SCO2 mode issues

[Otabir, Prince]

Dear concern,

I have this .in file where I am trying to simulate forsterite dissolution to precipitate magnesite. Whenever I use an injection rate of 1d-7, that is the only time the simulation runs, however, the results don't make sense. I expect to see pH reduce around the injection zone, instead, it increases, also there is no co2 gas plume to track, which makes me wonder if its because the injection rate is too low. I increased the porosity and permeability, but the issue still persists and I would really appreciate any better ways to fix this.

Regards,

Prince.

[Hammond, Glenn E]

Prince,

Your challenge is that the initial condition is not in equilibrium with Forsterite. When I Google the pH of water in equilibrium with Forsterite, the pH is much higher. I would set a pH that is close to what would be equilibrium with Forsterite and then constraint the magnesium concentration against Forsterite. For example:

CONSTRAINT initial

  CONCENTRATIONS

    H+        11.d0      P

    SiO2(aq)  1.9d-3    T

    Mg++      3.2d-2    M Forsterite

    HCO3-     1.5d-4    T

    Na+       1.d-2     T

    Cl-       1.d-2     Z

  /

  MINERALS

    Forsterite  0.85d0  1.0d5  m^2/m^3

    Magnesite   0.d0    2.4d3  m^2/m^3

    SiO2(am)    0.d0    3.0d2  m^2/m^3

  /

END

You can also use PHREEQC to determine a realistic initial condition.

Glenn

From: pflotra...@googlegroups.com <pflotra...@googlegroups.com> on behalf of Otabir, Prince <pmo...@utulsa.edu>
Date: Wednesday, June 17, 2026 at 9:24 AM
To: pflotra...@googlegroups.com <pflotra...@googlegroups.com>
Subject: [pflotran-users: 8800] SCO2 mode issues

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[benjami...@gmail.com]

Prince,

Forsterite has no thermodynamic stability at temperatures less than around 350C. My recommendation would be to use an alteration phase, such as brucite, to set the initial Mg concentration. 

Ben