lautrec,Every well is "damaged" during drilling. As the drilling...

lautrec,

Every well is "damaged" during drilling. As the drilling mud circulates through the wellbore, some of it inevitably leaches into the formation rock. This creates an annulus of "damaged" formation rock around the wellbore through which hydrocarbons flow poorly, as the formation pores are all blocked up from the drilling mud. Another name for this is the well's "skin".

http://oilgasglossary.com/formation-damage.html
http://oilgasglossary.com/skin.html

Fraccing allows easier paths through the damaged well "skin", increasing potential flowrates.

seboya