Anisotropic seismic velocity models from modeling and inversion of walkaway VSP data

Abstract

We propose a fast and efficient method to build anisotropic seismic velocity models by combining forward modeling and traveltime inversion of 2-D walkaway VSP data. Applying this approach, we derived anisotropic seismic velocity models for a 1200 m thick reservoir overburden consisting of horizontally layered shales and shaley sands in the Western Canadian basin. The models were determined by iteratively minimizing the misfit between the measured and modeled VSP first break times. The modeled times were calculated by 2-D ray tracing through isotropic and anisotropic velocity models. Once we achieved a fairly good match between the data and the model we then used inversion for fine-tuning. The proposed new method can help to provide good anisotropic velocity models for both surface and borehole seismic anisotropic migration.