Research On The Physical Facies Of Tight Sandstone In Xujiahe Formation Of Xinchang Structural Belt,Western Sichuan Depression

Xinchang structural belt is located on the large uplift belt of Xiaoquan-Fenggu structure in the middle section of the western Sichuan depression basin.Influenced by the rise of Longmenshan tectonic belt and the multi-stage tectonic adjustment since the late Triassic,several sets of source-reservoir-caprock association and gas-bearing layers have been formed.According to the current industrial gas wells,Xujiahe formation in the research area enjoys good exploration potential.Predecessors mainly studied the Xujiahe Formation from such aspects as deposition,provenance,Formation mechanism of reservoir densification and densification time,while few studies were conducted on the main control factors and lithogenous phase in the research area,which to some extent restricted the effective exploitation of exploration reserves.Guided by such discipline theories as sedimentary geology and petroleum geology,this thesis adopted a variety of testing methods(rock slice,electronic probe,scanning electron microscope,logging information,etc.)to conduct a detail study on the the diagenetic evolution,main controlling factors and petrophysical facies of reservoir.The main achievement and understanding are as follow:(1)The reservoir of Xujiahe Formation in western Sichuan tectonic belt of western Sichuan depression(the second Xujiahe Formation,the fourth section)owns low rock composition maturity.The rock types are mainly feldspar lithic sandstone,lithic quartz sandstone and lithic sandstone.The cement is composed of such authigenic minerals as kaolinite,chlorite and calcite.(2)There are mainly two types of diagenesis in Xujiahe Formation reservoir,namely constructive diagenesis(rupture and dissolution)and destructive diagenesis(consolidation and compaction).The accumulation of diagenesis with different strength and different types significantly affects the retention and destruction of primary and secondary pores in reservoir rocks.(3)Based on the study on the development and distribution characteristics of diagenesis,the diagenetic facies of the second Xujiahe Formation can be divided into compaction facies,siliceous cementation facies,chlorite cementation facies,carbonate cementation facies and dissolution facies;the diagenetic facies of the fourth section can be divided into dissolution facies,carbonate cement-dissolution facies,siliceous-dissolution facies,kaolinite cement-dissolution facies,carbonate cement facies and compaction facies.(4)Based on the study of sedimentary facies,diagenetic facies and fracture characteristics,the sandstone reservoir of Xujiahe Formation can be divided into five petrophysical facies,I: high porosity matrix-fractured reservoir;II 1: high porosity matrix reservoir;II 2: low porosity matrix-fractured reservoir;III: low porosity matrix reservoir;IV: mudstone.