In situ methane concentrations at Hydrate Ridge, offshore Oregon: New constraints on the global gas hydrate inventory from an active margin

Milkov, Alexei V.; Claypool, George E.; Lee, Young‐Joo; Xu, Wenyue; Dickens, Gerald R.; Borowski, Walter S; Party, Odp Leg Scientific

doi:10.1130/g19689.1

Cited by 140 publications

(84 citation statements)

References 13 publications

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“…Hydrate and Free Gas Zone As summarized by Table 2, both the gas hydrate saturation and the free gas saturation at the Nyegga prospect are low, on the order of 1-2% of the pore space. This is similar to other Class 4 hydrate reservoirs, as the <1% saturation reported from the Cascadia margin by Milkov et al [66]. At Cascadia, Riedel et al [35] outline four essentially independent methods for estimating the hydrate saturation, yet still come up with a large uncertainty of <5% to >25% of gas hydrate saturation.…”

Section: Gas Expansion Factorsupporting

confidence: 51%

First-Order Estimation of In-Place Gas Resources at the Nyegga Gas Hydrate Prospect, Norwegian Sea

2010

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Gas hydrates have lately received increased attention as a potential future energy source, which is not surprising given their global and widespread occurrence. This article presents an integrated study of the Nyegga site offshore mid-Norway, where a gas hydrate prospect is defined on the basis of a multitude of geophysical models and one shallow geotechnical borehole. This prospect appears to hold around 625 GSm 3 (GSm 3 = 10 9 standard cubic metres) of gas. The uncertainty related to the input parameters is dealt with through a stochastic calculation, giving a spread of in-place volumes of 183 GSm 3 (P90) to 1431 GSm 3 (P10). The resource density for Nyegga is found to be comparable to published resource assessments of other global hydrate provinces.

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Section: Gas Expansion Factorsupporting

confidence: 51%

First-Order Estimation of In-Place Gas Resources at the Nyegga Gas Hydrate Prospect, Norwegian Sea

2010

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“…Margin (Davie and Buffett, 2003) indicated that H is ~2%, and high volume fractions of methane hydrate are confined to localized faults (Davie and Buffett, 2003;Milkov et al, 2003). It is therefore implied that methane input from typical methane hydrate quantities in the sediment could supply the minimum amount of methane input only if H is unusually high or there are localized faults.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, the methane hydrate amount in the sediment which exceeds the minimum amount of methane input would not be found either in the deeper or shallower sea-floors. Recent estimates by direct measurement of methane concentration in sediments on Blake Ridge (Dickens et al, 1997) and Hydrate Ridge (Milkov et al, 2003) and by model for Blake Ridge and Cascadia…”

Section: Discussionmentioning

confidence: 99%

Modeling of methane bubbles released from large sea-floor area: Condition required for methane emission to the atmosphere

Yamamoto

Yamanaka

Tajika

2009

Earth and Planetary Science Letters

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Abstract:Massive methane release from sea-floor sediments due to decomposition of methane hydrate, and thermal decomposition of organic matter by volcanic outgassing, is a potential contributor to global warming. However, the degree of global warming has not been estimated due to uncertainty over the proportion of methane flux from the sea-floor to reach the atmosphere. Massive methane release from a large sea-floor area would result in methane-saturated seawater, thus some methane would reach the atmosphere. In this study, we discussed the possibility of the methane release from a large sea-floor area to the atmosphere focusing on methane saturation in the water column necessary for a methane bubble to reach the atmosphere. Using a one-dimensional numerical model integrated over time, we predict methane bubbles and methane concentration in the water column under the condition of continuous methane input from the sea-floor to the water column.We found that some methane bubbles reach the atmosphere even when the methane saturation fraction in the water column is much lower than 100%. We compared the methane input from the sea-floor required for a methane bubble to reach the atmosphere to the amount of methane in the sediment in the form of methane hydrate and free gas. In most cases, our results suggest that the typical amount of methane in the sediment (i.e., typical hydrate fraction of ~2% and free gas of two-thirds of the amount of hydrate) is significantly lower than the required minimum methane input. It is, therefore, suggested that, except in the case of an extraordinary methane flux, the massive quantity of methane bubbles released from sea-floor gas hydrate would not reach the atmosphere directly but would be dissolved in the seawater. With regard to global warming due to human activities, the release of methane bubbles due to methane hydrate decomposition may not be enough to significantly accelerate total global warming. In the case of metamorphic methane release during PETM, there is the possibility that the released methane resulted in methane-saturated seawater, allowing some methane to reach the atmosphere.

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“…The GHOZ was estimated to be between 10-30% of the GHSZ (Borowski et al 1999, Dickens 2001, with hydrate formation limited to the continental margins. At Blake Ridge (Dickens et al 1997) and Hydrate Ridge (Milkov et al 2003), hydrate saturations were approximately 2% of the GHOZ. By incorporating constraints from direct ocean drilling measurements, Milkov (2004) gave a more conservative assessment of 500-2500 Gt C. Buffett & Archer (2004) and Klauda & Sandler (2005) have provided estimates via the use of a mechanistic modeling approach.…”

Section: Estimates Of Worldwide Hydrate Depositsmentioning

confidence: 99%

“…Modeling structural-type gas hydrate accumulations (Milkov & Sassen 2002) would require much more extensive knowledge of their worldwide distribution and underlying petroleum systems and it is estimated that up to 10 7 of these structural deposits would be needed to have a significant global contribution (Milkov 2004, Milkov et al 2003.…”

Section: Estimates Of Worldwide Hydrate Depositsmentioning

confidence: 99%

Feasibility of Large-Scale Ocean CO2 Sequestration

Brewer¹

2008

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In situ methane concentrations at Hydrate Ridge, offshore Oregon: New constraints on the global gas hydrate inventory from an active margin

Cited by 140 publications

References 13 publications

First-Order Estimation of In-Place Gas Resources at the Nyegga Gas Hydrate Prospect, Norwegian Sea

First-Order Estimation of In-Place Gas Resources at the Nyegga Gas Hydrate Prospect, Norwegian Sea

Modeling of methane bubbles released from large sea-floor area: Condition required for methane emission to the atmosphere

Feasibility of Large-Scale Ocean CO2 Sequestration

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