| Long Hu-pao oil field is entering into a high water-cut stage from the full development in 1987. As one of the main pay zones, Sa Er-tu has high water-cut with 82.6% at present. In order to raise oil production of this field, 65 new infill wells have been drilled in 2007. Several factors, such as thinner reservoir, poor petrophysics, high heterogeneity, and so on, lead to the difficulty of water flooded zones. Therefore, it is very important work how to identify water-flooded from oil-bearing zones, quickly and effectively. The paper focus on the study for the water-flooding mechanism, log response and interpretation methods of water-flooded zones, Sa Er-tu, based on core, log, test and production data, so as to obtain more reasonable perforating intervals. The main contributions of this paper are as follows:1. The relationships between the resistivity of the mixed water liquid (Rwz), the resistivity of water flooded zones (Rt) and water saturation (Sw) have been derived in theory during water flooding process. The theoretical calculation results of Rwz and Rt are close to those of core experiment.2. Based on core experiment results of water-flooding mechanism, the Rt of oil-bearing zones decreases as injecting water increases under the conditions of water injection and production at present, and Rt has the great reduce in the early water flooding stage. Porosity exponent m and saturation exponent n decrease as water flooded level magnify. The empirical models of m and n have been established from core experiment.3. According to different log response study of oil-bearing and water flooded zones, the sensitive curves reflecting water flooded zones include: LLD (ILD), MNOR (MINV), ZDEN, DT, GR and SP. Water flooded zones can be identified from the following characters: dropping LLD (ILD), positive difference between MNOR and MINV (that is MNOR>MINV), decreasing overlay area between LLD and ZDEN, increasing DT, and baseline deflection of SP.4. Formation parameter models of water flooded zones, such as porosity, permeability, water saturation, water cut rate, qualitative and quantitative identification standards have been established from core, log and production data. It is realized to effective evaluation of water flooded zones in this field.5. Petrophysical evaluation of 65 new infill wells in 2007 has provided 180 oil-bearing zones with the thickness of 184m, 70 poor oil-bearing zones with 50.7m, 141 weak water flooded zones with 142.3m, 143 medium-high water flooded zones with 149.9m. The cumulate thickness of oil, poor oil and weak water flooded zones is 377m, and is about 46.1% of the total thickness.6. Thinner oil-bearing zones with poor petrophysics in new infill wells, 2007, are the reasonable perforating intervals because they are weakly (or not) washed by injecting water.
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