AVO Analyses from Four Wells in the West of Shetland - Spectral Decomposition

Geological models are currently used to aid AVO-analysis, usually thick-layered. In an actual thin-layered sub-surface medium, the AVO has some specifics, ignoring which may lead to errors in predicting hydrocarbon reservoirs. In the resonant frequency range periodic thin-layered stack, AVO inversion on the basis of the linearized Shuya formula produces an estimate of the effective Poisson coefficient much lower than one of a separate gas-saturated layer. Also, in the low-frequency range an effective Poisson coefficient estimate is much higher than one in case of a separate gas-saturated layer. Within a frequency range close to the resonant frequency (tuning thickness) for a thin-layered stack, favorable conditions occur for predicting multi-layer hydrocarbon reservoirs from the AVO-analysis. At the same time, disregarding absorption may lead to interpretation errors. A finite difference solution for the elastic wave equation and the Haskell-Thomson method in its visco-elastic variant were used to perform the investigation.