Deposition Mechanism And Reservoir Characteristics Of Gravity Flow In The 3rd Member Of Dongying Formation In The East Slope Of Chengdao

The study of gravity flow depositional process and law is a hot topic in sedimentary geology.In order to deepen the understanding of the sedimentary mechanism of proximal coarse-grained gravity flow in lake,explore its sedimentary law in the gentle slope of the rift basin and the development features of high quality reservoirs,the rheology test and sedimentary research for the turbidite of the 3rd Member of Dongying Formation in the east slope of Chengdao of Shengli Oilfield were carried out.Based on the analysis of core data,rheological tests of coarse-grained fluids with different gradations were designed and carried out,and with the results fluid types were divided.Combined with the analysis of seismic attributes,drilling and logging data,the genetic type and the spatial and temporal distribution characteristics of gravity flow deposition were defined.Based on identification of rock and mineral,conventional physical property test data and scanning electron microscopy result,the analysis of characteristics,classification and evaluation of the reservoir of turbidite were carried out.The main achievements include:1.According to the rheological test results,the content of sediment and clay are the key factors controlling fluid type and its conversion,and different grain size distribution can cause this conversion process to advance or lag.With the decrease of sediment and clay content,sediment gravity flow will successively manifest as the cohesive debris flow(yield-pseudoplastic fluid),the poorly cohesive debris flow(plastic fluid),non-cohesive debris flow(yield-dilatant fluid),high density turbidity(dilatant fluid)and low density turbidity flow(Newtonian fluid).2.Based on the analysis of core data,10 kinds of lithofacies and 6 kinds of lithofacies associations are identified.According to the differences between lithofacies and lithofacies associations,5 kinds of sedimentary microfacies are divided into main channel,braided channel,lobe,lateral edge of channel or lobe and thin turbidite,and the distribution of sedimentary facies of different layers is stratified.During the deposition of E_d9 Sand Group,the lower part of the3rd Member of Dongying Formation,the grain size of sediment was coarse and the fans were isolated and close to the basin edge,which may be affected by the decrease of flood frequency due to the wet and cold climate.During the deposition of E_d8 Sand Group,the upper part of the3rd Member of Dongying Formation,the grain size of sediment was relatively fine,and large contiguous fans were formed,which may be related to the intensification of flood activities carrying large amounts of fragmentary material into the basin due to the gradual warming of temperature.The fault trough and transition slope formed by fault growth and connection controlled the paleocurrent direction and sandstone deposition.3.The sandstone mainly belongs to medium-low porosity and medium-low permeability reservoir.The reservoir spaces are mainly primary intergranular pores.The lithofacies and sedimentation are the main controlling factor for the development of high-quality reservoirs.Cementation has little effect on reservoir physical properties,compaction is the main reason for the deterioration of reservoir physical properties,and dissolution has limited effect on reservoir physical properties.The statistical results indicate that the fine sandstone reservoirs formed by lobe or braided channel are the best quality reservoirs.