Keywords: 
• Songliao Basin /
• Nenjiang Formation /
• shallowwater deltas /
• subaqueous distributary channel /
• dense cluster wells

Abstract: With the application of well data  from 1 800 exploration and development wells with the inter distance of 200 m , identification of lithology and analysis of logging facies, we compile sand thickness map and joint wells section of sand body in sandunitⅠ, third segment of Nengjiang Formation. By the semiquantitative analyses on sand bodies, we find that the interval of interest is deposited as the shallowwater deltas front and the main kind of sand body is subaqueous distributary channel deposition, witch extends over 20 km and evolves into three types processing to the end of delta front: the sand body of meandering channel, which is characterized as long pod ,with the width from 600 m to 900 m , and branch off after stretched 8~10 km ; the sand body of branching channel ,which is characterized as short pad , with the width from 500 m to 900 m , and branch off after stretched 2~3 km ,distribute as the symbol of ‘人’or rhombusshaped ; the sand body of reticulate channel, which is distribute as nets, with the width from 300 m to 500 m ,and branch off after stretched 0.5~1 km. The evolution of subaqueous distributary channel sand body associated with the change of superimposed styles and microfacies. The former changed from vertical superposition to dislocated superposition to dislocatedlevel composited superposition to levelly related joint to isolated dispersion; the latter changed from crevasse channel to interchannel deposits to mouth bar. All of the above association are the result of gentle sedimentary basement，rich sediment supply，steadily falling lake level，stable subsea natural barrier and the energy transformation between rivers and lakes.