Choosing a Sequestration Method
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| Source:
Two options for disposing of CO2 - on the left,
gas (red line) is removed and CO2 (black line)
pumped into deep saline reservoirs. On the right, CO2
is pumped down to enhance recovery of oil and remains behind
in deep rock layers. Image - Australian Petroleum Cooperative
Research Centre |
The first
step after choosing to sequester carbon dioxide is to determine
where to store, as there are numerous options - mineral mines,
oceans, and geological formations. With each type of sequestration
technology we consider, certain factors play a role in assessing
the attractiveness of one option versus another. The following
general concerns must be taken into consideration when choosing
a type of sequestration and a site for sequestration.
Time
How long will the CO2 remain sequestered? Ideally,
we would like the carbon dioxide to remain permanently or at least
on a geological time scale. At the very least, we would hope
that the carbon would remain a couple of thousand years, without
substantial leaks to the atmosphere. After all, if the carbon
leaks, the sequestration effort was futile and the expense was
lost. We will have just ended up delaying the release of the carbon
dioxide to the atmosphere, sending ourselves back to square one.
Location
There are
depositories for carbon dioxide sequestration all over the world.
Oceans cover the 70% of the Earth. There are depleted oil and
gas reserves, coal beds, and aquifers on almost every continent
although due to size and accessibility limitations, not all may
be options for sequestering carbon dioxide.
Cost
The cost of
the project is clearly a key factor. The price tag of sequestration
is affected by numerous factors including distance from source
to deposit site (transportation costs), injection technology,
separation costs, and conversion of the CO2. Different
types of sequestration have different cost savings and cost increases.
For example, ocean sequestration is more cost efficient than geological
sequestration if the emissions site is near the coast, due to
the proximity of the source to the site. On the other hand, sequestration
in depleted oil and gas reserves may be more cost effective than
storage in coal seams because of already existing EOR technology.
Environmental Impact
The purpose
of carbon sequestration is to reverse the negative effects of
carbon dioxide on the environment. Clearly, it would be counterproductive
if sequestering the carbon created new environmental problems.
Various types of sequestration have various environmental impacts
that need to be taken into consideration. For example, ocean
sequestration could have an effect on the pH of the water, possibly
disturbing the ecosystem of the surrounding marine life. Another
example is if a leak occurs in an underground storage site, such
as an aquifer, causing groundwater contamination with excess carbon
dioxide. Careful consideration and much research must be done
to ensure the safety of sequestration before it is put to widespread
use.
Storage Capacity
Each type
of reservoir for sequestration has a different overall capacity
that must be taken into consideration before money is spent to
develop the technologies and begin the project. If the capacity
is too small too handle a significant amount of the carbon dioxide
output it is not worth investing the time or the money in it.
One must know beforehand, however, how much carbon they want to
sequester and how big the space is they want to put it in. For
example, aquifers can store billions of tons of CO2,
while coal seams can only store millions of tons of CO2.
Each of these
factors is key in choosing a site that will be environmentally
and economically feasible. While no one storage facility offers
optimal conditions in each, but if it does not meet basic safety
and storage needs, it will not be a viable option. Within this
site, we will attempt to discuss and compare these issues for
each type of sequestration, and come to a tentative conclusion
regarding the best methods for the future of carbon dioxide sequestration.
