Abstract:  The deep tight sandstone in the Yiqikelike Area of the Kuqa Depression presents both great exploration potential and challenge due to its complex reservoir densification & accumulation process, and strong heterogeneity. Here, the differential diagenetic evolution processes of this tight sandstone were studied through core observation, thin section identification, porosity and permeability measurements, and analyzes of fluid inclusions, fluorescence, carbon and oxygen isotopes, sandstone types and reservoir quality characteristics. Applying the modified Dickinson's triangle principle, the sandstone of the Ahe Formation are divided into four types based on the contents of calcium cement, ductile debris and rigid particles: type C, the calcareous cementitious sandstone; type A, the lithic sandstone with high rigid particle content; type D, the lithic sandstone containing medium level ductile debris (10%25%); and type B, the ductilerich lithic sandstone with more than 25% ductile debris. Types A and D are effective tight gas reservoirs where the blue fluorescence, representing the second oil (gas) filling, is strong as a result of high emposieu and structural fractures. The feldspar and ductile debris contents are somewhat high in type D, in which the porosity is high but permeability is low due to late dissolution. Most type D oil layer samples have yellow and blue fluorescence, and the average porosity of type D is higher at early oil filling but slightly declines after second oil and gas filling start. In comparison, types B and C have stronger compaction and cementation but poor physical properties; only a few samples emit yellow but no blue fluorescence; and they are all effective reservoirs. Notably, there are differences in diagenesis and accumulation between types A and D: the early oil filling of type D slowed the occurrence of structural compaction and carbonate cementation, conducive to the late acid dissolution and oil (gas) filling; whereas the structural fractures affecting the performance of type A was developed by the second rather than the early oil (gas) fillings.

Key words: tight sandstone, diagenetic evolution, diagenetic difference, Jurassic Ahe Formation, Yiqikelike Area, Kuqa Depression