Water-flooded zone identification for ordos Yan9 reservoir using conventional logs

Accurate identification and evaluation of water-flooded zones play a pivotal role in the efficient exploitation of oil reservoirs, as they directly govern reservoir development adjustment strategies and remaining oil recovery efficiency. In this study, comprehensive analyses of reservoir physical properties, rock electrical parameters, and relative permeability characteristics were conducted by integrating logging data, formation testing data, production performance data, and core test results, based on which a systematic identification method and quantitative evaluation criteria for water-flooded zones were established. The research findings demonstrate that the study area is characterized by an average porosity of 13.8% and an average permeability of 54.7 mD, classifying it as a medium-porosity and medium-permeability reservoir. For the Yan-9 oil formation, the lithology coefficient, saturation exponent, and cementation exponent are determined to be 1.0517, 1.944, and 1.5069, respectively. Three qualitative identification approaches for water-flooded zones-namely, the resistivity comparison method between new and old wells, the porosity-resistivity curve overlay method, and the spontaneous potential baseline shift method—exhibit excellent applicability and reliability in the study area. Furthermore, quantitative classification criteria for water-flooded zones are proposed: low water-flooded zones with Rt > 35 Ω·m and Sw < 35%; medium water-flooded zones with 20 < Rt < 35 Ω·m and 35% < Sw < 50%; and high water-flooded zones with Rt < 20 Ω·m and Sw > 50%. This research not only provides a robust scientific basis for reservoir development adjustment, remaining oil potential assessment, and efficient water control in the study area but also offers valuable insights and references for the identification of water-flooded zones in analogous oil reservoirs worldwide.