Transport Questions

[Heeho Park (Pakodot)]

Hi Glenn,

One of the input decks I received to analyze has UPDATE_MNRL_SURF_AREA_WITH_POR. It looks like this is now updated to
SURFACE_AREA_FUNCTION POROSITY_RATIO or POROSITY_VOLUME_FRACTION_RATIO
Which is it and what was the default value to for SURFACE_AREA_POROSITY_POWER <float> ?

Thanks,

Heeho

[Hammond, Glenn E]

Heeho,

If I am understanding correctly, I believe that you are asking what the default values of n and n’ are for Eq. 34 at:

https://documentation.pflotran.org/theory_guide/mode_reactive_transport.html#changes-in-material-properties

There are no default faults; they have to be set. You specify SURFACE_AREA_FUNCTION as POROSITY_RATIO, VOLUME_FRACTION_RATIO or POROSITY_VOLUME_FRACTION_RATIO. 

n is needed for VOLUME_FRACTION_RATIO (The theory guide above recommends 2/3 for n.)

n’ is needed for POROSITY_RATIO. 

For POROSITY_VOLUME_FRACTION_RATIO, both are required. 

Peter Lichtner, could you please advise Heeho on an appropriate value for “n’”?

Also, the following regression test illustrates their use:
https://bitbucket.org/pflotran/pflotran/src/6ee92553c9cca7eb8cf670939b6e80e298845ac6/regression_tests/default/materials/mineral_volume/mnrl_surf_area_porvolfrac_pwr.in#lines-143

Glenn 

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Date: Wednesday, March 4, 2026 at 8:47 PM
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Subject: [pflotran-users: 8692] Transport Questions

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[Heeho Park (Pakodot)]

Thanks, Glenn.

I was asking this because in the past, it looked like we didn't have to specify the value. We just used UPDATE_MNRL_SURF_AREA_WITH_POR.

But I can apply 2/3 for now with VOLUME_FRACTION_RATIO. I will wait for Peter to advise on POROSITY_RATIO.

Heeho

[Peter Lichtner]

The two-thirds value for the power law n appearing in the relation k = k0 (por/por0)^n, n = 2/3, n is based on a constant grain density. There is little to none experimental justification for this choice however. Better to treat n as a fit parameter.

Peter

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[Wenyu Zhou]

Dear Peter,

Really thanks for your replies! 

Yes, we are now using the fitting ‘n’ to combine the cubic law in fracture and Darcy equation in porous media. The calculated height of the fracture is very small (few micrometers) but it can fulfill our needs as a benchmark test for our own code. We have met some convergence issues and overshooting due the large time steps and meshes, but overall the results looks OK.

Best regards,

Wenyu Zhou

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发件人: pflotra...@googlegroups.com <pflotra...@googlegroups.com> 代表 Peter Lichtner <peter.l...@gmail.com>
发送时间: Thursday, March 5, 2026 9:24:01 PM
收件人: pflotran-users <pflotra...@googlegroups.com>
主题: Re: [pflotran-users: 8696] Transport Questions

 

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