Architectural analysis of subsurface meander-belt sandstones: A case study of a densely drilled oil field, Zhanhua sag, east of Bohai Bay Basin

Abstract

The Gudong oil field offers a unique opportunity to characterize thin meander-belt sandstones in an area with a dense network of wells (100 wells per square kilometer or 259 wells per square mile). The goal of this study is to evaluate the evolution of subsurface meander-belt complexes through analysis of their overall stratigraphic architecture defined by the spatial distribution of sedimentary structures and stratigraphic surfaces of stacked point-bar sandstones, which severely affect the potential for producing the remaining oil in these mature oil fields. Five types of superposition structures, which reflect the shapes of the point-bar sand bodies in the superimposed regions between point bars, are identified by combining stacked and migrated seismic profiles, seismic forward models, and wire-line log profiles. The point bars belong to different stages of channel stories through the analysis of their superimposed structures and the vertical offset of the basal surfaces of point-bar sandstones. Five channel stories are recognized in the thin meander belt. They can be distinguished by the analyses of stratal slices, wire-line log profiles, and tracer data. These channel stories were found to exhibit unique morphometric characteristics: the thickness and width of the channel stories changed with the discharge of the paleoriver; the widths of the later channel stories became more stable through time and were not affected by the flow discharge during the deposition of the channel stories. The identified superimposed structures between subsequent point bars and morphometric parameters of channel stories are useful for the modeling of the target reservoir.