gas hydrates: our energy (and climate) future? lecture outline: 1)what are gas hydrates anyway?...
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Gas Hydrates: Our Energy (and Climate) Future?
Lecture Outline:
1)What are gas hydrates anyway?
2)Gas hydrates as an energy source – pros and cons
3)Gas hydrates and climate change: adding fuel to the flames?
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Hydrates - What are they?
n Gas Hydrates are solids formed from hydrocarbon gas and liquid water
n They resemble wet snow and can exist at temperatures above the freezing point of water
n They belong to a form of complexes known as clathrates
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Clathrates - What are they?n Clathrates are substances having a lattice-like
structure or appearance in which molecules of one substance are completely enclosed within the crystal structure of another
n Hydrates consist of host molecules (water) forming a lattice structure acting like a cage, to entrap guest molecules (gas)
n CH4 (most common), CO2, H2S form hydrates
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http://walrus.wr.usgs.gov/globalhydrate/images/browse.jpg
white dot = gas samples recoveredblack dot = hydrate inferred from seismic imagingdotted lines = hydrate-containing permafrost
98% in ocean2% on land
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using seismic-reflection profiles
Bottom Simulating Reflection (BSRs)
http://woodshole.er.usgs.gov/project-pages/hydrates/hydrate.htm
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a methane hydrate lattice
Methane Hydrate stability diagram
-methane hydrates can occur at water temperatures up to 30°C, if the pressure is high enough
-stable over most of ocean floor!
redrawn after Kvenvolden (1993)
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“The Burning Snowball”
Methane hydrate supporting its own
combustion
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BENEFITS:- 1 cubic meter of gas hydrate (90% site occupied) = 163 m3 of gas
-there is A LOT of it, and it’s everywhere
-clean-burning natural gas
Methane Hydrates as an energy source
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• USA has gas hydrate reserves of 112,000-676,000 trillion cubic feet (tcf)
• USA has 2,200 tcf of natural gas reserves (EIA)• USA uses 25-30 tcf/yr of natural gas• India and Japan are leading the charge to hydrate recovery
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An Energy Coup for Japan: ‘Flammable Ice’
NYTimes, 3/12/13
Water depth: 1000msubfloor depth: 300m
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Methane Hydrates as an energy source
PROBLEMS:-hydrate dissociation upon recovery; engineering challenge
-expense of long pipelines across continental slope, subject to blockage with solid hydrate
-methane release into atmosphere problem for climate change(20x more potent than CO2)
-fragile ecosystems surround sediment surface hydrates & seeps
ice worm that lives in hydratephoto by Ian Mc Donald
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1 cubic meter of gas hydrate (90% site occupied) = 163 m3 of gas + .87 m3
Undersea slides (slope failures) may be caused by methane hydrate dissociation;implications for pipeline?
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Large, expensive pilot programs focus on drilling in frozenpermafrost areas
Ex: Mallik, Canada
http://energy.usgs.gov/other/gashydrates/mallik.html
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New ocean sediment drilling technologiesinvented for hydrate recovery and storage
an Ocean Drilling Program core lockerwith lone hydrate core in pressurized chamber
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dissociating methane hydrate at sediment/water interface
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Westbrook et al., 2009
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Westbrook et al., 2009
-lots of CH4 escaping from melting gas hydrates
-powerful positive feedback on global warming
-CH4 is a powerful greenhouse gas
-most likely oxidizes to CO2 before it enters the atmosphere… but still!
-see Archer et al., 2007 for detailed investigation of methane hydrate dissociation during global warming
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Park et al., PNAS, 2006
An interesting twist:
- replace CH4 with CO2 in the hydrate lattice
- have your energy cake and eat it too?
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Take-home point
Methane hydrates represent the largest fossil fuel reservoir,but problems ranging from yet-to-be-developed technologies and climate change feedbacks remain to be resolved.