Laura Stern: We make a number of different hydrates in the laboratory.
Some are with hydrocarbons.
Methane being the most abundant.
We also make carbon dioxide hydrate, ethane hydrate, propane.
A number of different structures.
Laura Stern: So liquid nitrogen is very cold.
It’s about a hundred degrees colder than the temperature at which these hydrate samples
would dissociate.
When they would decompose to ice plus gas on the table top.
In here we have a little piece of methane hydrate . It’s enclosed in a soft metal
jacket . So, the samples we make, they’re poly-crystalline.
They look like snow.
It looks like compacted snow.
But, honestly it does contain gas inside.
Laura Stern: Take a little piece off here and, as it warms up, you’ll begin to see
it pop, it’s reverting to ice plus gas, and then as the ice would melt , as it continues
to warm, it will end up being water plus gas.
So, this will form anywhere you have water and gas at moderately low temperatures or
high pressure.
Steve Kirby: My name is Steve Kirby.
I am a geophysicist here with the U.S. Geological Survey in Menlo Park.
I work with Laura Stern who is also a geophysicist in this lab that is devoted towards the investigation
of planetary ices and gas hydrates.
Laura Stern: Gas hydrates in nature occur in very remote places and they are very complex,
with the sediment interactions and the conditions that they form under.
And samples that are brought up are under some sort of alteration or decomposition.
Steve Kirby: We’ve educated ourselves by experiment in learning how to make them in
a form that’s suitable for doing material property tests.
Laura Stern: We start in the main portion of the lab making ordinary water ice that
we use as a reactant for the hydrates.
We grind and sieve that ice and we pack them into pressure vessels and we take that package
and we put it into this freezer and we load them onto these two ports and we evacuate
all of the pore space between the ice grains and then we have these reservoirs that have
pre-chilled gas in them that we then put into that pore space to react with that ice to
make hydrate.
So we start simple, we make the pure end member hydrates and then we add complexities in the
known fashion so that the properties that we measure we understand individual effects
of those complexities.
Unlike just looking at the samples that are retrieved from nature which are so difficult
to analyze.
Laura Stern: This is a sample of, this is a structure two gas hydrate.
It’s predominantly methane has a little bit of ethane in it.
We’re going to demonstrate how much gas is actually in this.
If you bring a cubic meter of methane hydrate from the ocean floor up to the lab and put
it on the table top it would release one hundred and sixty three times its volume of gas at
standard conditions.
So, it really is a very efficient way of storing gas.
We’re going to demonstrate that by lighting this sample on fire.
So, it’s decomposing to ice plus gas the gas is flaming and the ice will soon just
melt to water.
And you can see it’s not just a pile of snow that I was showing you.
Steve Kirby: They contain abundant amounts of natural gas.
This natural gas is thought to be a significant potential resource for our energy needs later
in this century.
Laura Stern: This is a gas hydrate from the Cascadia Margin so this is a natural hydrate
brought up from the ocean floor.
So, you can see the marine muds in here and these nice nodules of predominantly methane
hydrate.
Laura Stern: So, this laboratory is unique in that we have the low temperature capabilities
to make the samples.
So, we make different types of ice samples or gas hydrates or ammonia hydrates both planetary
ices and gas hydrates.
And we also have unusual capabilities in how we look at those samples afterwards with the
cryogenic capabilities on our x-ray diffractometer as well as, over in another laboratory, a
cryogenic set up for scanning electron microscopy.
Where you can actually look at the grain textures and pore structures of samples and how they
interact with the sediments and how they look in nature compared to how we make them in
the laboratory.
Steve Kirby: Lastly, we give insight from our laboratory experience as to the governing
kind of physical processes that say govern their stability in nature and how they respond
to deformation, changes in pressure and so on.
So this is an unusual lab, like I say, there are only a handful of them world wide and
we are very fortunate to be here at the geological survey and to have the opportunity of working
on them.
END