Different Types of Geological Formations
Underground storage of carbon dioxide in geological formations
is a viable sequestration option. It is not widely known that
underground storage has been occurring on a large scale for over
thirty years. Tens of millions of tons CO2 have already
been stored below the surface of the Earth. Collectively, there
is the possibility to store thousands of gigatons underground.
Using geological storage alone, it is predicted that there is
enough storage space to last through the fossil fuel age, which
may be hundreds or thousands of years from ending.
There are several
different types of geological formations that all provide different
advantages and drawbacks:
Aquifer storage is considered the most promising
storage possibility because of its tremendous magnitude. However,
because of the lack of data relating to the size and shape of
specific aquifers, it is difficult to predict the security, integrity,
and storage capacity of an individual site. Nevertheless, aquifers
have been proven a viable storage facility, and a large-scale
aquifer project has been underway in Norway since 1996.
Depleted Oil and Gas Reservoirs
do not have the storage capacity of aquifers, but most do have
data relating to their shape and size. Security is also not a
major issue, considering oil or natural gas had been stored in
the reservoir without leakage for millions of years prior to their
exploitation. Another advantage is that oil/gas reservoir sequestration
is considered a "value added" process; oil and small amounts of
natural gas can be recovered with the aid of CO2. The
process of using carbon dioxide to improve oil production is called
enhanced oil recovery (EOR), and has been a successful technique
in the oil business since the 1970s.
Coal Beds are another value added process. Injection
of carbon dioxide into coal beds causes methane desorption from
the surface and pores of coal and carbon dioxide adsorption in
its place. Coal bed sequestration can actually occur at a profit
when natural gas prices are high. In addition, coal beds are usually
located near high emissions sites, minimizing the cost of transportation.
Sequestration in coal beds is an attractive option, but unfortunately
there is not enough storage capacity to be able to stand on its
own as a long-term solution.
