Methane hydrate rock physics models for the Blake Outer Ridge
01 Jan 2001-
TL;DR: In this article, the effect of different hydrate models on elastic moduli and velocities of hydrate-bearing sediments was explored. But the results of the experiments were limited to the Blake Outer Ridge.
Abstract: Seismic analyses of methane hydrate data from the Blake Outer Ridge indicate high Pwave velocity and anomalously low S-wave velocity in sediments containing methane hydrates. In an attempt to explain this observed P-wave and S-wave velocity structure at the transition from gas to hydrates, the effect of different hydrate models on elastic moduli and velocities are explored. After construction of an initial gas model, the properties of the hydrates are estimated using the bound averaging method together with the Voigt and Reuss bounds for elastic moduli. The result suggests that the hydrates becomes part of the rock matrix and softens the pores by fracturing. The additional formation of ice is required to obtain the desired P- to S-wave velocity ratio in the hydrate bearing sediments, indicating temperature conditions around the freezing point of water.
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TL;DR: In this article, the authors built a rock physical model for load-bearing and pore-filling gas hydrate-bearing sediments, describing the mineral compositions, pore connectivity, and the pore shape using effective media theory, and calculated the shear properties of pore filling gas hydrates using Patchy saturation theory and generalized Gassmann theory.
Abstract: There are ambiguities and uncertainties in the recognition of gas hydrate seismic reflections and in quantitative predictions of physical information of natural gas hydrate reservoirs from seismic data. Rock physical modelling is a bridge that transforms the seismic information of geophysical observations into physical information, but traditional rock physics models lack descriptions of reservoir micro-structures and pore-filling materials. Considering the mineral compositions and pore micro-structures of gas hydrates, we built rock physical models for load-bearing and pore-filling gas hydrate-bearing sediments, describe the mineral compositions, pore connectivity and pore shape using effective media theory, calculated the shear properties of pore-filling gas hydrates using Patchy saturation theory and Generalized Gassmann theory, and then revealed the quantitative relation between the elastic parameters and physical parameters for gas hydrate-bearing sediments. The numerical modelling results have shown that the ratios of P-wave and S-wave velocities decrease with hydrate saturation, the P-wave and S-wave velocities of load-bearing gas hydrate-bearing sediments are more sensitive to hydrate saturation, sensitivity is higher with narrower pores, and the ratios of the P-wave and S-wave velocities of pore-filling gas hydrate-bearing sediments are more sensitive to shear properties of hydrates at higher hydrate saturations. Theoretical analysis and practical application results showed that the rock physical models in this paper can be used to calculate the quantitative relation between macro elastic properties and micro physical properties of gas hydrate-bearing sediments, offer shear velocity information lacking in well logging, determine elastic parameters that have more effective indicating abilities, obtain physical parameters such as hydrate saturation and pore aspect ratios, and provide a theoretical basis and practical guidance for gas hydrate quantitative predictions.
19 citations
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TL;DR: In this article, Biondi et al. presented a map of the Blake Outer Ridge, highlighting the area of known hydrate distribution as mapped from seismic bottom simulating reflectors (BSR).
Abstract: Blake Outer Ridge dataset Raw Data /data/2d_real/blake_outer_ridge/cmps-tp.HH Velocity Model N/A Stack N/A Zero-offset Migration N/A Usage AVO/methan hydrates: (Matsumoto et al., 1996; Ecker and Lumley, 1993, 1994; Ecker, 1994, 1995, 1997; Ecker et al., 1997; Ecker, 1998; Mora and Biondi, 1999), imaging/velocity estimation (Biondi and Sava, 1999; Clapp and Biondi, 1999; Sinha and Biondi, 1999; Fomel, 1999) Geometry /data/2d_real/blake_outer_ridge/cmps-tp.HH: in="stdin" expands to in="stdin" esize=4 n1=625 n2=48 n3=1105 n4=1 33150000 elem 132600000 bytes d1=0.004 d2=-0.1 d3=0.05 d4=1 Warning: d2 is negative. Legal, but risky. o1=4 o2=3.825 o3=0 o4=0 label1=Time label2=Trace-record number label3= Non-linear cable group spacing: 100 m at near offsets and 50 m at far offsets. Problem N/A History of Data The data were recorded at the Blake Outer Ridge, offshore Florida and Georgia. A map of the region is shown in Figure 1, highlighting the area of known hydrate distribution as mapped from seismic bottom simulating reflectors (BSR). The part of the seismic line is marked by the rectangular, and extends both from the hydrate region into an area without hydrate. The data were provided by USGS (Keith Kvenvolden, Myung Lee, and Bill Dillon). Preprocessing N/A Proprietary Considerations N/A REFERENCES Biondi, B., and Sava, P., 1999, Wave-equation migration velocity analysis: SEP–100, 11–34. 1email: sergey@sep.stanford.edu 1
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TL;DR: In this article, the authors discuss three important aspects of gas hydrates: their potential as a fossil fuel resource, their role as a submarine geohazard, and their effects on global climate change.
Abstract: Gas hydrates are naturally ocurring solids consisting of water molecules forming a lattice of cages, most of which contain a molecule of natural gas, usually methane. The present article discusses three important aspects of gas hydrates: their potential as a fossil fuel resource, their role as a submarine geohazard, and their effects on global climate change. 70 refs., 16 figs., 1 tab.
1,236 citations
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TL;DR: Waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a BSR and its thickness, and predicts that sediment pores beneath the BSR contain free methane for approximately 30 meters.
Abstract: Seismic reflection profiles across many continental margins have imaged bottom-simulating reflectors (BSRs) parallel to the seabed; these are often interpreted as the base of a zone in which methane hydrate "ice" is stable. Waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a BSR and its thickness. A test of this method at a drill site of the Ocean Drilling Program predicts that sediment pores beneath the BSR contain free methane for approximately 30 meters. The hydrate and underlying gas represent a large global reservoir of methane, which may have economic importance and may influence global climate.
245 citations
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TL;DR: In this article, the authors conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate and found that the formation of hydrate tends to cause a decrease in the thermal conductivities of a sediment.
Abstract: In order to better understand the occurrence and distribution of gas hydrates and their effects on acoustic and thermal measurements in ocean sediments, the authors have conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate. The most significant result of these studies is that the formation of hydrate tends to cause a decrease in the thermal conductivity of a sediment. This is contrary to what might be expected on the basis of an analogy with the behavior of frozen sediment and implies that some thermal gradients assumed in earlier studies of in situ deposits of hydrate may be too small. Other results of the research based on measurements of acoustic wave velocity confirm that both pure water and water-bearing sediment are converted to a stiff elastic mass by the formation of a sufficient quantity of hydrate. This clearly establishes the potential for a sharp acoustic impedance contrast at the boundary of a region of sediment containing a significant quantity of hydrate.
187 citations
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Book•
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01 Jan 1990
TL;DR: In this article, the authors present the science behind the Greenhouse effect, Steven Schneider biogeochemical feedbacks in global warming, David Schimmel modelling stabilization of the greenhouse gas content of the atmosphere, Mick Kelly.
Abstract: Part 1 Science: the science behind the Greenhouse effect, Steven Schneider biogeochemical feedbacks in global warming, David Schimmel modelling stabilization of the Greenhouse gas content of the atmosphere, Mick Kelly. Part 2 Impacts: the impacts of global warming, George Woodwell lessons from the climates of the past, Brian Huntley the health impacts of global warming, Andrew Haines. Part 3 Policy responses: policy responses to global warming, Jose Goldemberg energy efficiency in combatting global warming, Amory Lovins renewable energy production in combatting global warming, Carlo LaPorta transport policy in combatting global warming, Michael Walsh nuclear power in the abatement of global warming, Bill Keepin an integrated policy plan for a low-energy, non-nuclear future - the example of Sweden, Birgit Bodlund, et al emissions of Greenhouse gases from agriculture and the scope for their reduction, Ann Ehrlich deforestation and reafforestation, Norman Myers deforestation in Brazil, Philip Fearnside international debt - the scale of the problem, and its relevance to international policymaking in abating global warming, Susan George less developed countries in the international policy response to global warming, Kiliparti Ramakrishna.
107 citations
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01 Nov 1983
TL;DR: A recent DSDP Leg 11 report indicated the presence of gas hydrates in sediments of the Blake Outer Ridge as mentioned in this paper, and Leg 76 coring and sampling confirms that they are present there.
Abstract: Natural gas hydrates are clathrates in which water molecules form a crystalline framework that includes and is stabilized by natural gas (mainly methane) at appropriate conditions of high pressures and low temperatures. The conditions for the formation of gas hydrates are met within continental margin sediments below water depths greater than about 500 m where the supply of methane is sufficient to stabilize the gas hydrate. Observations on DSDP Leg 11 suggested the presence of gas hydrates in sediments of the Blake Outer Ridge. Leg 76 coring and sampling confirms that, indeed, gas hydrates are present there. Geochemical evidence for gas hydrates in sediment of the Blake Outer Ridge includes (1) high concentrations of methane, (2) a sediment sample with thin, matlike layers of white crystals that released a volume of gas twenty times greater than its volume of pore fluid, (3) a molecular distribution of hydrocarbon gases that excluded hydrocarbons larger than isobutane, (4) results from pressure core barrel experiments, and (5) pore-fluid chemistry. The molecular composition of the hydrocarbons in these gas hydrates and the isotopic composition of the methane indicate that the gas is derived mainly from microbiological processes operating on the organic matter within the sediment. Although gas hydrates apparently are widespread on the Blake Outer Ridge, they probably are not of great economic significance as a potential, unconventional, energy resource or as an impermeable cap for trapping upwardly migrating gas at Site 533.
94 citations
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