Geoscience Reference
In-Depth Information
the level of congestion along the route, and whether mountains, large rivers, or
frozen ground are encountered. Shipping costs are unknown in any detail,
however, because no large-scale CO
2
transport system (in millions of metric
tons of CO
2
per year, for example) is operating. Ship costs might be lower than
pipeline transport for distances greater than 1,000 kilometers and for less than
a few million metric tons of CO
2
(MtCO
2
)
11
transported per year.
12
Even though regional CO
2
pipeline networks currently operate in the
United States for enhanced EOR, developing a more expansive network for
CCS could pose numerous regulatory and economic challenges. Some of these
include questions about pipeline network requirements, economic regulation,
utility cost recovery, regulatory classification of CO
2
itself, and pipeline
safety.
13
CO
2
S
EQUESTRATION
Three main types of geological formations are being considered for carbon
sequestration: (1) depleted oil and gas reservoirs, (2) deep saline reservoirs,
and (3) unmineable coal seams. In each case, CO
2
would be injected in a
supercritical state—a relatively dense liquid—below ground into a porous rock
formation that holds or previously held fluids. When CO
2
is injected at depths
greater than 800 meters in a typical reservoir, the pressure keeps the injected
CO
2
in a supercritical state (dense like a liquid, fluid like a gas) and thus it is
less likely to migrate out of the geological formation. Injecting CO
2
into deep
geological formations uses existing technologies that have been primarily
developed and used by the oil and gas industry, and that could potentially be
adapted for long-term storage and monitoring of CO
2
. Other underground
injection applications in practice today, such as natural gas storage, deep
injection of liquid wastes, and subsurface disposal of oil-field brines, can also
provide valuable experience and information for sequestering CO
2
in
geological formations.
14
The storage capacity for CO
2
storage in geological formations is
potentially huge if all the sedimentary basins in the world are considered (see
discussion below of storage capacity estimates for the United States).
15
The
suitability of any particular site, however, depends on many factors, including
proximity to CO
2
sources and other reservoir-specific qualities like porosity,
permeability, and potential for leakage. For CCS to succeed, it is assumed that
each reservoir type would permanently store the vast majority of injected CO
2
,
keeping the gas isolated from the atmosphere in perpetuity.
