what is the difference between the MPHASE and SCO2 modes

[chenyao su]

Hi all,

  I noticed that the governing equations of MPHASE and SCO2 in PFLOTRAN look almost identical in the documentation, with SCO2 mainly adding salt.
However, SCO2 is strongly recommended for CO₂ sequestration.
Could someone explain the key differences in physical assumptions, EOS/phase equilibrium treatment, interphase mass transfer, and numerical formulation that make SCO2 fundamentally different from MPHASE, beyond what is visible in the equations? 

Thanks very much for your time and help!

Best regards

[Michael Nole]

Mostly SCO2 mode is newer, is compatible with the well model, and is the flow mode that was used in the recent SPE 11 code comparison. 

You can find all the details on EOS's, numerics, and usage here:

Michael

On Jan 15, 2026, at 7:57 PM, chenyao su <suche...@gmail.com> wrote:



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[chenyao su]

Thank you very much for your reply and for sharing the recent PFLOTRAN CO₂ sequestration paper.

I have read through the paper and found it to be a very comprehensive and well-structured work that clearly documents the EOS, numerical formulation, and intended usage of the SCO2 mode. It helped me better understand why SCO2 is the preferred flow mode for recent CO₂ sequestration studies.

Just to make sure I understand correctly:

for CO₂ geological sequestration–related problems, the SCO2 mode represents the recommended and most robust modeling choice within PFLOTRAN？

is the SCO2 flow model now fully coupled with the chemistry/reactive transport module, allowing consistent treatment of CO₂ dissolution/exsolution, and geochemical reactions?

Thank you again for your time and clarification.

Best regards

[Michael Nole]

Correct. SCO2 mode is the most up to date flow mode for modeling CO2 sequestration, and it can be coupled to reactive transport for geochemistry.

Michael

On Jan 17, 2026, at 2:11 AM, chenyao su <suche...@gmail.com> wrote:



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[Peter Lichtner]

Does the SCO2 mode use variable switching when phase changes occur?

Peter

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[Michael Nole]

Yes it does. 

Michael

On Jan 17, 2026, at 11:40 AM, Peter Lichtner <peter.l...@gmail.com> wrote:

Does the SCO2 mode use variable switching when phase changes occur?

To view this discussion visit https://groups.google.com/d/msgid/pflotran-users/66A494CD-EE97-4D8C-9796-B46FFE711E50%40gmail.com.

[chenyao su]

Thank you very much for the clarification and for taking the time to answer my questions. This was very helpful for my understanding.

Best regards,
Chenyao