Abstract: Casing hole formation resistivity logging has been paid more and more attention to in recent years，and ECOS
technology of Russia have been applied in some oilfields of China，and Chenbao Region，Jiangsu Oilfield，is one of those.
Insofar at present，the critical task is to locate the residual oil zones and to evaluate the flooding grade of oil-bearing formation.
Through comparison between ECOS-resistivity and conventional resistivity，we discover that the two kinds of resistivity have
roughly similar trend. However，there are relatively obvious amplitude differences between them，and usually，the latter is
larger than the former. The law is the more serious flooding，the larger amplitude difference. So this paper provides a novel
method，which is the relative resistivity change rate（IR），to evaluate the flooding grade. Through two cases，this method is
proved available. Finally，we conclude that the ECOS technology is suitable for Chenbao Oilfield.

Key words: Chenbao Oilfield, resistivity through casinghole, ECOS, water-flooding grade, resistivity gradient