Study On Heterogeneity Of Low Permeability Reservoir In The Middle Sub-member Of The Third Member Of Shahejie Formation In Niu 35 Block,Niuzhuang Subsag

Reservoir heterogeneity in the third member of Shahejie formation in Niu 35 block of Niuzhuang sub-sag is strong,and the genetic type of sand body,distribution of sedimentary facies and reservoir physical characteristics are not clear,which restricts the understanding of remaining oil distribution.In this paper,the isochronal stratigraphic framework of the study area is established by using the data of core,logging,seismic and production performance,and the types and distribution characteristics of sedimentary facies are defined.On this basis,the reservoir heterogeneity is characterized.Based on the understanding of regional sequence stratigraphy,the isochronal stratigraphic framework of the third member of Shahejie formation in the study area is established by synthesizing seismic,logging and core data.The third member of Shahejie formation in the study area is divided into five sand formations.The main three sand formations are further divided into eight sub-formations,and the lower 5-8 sub-formations develop eight single sand formations.Core,well logging and seismic are combined to carry out facies study in the study area,and turbidity channels,lobes and turbidity fan margins are identified in turbidity fan deposits.Among them,the turbidity channel extends to the lake basin from east to West in a narrow and long way,forming strip-like continuous sand body distribution along the direction of provenance,and irregular tongue-shaped distribution on the plane of lobes and fan margins.This paper describes the reservoir heterogeneity characteristics of main small and single sand layers from the aspects of sand body distribution,physical properties and interbed distribution,and carries out comprehensive evaluation of reservoir heterogeneity with multi-parameters.The distribution of sedimentary microfacies controls the uneven distribution of sand bodies and the development characteristics of interbeds in the study area.The turbidity channel sandstone has large thickness,good connectivity,relatively good reservoir physical properties and relatively weak reservoir heterogeneity;the multi-lobe reservoir physical properties and reservoir heterogeneity are moderate;the fan margin sandstone body is thin,reservoir physical properties are poor,interbed development,reservoir heterogeneity is the strongest.Through the study of main single sand layer heterogeneity,it is found that there are obvious differences among the layers 7-2,7-1 and 6-2 in the middle sub-member of the third member of Shahejie formation.From bottom to top,the reservoir heterogeneity presents strong-weak-strong changes.The heterogeneity in single sand layer is mainly controlled by the permeability rhythm and interbed development constrained by sedimentary rhythm,and the density of interbed also presents high-low-high changes,which match the energy change of turbidity flow.Heterogeneous comprehensive index distribution shows that the area with weak reservoir heterogeneity is narrow and long in East-West direction,which is consistent with turbidity channel distribution.The reservoir with lobes and fan margins has strong heterogeneity,which is characterized by irregular tongue-shaped and elliptical plane distribution,and is a favorable facies belt for the next step of remaining oil tapping potential.The research results of this paper provide a geological basis for tapping the potential of remaining oil in the next step.