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More than 1,000 meters below the North Sea lies what one oil company hopes
is an answer to global warming. Since 1996,
Statoil, Norway's largest producer of oil and natural gas
has separated carbon dioxide from natural gas during pumping operations on
one of its
ocean platforms. The company injects the CO2
down into an underground aquifer, where it hopes the gas will remain permanently
trapped.
It is one of the world's largest attempts to lock away a major contributor to the
current
dangerous build-up of greenhouse gases in the atmosphere.
Researchers at Scripps Institution of Oceanography,
at UC San Diego began monitoring the sequestration experiment to determine if
the co2
is truly remaining buried at sea. Carbon sequestration
is controversial, meaning it's controversial
from a purely technical standpoint, and that is once you put the carbon
back down to the ground, is it going to stay there? So the point of these very slight
experiments is to do reservoir monitor
to see whether or not the co2 is trying to escape from the cap rock permission, for
all these good
geological and theoretical reasons to believe that it's going to stay there.
Natural gas stays in the ground for millions of years.
We didn't do anything about it and you would think that co2 would also be the
same sort of issue.
But because we've done something
that we haven't done in the history of humanity, trying to put that carbon
back where it belongs, we need to make
diligent efforts in being sure that
it does what we hope it will. The formation that the
co2 is being pumped into is called the Utsira formation
and it lies about a kilometer
beneath the seafloor and it's a two or three hundred meter thick
layer of very well sorted
sand, so it has a very, is very porous.
So you have the ocean and then you have a thick layer of clay and shales, which are
kinds or rocks
that gas can't penetrate and then below that you have this
very porous sandy layer called the Utsira formation
and it's that sandy layer that the co2
is pumped into. To monitor the co2 mass,
Scripps research team built the ROV DOG, a remotely operated
deep-sea gravity meter. They headed to Norway to deploy their instruments along
a stretch of sea floor,
in order to monitor the changes in gravity above where the gas is trapped,
to determine if any is leaking out. We have a gravity meter which is a commercially
made
device designed to work on land
and in a gravity meter is basically a very simple thing,
it's a spring with a weight on the end of it and as gravity
increases then the weight moves downward, stretches the spring a little further.
Now we've taken that sensor and installed it
in the a casing that can survive at the bottom of the ocean
and that has a motorized
gimbles, to align it with the vertical
and a computer to monitor all of the operating parameters
and send the data to the surface.
As the gas is extracted from the
production platform, seawater takes its place, seawater infiltrates
through the ocean bottom, takes place of the gas, comes in from the bottom
fills it up. So now you've introduced high-density water
replace the low-density gas with high-density water
and then be a gravity signal associated with that. Also there's another signal
where the
c4 subsides, is you basically letting gas out of the balloon.
The researchers are using this information to create a snapshot of the
gravity at various points in time.
They have been able to detect small changes confirming that gas
is trapped inside. How much is leaked out, if
any, is not yet known. The research team anticipates the next round of monitoring
in the summer of 2009, will be able to tell researchers conclusively
if any of the gas is escaping. So if you were to measure gravity
at the same position as time goes on what you would notice
is that the value of gravity
gradually decreases as more and more co2 is pumped into the,
into the formation. So we measure gravity
at about 30 stations on the seafloor
above this formation and our goal
is for each of those sites to have a graph of the change in gravity as a
function
of time. Everybody thinks that the co2 will
go down there and stay down there and not leak out but
it's a significant volume of co2
and we don't want it to,
well if it's leaking out we want to know about it so we need to
monitor it.
This has been a presentation of Scripps Institution of Oceanography
at UC San Diego.