568
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proper strategies and technologies for storing CO
2
in
geologic formations must be determined with deep
consideration of the geological conditions of the potential sites.
Geological conditions (e.g., the pressure, geothermal gradient,
geology, geochemical characteristics, and mineralogy) govern
the interpretation of the geophysical responses of CO
2
-storage
reservoirs. Therefore, a fundamental understanding of the
geophysical responses of CO
2
-containing sediments in Korean
sedimentary basins is required. However, while a few studies
have been conducted on numerical reservoir modeling, there
have been few efforts to examine the geological suitability for
CO
2
storage and on geophysical characterizations of Korean
sedimentary basins to date.
This study provides a review and discussion of the
geological conditions and suitability of the potential CO
2
storage sites in Korea as well as CO
2
storage sites around the
world. Moreover, laboratory experiment results on the P-wave
velocity and the electrical responses of CO
2
-injected sediments
are presented, in which high
in-situ
effective stress conditions
were simulated on natural samples cored from the eastern
Bukpyeong basin, which is one of the candidate sites for
geologic CO
2
storage.
2 SITE CHARACTERIZATION FOR CO
2
SEQUESTRATION
2.1
Site-dependent strategies
CO
2
can be stored in various geological formations, such as
(1) deep saline formations, (2) coal beds, (3) depleted oil and
gas fields, and (4) oil and gas reservoirs during enhanced oil and
gas recovery efforts (EOR and EGR). Coal beds absorb and
contain gaseous CO
2
in micro-pores in coal. However, the
temperature and pressure effects on the CO
2
trapping process in
coals are not well understood (Larsen, 2003). CO
2
storage in
depleted oil and gas fields or the use of CO
2
for EOR (or EGR)
have been proven as effective GCS methods due to the
geological suitability for CO
2
storage, the existence of
geophysical and geological data, and the ready-made
infrastructure used for oil and gas production. However, several
problems remain poorly identified, including well plugging,
leakage induced by the overpressure of pore fluids, and the
injection depth. Deep saline formation is the most promising
method for safe and effective CO
2
storage due to its vast
capacity. The potential storage capacity of deep saline
formation is expected to be at least 1000 GtCO
2
, which is
approximately 200 to 300 times higher than the potential
storage offered by oil or gas fields and coal seams (IPCC,
2005). In particular, sedimentary basins that have permeable
formations (e.g., sandstone) with overlying low-permeable seals
(caprocks) are effective for both CO
2
injection and CO
2
leakage
prevention. The target depth is deeper than 1000 meters below
the ground surface.
2.2
Selected sites for CO
2
sequestration in America, Europe,
and Asia
There are more than 800 sedimentary basins around the
world (St John et al., 1984). Approximately 40 CO
2
storage
projects are under operation or in planning in North America,
Europe, Australia, and Asia. Among them, ten onshore projects
in the USA and two onshore projects in Canada are being
conducted. Two onshore projects and three offshore projects in
Europe are being undertaken, and two demo onshore projects in
Japan are being tested (Hosa et al., 2010). Additionally, other
potential sedimentary basins have been investigated and
proposed for pilot-scale testing. For instance, the Alberta basin
in Canada, where natural hydrocarbon resources had been
found, was evaluated to be the most suitable basin in Canada
owing to the existence of adjacent infrastructure (Bachu, 2003).
The offshore Gippsland basin in Australia is considered as an
effective target for CO
2
storage due to its complex stratigraphy,
high injectivity, low-permeable marginal reservoir, the
existence of several depleted oil fields, and its long migration
pathways (Gibson-Poole et al., 2008). In China, an ECBM
(enhanced coalbed methane recovery) pilot test and a single-
well micro-pilot test were successfully performed at the South
Qinshui basin (Wong et al., 2010).
One of the most well-known CO
2
storage attempts is the
Sleipner project, targeting the Utsira Sand formation, which was
launched in 1996. It was the first commercial-scale project to
store CO
2
in a saline formation. The geologic condition of this
site is a brine-saturated sandstone layer (250 m thick) with an
overlying thin shale cap layer. Its storage capacity is expected to
be 25 MtCO
2
(Hosa et al., 2010). The Nagaoka project at
Nagaoka City, Japan, was the first pilot-scale attempt in Asia. In
this pilot-scale test, CO
2
was injected into a Haizume-formation
sandstone layer. The injection efficiency differs between the
two formations (e.g., the Utsira Sand formation and the
Haizume formation). In detail, the Utsira Sand formation (2800
tons/day) has a storage capacity of approximately 70 times that
of the Haizume formation (a maximum 40 tons/day), as the
permeability of the Haizume formation (i.e., 6 mD) is much
lower than that of the Utsira Sand formation (i.e., 5 D) (Hosa et
al., 2010) though both formations have relatively high porosities
(37% for the Utsira formation and 22.5% for the Haizume
formation) and similar injection depths (about 1000
‒
1100 m).
Therefore, it can be tentatively concluded that the permeability
is a major controlling parameter for CO
2
injectivity rather than
the porosity or injection depth.
2.3
Geologic characteristics of sedimentary basins in Korea
There are several potential geologic formations for GCS on
the Korean Peninsula. The porosity, storage capacity, and
geologic characteristics of those proposed sites are listed in
Table 1. However, the geological information of offshore basins
is still poorly identified due to insufficient exploration.
Table 1. Porosity and storage capacity of potential Korean geological
storage sites
1
The values are from Kim et al. (2011) and
2
MEST (2008).
Korean offshore sedimentary basins have thickness ranges
from 3 km to 10 km (MEST, 2008). The vast coverage area and
high porosity of Korean offshore sedimentary basins are
expected to show that these have larger storage capacities than
onshore basins. Moreover, Korean offshore sedimentary basins
show geologically structural similarity with natural hydrocarbon
reservoirs, which indicates good suitability for GCS. For an
example, the Gunsan basin and the Jeju basin show high
potential for GCS because the geologic structures are similar to
natural hydrocarbon reservoirs in analogous Chinese basins
(Hong et al., 2005). The Ulleung basin contains natural gas
deposits and is located more than 1000 m below the sea level.
Thus, structural trapping may be feasible (Hong et al., 2005).
To evaluate the storage and economic efficiencies of
sedimentary basins in Korea, a systematic and quantitative
evaluation method (Bachu 2003) was employed in this study.
Fifteen criteria (e.g., geological characteristics, basin resources,
maturity, and infrastructure, among others) are considered with
weight factors to assess the suitability (Table 2). Bachu’s (2003)
method classifies the proposed sites with dimensionless values
between 0 and 1. The value can be used as a decision criterion
Basin
Porosity
(%)
Storage Capacity
(Mton)
Geologic
Characterstics
Bukpyeong
N.A.
877
1
Saline aquifer
Ulleung
10.6
2
3,018
2
EGR
Jeju
15.7
2
95,101
2
Saline aquifer
Gunsan
10
2
254
2
Saline aquifer
Heuksan
N.A.
N.A.
Saline aquifer
Pohang
N.A.
38
2
Saline aquifer
