Geoscience Reference
In-Depth Information
Advantages and Disadvantages
Unmineable coal seam injection projects would need to assess several
factors in addition to the potential for CBM extraction. These include depth,
permeability, coal bed geometry (a few thick seams, not several thin seams),
lateral continuity and vertical isolation (less potential for upward leakage), and
other considerations. Once CO
2
is injected into a coal seam, it would likely
remain there unless the seam is depressurized or the coal is mined. Many
unmineable coal seams in the United States are located relatively near
electricity-generating facilities, which could reduce the distance and cost of
transporting CO
2
from large point sources to storage sites.
Not all types of coal beds are suitable for CBM extraction. Without the
coal-bed methane resource, the sequestration process would be less
economically attractive. However, the displaced methane would need to be
combusted or captured because methane itself is a more potent greenhouse gas
than CO
2
. Once burned, methane produces mostly CO
2
and water.
Without ongoing commercial experience, storing CO
2
in coal seams has
significant uncertainties compared to the other two types of geological storage
discussed. According to IPCC, unmineable coal seams have the smallest
potential capacity for storing CO
2
globally compared to oil and gas fields or
deep saline formations. The latest assessment from DOE also indicates that
unmineable coal seams in the United States have less potential capacity than
U.S. oil and gas fields for storing CO
2
. (See following discussion.) No
commercial CO
2
injection and sequestration projects in coal beds are currently
underway in the United States.
G
EOLOGICAL
S
TORAGE
C
APACITY FOR
CO
2
IN THE
U
NITED
S
TATES
As
Figure 1
indicates, geologic basins containing at least one of each of
these three types of potential CO
2
reservoirs occur across most of the United
States, in relative proximity to many large point sources of CO
2
, such as fossil
fuel power plants or cement plants. The DOE Regional Sequestration
Partnership Program has produced estimates of the potential storage capacity
for each of these types of reservoirs and published the estimates in a Carbon
Sequestration Atlas. The 2010 Carbon Sequestration Atlas (third edition)
updates the 2008 version (second edition), and a summary of the storage
estimates for both editions is compared in
Table 2
.
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