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 ) |
Definition suggest that
- deteriorated near-well reservoir zone
k_s < k is characterized by a positive skin-factor
S>0,
- improved near-well reservoir zone k_s > k is characterized by a negative skin-factor S<0.
The most popular practical range of skin-factor variation is -5 < S < 8.