VSP Anisotropic NMO Correction and Its Application to Attenuate Noise

Abstract

Summary Normal moveout (NMO) correction is an important data processing step for VSP CDP transform and other applications. Most of the previously used VSP NMO correction methods are valid for isotropic media, but can cause significant errors in multi-layered and/or anisotropic (VTI) media. We present a new methodology to accurately and efficiently perform VSP anisotropic NMO correction for walkaway VSP (WVSP) or 3DVSP data. We adapt the Fomel and Stovas’ NMO correction formulation originally developed for surface seismic data, to NMO correction for WVSP or 3DVSP data in multi-layered VTI media. We employ a simulated annealing (SA) algorithm to automatically search for four parameters in the Fomel and Stovas’ formulation. In the SA algorithm, we use semblance coherence analysis in the VSP common receiver gather domain as an object function. That is, after a correct NMO correction, a reflection event is aligned and its semblance coherence coefficient is maximized. To attenuate both coherent and incoherent noise in the reflection wavefield of VSP data, we utilize a three-step processing flow consisting of NMO correction, median filtering, and reverse NMO correction. We demonstrate a significant improvement in the image quality of a field WVSP data after attenuating noise by this new methodology.