquid water; Class 2 deposits consist of a hydrate zone which overlies a zone of mobile water; Class 3 deposits consist of a single hydrate layer with no underlying mobile fluids; and Class 4 refers to disperse, low saturation deposits which occur in oceanic sediments and which lack confining geologic strata.…”

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confidence: 99%

Towards Commercial Gas Production from Hydrate Deposits

Silva

Dawe

2011

Energies

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Over the last decade global natural gas consumption has steadily increased since many industrialized countries are substituting natural gas for coal to generate electricity. There is also significant industrialization and economic growth of the heavily populated Asian countries of India and China. The general consensus is that there are vast quantities of natural gas trapped in hydrate deposits in geological systems, and this has resulted in the emerging importance of hydrates as a potential energy resource and an accompanying proliferation of recent studies on the technical and economic feasibility of gas production from hydrates. There are then the associated environmental concerns. This study reviews the state of knowledge with respect to natural gas hydrates and outlines remaining challenges and knowledge gaps.

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Rock physics characterization of hydrate-bearing deepwater sediments

Cited by 29 publications

References 0 publications

Elastic properties of sands, Part 2: Implementation of contact‐based model to determine the elasticity of the grains from ultrasonic measurements

Elastic properties of sands, Part 2: Implementation of contact‐based model to determine the elasticity of the grains from ultrasonic measurements

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

Towards Commercial Gas Production from Hydrate Deposits

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