Gulf of Mexico Case Study of Localized Anisotropic Tomography with Checkshot

Reliably deriving parameters for anisotropic depth models requires use of borehole information. Localized tomographic inversion attempts to streamline and automate this process by directly incorporating the available well data into conventional reflection tomography. We present a case study from Gulf of Mexico where we conduct local VTI anisotropic tomography using a joint dataset consisting of seismic and checkshot data. Because this area has low structural dip, the results can be compared with more traditional manual 1D layer-stripping inversion. Tomographic inversion for three VTI parameters produces a smooth velocity model that both fits the checkshot traveltimes and flattens all seismic gathers. To regularize tomographic inversion, we apply smoothing operators that are oriented along predominant dips of seismic event and have large lateral extent. The anisotropic profiles derived by tomography and 1D inversion have similar low-frequency components, but differ in finer details. Borehole data require careful conditioning before joint inversion because of potential difference in water velocity between seismic and well surveys. The workflow we present can be applied to calibrating anisotropic parameters in the more general case of 3D models with structural dip and borehole data from deviated wells.