Abstract: In order to make clear the characteristic and genesis of tight sandstone diagenetic facies in Shahezi Formation, the core, thin-section, SEM, physical properties and X-ray analysis have been combined and systematically studied in Xujiaweizi Fault Depression. The result is that there are five kinds of diagenetic facies such as muddy-filling diagenetic facies, feldspar-debris dissolution diagenetic facies, quartz overgrowth diagenetic facies, chlorite cementation diagenetic facies and carbon cementation diagenetic facies. The difference of mineral constituent and texture between different diagenesis facies which is controlled by sedimentation is the origin of porosity evolution, the type of main diagenesis and its intensity determine the porosity evolution path in different diagenetic facies and result in spatial differentiation of properties in macroscopic and pore structure in microscopic. Even though diagenesis destroy a lot of primary pore in feldspar-debris dissolution diagenetic facies in braided delta front and chlorite cementation diagenetic facies in fan delta front, they still retain a high property before gas injection in stage B of middle diagenesis phase, which make them a favorable reservoir for gas accumulation. The reservoir in muddy-filling diagenetic facies, carbon cementation diagenetic facies and quartz overgrowth have loss most of primary pore and complete the densification process before organic matters get matured, which make it difficult for gas injection and accumulation.

Key words: diagenetic facies, tight sandstone, porosity evolution, Shahezi Formation, Xujiaweizi Falut Depression