Uncertainty and nonuniqueness in linearized AVAZ for orthorhombic media

Abstract

Orthorhombic symmetry is one of the simplest models capable of representing fractured media such as naturally fractured shale reservoirs. However, low elastic symmetry translates to a large number of unknown elastic parameters, which affects the ability to obtain unique solutions. Therefore, the uncertainty associated with seismic-amplitude inversion must be considered for better understanding of the limitations and potential benefit of the inversion. An analysis of linearized amplitude variation with azimuth (AVAZ) inversion resulted in the development of workflows for practical AVAZ parameter estimation with uncertainty analysis. The inverted orthorhombic parameters are ranked by their uncertainty. Inversion attributes have clear meaning and can be used quantitatively when performing anisotropic orthorhombic subsurface characterization. The technique was applied in a field case for estimation of reservoir properties in orthorhombic media.