Reservoir Diagenetic Facies And Pore Evolution Of The Shaximiao Formation In Pengzhou Area,Sichuan Province

The reservoir of the Jurassic Shaximiao Formation in Sichuan Basin is a typical continental tight sandstone reservoir with complex evolution.At present,the exploration of Pengzhou area in Western Sichuan is not enough,and the basic geological research is not mature.The relationship between diagenetic facies and porosity evolution is not clear,and the relationship between porosity evolution and hydrocarbon accumulation period is not clear,too.It has seriously restricted the discovery and breakthrough of this series.Rely on the geological technology,this study made use of the outcrop profile,drilling,logging and other geological data of the Shaximiao Formation in Pengzhou area,Sichuan Province.By applying the reservoir petrological characteristics,this paper made sure the diagenetic facies types and the diagenetic strength.The contribution of diagenesis to reservoir physical properties and the diagenetic stages were clarified.Combined with the previous methods of pore recovery,the pore evolution process has been recovered.It is helpful to study the process of oil and gas accumulation and geological conditions,so as to clarify the changes in the whole process of oil and gas accumulation.It also has positive significance for the next exploration and development of oil and gas in Pengzhou area.The main rock types of the Shaximiao Formation in Pengzhou area were lithic sandstone and lithic quartz sandstone.The sandstone consist ed of primary pores and dissolved pores.The average porosity of the reservoir is about 4.6%,and the average permeability is less than 0.2m D.This reservoir belongs to the reservoir with ultra-low porosity and ultra-low permeability.According to different pore structure,two types of reservoir were divided,which included the type of pore and the type of pore-crack.The reservoir of the Shaximiao Formation were divided into six diagenetic facies:compaction facies,calcite cementation facies,kaolinite cementation facies,chlorite facies,dissolution facies and fracture facies.The compaction facies and cementation facies have the effect of reducing porosity,while the dissolution facies have the effect of increasing porosity because of secondary porosity.Different diagenetic facies can be identified their own parameter characteristics in logging curves.The diagenetic evolution has obvious stages,and the reservoir of the Shaximiao formation was in the middle diagenetic stage A.The staged diagenetic facies alternately happened.The gas in Pengzhou area is characterized by " compacted before accumulated".From the end of Late Jurassic to the middle of Early Cretaceous,the reservoir of the Shaximiao Formation reache d the peak of densification.