Near-well formation damage

Effect when a formation permeability  $//<![CDATA[ \begin{array}{l}k_s\end{array} //]]>$ in certain near-well reservoir zone is different to that of initial before drilling/treatments $//<![CDATA[ \begin{array}{l}k\end{array} //]]>$:  $//<![CDATA[ \begin{array}{l}k_s \neq k\end{array} //]]>$

The usual formation damage is around few centimetres but may extend to few dozens of centimetres. 

In many flow models this zone is considered as thin sandface film between wellbore and rocks and quantified by integral value of skin-factor.