For low resistivity pay zones and the adjacent water sand or mud sand show little difference in resistivity from each other, it is difficult to distinguish the oil and the water and the evaluation of low resistivity pay zones has drawn great attention in well log interpretation. Some low resisitivity pay layers were discovered in the Shizigou N1 reservoir, the resisitivity indexes of those layers are less than 3 and the resisitivity is only 2.2 Ω·m (Middle 40 Well Ⅱ-37), while the highest resisitivity of the water sand is 4.9 Ω·m（Middle 11 Well Ⅱ-11）and the average value is 2.74Ω·m. For the approximate values, it is difficult to distinguish them. By analyzing the present producing test data, the main reasons for the low resistivity can be summarized as: (1) fine reservoir lithology; (2) high shale content, which results in large exchange of positive ions in reservoir beds; (3) lower reservoir amplitude, small difference in the density of oil and water, low oil saturation; (4) higher salinity of formation water; (5) complicate pore structures due to faults. It is deficient to study on the zones only by the routine interpretation criterions and charts. So further study should be carried out, new interpretation model should be constructed to improve the development of Shizigou N1 reservoir, by means of well test and PVT test.
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