Sedimentary Facies Study And Favorable Reservoir Prediction Of The Paleogene Shahe Street Formation In The North Zone Of Bonan Depression

The geographical position of the Bohai north zone is in the northern part of the Bonan depression.In recent years,oil and gas bearing blocks have been discovered successively in the first to three segments of the Shahe Street formation,showing the great exploration potential of the gravel rock mass,but with the deepening of the exploration and development of the rolling exploration,the multiple wells have lost profit,and the sedimentary facies of the gravel rock mass in this area have been found.And the distribution of the reservoir is still insufficient.Based on the seismic,log and lithologic data,the T-R sequence division interface is divided and the isochronous sequence stratigraphic framework is established.On this basis,the types of sedimentary facies and the formation model of sand bodies are studied.According to the case of exploratory well drilling in the study area,the sedimentary evolution law is further confirmed,combining the dominant sedimentary facies and dominant facies of the dominant facies,the comparative analysis of different sedimentary facies is made and the favorable reservoir position is predicted.The following points have been made:On the basis of reidentifying the unconformity surface,the T-R sequence interface is established,and the Paleogene Shahe Street formation is divided into 3 three order sequences,namely sequence I,sequence II and sequence III.Different sedimentary structures are separated from the different control factors in the depression zone and the steep slope zone,and two sequence models of single type sand and gravel and complex sand and gravel are established.On the basis of core observation and description and analysis of laboratory data,it is clear that the study area is mainly composed of two sedimentary facies: nearshore subaqueous fan and fan delta.Among them,the retrograde fan is a nearshore subaqueous fan,and the accretion and progradation fan is fan delta.The subaqueous fan in this area is dominated by gravity flow deposition,with relatively coarse grain size,complex grain size and large single stage thickness in vertical direction.Fan delta has the characteristics of gravity flow and traction flow deposition,the grain size is relatively fine,the vertical upstream distributary channel is dominated by positive grain order,and the distributary estuary sand dam is in reverse order.Main,single phase deposition thickness is relatively small.On the basis of the above research,the favorable factors of formation and development of high quality reservoirs are deeply selected,and favorable sedimentary microfacies are selected,which are favorable lithofacies(fine sandstone,gravel sandstone and gravel sandstones),and the physical properties of the reservoir are combined with the favorable sedimentary microfacies(the near shore fan braid channel,the fan delta front subaqueous distributary channel and the distributary estuary sand bar).Based on the analysis of the factors and the comprehensive parameters such as sedimentary microfacies and reservoir physical properties,three favorable reservoirs in the study area are proposed.