Keywords: 
• Sanjianfang Formation reservoir /
• microfacies /
• characterisics of sandbody distribution /
• waterflooding developmemt result

Abstract: he braided river delta plain and front are well developed in Sanjianfang Formation reservoir,in which the main microfacies include braided river distributary channel,channel bar,underwater distributary channel and zones between distributary channels.The sedimentary microfacies in Sanjianfang reservoir and its effect on waterflooding result are studied through determination of sedimentary,combination of dynamic and static information as well as observation of production test.Based on the analysis of lithological,electrical and corresponding physical characters,the relationship between lithology and electricity is firstly set up,then according to the depositional cycle developped by sedimentation of each distributary river from formation to development and abandonment,the layer correlation is made by each well in matrix profiles.On the basis of what mentioned above,the top and bottom are as well as distribution range of every unit, i.e.,sandstone group,sandstone layer and substratum are determined.Finally,Sanjianfang Formation is subdivided into five sandstone groups,eighteen sandstone layers and twenty-four substrata. Controlled by the depositional microfacies,the movement of water—oil and the variation of production are primarily affected by the horizontal distribution of sandbodies.The relatively good physical properties,connection and high water-intake capacity results in high velocity of injecting water in distributary channels and quick increase of water in production wells.For this reason the high-yield wells produces no water at the beginning and much water at last. In vertical profiles,controlled by the sedimentary cycles,the highly produced layers are mainly the third and the forth substrata located in the middle-low part of every sandstone group.On the whole,affected by the plane and vertical heterogeneity,the injected water tends to breakthough in one direction horizontally and one layer vertically which further increases contradivtion between intralayer and interlayer during waterflooding.