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?

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

3

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

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

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 m3 of gas

-there is A LOT of it, and it’s 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: 1000msubfloor 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 CO2)

-fragile ecosystems surround sediment surface hydrates & seeps

ice worm that lives in hydratephoto by Ian Mc Donald

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?

Large, expensive pilot programs focus on drilling in frozenpermafrost areas

Ex: Mallik, Canada

http://energy.usgs.gov/other/gashydrates/mallik.html

New ocean sediment drilling technologiesinvented for hydrate recovery and storage

an Ocean Drilling Program core lockerwith lone hydrate core in pressurized chamber

dissociating methane hydrate at sediment/water interface

Westbrook et al., 2009

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

Park et al., PNAS, 2006

An interesting twist:

- replace CH4 with CO2 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.