Reconstruction of sediment-dispersal patterns using seismic sedimentology in the southeastern Zhanhua Sag, Bohai Bay Basin, China

Abstract

Reconstruction of sediment-dispersal patterns not only provides insight into paleogeographic evolution, but also sheds light on facies and reservoir prediction. By integrating core, wireline logs, and 3D seismic data, seismic sedimentologists have discovered several advantages to sediment-dispersal reconstruction and paleogeographic-environment analysis. We have subdivided the third member of the Shahejie Formation (Es3) of the southeastern Zhanhua Sag (Sanhecun Block) into three third-order sequences, namely SQ1, SQ2, and SQ3 from bottom to top. The facies architecture was analyzed by using the seismic sedimentology approach based on 3-D seismic data. Seismic RMS-amplitude stratal slices reveal different characteristics of the lobes among the southwest gentle slope, southern slope-break belt and north fault-controlled slope from source to sink. On the basis of an integrated analysis of well log, core data, seismic facies based on RMS attributes, three depositional environments (e.g., “fan-delta”, “turbidite” and “lacustrine” facies) have been recognized. Seismic RMS-amplitude stratal slices indicate that the depositional environments of these sequences evolved from medium-sized gravel-rich fan-delta and turbidite-fan deposits to small-scale mud-rich fan-delta deposits, and lastly to large-scale sand-rich fan-delta deposits. The changes of relative lake level and sediment supply rate control the lithology and size of different depositional systems. This study also suggests that the temporal and spatial evolution and distribution of depositional systems are influenced significantly by paleotopography and slope break in the systems tracts of different sequences of the Es3 in the southeast Zhanhua Sag, Bohai Bay Basin. In addition, fan-delta-front deposits could also be considered as future potential exploration targets because they are relatively sand- or gravel-rich, given the reconstruction of the sediment-dispersal pattern.