How Do The Varying Water Chemistry Parameters, Such As PH And Alkalinity, In Different Types Of Aquifers Affect The Long-term Storage Integrity And Geochemical Stability Of Injected CO2 In Saline Formations, Particularly In The Context Of Large-scale Carbon Capture And Storage (CCS) Projects In Sedimentary Basins With Complex Geological Histories?

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The varying water chemistry parameters, particularly pH and alkalinity, in different aquifers significantly influence the long-term storage integrity and geochemical stability of injected CO2 in saline formations within sedimentary basins. Here's a structured summary of the key points:

  1. pH and Alkalinity Impact:

    • High Alkalinity: Buffers against pH drops caused by CO2 injection, enhancing geochemical stability. This promotes mineral trapping of CO2, improving long-term storage.
    • Low Alkalinity: Results in significant pH drops, increasing reactivity with rock minerals. While this can lead to mineral dissolution, it may also compromise formation integrity if dissolution is excessive.

  2. Geochemical Reactions and Stability:

    • CO2 reacts with water and minerals, forming carbonic acid and potentially precipitating carbonate minerals. High pH and alkalinity favor stable mineral trapping.
    • In low pH conditions, CO2 remains more soluble or gaseous, which may be less stable long-term.

  3. Geological Complexity in Sedimentary Basins:

    • Varied mineral compositions across different rock layers affect CO2 interaction. Rapid-reacting minerals can enhance trapping, while others may slow processes.
    • Temperature and pressure influence reaction rates and solubility, with temperature increasing reaction rates and pressure affecting CO2 solubility.

  4. Mineral Precipitation and Permeability:

    • Presence of ions like calcium and magnesium can lead to carbonate mineral precipitation, trapping CO2. However, mineral dissolution or precipitation can alter permeability, affecting storage integrity.

  5. Long-term Considerations:

    • Initial water chemistry dictates short-term processes, while mineral trapping dominates long-term. Understanding local chemistry is crucial for predicting storage behavior.

In conclusion, higher alkalinity supports stable CO2 storage, while low alkalinity and pH may lead to complex reactions affecting storage integrity. The geological complexity of sedimentary basins necessitates detailed understanding of local conditions for effective CCS projects.