 |
| Titel |
The fractionation of Fe and Cu between brine and CO2 at up to 130 °C and 8.4 MPa, with implications for metal mobilization in CO2 storage reservoirs |
| VerfasserIn |
Kirsten U. Rempel, Axel Liebscher, Georg Schettler, Wilhelm Heinrich |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039606
|
|
|
|
|
|
| Zusammenfassung |
| In order to better understand the long-term effects of CO2 storage in saline aquifers, there has
been increasing interest in the mobilization of metals in brine-CO2 systems, in the context of
both permanent mineral trapping and the potential spreading of contaminants. Owing to the
fact that the brine is a stronger solvent than CO2for polar metal complexes, previous
studies have focused primarily on brine-reservoir rock interactions (e.g., Gunter et
al., 1997; Wigand et al., 2008), and the role of CO2 as a separate solvent has yet
to be considered. While CO2 may not be a strong solvent, even ppm-level metal
concentrations represent a considerable amount of mobilization in reservoirs that are
host to millions of tonnes of CO2, so a quantitative evaluation of this process is
desirable.
To this end, we have conducted an experimental investigation of vapour-liquid equilibria
in the systems FeCl3-NaCl-CO2-H2O and CuCl2-NaCl-CO2-H2O at 60-130Ë C and 6.5-8.5
MPa. The experiments were carried out in a large-volume autoclave loaded with a solution
containing 20 wt% NaCl and either 100 ppm Fe or 1000 ppm Cu, as well as pressurized
CO2. Paired samples of brine and CO2 were extracted from separate capillary lines
at successive pressure-temperature intervals, and analyzed for Fe and Cu using
ICP-AES. The CO2 samples were found to contain concentrations of 0.5 to 2.0 ppm
Fe and 0.5 to 6.7 ppm Cu, which generally displayed a positive correlation with
fluid density. Given the relatively small degree of metal fractionation into the CO2
as compared to the brine, the concentrations in the brines remained constant at
100 ppm Fe and 1000 ppm Cu. From these data, it can be seen that the Fe and Cu
concentrations in the CO2 are approximately 1% and 0.1% of those in the brine,
respectively.
Considering the metal concentrations typical to brines that have reacted with CO2 and
sandstone (20-200 ppm Fe, 1 ppm Cu; e.g., Gunter et al., 1997; Wigand et al., 2008), these
results suggest that a plume of injected CO2 could contain up to 0.2-2 ppm Fe and 0.001 ppm
Cu. At a hypothetical injection site used to store 10 Mt of CO2, this would lead to the
mobilization of 20 t of Fe and 0.01 t of Cu. Further, as the dissolution of Fe and Cu is
chemically similar to that of other metals such as Pb and Zn, the relocation of significant
quantities of additional metals may also be expected. The potential consequences of these
results for long-term CO2 storage include the precipitation of metal carbonate minerals in
shallower, more distal regions of the aquifer and the transferral of metals to adjacent aquifer
systems.
References
Gunter, W.D., Wiwchar, B. and Perkins, E.H. (1997) Aquifer disposal of CO2-rich
greenhouse gases: extension of the time scale of experiment for CO2-sequestering reactions
by geochemical modelling. Miner. Petrol. 59, 121-140.
Wigand, M., Carey, J.W., Schütt, H., Spangenberg, E. and Erzinger, J. (2008)
Geochemical effects of CO2 sequestration in sandstones under simulated in situ conditions of
deep saline aquifers. Appl. Geochem. 23, 2735-2745. |
|
|
|
|
|
|