Sedimentary Facies And Reservoir Characteristics Of The Dongying Formation In The East Slope Zone Of The Chengdao

Taking the Dongying Formationg in the east slope zone of the Chengdao area as the research object,under the guidance of sedimentology and reservoir geology,and on the basis of clarifying the sedimentary facies types of Dongying Formation,the sedimentary and reservoir characteristics of the main oil-bearing strata(EdⅢ2-EdⅣ)are mainly studied.The sedimentary facies,the microscopic characteristics of the reservoir and the plane distribution of the favorable reservoir were clarified in this thesis.The Ed IV strata was dominant by the gravity flow deposition,which was consist by sublacustrine fan and nearshore subaqueous fan,whereas Ed III1 strata mainly develop fan-delta deposits with both gravity flow and tractive flow.In EdⅢ2 sedimentary period,the fan-delta deposits with both gravity flow and tractive flow are developed.The sublacustrine fan is mainly developed the second slope-break of the study area.The main lithology of it is pebbly sandstone and fine-grained sandstone,which has experienced the evolution from debris flow to hyperpycnal flow.The sublacustrine fan in the study area mainly develops the middle fan braided channel microfacies and the middle fan front microfacies.The sand body has strong continuity,and there are fan-shaped with long and narrow channels in the plane.The nearshore subaqueous fan is mainly developed fault terrace of the study area.The main lithology which is coarse grained sandstone and medium-grained sandstone,experienced the evolution from debris flow to turbidity current.The nearshore subaqueous fan in the study area is mainly composed of braided channel microfacies,weak continuity of sand body and fan-like distribution without channel on the plane.There are pebbly sandstone and moderate coarse sandstone in fan delta,which microfacies are underwater braided channel,estuary dam and sheet sand of fan delta.The continuity of fan delta sandbodies is weak,and most of them are lenticulars and divided into two fan bodies in the north and south in the plane.The south fan body of then is fan shaped,and the northern one is tongue-like.The diagenesis of Dongying formation in the study area includes compaction,cementation,replacement and dissolution.The stage of diagenesis is mesogenetic stage A.The diagenetic evolution stage is in A period of middle diagenesis,in which A1 substage is affected by organic acids and the diagenetic medium is highly acidic.The p H value increased somewhat,but it was still dominated by acidity.The reservoir space types are mainly dissolution porosity and microfracture.The reservoir property of EdⅢ2 is better than that of EdⅣ.The properties of reservoir has positive correlation with grain size,and are less affected by sorting coefficient and mud matrix content.Different sedimentary facies have different physical properties.The mouth bar and sand sheet of fan delta have the best physical property,followed by underwater braided channel of fan delta,braided channel of sublacustrine fan,braided channel of nearshore subaqueous fan,and middle-fan front microfacies of sublacustrine fan has the worst properties.the dissolution of feldspar components improved permeability apparently,which formed anthigenic kaolinite and secondary porosity.In order to describe the reservoir characteristics and distribution law of the main oilbearing member of Dongying Formation in the study area accurately,lithology,physical property,sedimentary microfacies and diagenetic characteristics were selected as reservoir evaluation parameters,and the comprehensive reservoir evaluation criteria for each sand group were established.The results showed that there are five types of reservoirs developed in the study area during the sedimentary period of ED Ⅳ.The favorable reservoir physical properties are above medium porosity to low permeability.The main microfacies type is braided channel of sublacustrine fan,and the lithology is mainly pebbled sandstone.On the plane,it mainly develops near the second slope-break of the study area.During the sedimentary period of EdⅢ2,four types of reservoirs developed.The favorable reservoir physical properties are above medium-porosity and medium-permeability,and the fan-delta deposits are developed.The lithology is mainly pebbled sandstone and fine sandstone,and the secondary dissolution pores are dominant.On the plane,the favorable reservoirs developes near well CB36 in the south and near well CB830 in the north.