Sequence stratigraphy, seismic sedimentology, and lithostratigraphic plays: Upper Cretaceous, Sifangtuozi area, southwest Songliao Basin, China

摘要

Lithostratigraphic plays are one of the major targets for reserve growth in the nonmarine Songliao Basin, China. In this article, an integrated approach was adopted that applies principles and techniques of sequence stratigraphy and seismic sedimentology to the study of higher order sequences, depositional environments, and lithostratigraphic trapping styles. In the Sifangtuozi area, 20 higher order (fourth- or fifth-order) sequences in four third-order sequences were identified in an Upper Cretaceous interval using well and seismic data. Core description and wireline log classification helped identify distributary channel fill, distributary mouth bar, sheet sand, distal bar, prodelta/shal-low lake, and semideep to deep lake deposits in fluvial-dominated deltaic systems. In two three-dimensional (3-D) seismic survey areas, seismic inversion and 90° phasing of seismic data converted seismic traces to pseudolithologic logs. Stratal slicing made it possible to interpolate and extrapolate well-data-derived sequence and facies interpretation to whole 3-D seismic surveys and then make broader interpretations and predictions on sand content, sandstone thickness, and geomorphological information. Play analysis using sandstone isopach or amplitude stratal slices and superimposed structural maps identified potential accumulations in small structural, lithostratigraphic, and combination traps. These traps are all significantly controlled by lithology, reservoir distribution, sealing conditions, and closure.