Diagenesis Of Carbonate Rocks Of The Lower Triassic Feixianguan Formation In Jiangyou Area,Sichuan Basin

The Feixianguan Formation of the lower Triassic plays an important role in the hydrocarbon bearing marine carbonate strata in the Sichuan basin,showing great potential for oil and gas exploration,but the scope of the study is mostly confined to the northeast of Sichuan basin.Until recently,people had invested more enthusiasm in the study of the Feixianguan Formation in northwestern Sichuan,but overall it was still in the preliminary stage of exploration and development.Based on the current research status,this paper takes the modern sedimentary geology and reservoir geology theory as the guide,and uses the Feixianguan Formation marine carbonate rock in the Jiangyou area as the entry point.According to the investigation of the outcrop profile in the field,Combined the petrological characteristics and geochemical analysis data in the Jiangyou area,completed sedimentary facies in the study area.and the diagenesis of carbonate rocks in the Feixianguan Formation was thoroughly investigated.The stages of diagenetic evolution were analyzed in detail,and the effect of diagenesis on the control of the carbonate reservoir in the Feixianguan Formation was described.The lithology of Jiangyou area is dominated by carbonate rocks and contains a small amount of clastic rock.The main rock types of the carbonate rocks in the Feixianguan Formation include: oolitic spariteand,brilliant-grained limestone,crystalline limestone,microcrystalline dolomite,silty-crystal dolomite,lime-dolomite,etc.Clastic rocks mainly include mudstone and muddy siltstone.The petrographic characteristics of the carbonate rocks in the Feixianguan Formation were described in detail through thin section identification and cathodoluminescence analysis.Combined with previous research data,field profile characteristics,paleontological characteristics,etc.,it was identified that the Feixianguan Formation in the area mainly develops the platform edge facies,the open platform facies,and the restricted platform facies,and the corresponding sedimentary subfacies are divided.The carbonate rocks of the Feixianguan Formation in the Jiangyou area of the Sichuan Basin have undergone a complex diagenesis process.The types of diagenesis are various,and the degree of participation in the construction of the reservoir is not the same.Among them,the dolomitization and dissolution(early dissolution,late dissolution)are very constructive for the development of good reservoirs,and compaction,late cementation,and cavity filling have also been extremely destructive to the development of high-quality reservoirs.The diagenetic stage can be divided into four stages of diagenesis: syngenetic,early diagenesis,middle diagenesis and late diagenesis,involving seawater diagenetic environments and burial.Diagenetic environment,meteoric freshwater environment.Based on the results of geochemical data analysis,it is believed that most of the samples in the study area retain the information of seawater or sea-derived fluids at that time,and the seawater or sea-source fluids in the syngenetic or para syngenetic are the main sources of dolomitization fluid in the Feixianguan Formation.The mechanism of dolomitization is mainly the mechanism of seawater seepage reflux during the para syngenetic-shallow burial period.The reservoir space of the carbonate reservoir in the Feixianguan Formation of the study area is mainly composed of dissolved pores and a small amount of fractures.The formation of these reservoir spaces is controlled by both sedimentation and diagenesis.Among them,sedimentation is the foundation and diagenesis is the key.Sedimentation has laid the foundation for the reservoir's basic geological conditions,diagenesis forms and transforms the reservoir space and controls the overall development of the reservoir.