in January 2012, and the Big Sky Carbon
Sequestration Partnership (BSCP) in the
northwest United States near Wallula, Wash-
ington, where injection started in July 2013
(8, 9). A major difference between these two
projects is the method through which the
CO2 is injected. In the BSCP project, pure
CO2 is injected as a separate buoyant phase
into a porous basaltic layer at more than
800-m depth; it is anticipated that the pres-
ence of an impermeable layer will keep the
CO2 from escaping back to the surface. In
the CarbFix project, CO2 is released as small
bubbles at 350-m depth into down-flowing
water within the injection well. The CO2
bubbles dissolve in the water before it enters
the rock. Once dissolved in water, CO2 is no
longer buoyant, and the CO2-charged water
accelerates metal release from basalt and
formation of solid carbonate minerals. Once
stored as a mineral, the CO2 is immobilized
for geological time scales. More than 80% of
CO2 injected into the CarbFix injection site
was carbonated within a year at 20° to 50°C
and 500- to 800-m depth [(10, 11); see the
figure, panel B]. This result suggests that the
CarbFix method can change the time scale
of mineral carbon trapping considerably.
The CarbFix method requires substantial
water; only 5% of the injected mass is CO2.
Porous basalts near the continental margins have huge storage capacities adjacent
to nearly unlimited supplies of seawater.
On the continents, the water present in the
target storage formation can be pumped up
and used to dissolve CO2 during the injection. Although the pumping of water from
the subsurface may increase costs, water
pumping is also necessary during the later
stages of pure CO2 injection into sedimentary basins, when a large portion of the pore
space has been filled with CO2.
A major challenge to all carbon capture
and storage projects is the cost. The esti-
mated cost of storing and transporting a
ton of CO2 at maximum reservoir exploita-
tion at the CarbFix site via dissolved water
injection is about $17 (12); this cost is about
twice that of geologic storage via direct
CO2 injection at the BSCP site and in typi-
cal sedimentary basins (9, 12, 13), but offers
enhanced security because CO2 dissolved in
water is not buoyant. However, the cost of
carbon capture and storage is dominated by
capture and gas separation, which costs $55
to $112/ton CO2 (13). In contrast, the cur-
rent price for a ton of CO2 emission at the
European Union Emission Trading Scheme,
the world’s largest carbon market, is about
$7/ton CO2. Until either market forces or
taxes result in a higher price on carbon emis-
sion, there is no financial incentive for car-
bon capture and storage using any of these
Carbon storage via basaltic rock carbonation is still in its infancy, but if it can
be scaled up, it may provide a more secure
alternative to the injection of pure CO2 into
sedimentary basins. Natural analogs have
shown that up to 70 kg of CO2 can be stored
in a cubic meter of basaltic rock (14). This
means that the storage potential of all the
ocean ridges is an order of magnitude larger
than the estimated CO2 emissions stemming from burning all fossil fuel resources
on Earth. How much of this storage potential will be of practical use in the future may
depend more on political will and economic
realities than on scientific efforts.
References and Notes
1. D. Archer, J. Geophys. Res. 110, C09S05 (2005).
2. S. M. V. Gilfillan et al., Nature 458, 614 (2009).
3. T. Schaef, B. P. McGrail, A. T. Owen, Int. J. Greenh. Gas
Control 4, 249 (2010).
4. S. R. Gislason et al., Int. J. Greenh. Gas Control 4, 537
5. R. J. Rosenbauer, B. Thomas, J. L. Bischoff, J. Palandri,
Geochim. Cosmochim. Acta 89, 116 (2012).
6. D. S. Goldberg, T. Takahashi, A. L. Slagle, Proc. Natl.
Acad. Sci. U.S.A. 105, 9920 (2008).
7. E. S. Aradóttir, E. Sonnenthal, G. Bjornsson, H. Jonsson,
Int. J. Greenh. Gas Control 9, 24 (2012).
8. B. P. McGrail, F. A. Spane, E. C. Sullivan, D. H. Bacon, G.
Hund, Energy Procedia 4, 5653 (2011).
9. B. P. McGrail et al., Int. J. Greenh. Gas Control 9, 91
10. S. R. Gislason et al., Min. Mag. (Lond.) 77, 1178 (2013).
11. J. M. Matter et al., American Geophysical Union Fall
Meeting, abstract V41A-2753 (2013).
12. E. Ragnheidardottir, H. Sigurdardottir, H. Kristjansdottir,
W. Harvey, Int. J. Greenh. Gas Control 5, 1065 (2011).
13. Global CCS Institute, Economic Assessment of Carbon
Capture and Storage Technologies: 2011 Update; see
14. F. Wiese, Th. Fridriksson, H. Ármannsson, Tech. Rep.,
ÍSOR-2008/003, Iceland Geosurvey, www.os.is/gogn/
15. S. Benson et al., in IPCC Special Report on Carbon
Dioxide Capture and Storage, B. Metz, O. Davidson, H.
Coninck, M. Loos, L. Meyer, Eds. (Cambridge Univ. Press,
New York, 2005), pp. 195–276.
Acknowledgments: The authors are grateful for these
grants: FP7-ENERGY-2011-1-283148 CarbFix, I TN-FP7-PEO-
PLE-2012-ITN-317235-CO2-REACT, 11029-NORDICCS, and
GEORG. S. R. G. is the chairman and E. H.O. a member of the
Scientific Steering Committee of CarbFix.
C02 gas bubbles Basaltic rock
Carbon storage in sedimentary basins and basaltic rocks. (A) Carbon storage in sedimentary basins proceeds via the injection of pure CO2 into porous sedimentary rocks. Ideally this CO2 is trapped below an impermeable cap rock. Eventually some of this CO2 becomes stuck in small pores, limiting its mobility (structural
and residual trapping) ( 15). Over time, CO2 dissolves in the formation water (solubility trapping). Some of this
dissolved CO2 reacts to form stable carbonate minerals (mineral trapping). As one progresses from structural
to mineral trapping, the CO2 becomes more immobile and thus the storage more secure, though this process
can take thousands of years or more (15). (B) In the CarbFix method, CO2 is dissolved into water during its
injection into porous basaltic rocks. No cap rock is required because the dissolved CO2 is not buoyant and
does not migrate back to the surface. Solubility trapping occurs immediately, and the bulk of the carbon is
trapped in minerals within 1 year (10, 11).