Abstract: The genesis and distribution of tight sandstones are the key factors that restrict the exploration of tight gas in Shahezi Formation. We studied the diagenetic characteristics of tight sandstones in Shahezi Formation and divided it into 5 kinds of diagenetic facies according to the multiple qualitative and quantitative parameters and on the basis of making full use of core, thin-section, SEM, physical properties and X-ray analysis. They are strongly compacted argillaceous filling facies, moderately compacted feldspar detritus dissolution facies, moderately compacted quartz secondary enlargement facies, moderately compacted chlorite rim cementation facies, and weakly compacted carbonate cementation facies. The different mineral constituent and texture of clastic rocks controlled by sedimentation are the material basis and origin of porosity evolution of different diagenetic facies, the compaction and filling of matrix are the material cause that lead to the loss of porosity in early diagenetic system, and the physical properties are retained and improved by the chlorite rim cementation and feldspar detritus dissolution. The type and intensity of diagenesis are different in different diagenetic facies, which results in the difference of macro properties and micro pore structures. The moderately compacted chlorite rim cementation facies and moderately compacted feldspar detritus dissolution facies show the best reservoir quality in Shahezi Formation, which can be taken as the best future exploration target in the study area.

Key words: diagenesis, tight sandstone, porosity evolution, Shahezi Formation, Xujiaweizi falut depression