Abstract
Reservoir characterization specific to CO2 storage is challenging due to the dynamic interplay of physical and chemical trapping mechanisms. The mineralization potential for CO2 in a given siliciclastic sandstone aquifer is controlled by the mineralogy, the total reactive surface areas, and the prevailing reservoir conditions. Grain size, morphologies and mineral assemblages vary according to sedimentary facies and diagenetic imprint. The proposed workflow highlights how the input values for reactive mineral surface areas used in geochemical modelling may be parameterized as part of geological reservoir characterization. The key issue is to separate minerals both with respect to phase chemistry and morphology (i.e., grain size, shape, and occurrence), and focus on main reactants for sensitivity studies and total storage potentials. The Johansen Formation is the main reservoir unit in the new full-value chain CO2 capture and storage (CCS) prospect in Norway, which was licenced for the storage of CO2 as of 2019. The simulations show how reaction potentials vary in different sedimentary facies and for different mineral occurrences. Mineralization potentials are higher in fine-grained facies, where plagioclase and chlorite are the main cation donors for carbonatization. Reactivity decreases with higher relative fractions of ooidal clay and lithic fragments.
Highlights
Saline aquifers hold the largest potential for geological CO2 storage considering total volume, economic and environmental factors [1]
We show how to more accurately estimate input parameter values for reactive mineral surface areas, as used in the geochemical modelling of long-term mineralization potential for CO2
The reactivity depends on the mineral assemblage, grain size and morphology, which all vary according to sedimentary facies within one sandstone reservoir unit, as well as on the diagenetic imprint and in-situ reservoir conditions
Summary
Saline aquifers hold the largest potential for geological CO2 storage considering total volume, economic and environmental factors [1]. Predictions of the CO2 trapping potential of a storage reservoir over hundreds to thousands of years requires a sound understanding of the geochemical reactions that will come about when CO2 is injected and the thermodynamic system is perturbed [6] Such predictions ideally require detailed knowledge about the mineralogy, formation water chemistry, mineral surface reactivities, and reaction. The relative importance of the various trapping mechanisms for injected CO2 in aquifers has been discussed ever since Gunther and co-workers published their geochemical simulations on solubility, ionic, and mineral trapping in the early nineties [19,20] This relates especially to how fast these reactions are, and if they will impose porosity/permeability changes. It is useful define reactivity and(I): make separate geochemical categories within the
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