Wellbore damage and skin effect is a concept which has been introduced in order to account for the apparent differences in the inferred permeability, as derived from the flow data, versus the inferred permeability as derived from the shut-in data. This is often manifest in very low recovery, accompanied by a very high rate of buildup, (i.e., the build-up data indicate high permeability, while the flow data indicate low permeability). This particular circumstance is known as skin effect.
Other types of damage are interpreted when successive build-up curves indicate ever increasing permeability, or the shut-in curve has an "s-shape". Tests in which damage is suspected should be referred to an "expert" for confirmation.
Closed chamber testing will affect the analysis of bottom-hole pressure charts during the flow periods. During the flow periods compression in the chamber will create an increasing pressure curve, similar to fluid influx in an open hole test, no matter which fluid is actually flowing. i.e., a significant gas flow will appear the same as an oil or water flow.