Sedimentary And Reservoir Characteristics Of The Third Member Of The Shahejie Formation In The Central Part Of The Liuxi Region

As a typical structural-lithological reservoir and effected by faults,the Liuxi oilfield is hard to explore and exploit.Integrated controlled by various factors,the Liuxi oilfield belongs to low permeability reservoir.Due to the complexity of broken reservoir,variable reservoir,and many problems in exploiting,it needs a comprehensive geological description of reservoir research.Based on the sedimentary theory,the paper combined core and thin section observation,logging,laboratory testing and production data to study the sedimentation characteristics,and reservoir characteristics of the third member of Shahejie formation of Liu 17 block and Lu 44 block of Liuxi oilfield.Sediments in the research are maily grey,hoary fine-grained sandstone and some grey and celadon siltstone,dark grey and fuchsia mudstone.Because the sufficient clastic material supply from the southeastern Xianxian lobe,large-scale braided river delta deposits have been developed in the study area during the sedimentary period of the third member of Shahejie Formation,forming microfacies as braided channels and overbank deposit on the braid river delta plain,and underwarer distributary channels,underwater distributary bays,estuary dams and sheet sands in the braid river delta front.In the sedimentary period of ? oil group,underwarer distributary channels developed in the study area.Subsequently the water body became shallow for a short time,and braid river delta plain developed during the early ? oil group.Underwarer distributary channels developed again and underwater sedimentary range increased due to water becoming deepen hereafter,and estuary dams and far bars developed in the whole study area until the late ? oil group.Integrating sedimentary characteristics of study area,the paper established facies model of the Liuxi oilfield.Through the thin slice and the physical property data analysis,the main reservoir space are dissolved pores affected by burial depth,which are dominated by intergranular dissolution pore and intragranular dissolution pore,and primary pores are less preserved.Controlled by both sedimentation and diagenesis,reservoir properties of these two block shows different that the overall performance of Liu 17 blocks has a better physical properties than Lu 44 block.Based on these two blocks' characteristics of reservoir development,the reservoirs of the third member of Shahejie Formation in the study area are divided into four types.The best reservoirs with middle porosity and high-middle permeability called type?is only developed in the river of Liu 17 block of small range.Reservoirs with middle porosity and middle-low permeability called type ? and reservoirs with low porosity and permeability called type ? mainly distribute in braided channels,underwater distributary channels and estuary dams,which are the main reservoir type in the study area.Reservoirs with ultra-low porosity and permeability called type ? are bad reservoirs with poor reservoir physical property,and mainly distribute channel edges or thin body of estuary dams or sheet sands.Controlled by many factors,development effect of the study area is poor.Most of the well water injection effect is poor,water injection wells difficult.The study shows that the drop of reservoir pore constriction connectivity and poor seepage channel of low permeability reservoir are mainly affected by content of clay mineral,reservoir sensitivity,pore throat structure,and eventually lead to poor water flooding effect.Due to the impact of developmental cracks in a few wells,the development characteristics of fractures should be considered in the process of water injection to avoid flooding.