Research On Sedimentary Facies Of The Second Member Of Dongying Formation?Ed₂? In The Dalujia Region Of Huimin Sag

Dalujia region is located in the downthrown side of Linyi large fault in centraluplift belt of Huimin depression.It is a typical antithetic drag anticline structure associated with Linyi large fault and complicated by fault.The main oilbearing series in the study area is the second member of Dongying formation.The difficulty of development gradually increases with the increase of oil and gas production,oil recovery remains low.One of the reasons for this situation is that the basic geology such as sedimentary facies and reservoir distribution of oil-bearing strata in this area is unclear.In this study,under the theoretical guidance of sedimentology,petroleum geology,logging geology and other disciplines,using the collected data of logging and reservoir physical property,combined with regional geological background,small layer division and correlation,sedimentary facies study and reservoir characteristics study were conducted.Gained the following understanding.According to stratigraphic division and correlation,Ed₂ is divided into four sand groups and 31 layers.The study of sedimentary facies shows that delta facies developedinEd₂,including delta front subfacies and predelta subfacies,can be further divided into underwater distributary channel microfacies,main body of branch estuary bar microfacies,lateral edge of branch estuary bar microfacies,far sand bar microfacies,intertributary bay microfacies and foredelta mud microfacies.The thickness isoline of sand body and the sedimentary facies distribution mapreflect that the thickness of sand body in the north and middle part of the study area is larger,and the thickness decreases gradually from northwest to southeast.The mostly developed sedimentary microfacies is the main body of branch estuary bar microfacies,which is distributed all over the study area as sheet.7 sand group corresponds to a process of lake advance and lake retreat.6 sand group and 5 sand group corresponded to a continuous and slow lake retreat process.Two lake retreats occurred in 4 sand group.The scale ofdelta increased gradually.Reservoir physical property analysis shows that the north and middle of the study area has a high porosity and permeability,and its change rule is obviously affected by the sedimentary facies,which is generally consistent with the development of sand body,the area with a large sand body thickness has better physical property.The intrastratal heterogeneous features of the lateral edge of branch estuary baris better than the main body of branch estuary bar.Plane heterogeneity and interlayer heterogeneity are not strong.Different sedimentary microfacies show different reservoir characteristics.The main body of branch estuary bar has better porosity and permeability,the physical property of the reservoir is good,followed by the lateral edge of branch estuary bar andfar sand bar.