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| Titel |
Hematite and K-feldspar dissolution rates in an exhumed CO2reservoir, Green River, Utah |
| VerfasserIn |
M. Wigley, M. Bickle, B. Dubacq, N. Kampman |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066007
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| Zusammenfassung |
| Reactions between CO2 injected into geological formations and aquifer minerals may lead to
permanently storage of the CO2 as carbonate minerals, or cause leakage via corrosion of
caprock and well seals [1]. Reactive transport models aimed at predicting the long
term fate of injected CO2 suffer from a poor knowledge of kinetic reaction rate
parameters, which is in part due to a 2-5 orders of magnitude discrepancy between
reaction rates measured in the field and laboratory experiments [2]. Despite the need
for accurate determination of these key model parameters, very few studies have
calculated mineral dissolution rates from natural CO2-water-rock systems (e.g.
[3]).
Near Green River, Utah, USA, regionally extensive portions of the red-bed Entrada
sandstone have been locally bleached white/yellow by CO2-charged fluids [4]. This bleaching
is related to dissolution of fine-grained iron oxide grain coatings, which give the rock its
distinct red coloration. Secondary calcite precipitation is observed together with growth of a
band of oxide and carbonate at the reaction front. The site therefore provides an analogue
for long term fluid-mineral reactions between CO2-charged brines and reservoir
minerals.
We calculate kinetic dissolution rates for hematite and K-feldspar in CO2-charged brines
by fitting the reactive transport equation to mineralogical profiles across reaction fronts. We
show that dissolution rates for K-feldspar are between 2.04x10-15 and 3.86x10-15
mol/m2/sec. These are several orders of magnitude lower than those predicted by laboratory
studies, and are consistent with other estimates from natural CO2 systems [3]. Hematite
reaction rates range from 2.94x10-14 to 6.69x10-13, several orders of magnitude faster than
those for K-feldspar.
Calculated mineral dissolution rates are used to build a simple model including mineral
dissolution-precipitation, advective-diffusive transport and trace metal adsorption.
The model reproduces the observed patterns of primary and secondary mineral
dissolution/precipitation, as well as trace element geochemical profiles across the reaction
front.
References
[1] Bickle (2009), Nature Geoscience. 2, 815-818.
[2] White and Brantley (2003), Chem. Geol. 202, 479-506.
[3] Kampman et al (2009), Earth Planet. Sci. Lett. 284, 473-488.
[4] Wigley et al (2012), Geology, In Press. |
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