Elastic moduli parameterization and inversion considering nanopores effects in shale

Abstract

Nanopores are widely developed in organic kerogen in shale. Due to the large surface-bulk ratio, nanopores cause significant surface effects that affect the overall elastic properties of shale. It is essential to consider the effects of nanopores when applying the prestack seismic inversion technique for shale reservoir prediction. Based on classical elastic theory, the technique of amplitude variation with offset (AVO) can usually extract velocity of the longitudinal wave and shear wave, elastic modulus, and density in shale reservoir from prestack seismic amplitudes but often ignores the surface effects of nanopores. For this reason, we have derived a new AVO parameterization combining the nanoporoelasticity theory and AVO technique. The newly derived parameterization contains four parameters (shear modulus of matrix, nanopores-related parameter, shear modulus of saturated rock, and density) which can be used to estimate the nanopore properties of shale. The model test and real seismic data examples verify the feasibility and suitability of the proposed method by applying the Bayesian inversion technique with smooth background constraint.