Transcript Methane Hydrates Jake Ross and Yuliana Potenza

Methane Hydrates
Jake Ross and Yuliana Proenza
The Three Questions
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What is a Gas Hydrate?
What is their potential as an energy resource?
What role do they play in global climate
change?
What is a Gas Hydrate?
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A gas hydrate is a crystalline solid; its building blocks consist
of a gas molecule surrounded by a cage of water molecules.
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It is similar to ice, except that the crystalline structure is
stabilized by the guest gas molecule within the cage of water
molecules.
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Suitable gases are: carbon dioxide, hydrogen sulfide, and
several low-carbon-number hydrocarbons. Most gas hydrates ,
however are Methane Hydrates.
Hydrate Samples
Gas hydrates in sea-floor mounds Here methane
gas is actively dissociating from a hydrate mound.
Gas hydrate can occur as nodules, laminae, or veins within sediment.
CH4 Hydrate Stability
Where are Methane Hydrates
located?
Found in 4 major location types
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Subduction zones (e.g., Nankai Trough Japan, Cascadia Basin)
Passive Margins (e.g., Blake Ridge on the southeast cost of the US)
Off-shore hydrocarbon (e.g., Gulf of Mexico, North Slope Alaska)
On-shore Arctic Permafrost (e.g., Mackenzie Delta, Arctic Russia,
Arctic Alaska)
Where are Methane Hydrates
located?
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Methane hydrate occurs in a zone referred to as the
hydrate stability zone.
The zone lies roughly parallel to the land or seafloor
surface.
Permafrost regions,
depths about 150 - 2000 m below the surface.
In oceanic sediment
ocean is at least 300 m deep,
depths of 0 - 1,100 m below the seafloor.
Where are Methane Hydrates
located?
Hydrate concentration occurs at depocenters
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Where there is a rapid accumulation of organic detritus (from which
bacteria generate methane). Carbon isotope analyses indicate most of
the methane in hydrates is microbial, however thermogenic sources
have been identified in the Gulf of Mexico
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Where there is a rapid accumulation of sediments (which protect
detritus from oxidation).
What is the potential of
CH4 Hydrates as an energy resource
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The estimated conventional gas resources and reserves in the
United States alone are 1,400 trillion cubic feet.
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If it could be safely and economically recovered, one 50 by 150
kilometer area off the coast of North and South Carolina is
estimated to hold enough methane to supply the needs of the
United States for over 70 years
Conceptual Drawing of Blake Ridge
Why are CH4 Hydrates a good energy
resource
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The gas is held in a crystal structure, therefore gas molecules are
more densely packed than in conventional or other unconventional
gas traps.
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Hydrate forms as cement in the pore spaces of sediment and has the
capacity to fill sediment pore space and reduce permeability. CH4 hydrate-cemented strata thereby act as seals for trapped free gas
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Production of gas from hydrate-sealed traps may be an easy way to
extract hydrate gas because the reduction of pressure caused by
production can initiate a breakdown of hydrates and a recharging of
the trap with gas
A Proposed Method
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For the gas production from
hydrates and the seabed
stability after the production,
we proposed a new concept.
The figure illustrates the
molecular mining method by
means of CO2 injection in order
to extract CH4 from gas hydrate
reservoirs. The concept is
composed of three steps as
follows; 1) injection of hot sea
water into the hydrate layer to
dissociate the hydrates, 2)
produce gas from the hydrate, 3)
inject CO2 to form carbon
dioxide hydrate with residual
water to hold the sea bed stable
CH4 Hydrates and Climate Change
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Methane is a very effective greenhouse gas. It is ten times more
potent than carbon dioxide.
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There is increasing evidence that points to the periodic massive
release of methane into the atmosphere over geological timescales.
Are these enormous releases of methane a cause or an effect of global
climate change?
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Global warming may cause hydrate destabilization through a rise in ocean
bottom water temperatures. The increased methane content in the
atmosphere in turn would be expected to accelerate warming, causing
further dissociation, potentially resulting in run away global warming.
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Sea level rise, however, during warm periods may act to stabilize hydrates
by increasing hydrostatic pressure, thereby acting as a check on warming.
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Hydrate dissociation may act as a check on glaciations, whereby reduced
sea levels may cause seafloor hydrate dissociation, releasing methane and
warming the climate.
This diagram illustrates the affect sea level change has on the stability
of hydrates.
The Past
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A prominent negative shift in δ 13C has been recorded in Late
Paleocene sediments worldwide.
The late Paleocene-early Eocene interval (55.5 mya) was a thermal
maximum
Ocean bottom waters warmed rapidly by as much 4 degrees C, along
with a concurrent rapid shift in δ 13C values of all the carbon
reservoirs in the global carbon cycle
Data from sediments cores suggest that the isotopic shift occurring
within no more than a few thousand years
Only a catastrophic infusion of δ 12C-enriched carbon from methane
hydrates could cause such a rapid shift.
CH4 Hydrates and the Atmosphere
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An important aspect of methane hydrates and their affect on climate
change is their potential to enter the atmosphere
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Methane concentration in seawater is observed to decrease by 98%
between a depth of 300m and the sea surface as a result of microbial
oxidation.
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The flux of methane into the atmosphere is thus lowered 50-fold
(Mienert et al., 1998)
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However during catastrophic events such as large–scale sediment
slumping much higher proportions of methane would be released.
The Future of Methane Hydrates
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Worldwide gas production in the next 30-50 years
Areas with unique economic and/or political motivations could see
substantial production within 5-10 years
We need to better understand the mechanisms of hydrate
disassociation and its role in global warming, either as an accelerator
or and inhibitor