Abstract: The oil zone, oil-water transition zone and aqueous layer of Cretaceous Tugulu group in Junggar basin occur obvious resistivity lower than that found in reservoirs of Jurassic Toutunhe formation and Xishanyao formation. The study shows the reason or origin is due to the fact that the water cul in Tugulu reservoirs is higher than that of Jurassic; water bearing clay film developed in Cretaceous could greatly enlarge the cro8s-sectional area of electric conductive network, so the clay film is mainly responsible for existing low resistivity of Cretaceous reservoirs. In addi-tion, the difference of clay minerals has effect on the low resistivity reservoirs.

Key words: Junggar basin, resistivity, water cut, clay mineral