Abstract: Bohai Block BZ19-X is characterized by the development of multi-stage superimposed lobate shallow-water delta sandbodies. However, the unclear understanding of the internal depositional sequences and superimposition patterns of these composite lobate bodies has constrained the potential for remaining oil recovery in the block. To address this issue, core samples, analytical tests, well logging, and seismic data have been utilized to determine the depositional characteristics of lobate shallow-water delta deposits and to establish well-to-seismic response models. By using the sandbody boundaries delineated by planar seismic attributes as a control and integrating well-to-seismic fusion with bed flattening and isochronous stratigraphic slicing, the fine characterization of different superimposed types of composite lobate shallow-water delta sandbodies has been achieved, thus providing a foundation for the potential of remaining oil recovery. The results show that: within the study area, the fluvial control over lobate shallow-water delta deposits is evident, and the plane can be divided into channel areas, bar complex areas, and shallow lake areas. Affected by the lateral migration and vertical cutting of channels, multiple lobate bodies develop both laterally and vertically. The main lateral contact styles are separated, side-lapping, side-cutting, and inter-connected, while the vertical superimposition patterns are primarily divergent, weakly-cutting, shallow-cutting, and deep-cutting. Lateral contact and vertical superimposition lead to the continuous development of sandbodies. Affected by the contact and superimposition styles of sandbodies, as well as the degree of well network control, single-stage sandbodies without well control and those with an incomplete well network, as well as composite sandbodies with a high degree of well control, tend to have concentrated remaining oil in the interwell and marginal areas. The results of this study provide effective guidance for the recovery of remaining oil in high water-cut oil reservoirs in the block and have reference significance for the development adjustment of similar blocks at home and abroad.

Key words: shallow-water delta, stacking style, seismic phase, sandbody characterization, remaining oil, Bohai Block BZ19-X