Abstract: In order to clarify the distribution characteristics of tight reservoirs in the Upper Triassic Xujiahe Formation in the northern part of the Western Sichuan Depression, we obtained reservoir sedimentary microfacies types and mineral composition characteristics by core description, logging interpretation and X-ray diffraction mineral analysis, combined with the diagenesis obtained from the rock thin section and field emission scanning electron microscopy observation, pore permeability and mercury injection test and the analysis results of the reservoir pore structure, and carried out a study on the factors influencing the tightness of reservoirs in the Member 2 of the XujiaheFormation.A comprehensive classification evaluation standard was established for the reservoirs Member 2 of the Xujiahe Formation in Northwest Sichuan. The result shows that the main reason for the development of tight reservoirs in the Member 2 of the Xujiahe Formation is that the reservoir porosity is controlled by lithology, and the differences in mineral components make the sandstone in the Member 2 of the Xujiahe Formation characterized by strong cementation, moderate compaction and weak fracture. The study results provide a basis for the screening of favorable sites for the development of tight reservoirs in this area and the favorable target areas for further exploration of tight gas reservoirs.

Key words: pore structure, reservoir characteristics, tight reservoir, diagenesis, Xujiahe Formation, northwest Sichuan