Seismic Anisotropy Characterization in Heterogeneous Formations Using Borehole Sonic Data

Heterogeneity is a common phenomenon that needs to be taken into account when characterizing the elastic anisotropic properties of formations. Anisotropic elastic properties can be obtained from comprehensive borehole sonic datasets consisting of monopole compressional, dipole fast and slow shear, and Stoneley shear velocities. This can be done successfully through a methodology involving careful binning of the velocity data on the basis of independent, petrophysical information, followed by an inversion process that is carried out on each bin individually. The resulting table of anisotropic parameters per bin can then be used to derive, among other results, correlations between formation petrophysical and anisotropic properties. A new workflow was successfully applied to determine the elastic, transversely isotropic properties of heterogeneous sand-shale sequences. The results of the methodology have significant practical implications. One of these is that synthetics based on the anisotropy-corrected deviated well logs yield stronger and more apparent reflections, as well as a significantly different time-depth relation. Additional applications include the use of the inversion workflow results as inputs into anisotropic seismic velocity models and AVOs.