1. Changchun Oil Production Plant of Jilin Oil Field，Changchun 130061，China; 2. College of Earth Sciences，Jilin University，Changchun 130061，China

The second member of Shuangyang Formation in C Block of Changchun oil field is the main explo- ration layer． The second member has been divided into 5 sand groups，in which the sand groups III and IV are the main oil- produced groups． Based on the sedimentary characteristics，the second member is considered as the fan delta deposition． The groups I and V are the fan delta front deposition，and sand groups II- IV are the fan delta plain deposition． The distribution of sand bodies is obviously controlled by the sedimentary facies belts and shown along with the north- west direction． On the basis of defining the stratigraphically sedimentary characteristics in this area，the reservoir forming conditions of hydrocarbon reservoir in this area are studied． It is considered that the south depression has the hydrocarbon supplying ability， and the Shuangyang Formation is the hydrocarbon supplying formation． The dark mudstone in the third memeber of the Shuangyang Formation is regional caprocks． No. 17 fault and a series of derived faults with nearly SN- trending communicate oil source and dredge oil gas in the earlier stage， and act plugging effect in the later stage． Vertically in direction，the single well of C Block is a combination in general of the oil reservoir- oil and water reservoir- water reservoir in which overall，the updip is the oil reservoir and the downdiptraps is the oil- water and water reservoirs． The oil and water is easy to balance within the range of struc- tural trap，and the oil- water interface formed uniformly in －1 695 m． The second member of the Shuangyang For- mation is a reservoir forming system and is a hydrocarbon reservoir of fault block． The reservoirs of low permeabili- ty- middle porosity，low permeability- low porosity and ultra low permeability- low porosity are the main distributive areas of remaining oil． The formation of remaining oil is influenced by the facies control and structural control， which is mainly developed in the river reservoir．