A major feature was recently incorporated into AxRTM allowing for the propagation of seismic waves in anisotropic media. In seismic jargon, the anisotropy is widely known as tilted transverse isotropy (TTI) whereby the axis of symmetry for wave propagation can have arbitrary tilt which usually corresponds with the dip angle of geological substructures.

In the presence of anisotropy, isotropic migration will incorrectly image the position of seismic structures below dipping anisotropic bedding. TTI is an effective method for correctly imaging the position of geological substructures located below dipping anisotropic overburdens. Imaging with anisotropic modeling capabilities reduces the risk in oil-and-gas exploration drilling decisions. Incorporating anisotropic modeling into vanilla isotropic reverse time migration means that each migration now requires not only the velocity model, but also the Thomsen anisotropy parameters, dip angle and azimuth angle (in the case of 3D migrations).

The BP 2007 TTI model was migrated using both isotropic and TTI anisotropic propagation. Image (a), produced using isotropic AxRTM, shows a lateral shift in the position of the vertical column below the salt. Image (b), produced using TTI anisotropic AxRTM correctly positions the vertical column below the salt. Compare the images with the velocity model shown in image (c).

In conclusion, reverse time migration with TTI anisotropy correctly images the lateral position of vertical columns below dipping anisotropic overburdens. The ability to model with anisotropy provides another tool to confirm the correctness of a given velocity model with more confidence.

Image: (a)