Formation mechanism of high-quality reservoir of calcarenaceous sandstone in fourth member of Xujiahe Formation, Fenggu area, Western Sichuan Depression

The calcarenaceous sandstone reservoir in the fourth member of the Xujiahe Formation in Fenggu area of the Western Sichuan Depression is a typical tight sandstone reservoir characterized by high content of carbonate debris(accounting for over 90% in total debris),well-developed carbonate cementation,low porosity and low permeability;however,under the background of general dense,favorable reservoirs also develop in some intervals with the porosity of over 12%.The analysis of reservoir feature and diagenesis has indicated that the differential cementation of reservoir calcite is the key for the preservation of primary pore in high-quality reservoir.Then disruption communicates reservoir and acid fluid of hydrocarbon emplacement,improving reservoir quality.The later hydrocarbon charge protects reservoir porosity.