Natural Resources, 2010, 1, 1-10
doi:10.4236/nr.2010.11001 Published Online September 2010 (http://www.SciRP.org/journal/nr)
1
Sorption Characteristics of CO2 on Rocks and
Minerals in Storing CO2 Processes
Takashi Fujii1, Satomi Nakagawa1, Yoshiyuki Sato2, Hiroshi Inomata2, Toshiyuki Hashida1
1Fracture and Reliability Research Institute, Tohoku University, Sendai, Japan; 2Research Center of Supercritical Fluid technology,
Tohoku University, Sendai, Japan.
Received July 8th, 2010; revised August 18th, 2010; accepted August 31st, 2010.
ABSTRACT
As CO2 is injected into pore spaces of water-filled reservoir rocks, it displaces much of the pore fluids. In short terms
(several to tens of years), the greater part of the injected CO2 is predicted to stay as free CO2, i.e. in a CO2 rich dense
phase that may contain some water. This paper investigates the sorption characteristics for rocks (quartzose arenite,
greywacke, shale, granite and serpentine) and minerals (quartz and albite) in the CO2 rich dense phase. The measure-
ments were conducted at 50˚C and 100˚C, and pressures up to 20 MPa. Our results demonstrated that significant quan-
tities of CO2 were sorbed with all the samples. Particularly, at 50˚C and 100˚C, quartzose arenite showed largest sorp-
tion capacity among the other samples in higher pressures (>10 MPa). Furthermore, comparison with model prediction
based on the pore filling model, which assumed that CO2 acts as filling pore spaces of the rocks and minerals, sug-
gested the importance of the sorption mechanism in the CO2 geological storage in addition to the pore-filling mecha-
nism. The present results should be pointed out that the sorption characteristics may have significant and meaningful
effect on the assessment of CO2 storage capacity in geological media.
Keywords: Sorption Characteristics, Rocks, Minerals, Storing CO2 Processes, CO2 Geological Storage
1. Introduction
It is a well-established fact that the c on cen tr atio n s of CO 2
in the atmosphere have been increasing steadily and has
increased globally by about 100 ppm (36%) over the last
250 years, from a range of 275 to 285 ppm in the
pre-industrial era to 379 ppm in 2005 [1], and predictions
are that, if continuing in a business-as-usual scenario, by
the end of this century, humankind will be facing sig-
nificant climate change, which may affect human health
[2]. Thus, a major challenge in mitigating the climate
change is a deep reduction of anthropogenic CO2 emis-
sions to the atmosphere, which hopefully will lead to a
stabilization of CO2 concentration at around 550 ppm
(i.e., double of the pre-industrial level). However, the
challenge of stabilizing atmospheric CO2 levels becomes
increasingly difficult as the problem matures because
fossil fuels, which today provide about 75% of the
world’s energy, are likely to remain a major component
of the world’s energy supply for at least the next century.
In recent years, there are a number of ways by which
CO2 emissions can be reduced, among them being CO2
capture and geological storage (CCGS) technology. CCGS
technology is an enabling technology that will allow the
continued use well into this century of fossil fuels for
power generation and combustion in industrial processes
and also has the potential of the deepest cuts in anthro-
pogenic CO2 emissions from large stationary sources
(e.g., power generation, iron and steel production, ce-
ment manufacture). The technology involves the de-
ployment of a set of technologies for capturing CO2
emitted from the large stationary sources, transporting it
usually by pipeline and injecting it into geological stor-
age reservoirs, including depleted oil and gas reservoirs,
unminable coal seams, and deep saline aquifers, which is
filled with water (most commonly formation brine) into
pores spaces of reservoir rocks.
In terms of CO2 migration process in the deep saline
aquifers, if CO2 moves into, or invades a porous medium
saturated with formation brine, the latter is displaced
from some of the pore space (a process referred to as
drainage) [3], and then the injected CO2 stays in the in-
jection zone for a long time, is dissolv ed in the formation
brine, and becomes trapped by mineralization. The extent
of CO2-water-rock interaction during migration of the

Sorption Characteristics of COon Rocks and Minerals in Storing CO Processes
2 2 2
injected CO2 is the main control on the fate of the CO2.
Johnson et al. [4] has reported that reactive transport
modeling of a Sleipner-like storage reservoir, which is
the world’s first saline-aquifer CO2 storage site that the
fate and transport of injected CO2 has been successfully
monitored by seismic time-lapse surveys, suggested that
15-20% was still dissolved in the formation brine after 20
years. The remainder stayed as an immiscible condition,
i.e. in a CO2 rich dense phase that may contain little wa-
ter. Consequently, the result from this study indicates
that, through the CO2 migration process within the deep
saline aquifers, the fate of injected CO2 would be pre-
dicted to be mostly th e immiscible condition in the order
of short term storage (e.g. several years or ten years).
Many researchers have investigated about mineral
trapping processes among CO2, water, and rock in
CO2-water-rock system [5-9]. However, interactions
among CO2 and rock that simulates the CO2 rich dense
phase have only been conducted by Lin et al. [10].
Up to now, gas sorption isotherm experiments in
CO2/rock or CO2/water/rock systems have been con-
ducted using shale at 45-50˚C and pressures up to 20
MPa [11] and sandstone and granite at 33-200˚C, and
pressures up to 20 MPa [12-14]. Fujii et al. [13,14] indi-
cates that at high pressures (> 10MPa), the amount of
CO2 sorbed by granite is co mparable to that by sandstone,
but the sorption mechanisms and processes for sandstone,
shale, and granite has not been elucidated. Therefore,
knowledge of CO2 sorption characteristics for various
rocks will be required for the screening and assessment
of suitable CO2 storage sites for sequestration of CO2 in
geological reservoirs. Thus, for this comparison, in addi-
tion to the rock samples reported in the previous litera-
tures, we included samples from other types of rocks
(e.g., sedimentary rock, volcanic rock, metamorphic rock)
in this experiment. Additionally, to better understand the
mechanisms related to sorption of CO2 on rocks, CO
2
sorption measurements for silica and silicate minerals,
which are main component of reservoir rocks, were also
conducted.
The purpose of this study is to evaluate sorption char-
acteristics of CO2 for rocks (sedimentary rocks, meta-
morphic rocks, and volcanic rocks) and minerals (silica
and silicate minerals) in the CO2 rich dense phase at
geological-relevant temperatures and pressures.
2. Experimental
2.1. Samples and Preparation
Samples from five different blocks of rocks (quartzose
arenite, greywacke, shale, granite, and serpentine) were
used in the experiments. Quartzose arenite and grey-
wacke are well known as quartz-rich sandstone and feld-
spar-rich sandstone, respectively. In this study, Berea
sandstone (from Ohio, USA) and Kimachi sandstone
(from Shishido-cho, Shimane, Japan) were chosen as the
representation of quartzose arenite and greywacke, re-
spectively.
Berea sandstone composition was determined by point
counting (500 points) under a polarizing microscope
(OLYMPUS, A6400BX). Berea sandstone consisted
mainly of quartz (= 90.7 vo l. %), and the observation was
in agreement with the results of Wang and Nur (1989).
Kimachi sandstone consisted mainly of plagioclase (=
89.9 vol. %) [15]. A sample of shale was obtained from
Tedori-group, Niigata, Japan. A sample of granite was
obtained from Iidate, Fukushima, Japan. The granite
consisted mainly of quartz (= 37.1 vol. %), plagioclase (=
34.0 vol. %) and K-f eldspar (= 21.8 vol. %) [15]. A sam-
ple of serpentine was obtained from Okaya, Nagano,
Japan. Examination of the serpentine using X-ray dif-
fraction verified the abundance of chryso tile and lizardite.
Additionally, natural single crystals of quartz (from Alto
de Cruzes Santander, Colombia) and albite (from Kotaki,
Itoigawa, Niigata, Japan) were used in the experiment.
These rock and mineral specimens were shown in Figure
1. The American Society for Testing and Materials
(ASTM) procedure [16] was used to determine density
and porosity of the samples based on the fundamental
Archimedes principle. Specific surface areas were deter-
mined by low-pressure nitrogen sorption measurements
using the Brunauer-Emmett-Teller (BET) method [17].
The nitrogen sorption measurements were performed at
77 K using a Quantachrome NOVA 2000 series auto-
mated volumetric instrument. Prior to each analysis, the
samples were degassed at 105˚C under vacuum. The ob-
tained values were listed in Table 1.
Core specimens of Berea sandstone, Kimachi sand-
stone, and Iidate granite were cored from these blocks
with a thin-wall diamond bits and were cut with a dia-
mond saw. All cores were drilled perpendicular to the
bedding plane. These core specimens were each about 16
mm in diameter and about 10 mm in length. The speci-
men of shale was broken into angular fragments ap-
proximately 5 to 10 mm in largest dimension. The
specimen of serpentine was cut into approximately 10 × 10
mm2 in cross-section and 15 mm in length. The speci-
mens of quartz and albite with dimensions of 65 × 20
mm3 and 10 × 10 × 10 mm3, respectively, were prepared
from each natural single crystals.
These cut specimens were washed with distilled water
and were dried under vacuum in an oven for at least 24
hours at 105˚C using a rotary vacuum pump.

Sorption Characteristics of CO2 on Rocks and Minerals in Storing CO2 Processes
3
5 mm 5 mm 5 mm
(a) (b) (c)
5 mm
5 mm
(d) (e)
5 mm 5 mm
(f) (g)
Figure 1. Photographs of rock and mineral specimens tested in the experiment. (a) Berea sandstone; (b) Kimachi sandstone;
(c) Shale; (d) Serpentine; (e) Granite; (f) Quartz; (g) Albite.
Table 1. Rocks and minerals properties for CO2 sorption measurement.
Materials Specific surface area (m2/g) Bulk density (g/cm3) Porosity (vol. %)
Kimachi sandstone 2.80 2.51 20.0
Berea sandstone 0.84 2.11 19.0
Granite - 2.62 1.1
Shale 0.65 2.60 3.4
Serpentine - 2.51 4.9
Quartz - 2.60 < 0.1
Albite - 2.60 0.9

Sorption Characteristics of COon Rocks and Minerals in Storing CO Processes
4 2 2
2.2. Apparatus and Procedure
The magnetic suspension balance (MSB) from Rubotherm
Präzisionsmesstechnik GmbH [18] rated at 350˚C and 35
MPa was used to measure the CO2 sorption capacity of
rocks and minerals, as illustrated in Figure 2. The MSB
consisted of a sorption chamber that was used to expose
the sample to CO2 at elevated temperatures and pressures,
and microbalance, which was isolated from the sample
and existed at ambient conditions. All of the details for
the MSB and its operational procedures have been de-
scribed in previous literatures by Sato et al. [19] and
Blasig et al. [20]. A schematic of the experimental appa-
ratus was shown in Figure 3. The experimental apparatus
consisted of a high CO2 pressure supply system, which
was used to pressurize CO2 up to 20 MPa, a data acquisi-
tion system and a MSB system.
In the experiment, the sorption measurements were
performed at 50˚C and 100˚C, and pressures up to 20
MPa.
In a typical experiment, a sample was weighed and
placed in a sample basket suspended by a permanent
magnet through an electromagnet, as shown in Figure 2.
After closing the sorption chamber, the sample was de-
gassed by evacuating the sorption chamber at elevated
temperatures until the weight measured by the microbal-
ance remained unchanged over time. A heating circulator
(Julabo, model F25) was used to control the temperature
of the chamber, which was measured with a calibrated
platinum resistance thermometer to an accuracy of ± 0.05
Figure 2. Principle of the magnetic suspension balance
(MSB).
Figure 3. Schematic diagram of the experimental apparatus for CO2 sorption measurement by using the MSB system (source:
ato et al. [19]). S

Sorption Characteristics of COon Rocks and Minerals in Storing CO Processes 5
2 2

K. The sample weight, read from the microbalance under
vacuum and at temperature T, was record ed as w (vac, T)
prior to CO2 injection into the sorption chamber.
CO2 was introduced into the sorption chamber by the
following way. A t low pr essure up to 5 MPa, the so rp tion
chamber was flooded with CO2 from a gas cylinder and
the pressure was controlled by a regulator. Whereas, at
the pressures above 5 MPa, CO2 was introduced by
passing through a high-performance liquid chromatog-
raphy (HPLC) pu mp (Jasco 880PU). CO2 pressure inside
the sorption chamber was measured by using Paroscien-
tific pressure transducer (46KR, 41.4 MPa F.S., accuracy
0.01% F.S.).
The change in the mass of the sample as well as the
temperature and pressure were measured continuously
until the thermodynamic equilibrium was reached.
Eventually, an equilibrium sorption was reached, that is,
the mass of the sample stopped increasing. The equilib-
rium sorption was achieved in about 90 minutes at every
pressure steps. At this final saturation stage, the weight
reading from the microbalance at pressure P and tem-
perature T was recorded as w (P, T).
The mass of the sorbed CO2 on the rock and mineral
samples was calculated based on the consideration of a
buoyancy of instruments, which was housed in the sorp-
tion chamber, at different gas pressures and different
densities as shown in the Equation (1).
Where ng
ex (P, T) was CO2 sorbed amount on the sample
and was termed excess CO2 sorption capacity. ρCO2 (P, T)
was CO2 phase density at P and T. mCO2 was the molecular
weight. Vr and Vb were the volumes of the sample and of
the sample basket, respectively. The last term of the above
equation, ρCO2 (P, T)･(Vb + Vr) represented the buoyancy
force caused by the compress ed gas, which lifted the sam-
ple and sample basket. CO2 phase density, ρCO2 (P, T), was
calculated from the Wagner EOS [21].
The volume of the sample basket, Vb, was determined
using Equation (2) from a buoyancy experiment, that is,
the MSB experiment was performed without a sample in
the sample basket at the experimental temperature and
pressure.
  
2
,,
b
VwvacTwPT PT   ,
CO
(2)
The result obtained from the buoyancy experiment in-
dicated that, at 50˚C and 100˚C, the values of the sample
basket were constant within limited pressure ranges (~20
MPa) and were 1.69 cm3 at 50 ˚C and 1.71 cm3 at 100˚C,
respectively. The volume of the sample, Vr, was calcu-
lated from mass and density of the sample.
After the experiment, the samples were reweighed un-
der vacuum con dition in the sorption chamber.
3. Results and Discussion
The excess sorption data of CO2 obtained on the five
rock samples (Berea sandstone, Kimachi sandstone, ser-
pentine, shale, granite) and the two mineral samples
(quartz and albite) are shown in Figure 4 under the pres-
sures up to 20 MPa at 50˚C in Figure 4(a) and 100˚C in
Figure 4(b), respectively.
The excess sorption data are shown on a sample vol-
ume basis in Figure 4. It has been shown that shale [11]
and sandstone and granite [12-14] have a certain degree
of sorption capacities for CO2 under air-dry conditions.
The experimental data obtained in this study confirm the
results of the previous literatures. Figure 4 reveals that
the Berea sandstone samples show significantly larger
weight changes compared with the other types of rocks,
in particular with the Kimachi sandstone samples. The
maximum sorption capacity of Berea sandstone for CO2
exhibits 3.7 mmol/cm3 (= 82.9 cm3 STP/cm3) at 50˚C and
20 MPa and 2.8 mmol/cm3 (= 62.7 cm
3 STP/cm3) at
100˚C and 20 MPa, respectively. It should be mentioned
here that the pore volume of Berea sandstone (porosity:

17.9 vol.%) is slightly smaller than that of Kimachi
sandstone (porosity:

20.0 vol. %). As mentioned in the
section of Experimental, B.E.T. tests were carried out to
evaluate the specific surface area of the rock samples
using N2 sorption isotherms. Valid experimental data for
specific surface area were obtained only for Berea sand-
stone, Kimachi sandstone, and shale, which showed no
dependence of the sample sizes used for the B.E.T. tests.
In contrast, the other types of rocks exhibited specific
surface areas which varied with the sample size used. In
view of the B.E.T. results, the excess sorption data per
unit surface area are given only for Berea sandstone,
Kimachi sandstone, and shale in Figures 5(a) and 5(b). It
is apparent that Berea sandstone outperforms Kimachi
sandstone and shale in the CO2 sorption capacity.
Coal studies on sorption revealed that maximum ex-
cess CO2 sorption values were approximately 2.0 mmol/g
for various coal samples on dry basis at around 50˚C
[22-24]. Based on CO2 gravimetric capacity for the rock
and mineral samples, at 50˚C, maximum CO2 excess
sorption values were approximately 1.8 and 0.5 mmol/g
for Berea sandstone and the other rock and mineral sam-
ples, respectively. It can, therefore, be said that Berea
sandstone exhibits comparable capacity as coals and has
a significantly sorption capacity.
  

2
,,,,
ex
2
g
COb rCO
nPTwPT wvacTPTVVm    (1)

Sorption Characteristics of COon Rocks and Minerals in Storing CO Processes
6 2 2
(a) (b)
Figure 4. Gravimetric CO2 excess sorption uptake per unit volume for rocks and minerals under air-dry condition in
CO2/rock or CO2/mineral systems: (a) at 50˚C and (b) at 100˚C.
(a) (b)
Figure 5. Gravimetric CO2 excess sorption uptake per unit surface area for rocks and minerals under air-dry condition in
CO2/rock or CO2/mineral systems: (a) at 50˚C and (b) at 100˚C.
It is also shown in Figure 4 that the two mineral sam-
ples (quartz and albite) are capable of sorbing CO2 in the
CO2 rich dense phase. Both quartz and albite is a com-
mon and fundamental constitutes of most types of rocks.
The above result for the quartz and albite samples sug-
gests that the CO2 sorption capacity of the rocks tested in
this study can be attributed to the sorption of CO2 onto
silica and silicate minerals.
It is shown in Figure 4(a) that the sorption isotherms
at 50˚C exhibit a rapid increase in the excess CO2 sorp-
tion for more or less all the rocks and minerals tested,
even though the increasing trend is unclear except for
Berea sandstone. The rapid increase in the excess CO2
sorption takes place when the pressure exceeds the criti-
cal point of CO2 (31.0˚C, 7.38 MPa) for 50˚C. In contrast,
the results for 100 ˚C show a nearly lin ear increase trend
with increasing pressure for the majority of the rock s and
minerals. It is interesting to note that the results may
correlate with the pressure dependence of CO2 density. In
fact, the CO2 density shows a sharp jump at the critical
point of CO2 for 50˚C, whereas an approximately linear
increase is observed for 100˚C [21].
The amount of CO2 sorbed at 50˚C decreases with in-
creasing pressure in the higher pressure range (> 10
MPa), except for Berea sandstone. This trend is in
agreement with the result reported by Romanov et al.
[22], who have shown for coal samples th at at high pres-
sures above 10 MPa, the amount of CO2 sorbed reduced
as increasing pressure.
The decreasing trend of the sorption isotherms for
50˚C in the high pressures may be due to the buoyancy
force acting on the volume of sorbed CO2 phase. The
sorbed CO2 phase may alter the buoyancy of the sample
in the ambient CO2 pressures and temperatures during

Sorption Characteristics of COon Rocks and Minerals in Storing CO Processes 7
2 2
the experiment, in addition to the volume of the sample,
Vr, the sample basket, Vb, and the other measurement
instrument. However, the calculation of the excess CO2
sorption capacity based on Equation (1) ignores the
buoyancy effect of the volume of the sorbed CO2 phase,
thus introd ucing error. Therefore, the error caused by the
above-mentioned buoyancy force would be larger at the
high pressure range (above the critical pressure) than the
low pressure region (~5 MPa) because the CO2 density
and the sorbed phase volume usually increases as the
CO2 pressure increases. The observation suggests that the
buoyancy effect may cause the reduction in the excess
sorption for the high pressure range.
The amount of sorbed CO2 for Berea sandstone, how-
ever, showed a monotonous increase with increasing CO2
pressure, even in the higher pressure range. The com-
parison suggests th at the so rption mechanism may form a
denser CO2 sorbed phase in the case of Berea sandstone.
The reason for this is unclear and requires further inves-
tigation.
As shown in Figure 4(b), the sorption capacity for
100˚C is lower compared with the results for 50˚C and
shows an approximately linear increase up to 20 MPa,
except for Kimachi sandstone.
In contrast, no decreasing trend in the excess sorption
is observed for 100˚C. Reason for this may be attributed
to the decrease of the buoyancy force due to the tem-
perature increase. The buoyancy force associated with
sorbed phase volumes was mainly determined by the
density of CO2 phas e and CO2 sorbed phase, and the CO2
sorption amount. The value of CO2 density calculated by
the Span and Wagner EOS [21] for 100˚C and 20 MPa is
shown to be approximately half as much as that at 50˚C.
In addition, the sorbed phase density predicted by
Dubinin (1965) [25] decreases with increasing tempera-
ture. These results indicates that the buoyancy effect for
100˚C is smaller that than for 50˚C. Consequently, the
error induced by the buoyancy effect for 100˚C may be
smaller than that for 50˚C.
Sorption and desorption isotherms are shown for Berea
sandstone and serpentine at 50˚C in Figure 6. The de-
sorption isoth erms coincide appro ximately with the sorp-
tion data. Furthermore, weight measurements for the
samples have shown almost no change after the CO2
sorption experiment. These results indicate the reversible
nature of CO2 sorption-desorption process at 50˚C. The
same trend has been observed for 100˚C.
4. Comparison with Prediction Value Based
on Pore-Filling Model
Based on the above discussion, the experimental excess
sorption data are corrected for the buoyancy force for the
sorbed phase volume using the following equation [26]:
(a)
(b)
Figure 6. Excess sorption and desorption isotherms of CO2
at 50˚C for (a) Berea sandstone and (b) Serpentine under
air dry condition in CO2/rock system.

2,
cex a
gg
aCO
nn PT










(3)
where ncg is the CO2 sorption capacity corrected for the
buoyancy effect, nexg is the sorbed amount without cor-
rection (as measured by the MSB method), ρCO2(P,T) is
the CO2 density of the gas phase, and ρa is the CO2 den-
sity of the sorbed pha se. In this study, we used th e sorb ed
phase density, ρa, calculated by Dubinin-Nikolaev for-
mulation [25]. The value of ρa is usually assumed to be
constant over the entire pressure range at temperatures
above the critical temperature (31.1˚C). The calculated
values of ρa at 50 ˚C and 100 ˚C were 0.994 g/cm3 and
0.912 g/cm3, respectively. The CO2 phase density, ρCO2
(P, T), was calculated from Span and Wagner EOS [21].
The data for the corrected sorption amount are shown in
Figures 7 and 8. In addition to the corrected CO2 sorption

Sorption Characteristics of CO2 on Rocks and Minerals in Storing CO2 Processes
8
(a) (b)
(c) (d)
(e)
Figure 7. Comparison of the predicted values based on the pore-filling model, with corrected sorption capacity,
considering CO2 sorbed phase density for three sedimentary rocks (Berea sandstone, Kimachi sandstone, and
shale), one ultramafic rock (serpentine) and one volcanic rock (granite) at 50˚C and 100˚C. The solid and dashed
lines represent the corrected experimental data and the calculated data, respectively. ( ) is the porosity of rock
specimens. (a) Berea sandstone (

19.0); (b) Kimachi sa ndstone (

20.0); (c) Serpentine (

4.9); (d) Shale (

3.4);
(e) Granite (

1.1).

Sorption Characteristics of COon Rocks and Minerals in Storing CO Processes 9
2 2
(a) (b)
Figure 8. Comparison of the predicted values based on the pore-filling model, with corrected sorption capacity, considering
CO2 sorbed phase density for quartz and albite at 50˚C and 100˚C. The solid and dashed lines represent the corrected ex-
perimental data and the calculated data, respectively. ( ) is the porosity of mineral specimens. (a) Quartz (

0.1); (b) Albite
(

0.9).
data, the results predicted from the pore-filling model are
plotted in these figures. The pore-filling model assumes
that the CO2 storag e capacity of the rock mass is equal to
the amount of CO2 used to fill the pore volume in the
rock, which is given by the following equation:
2
pore fillingrockCOCO
nm
2


 (4)
where

rock is the porosity of the rock sample, and mCO2
is the molecular weight of CO2. It is seen that the sorp-
tion capacity corrected for the buoyancy effect shows a
steady increase with respect to pressure at the higher
pressure regime, except for the data of the granite and
albite at 50˚C. The reason for th is r esult pr obably may be
due to the error in estimating the sorbed phase density,
and needs to be further investigated in the future. In the
lower pressure range (< 5 MPa), the corrected sorption
capacity appears to give a value close to that computed
based on the pore-filling model. It is demonstrated that
the corrected sorption capacity is significantly higher
than the model predicted data for the rocks and minerals,
except for Kimachi sandstone. For Kimachi sandstone,
the corrected result is relatively close to the model pre-
dicted data over the entire pressure range. For example,
the corrected sorption capacity is shown to be approxi-
mately 5 times higher than the model prediction in the
case of Berea sandstone, and about 10 times higher for
the granite. The comparison may suggest the importance
of the sorption mechanism in the CO2 geological storage
in addition to the pore-filling mechanism. The sorption
process may provide an additional CO2 storage mecha-
nism and contribute to the significant part of the CO2
storage capacity of a rock mass. The effect of water and
salinity on the CO2 sorption capacity is now under inves-
tigation.
5. Conclusions
This paper presents the CO2 sorption capacities of the
five rock samples (Berea sandstone, Kimachi sandstone,
shale, serpentine and granite) and the two mineral sam-
ples (quartz and albite), measured at 50˚C and 100˚C,
and under pressures up to 20 MPa in CO2-rock or
CO2-mineral systems that simulate the CO2 rich dense
phase. The CO2 sorption capacities have been determined
by a gravimetric method and corrected for the buoyancy
effect. In higher pressure region (> 10 MPa), Berea sand-
stone has shown a significantly higher CO2 sorption ca-
pacity compared to the other rocks and minerals at both
50˚C and 100˚C and exhibited a maximum sorption ca-
pacity of 3.7 mmol/cm3（= 82.9 cm3 STP/cm3）at 50 ˚C
and 20 MPa and 2.8 mmol/cm3 (= 62.7 cm3 STP/cm3) at
100˚C and 20 MPa. Thus, arkosic sandstone such as
Berea sandstone may provide a significant potential for
CO2 geological sequestration for a suitable reservoir rock.
It is also shown that the major constituent minerals for
the rocks tested in this study (quartz and albite) have a
CO2 sorption behavior.
It has been demonstrated that the CO2 sorption capac-
ity measured in this stud y is significantly h igher than that
predicted by the pore-filling model for the rocks and
minerals. The comparison suggests that the CO2 sorption
characteristic may provide an importan t mechanism in th e
assessment of CO2 storage capacity in geological media.
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