Fluid discrimination incorporating viscoelasticity and frequency-dependent amplitude variation with offsets inversion
Zhaoyun Zong, Yan-Wen Feng, Xingyao Yin, Kun Li, Guangzhi Zhang
Abstract
Frequency-dependent amplitude versus offset (FAVO) inversion is a popular method to estimate the frequency-dependent elastic parameters by using amplitude and frequency information of pre-stack seismic data to guide fluid identification. Current frequency-dependent AVO inversion methods are mainly based on elastic theory without the consideration of the viscoelasticity of oil/gas. A fluid discrimination approach is proposed in this study by incorporating the viscoelasticity and relevant FAVO inversion. Based on viscoelastic and rock physics theories, a frequency-dependent viscoelastic solid-liquid decoupling fluid factor is initially constructed, and its sensitivity in fluid discrimination is compared with other conventional fluid factors. Furthermore, a novel reflectivity equation is derived in terms of the viscoelastic solid-liquid decoupling fluid factor. Due to the introduction of viscoelastic theory, the proposed reflectivity is related to frequency, which is more widely applicable than the traditional elastic reflectivity equation directly derived from the elastic reflectivity equation on frequency. 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.