Assuming that something changes the permeability near the wellbore. One simple model of this effect is to assume that this altered zone has uniform permeability, $k_a,$ and radius, $r_a,$ and that the rest of the reservoir is undisturbed. Using Darcy's equation and the definition of $p_s$ skin:

$p_s=\frac{141\mathrm{.}2qB}{kh}s$

Derive the Hawkins' Formula, given as:

$s=(\frac{k}{k_a}-1)ln(\frac{r_a}{r_w})$