The conventional spectral bluing technique is mainly utilized for post-stack seismic frequency expansion.It is applicable to the shallow strata where sandstones and mudstones can be effectively identified based on the wave impedance of logs.However,this technique has many limitations for the impedance aliasing zones of moderately deep strata.The amplitude versus offset (AVO) gradient reflects the change in the relative reflection coefficient with offset and is positively correlated with the rate of change in Poisson's ratio,which can distinguish between sandstones and mudstones in moderately deep strata.Through forward modeling,this study first proved the reliability and stability of the AVO gradient in identifying the top interface of sandstones in moderately deep strata according to the changes in parameters such as lithologic association,physical properties,and fluids.Furthermore,to improve the characterization precision of thin sandstone interbeds in moderately deep strata,this study proposed a AVO gradient-based spectral bluing for seismic frequency expansion.The model tests and practical applications show that the spectral bluing based on AVO gradient can directly identify the information on reservoir interfaces and simplify the multi-parameter lithology prediction method based on CRP gathers or partial angle stack data.Moreover,the new technique proposed in this study can effectively characterize the thin sandstones in deeply buried strata in the XH sag and provides a reference for high-resolution seismic processing of moderately deep strata.
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