The resistivity of water layers of part of Chang-8 oil formation of Huaqing area in Ordos Basin is higher than that of conventional ones

which leads that the water layers are often explained to be oil layers and limit the process of exploration and development of this area. In order to solve this problem

the reason is analyzed by fluid inclusions

scanning electron microscope and geology data. The results show that Chang-8 oil formation has three times of hydrocarbon flooding

the third that is the biggest extent destroyed the early formed oil-water relation. The tectonic activity from the beginning of the late Jurassic emphasizes the destroyed extent

which result in residual oil detained in the pores. Shaly interbeds further the restrain the residual oil migrating outward. The residual oil in the pore increases the resistivity of reservoir. Chlorite mineral is developed in water layers with high resistivity

whose relative content distributes in 34.32 %~81.11 %

higher than that of oil layers. The higher resistivity of water layer is caused by the adsorption of crude oil in pores by chlorite minerals on the surface of particles. In addition

carbonate minerals is also a factor of high water layer resistivity. When its content is more than 4.9 %

it will lead to high resistance of the water layer. The results reveal the formation mechanism of water layers with high resistance in Chang-8 formation in Huaqing area

which lays a foundation for the identification of high resistivity water layers in Chang-8 oil formation

the study of oil and water distribution rules and the improvement of exploration success rate in Huaqing area.