Anisotropic depth imaging in presence of stress: transversely Isotropic or orthorhombic?

SUMMARY Presence of oriented stresses and fractures in the subsurface can pose significant challenge when imaging wide-azimuth and multi-azimuth data using transverse isotropy as an approximation to describe the medium. We describe the key components of an orthorhombic modelbuilding and updating workflow for depth imaging in areas affected by stress. We discuss several different options for deriving the initial parameters describing orthorhombic medium and their dependencies on the geometry of the available seismic data. We demonstrate the effectiveness of the workflow on real data from the Gulf of Mexico. Compared to transversely isotropic imaging, the orthorhombic imaging flattens the common-image-point gathers in all azimuths and results in improvements of image focussing.