Estimation of carbon dioxide (CO2)-storage capacity is a key step
in the appraisal of CO2-storage sites. Different calculation methods
may lead to widely diverging values. The compressibility method is a commonly
used static method for estimating storage capacity of saline aquifers: It is
simple, is easy to use, and requires a minimum of input data. Alternatively, a
numerical reservoir simulation provides a dynamic method that includes Darcy
flow calculations. More input data are required for dynamic simulation, and it
is more computationally intensive, but it takes into account migration pathways
and dissolution effects, so it is generally more accurate and more useful. For
example, the CO2-migration plume may be used to identify appropriate
monitoring techniques, and the analysis of the trapping mechanism for a certain
site will help to optimize well location and the injection plan.
Two hypothetical saline-aquifer storage sites in the UK, one in Lincolnshire
and the other in the Firth of Forth, were analyzed. The Lincolnshire site has a
comparatively simple geology, while the Forth site has a more complex geology.
For each site, both static- and dynamic-capacity calculations were performed.
In the static method, CO2 was injected until the average pressure
reached a critical value. In the migration-monitoring case, CO2 was
injected for 15 years, and was followed by a closure period lasting thousands
of years. The fraction of dissolved CO2 and the fraction immobilized
by pore-scale trapping were calculated.
The results of both geological systems show that the migration of
CO2 is strongly influenced by the local heterogeneity. The
calculated storage efficiency for the Lincolnshire site varied between 0.34 and
0.65% of the total pore-volume, depending on whether the system boundaries were
considered open or closed. Simulation of the deeper, more complex Forth
geological system gave storage capacities as high as 1.05%.
This work was part of the CO2-Aquifer-Storage Site Evaluation and
Monitoring (CASSEM) integrated study to derive methodologies for assessment of
CO2 storage in saline formations. Although static estimates are
useful for initial assessment when fewer data are available, we demonstrate the
value of performing dynamic storage calculations and the opportunities to
identify mechanisms for optimizing the storage capacity.
© 2012. Society of Petroleum Engineers
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- Original manuscript received:
20 September 2011
- Meeting paper published:
14 June 2010
- Revised manuscript received:
17 February 2012
- Manuscript approved:
20 April 2012
- Published online:
29 November 2012
- Version of record:
6 December 2012