Abstract
Feldspar dissolution rates measured using phase-shift interferometry: Implications
to CO2 underground sequestration
Applied Geochemistry, 22, 2795-2809, 2007.
Sorai M., Ohsumi T., Ishikawa M., Tsukamoto K.
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.
2007 Elsevier Ltd. All rights reserved.
Copyright(C) Research Institute of Innovative
Technology for the Earth (RITE). All rights reserved.