Located within the Tianhuan Depression of the Ordos Basin, Block H exhibits widespread low-amplitude structures that dominantly control hydrocarbon accumulation. To address challenges in identifying reservoir fluid properties and the low consistency rate of logging interpretations in the extended exploration area of Block H, a genetic analysis of low-contrast reservoirs was conducted using integrated datasets including core samples, water analysis data, conventional logging, and geological data. Key controlling factors influencing electrical responses in oil and water layers were systematically clarified. Building on these findings, an innovative evaluation methodology was proposed to distinguish fluid types by quantitatively characterizing the resistivity variation rate. A fluid identification chart was established, with the liquid property index as the primary controlling parameter and the dual formation water resistivity ratio as the secondary parameter. The results indicate that the low contrast of reservoir characteristics in Block H is mainly influenced by two factors: first, the low saturation of the reservoir caused by the low amplitude structure and complex pore structure of the region, and second, the frequent variation of formation water salinity on the plane interferes with the establishment of electrical interpretation standards for the expansion area. The FPI chart, developed based on morphological and numerical discrepancies in logging curves between oil-producing and water-producing wells, demonstrates enhanced differentiation capability compared to conventional acoustic-resistivity crossplots. Field applications yielded promising outcomes, with the new chart achieving an 84% consistency rate validated by testing results from 25 layers across 23 wells. This approach provides critical technical support for re-evaluating legacy wells and optimizing perforation intervals in new wells within the study area.