Abstract: The oil reservoir in the Chang 8 member in the Huaqing area of the Ordos Basin is a typical low-porosity and low-permeability reservoir. It has poor physical properties, high content of interstitial materials, and a generally developed high-resistivity water layer. The coincidence rate of well logging interpretation is low, and identification of fluid properties is difficult. Causation analysis of the high-resistivity water layer indicates a high content of chlorite membrane in the study area. An asphaltene oil film is formed when asphaltene is adsorbed by the chlorite membrane, which blocks the pores, complicates the conductive path, and causes the phenomenon of “water in oil”. When combined with low-salinity formation water in the area, the resistivity of the water layers eventually becomes high. The well logging response of high-resistivity water layers is characterized by a high resistivity curve with a concave shape and high values for physical properties (permeability >1 mD, and porosity>15%). The well logging response of oil layers is characterized by a high resistivity curve with a convex shape and low values for physical properties (permeability <1 mD and porosity <15%). The petrophysical properties and formation mechanism of high-resistivity water layers can be determined from well logging response characteristics and identification methods such as a chart distinguishing curve morphology, a cross-plot of chlorite membrane content and resistivity, and correlation analysis of resistivity-porosity. These identification methods have solved the problem of high-resistivity water layer identification in the oil reservoir in the Chang 8 member, with the coincidence rate of well logging interpretation for each method increasing to more than 80%.