Presentation on theme: "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."— Presentation transcript:
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?
2 Hydrates - What are they? Gas Hydrates are solids formed from hydrocarbon gas and liquid water They resemble wet snow and can exist at temperatures above the freezing point of water They belong to a form of complexes known as clathrates
3 Clathrates - What are they? 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 Hydrates consist of host molecules (water) forming a lattice structure acting like a cage, to entrap guest molecules (gas) CH 4 (most common), CO 2, H 2 S form hydrates
http://walrus.wr.usgs.gov/globalhydrate/images/browse.jpg white dot = gas samples recovered black dot = hydrate inferred from seismic imaging dotted lines = hydrate-containing permafrost 98% in ocean 2% on land
using seismic-reflection profiles Bottom Simulating Reflection (BSRs) http://woodshole.er.usgs.gov/project-pages/hydrates/hydrate.htm
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)
7 The Burning Snowball Methane hydrate supporting its own combustion
BENEFITS: - 1 cubic meter of gas hydrate (90% site occupied) = 163 m 3 of gas -there is A LOT of it, and its everywhere -clean-burning natural gas Methane Hydrates as an energy source
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
An Energy Coup for Japan: Flammable Ice NYTimes, 3/12/13 Water depth: 1000m subfloor depth: 300m
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 CO 2 ) -fragile ecosystems surround sediment surface hydrates & seeps ice worm that lives in hydrate photo by Ian Mc Donald
1 cubic meter of gas hydrate (90% site occupied) = 163 m 3 of gas +.87 m 3 Undersea slides (slope failures) may be caused by methane hydrate dissociation; implications for pipeline?
Large, expensive pilot programs focus on drilling in frozen permafrost areas Ex: Mallik, Canada http://energy.usgs.gov/other/gashydrates/mallik.html
-lots of CH 4 escaping from melting gas hydrates -powerful positive feedback on global warming -CH 4 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
Park et al., PNAS, 2006 An interesting twist: - replace CH 4 with CO 2 in the hydrate lattice - have your energy cake and eat it too?
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.