Abstract: After the S Oilfield in Bohai enters its high water cut period, the intra-layer contradiction becomes more prominent, and the distribution of remaining oil under the control of reservoir internal structure becomes more complicated. Aiming at the problem that the interface of delta facies configuration is not able to be effectively identified, based on the data from sealed coring wells, the concept of GR return rate is introduced by the authors in this paper. Through the calibration of core and electrical logging curves, the quantitative identification chart of interface of different configurations in a composite estuary bar is established, and the distribution pattern of interface of configurations in layer is defined. The dip angle, width and extension range are quantitatively described. The results show that there are two main types of configurational interfaces with certain shielding capacity in estuary bars: superimposed horizontal interface (Grade 4) in the composite bar and oblique front interface (Grade 3) in the single bar. Among them, the control of the remaining oil by the Grade 4 interface is mainly vertical occlusion and top enrichment, while the control of the Grade 3 interface is mainly lateral occlusion and local enrichment. In view of the different remaining oil distribution patterns mentioned above, the adjustment strategies of "oil prospecting on water" and "oil digging under water" by means of horizontal wells are proposed respectively, which can effectively improve the in-formation utilization of thick estuary bar sand bodies, and have a strong guiding significance for the later adjustment of similar high water cut old oilfields.