Dimensionless value characterising permeability change in a thin layer around the well or fracture plane caused by stimulation or deterioration.
It contributes to the total skin estimated in transient well testing.
For the radial-symmetric permeability change around a well it can be represented by Hawkins equation:
| (1) | S_M = \left ( \frac{k}{k_s} - 1 \right ) \ \ln \left ( \frac{r_s}{r_w} \right ) |