How this calculator works
Permeability is inferred from Darcy flow in a horizontal saturated sample. Effective porosity is inferred separately from the volume participating in transport: under a plug-flow interpretation, this is discharge times mean residence time. Tracer first arrival is usually not the mean residence time. Total porosity measured geometrically can exceed effective porosity because some pores do not transmit flow. No unique universal conversion exists between porosity and permeability.
Formula
k = Q mu L/(A delta p). Effective porosity ne = Qt/(AL); t = ne AL/Q; mean pore velocity = Q/(ne A). Total porosity n = Vpore/Vbulk.
Worked example
A 0.01 m2 by 1 m sample passing 1e-5 m3/s at 10000 Pa with mu = 0.001 Pa s has k = 1e-10 m2. A 250 s mean residence time gives effective porosity 0.25.
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Frequently asked questions
Can high porosity mean low permeability?
Yes. Small or poorly connected pores can store considerable fluid while transmitting it slowly.
Is residence time the first tracer arrival?
Use a representative mean transport time for this model. First arrival can follow a fast pathway and underestimate participating pore volume.
Can porosity exceed one?
No. A pore-volume fraction above one indicates inconsistent measurements or an unsuitable transport model.