Estimation of Thomsen VTI parameters for seismic imaging using vertical and deviated wells

Summary Seismic data processing by pre-stack depth migration (PrSDM) requires a reliable initial velocity model. An accurate velocity model secures pre-stack gather flatness by short offset spread; however, a vertical transverse isotropy (VTI) model, for characterizing horizontal layering, should be sufficiently considered to extend offset usage and maximize image quality. This study sought a robust workflow of Thomsen VTI parameters, e and δ, estimation to stabilize anisotropic tomography analysis. Vertical and deviated wells offered the opportunity to derive the target parameters in a rather simple and elegant way. Anisotropic Backus averaging combined intrinsic and apparent anisotropy at seismic scale. In our case study, the calculated anisotropic parameters profiles were validated by WAVSPs and by the surface seismic data, which could be flattened effectively all the way to the largest offsets. In particular, steps like refraction FWI need an accurate anisotropic starting model to converge effectively. Cross-spread 3D seismic surveys are particularly ill suited for deriving shallow anisotropic velocity models and the vertical and deviated wells method provides a welcome alternative.