『Abstract
To assess CO2 underground sequestration
from a geochemical viewpoint, the anorthite dissolution rate,
which is an important parameter of risk analysis, was measured
in a CO2-water system. The authors sought
to obtain precise dissolution rate data in a short time observing
a crystal surface on a nanoscale. For this purpose, phase-shift
interferometry was applied. Using this method, uncertainty of
the reactive surface area that is imparted on calculation of the
dissolution rate constant can also be avoided. The time-course
profile of vertical retreat of the surface revealed that the anorthite
dissolution process changes from the initial transient state to
a later steady state, which is consistent with results of numerous
precedent studies. The transient dissolution rate depends strongly
on local features (e.g., density of defects, variation of chemical
compositions) of the crystal surface, rather than on temperature.
Therefore, it is very important to determine the original properties
of the anorthite surface for the examination of subsequent dissolution
process. Contrary to general expectations, the anorthite dissolution
can alter the physical properties of reservoir rock immediately
after CO2 injection. The simple estimation
using the anorthite dissolution rate obtained in this study, which
was done as a test case for the CO2 underground
sequestration project conducted by RITE, revealed that porosity
of reservoir rock increased about 2％(23-23.4％) of initial values
during 60 a. That change in physical property in such a short
time might enhance the diffusion of injected CO2
and formation water, and therefore accelerate further geochemical
reactions. Results of this study demonstrate that the geochemical
water-rock interaction, which is generally regarded as a longer-term
phenomenon than various physical processes, can also affect the
reservoir system from the initial stage.』
1. Introduction
2. Phase-shift interferometry
3. methods
4. Results
5. Discussion
5.1. Anorthite dissolution rate
5.2. Implications for underground CO2 sequestration
6. Conclusions
Acknowledgements
Appendix A. Analytical principle of PSI
Appendix B. Dissolution rate data
References