Spectral analysis of heterogeneous sandstone for different fluids by physical modeling

Summary Fluid identification is a key problem in seismic exploration, and attenuation of seismic wave can often be used to identify fluid. However, both absorption and scattering of heterogeneity can attenuate seismic wave. Therefore, a physical model which contains both strong and weak heterogeneous sandstone is made in this paper, and seismic experiments are conducted with the reservoir unit filled with gas, oil or water. In order to study the attenuation effect of seismic wave caused by absorption and heterogeneous scattering, we calculate the amplitude spectra of both strong and weak heterogeneous reservoirs for different fluids at the top, middle and bottom parts of the reservoirs. Results show that attenuation of peak frequency is related to the two factors above. And the scattering attenuation of seismic wave dominates in strong heterogeneous reservoir. In addition, through spectral decomposition for sections with different fluids, the phenomenon of low frequency shadow beneath gas-filled reservoir is verified. Besides, we can conclude that gas exploration through low frequency shadow is not ideal when the heterogeneity of reservoir is strong. This can provide helpful guidances for real seismic data interpretation.