Discussion About Strata Thickness Reduction Model of Putaohua Oillayer of Sanzhao Sag in Songliao Basin

Formation thickness of Putaohua oil layer in Sanzhao depression, Songliao basin, reduces gradually from north to south, and the thinning mode is always controversial,result in hydrocarbon vertical distribute confusion. Curves of 1024 wells and core data of 10 wells analysised formation structure of Putaohua oil layer and sedimentary features of reservoirs show formation of Putaohua oil layer is a process of gradually thinning by layers controlled by uplift of syndeposition structure at the end of deltas, and surfaces of sand-clay discontinuity at the top and bottom of Putaohua oil layer are not genuine interfaces, that is sand-clay connecting mode formed by gradually changing from northern sand to southern clay; shallow deltas typically developed in Putaohua oil layer, concentrated and continuous straightly-underwater channels and river-dominated extremity sheet sands are the main microfacies; Putaohua oil layer vertical develop sedimentary evolution of sequence with first fast dereliction then slowly transgression, the central Putaohua oil layer(lowstand) distributary channel sand body development, that compose hydrocarbon advantages transporting channel of parallel migration and rich layer.