Abstract: The source of formation damage ( SFD ) is defined as materials which cause changes in pore structure and de-creases in permeability during well drilling, completion and production due to alterations of reservoir components
and / or interactions between reservoir components and the working fluids. SFD can be divided into three parts:inner SFD, outer SFD and complex SFD. The inner SFD is inherent; the outer SFD is introduced by working
fluids, while the complex SFD is a result of interaction of the two mentioned above. Studies of formation damage mechanism indicate that SFD is a complicated system with clear structures and functions. And such a system can be better studied using the five-level description scheme proposed in this paper.

Key words: Reservoirs stratum, Poresity, Pollution source, Systems, Joints