High resolution sequence stratigraphy and reservoir prediction of northern Wuerxun Sag,the Hailar Basin

The reservoir types are unclear in the northern Wuerxun Sag,the Hailar Basin,due to the complex fractures and various sedimentary genetic types.Based on the core,seismic and logging data,a high resolution sequence framework was established through the identification and comparison of key boundaries of the main oil-bearing formations,i.e.the second member of Nantun Formation(K1n2) and the first member of Damoguaihe Formation(K1d1).The pay zones cross two third-order sequence boundaries in the Su 131 and Su 102 fault-block reservoirs.The main reservoir is the low-system-tract slumped turbidite located at the bottom of the third-order sequence instead of the fan-delta front sand body located at the top of third-order sequence.Based on redefinition of the sequence-stratigraphic position of the main pay zone and analysis of reservoir genetic types,it is proposed that the reservoir in the northern Wuerxun Sag is of structural-lithologic type.In addition,the temporal and spatial distribution of sand units is analyzed.These understandings lay a solid basis for further development and extension of the oilfield.