A Modeling Study of the Role of Selected Minerals in Enhancing CO₂ Mineralization During CO₂ Aquifer Storage

CO₂ mineralization is a process whereby the CO₂ that is injected into a geological formation dissolves into the formation water, reacts with the in situ minerals and ions, and precipitates as carbonate minerals. This process governs the long-term fate of the injected CO₂ and ensures a safe storage once CO₂ has been converted into minerals.

In a previous study involving the modelling of the long-term fate of CO₂ in the Utsira aquifer storage, the authors observed that CO₂ mineralization was not possible if mineral reactions were limited to Calcite and Dolomite precipitation and dissolution.

Indeed, to mineralize CO₂, non carbonate minerals that are present in the formation have to:

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  dissolve in order to buffer the pH decrease resulting from the CO₂ injection;

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  provide cations such as Ca²⁺, Mg²⁺, Fe²⁺ to the formation water;

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  not release bicarbonate (HCO₃⁻) to the formation water.

Then the released cations react with HCO₃⁻ resulting from the dissolution of the injected CO₂ and precipitate new carbonate minerals.

In this study, the CO₂ mineralization process is modelled, taking into consideration various possible reactive pathways.

In the first step, the different reactive pathways are investigated in terms of reactive potential, CO₂ mineralization potential and consequences on the porous network.

In the second step, simulation of flow and dissolution of CO₂ together with geochemical reactions is performed to examine the mineralization process in space and time for two different time scales:

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  1000 years with a finer grid to examine how chemistry interacts with the CO₂ dissolution process; and

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  18,000 years with a coarser scale to reach geochemical equilibrium in the aquifer.

This work shows that a limited amount of non-carbonate reactive minerals (for a given time scale) can contribute to the mineralization of CO₂ that is significant for an industrial CO₂ storage project. As such, the identification of the reactive pathways leading to CO₂ mineralization is a key step to evaluate the long-term fate of the injected CO₂ in a geological storage project.