Building TTI depth models using anisotropic tomography with well information

Tilted transverse isotropy (TTI) is becoming recognized as a more realistic description of anisotropy in sedimentary formations than vertical transverse isotropy (VTI). This is especially true in complex geological settings. While model building approaches for VTI are well understood, similar approaches for TTI media are in their infancy, even when symmetry-axis direction is known. We present an approach that allows building localized anisotropic models utilizing joint inversion of seismic and well data. We present a synthetic data example of anisotropic tomography applied to a layered TTI model with a symmetry-axis tilt of 45 degrees. We demonstrate three cases of introducing additional information. In the first case velocity along the symmetry axis is known and tomography inverts for Thomsen’s ε and δ. In the second case, tomography inverts two Thomsen parameters and velocity from a joint dataset that consists of seismic data and vertical checkshot traveltimes. In contrast to the VTI case, such inversion is non-unique. To combat non-uniqueness in the third case we supplement checkshot and seismic data with the Thomsen’s δ profile from an offset well. This allows recovery of correct profiles for velocity along the symmetry axis and Thomsen’s ε. We conclude that TTI model building may remain non-unique even in the presence of well information. Therefore additional assumptions need to be added or uncertainty analysis has to be conducted to pick a geologically plausible model from a range of equivalent models.