The presence of vertically aligned fractures can produce measurable seismic azimuthal anisotropy. An azimuthal AVO (AVOA) analysis can be employed for fracture characterisation as it allows for the estimation of the magnitude and orientation of the fracture-induced anisotropy. This study demonstrates that optimal basis formalism can be employed for the inversion of fracture density from synthetic AVOA data from a caprock within a geological setting with large impedance and anisotropy contrasts. The method is case specific – very dependent on knowledge of the in-situ rock properties. In this case-study, the method is particularly advantageous because it is independent of the impedance contrasts of the layers. The model-based approach thus allows for direct quantification of the magnitude of anisotropy from an inversion of the P-wave amplitudes along the interface of interest within the high contrast geological setting. This evaluation is the first step toward an AVOA analysis of the true seismic amplitudes obtained at the Aquistore CO2 storage site.


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