Frequency-Dependent AVO Inversion for Viscoelastic Solid-Fluid Decoupling Factor

Abstract

Summary Frequency-dependent amplitude variation with offsets (FAVO) inversion is a popular method for the estimation of the frequency-dependent elastic parameters to guide fluid discrimination. However, current frequency-dependent AVO inversion approaches usually begin with elasticity theory and lack the consideration of the viscosity of the oil/gas reservoirs. A fluid discrimination approach is initially proposed by incorporating the viscoelasticity and relevant FAVO inversion. Starting from viscoelasticity and rock physics theory, a frequency-dependent viscoelastic solid-liquid decoupling fluid factor is firstly constructed and verified to be more sensitive in fluid discrimination by comparison with other popular fluid factors. And then, a novel reflectivity equation is derived in terms of the viscoelastic solid-liquid decoupling fluid factor. More important, the novel derived reflectivity is frequency dependent due to the involved the viscoelasticity theory, which make the derivation of the equation to frequency is more grounded by comparison with the direct derivation of the elastic reflectivity on frequency with the conventional elastic reflectivity equations. Finally, a pragmatic frequency-dependent inversion method is introduced to verify the feasibility of the equation for frequency-dependent viscoelastic solid-liquid decoupling fluid factor prediction. Synthetic and field data examples demonstrate the feasibility and stability of the proposed approach in fluid discrimination.