Seismic Evidence for Widespread Possible Gas Hydrate Horizons on Continental Slopes and Rises

Shipley, Tom H.; Houston, M. H.; Buffler, Richard T.; Shaub, F. Jeanne; McMillen, Kenneth J.; Ladd, John W.; Worzel, J. Lamar

doi:10.1306/2f91890a-16ce-11d7-8645000102c1865d

Cited by 125 publications

(27 citation statements)

References 13 publications

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“…This leads to a sharp decrease in seismic impedance, the product of compressional wave velocity and bulk density, across the BHSZ, and causes a reflection with reverse polarity with respect to the seafloor, called a bottom simulating reflection (BSR). The BSR is commonly used as a proxy for the presence of gas hydrate (Majumdar et al, 2016;Shipley et al, 1979). Widespread BSRs have been detected along continental margins, assisting the discovery of gas hydrate.…”

Section: Methane Hydrate Stability Zone (Hsz)mentioning

confidence: 99%

Mechanisms of Methane Hydrate Formation in Geological Systems

You

Flemings

Malinverno

et al. 2019

Reviews of Geophysics

147

110

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Natural gas hydrate is ice‐like mixture of gas (mostly methane) and water that is widely found in sediments along the world's continental margins and within and beneath permafrost and glaciers in a near‐surface depth interval where the pressure is sufficiently high and temperature sufficiently low for gas hydrate to be stable. We categorize the myriad of geological gas hydrate deposits into five characteristic types. We then review the multiple quantitative models that have proposed to describe the genesis of these deposits and describe how each may have formed. We emphasize the importance of coupling multiphase flow (free gas and liquid water) and multicomponent reactive transport with geological history to describe the dynamical processes of gas hydrate formation and evolution in geological systems. A better insight into the kinetics of methane formation from microbial biogenesis and the processes of multiphase flow at the pore scale will advance our knowledge of how these systems form. By understanding the generation and evolution of gas hydrate through time, we will better decipher the role of gas hydrate in the carbon cycle, its potential to contribute to climate change and geohazards, and how to design optimal strategies for gas production from hydrate reservoirs.

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Section: Methane Hydrate Stability Zone (Hsz)mentioning

confidence: 99%

Mechanisms of Methane Hydrate Formation in Geological Systems

You

Flemings

Malinverno

et al. 2019

Reviews of Geophysics

147

110

View full text Add to dashboard Cite

show abstract

“…A bottom-simulating reflection (BSR), is commonly associated with the presence of gas hydrate under the seafloor. The BSR generally indicates the boundary between free gasbearing sediments below and hydrate-bearing sediments above (Shipley et al 1979;Yamano et al 1982;Singh et al 1993). BSRs can be observed in seismic reflection data due to the acoustic impedance contrast between sediments bearing hydrate and free gas (Kvenvolden 1995).…”

Section: Introductionmentioning

confidence: 99%

Estimating the composition of gas hydrate using 3D seismic data from Penghu Canyon, offshore Taiwan

Sahoo¹,

Chi²,

Han³

et al. 2018

Terr. Atmos. Ocean. Sci.

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Direct measurements of gas composition by drilling at a few hundred meters below seafloor can be costly, and a remote sensing method may be preferable. The hydrate occurrence is seismically shown by a bottom-simulating reflection (BSR) which is generally indicative of the base of the hydrate stability zone. With a good temperature profile from the seafloor to the depth of the BSR, a near-correct hydrate phase diagram can be calculated, which can be directly related to the hydrate composition. However, in the areas with high topographic anomalies of seafloor, the temperature profile is usually poorly defined, with scattered data. Here we used a remote method to reduce such scattering. We derived gas composition of hydrate in stability zone and reduced the scattering by considering depth-dependent geothermal conductivity and topographic corrections. Using 3D seismic data at the Penghu canyon, offshore SW Taiwan, we corrected for topographic focusing through 3D numerical thermal modeling. A temperature profile was fitted with a depth-dependent geothermal gradient, considering the increasing thermal conductivity with depth. Using a pore-water salinity of 2%, we constructed a gas hydrate phase model composed of 99% methane and 1% ethane to derive a temperature depth profile consistent with the seafloor temperature from in-situ measurements, and geochemical analyses of the pore fluids. The high methane content suggests predominantly biogenic source. The derived regional geothermal gradient is 40°C km-1. This method can be applied to other comparable marine environment to better constrain the composition of gas hydrate from BSR in a seismic data, in absence of direct sampling.

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“…At the basin scale, the thickness of the MHSZ is often determined from in situ pressure and temperature trends with the assumptions that pore water salinity is equal to that of seawater and the influence of pore size may be neglected [e.g., Burwicz et al, 2011;Wallmann et al, 2012]. The resulting MHSZ thicknesses are often in agreement with other indicators of MHSZ thickness, such as bottom-simulating reflections (BSRs) observed on seismic data [e.g., Shipley et al, 1979;Yamano et al, 1982;Foucher et al, 2002;McConnell and Kendall, 2003]. However, local changes in stability conditions can cause the MHSZ thickness to vary.…”

Section: Introductionmentioning

confidence: 99%

Pore size controls on the base of the methane hydrate stability zone in the Kumano Basin, offshore Japan

Daigle

Dugan

2014

Geophysical Research Letters

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The base of the methane hydrate stability zone (MHSZ) in the Kumano Basin, offshore Japan, is marked by a bottom-simulating reflection (BSR) on seismic data. At Integrated Ocean Drilling Program Site C0002, which penetrates this BSR, the in situ temperature profile combined with bulk seawater methane equilibrium conditions suggest that the base of the MHSZ is 428 m below seafloor (bsf), which is 28 m deeper than the observed BSR (400 m bsf). We found that submicron pore sizes determined by mercury injection capillary pressure are sufficiently small to cause 64% of the observed uplift of the base of the MHSZ by the Gibbs-Thomson effect. This is the most thorough characterization of pore sizes within the MHSZ performed to date and illustrates the extent to which pore size can influence MHSZ thickness. Our results demonstrate the importance of considering lithology and pore structure when assessing methane hydrate stability conditions in marine sediments.

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Seismic Evidence for Widespread Possible Gas Hydrate Horizons on Continental Slopes and Rises

Cited by 125 publications

References 13 publications

Mechanisms of Methane Hydrate Formation in Geological Systems

Mechanisms of Methane Hydrate Formation in Geological Systems

Estimating the composition of gas hydrate using 3D seismic data from Penghu Canyon, offshore Taiwan

Pore size controls on the base of the methane hydrate stability zone in the Kumano Basin, offshore Japan

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