Abstract: The well logging response variation caused by drilling mud invasion into formation is studied, by which the method for distinguishing the formation contamination or damage type is presented, combined with water saturation change; the model for quantitative assessment of permeability damage is developed by means of the relationship between permeability and porosity, and the formula for calculating damage radius is given using the coefficient of the normal device. Case study indicates that the skin factor from well logging is well accordant with that from drill stem test (DST) by using this method.

Key words: drilling, mud, formation contamination, permeability damage, well logging, evaluation, assessment