Type IV delta deposit in the 3rd member of Qingshankou formation in Daqingzijing area,Songliao Basin

The 3rd member of Qingshankou formation is an important horizon of Gaotaizi reservoir,the major oil-bearing measures in Daqingzijing area,Songliao Basin,and is taken as target strata to study sedimentary microfacies,distribution features and evolution process based on regional geologic background,core observation,logs and seismic data.The results indicate that Type IV delta deposit system had developed in the 3rd member of Qingshankou formation,and can be divided into three subfacies including delta plain,delta front and prodelta,which can be further divided into multiple microfacies based on different sedimentary characteristics.A sedimentation model has been built for the 3rd member of Qingshankou formation on this basis.The delta sand bodies in the study area mainly deposited along the northwest-southeast axis,generally distributing from southwest to northeast.The major sand body was river mouth bar,which was locally thickened and developed into front bar and barrier bar under lake wave transformation.This is the main feature of Type IV delta deposit.The river mouth bar,front bar and barrier bar constitute major reservoir bodies.