| (1) | k = k_1 \, \phi^{m_1} + k_2 \, \phi^{m_2} |
where
Usually, the first component k_1 \, \phi^{m_1} is related to low permeabilities while k_2 \, \phi^{m_2} is related to high permeabilities.
This model was thought to be empirical for a very long time but later on it was shown that it has a clear physical meaning as percolation theory based on the fractal structure of the pore volume.
See also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics / Absolute permeability / Absolute permeability @model