Suppressing residual low-frequency noise in VSP reverse time migration by combining wavefield decomposition imaging condition with Poynting vector filtering

Abstract

Due to high imaging precision and adaptability for steep-dip interfaces, reverse time migration (RTM) has become the preferred choice in seismic imaging. However, low-frequency noise is a common problem in RTM and effects the clarity of the final image. The noise is formed by the cross-correlation of source and receiver wavefields that propagate along the same paths. A wavefield decomposition imaging condition (WDIC) can eliminate this low-frequency noise by separating the wavefield into up–down or left–right directions and then cross-correlating source and receiver wavefields along the different propagation paths. Nevertheless, many backscattered waves propagating along horizontal, nearly horizontal, vertical and nearly vertical directions exist in vertical seismic profile (VSP) data. These waves are difficult to separate and generate the residual low-frequency noise when applying WDIC to VSP RTM. To overcome this, Poynting vector filtering is combined with WDIC to attenuate the noise. Several numerical case studies testify to the effectiveness of the analysis and method.