Skin:
1.The area of the formation that is damaged because of the invasion of foreign substances into the exposed section of the formation adjacent to the wellbore during drilling and completion.
2.
The pressure drop from the outer limits of drainage to the wellbore caused by the relatively thin veneer (or skin) of the affected formation.
Skin is expressed in dimensionless units: a positive value denotes formation damage; a negative value indicate improvement.
Also called skin effect.
3.
A dimensionless estimation of obstruction to flow.
An undamaged well would have a skin of zero.
A damaged well has a positive skin above zero and a stimulated well has a negative skin.
