Permeability power and equations mistake in user guide website

[Wenyu Zhou]

Dear Pflotran developer,

In our study, we just noticed there is maybe a small (but important) mistake in the Pflotran user guide. Please find it in:

https://documentation.pflotran.org/theory_guide/mode_reactive_transport.html?highlight=permeability%20power

In the section "Change in material properties", the function for updating the permeability via porosity used the term "n", which is marked as surface volume ratio below. I am not sure KC equation can be simplified as this. I also checked the user manual in PDF version in 2015, where the same equation used the term "a". And this is correct in theory. Please find the attached document (page 206) in following website:

 https://bytebucket.org/pflotran/pflotran/wiki/Depreciated/Documentation/Files/user_manual.pdf?rev=f8f2c75ed07230a305fae0520ca63a9e6badd433

We are dealing with a reactive transport in fracture-matrix system where the porosity change can be varied from 2%-100%. Could you also give us some advice on how to treat this question by Pflotran, especially on porosity/permeability setting.

Best regards,

Wenyu Zhou

CNRS 

[Hammond, Glenn E]

Wenyu,

To clarify, your question is whether n = 2/3 is appropriate for

f = ((\phi - \phi_c)/(\phi_0 - \phi_c))^n

with porosity \phi, initial porosity \phi_0 and critical porosity \phi_c, and where f is a scaling factor for the intrinsic permeability, correct?

There is discussion below these equations, in the paragraph beginning with “The two-thirds power arises from the assumption that…”, that explains the assumption of spherical mineral grains. If your porosity will approach 100%, I agree that the assumption is likely not applicable to your conceptual model.

Peter,

Do you want to comment on this?

Glenn

From: pflotra...@googlegroups.com <pflotra...@googlegroups.com> on behalf of Wenyu Zhou <zhou.we...@gmail.com>
Date: Friday, February 20, 2026 at 7:54 AM
To: pflotran-users <pflotra...@googlegroups.com>
Subject: [pflotran-users: 8673] Permeability power and equations mistake in user guide website

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[Wenyu Zhou]

Dear Glenn,

Thanks for your kind reply! Actually, my major concern is that the porosity-permeability power-law equation may be mistakenly used with the symbol "n" on the website: In the equation: f = ((\phi - \phi_c)/(\phi_0 - \phi_c))^n

The "n" is not the "n" in the next paragraph for the reactive surface area equation, which is the surface volume ratio. Here, "n" is the permeability power exponent, which is used as "a" in the pdf version manual book (this value can be ~3).

Best wishes,

Wenyu

'Hammond, Glenn E' via pflotran-users <pflotra...@googlegroups.com> 于2026年2月24日周二 00:13写道：

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