Tahe Oilfield is located in the southern Ackulie Arch of Xayar Uplift in northern Tarim Basin. The Ordovician limestone reservoir is a unique kind of composite one with multi-units of fractures and/or vugs (or caverns) so it is similar with neither fractural one nor buried-hill one. The height of the reservoir is much larger than the relief of residual trap. Distribution of hydrocarbon is under the control of developing reservoir. Reservoir bodies are composed of fractures and vugs formed by karstification and tectonization, which are not continuous in longitudinal, and usually a single fractured-vuggy reservoir body is an isolated oil/water system. 10 connecting permeable-stored units and 20 isolated or constant-volume sealed bodies of the reservoir are subdivided and described in feature. The whole oilfield has not unitive basal groundwater and quite different quality of fluids exists in different reservoir bodies.