Abstract: Based on the lab data of cast thin section, scanning electron microscope and high pressure mercury injection, etc., the study of sandstone reservoir of Xishanyao formation in Baka oilfield in Tuha basin is conducted. The result shows that the lithology of this reservoir is feldspar lithic sandstone, with low maturity of composition and texture; the pore space of reservoir is dominated by intergranular pore and dissolved pore, belonging to the reservoir with poor quality, low original productivity and serious heterogeneity. The reservoir is influenced by sedimentary mirofacies, diagenesis, microfracture, among which the channel mouth bar and underwater distributary channel act as favorable microfacies for reservoir development. In the early stage of diagenesis, the large quantities of clay films were formed, which were favorable for preservation of original pores and throats, while existence of numerous microfractures allowed various pores to be efectively connected, thus improving the permeability of the reservoir.

Key words: reservoir feature, pore structure, sedimentation, diagenesis, microfracture, microcrack