Abstract: Water injection is a commonly used way to develop oil field, which can maintain reservoir pressure to ensure steady wellhead oil rate. In the process of waterflooding, there may occur physical or chemical reaction between the injected water and reservoir porous media, which would result in the increase
of fluid flow resistance and the reduction of reservoir permeabili-ty. In general, the formation damage is evaluated by transient test, which only reflects the damage of neighborhood wellbore while as for deep inner formation damage there were few further researches published. We analyzed the characteristics of deep inner formation damage on transient test curves based on the
typical example data .The factors leading to formation damage were also studied. Thus, we found the method to evaluate deep inner formation damage by transient test data. This method has been proven practical in guiding water injection operation.

Key words: waterflooding, formation damage, transient test curve, water injection under high pressure, reservoir model