Abstract: The Yingshan Formation marine carbonate reservoirs in Yubei Area were examined by applying various data such as cores, FMI, 3D seismic attributes and thin sections. Although extensive erosion has led to the absence of the Upper Ordovician in the study area, the carbonate reservoirs are not typical weathering-crust reservoirs, but fault-controlled karst reservoirs. The reservoir spaces are mainly small-scale solution vugs and fractures, the distribution of which is strongly controlled by fault systems. This paper first studied the timing of fault, structural styles and the azimuth of fractures in a macroscopic view, then analyzed the features of fracture in a microscopic view, and finally discussed the relationship between the fractures and reservoir reconstruction. The results show that meteoric corrosion downward along faults is critical to reservoir reconstruction. Whereas the burial diagenesis (deep hydrothermal erosion or organic acid) also has influences on reservoir pores but is not the main factor. Faulted reservoirs occur in the whole Ordovician in Yubei Area, especially in the top weathering crust and the bottom transition from dolomite to limestone. The overthrust system of NE-trending cap rock detachment type in the middle structural layer of east fault-fold structural belt is adjacent to the NE-trending vertical strike slip fault in the lower structural layer. They together consist of the hydrocarbon migration pathway in the eastern faulted horst belt, which is the most favorable zone for fractured or fractured-vuggy reservoirs.

Key words: fault system, fracture characteristics, carbonate reservoir, Yubei area, Tarim Basin