Genetic Analysis and Identification of Yanchang 8 High-resistivity Water Layer in Huaqing Area, Ordos Basin

The high-resistance water layer is generally developed in Chang 8 reservoir, Huaqing area of Ordos Basin. There is little electrical difference between the water layer and the oil layer in the same reservoir sand body. The oil saturation calculated in water layer is obviously higher, and the traditional well-logging interpretation has a low agreement with fracturing test. Combined with logging interpretation, formation testing, production testing and laboratory data analysis, the formation and control factors of high resistivity layer were analyzed, and the fluid identification standard was established by using the resistivity morphological difference method. The results show that the Chang 8 reservoir of Huaqing area is oleophylic, chlorite membrane developed and asphaltene is generally filled with pores. Chlorite membrane-organic matter complex is formed under the action of self-priming and particle surface adsorption and results in high resistivity logging response, while the non-wetted water phase occupied the relatively unobstructed larger pore throat and easy to flow. In the low enrichment of oil and gas, water produced. By means of resistivity-curve-shape method, the chart "convex" and "concave" logging identification chart and fluid identification standard are established respectively. Convex reservoir is Δt ≥ 216μs/m,Rt ≥ 36Ω.m and the concave reservoir is Δt ≥ 221 μs/m, Rt ≥ 60 Ω.m. As a whole, the coincidence rate between logging interpretation and oil test production increases more than 15%, compared with the conventional plate intersection method. It has a remarkable effect on the identification of high resistivity water layer.