Characterizing seismic anisotropy and AVO using walkaway VSP: Willow oilfield, Alaska

Abstract

Amplitude versus offset (AVO) analysis of surface seismic data has been commonly used for lithology and fluid identification. Isotropic AVO synthetic gathers created using log data are found to differ from the response observed on surface seismic gathers. A walkaway vertical seismic profile (VSP) survey was designed to sample the wavefield along depth and with varying offset. These data are analyzed to determine intrinsic anisotropy for building a calibrated 1D vertical transverse isotropy (VTI) model, followed by further processing and analysis to determine the AVO response at the target zone. AVO synthetics generated with a calibrated VTI model are shown to match the true AVO response measured from the walkaway VSP. Walkaway VSP analysis for anisotropy and AVO are shown to reconcile the responses observed between logs and surface seismic data.