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 (S1 k 1 1 and S1 k 1 3 ). 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 S1 k 1 3 Formation shows relative better physical characteristic than the lower S1 k 1 1 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 (S1 k 1 1 sandstones) and sand flat (S1 k 1 3 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 (S1 k 1 1 ) sandstones, sand flat sandstones (S1 k 1 3 ) 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 S1 k 1 1 and S1 k 1 3 reservoir. Type II is moderate reservoir. It is located in the middle of S1 k 1 1 reservoir and in the north of S1 k 1 3 reservoir. Type III is the poor reservoir. It is only located in the north of S1 k 1 1 reservoir.