Reservoir Characteristics and Controlling Factors of Silurian Lower Kepingtage Formation in Tahe Area, Tarim Basin, NW China

With the breakthrough of exploration in Well TP16-1, the lower Kepingtage Formation becomes a key target for petroleum exploration of deep clastic reservoir in Tahe area. In this paper we focused on the research of the reservoir characteristics and its controlling factors in two sub-member formations (S₁k₁¹ and S₁k₁³). Based on X-ray diffraction, conventional physical properties data (porosity and permeability) and reservoir storage space data (casting thin section and scanning electron microscope), we determined that the S₁k₁ Formation belongs to extra-low porosity and permeability reservoir, although the upper S₁k₁³ Formation shows relative better physical characteristic than the lower S₁k₁¹ Formation. The development of storage space in the study area is controlled by sedimentary microfacies, diagenesis process. Reservoirs in S₁k₁ Formation are mainly located in channel (S₁k₁¹ sandstones) and sand flat (S₁k₁³ sandstones). The sand flat sediments with a more coarse grain size compared with the channel. In diagenesis, compaction is the major controlling factor for reducing the porosity, followed by cementation. Dissolution of diagenesis is the major controlling factor in enhancing the reservoir porosities. Compared with channel (S₁k₁¹) sandstones, sand flat sandstones (S₁k₁³) have better reservoir quality for its weaker compaction, cementation and stronger dissolution. On the basis of sedimentary characteristics (grain size and subfacies), physical property (porosity and permeability) and reservoir storage space, we divide the S₁k₁ reservoir into three categories (Ⅰ, Ⅱ and Ⅲ). Type Ⅰ reservoir is high quality reservoir. It is mainly distributed in the south area of S₁k₁¹ and S₁k₁³ reservoir. Type Ⅱ is moderate reservoir. It is located in the middle of S₁k₁¹ reservoir and in the north of S₁k₁³ reservoir. Type Ⅲ is the poor reservoir. It is only located in the north of S₁k₁¹ reservoir.