Scattering attenuation from the coal seams (Copper Basin, Australia)

Abstract

Attenuation affects seismic amplitudes during wave propagation and understanding of this phenomenon is therefore critical for successful reservoir characterisation. In some geological settings high contrasts in elastic properties between formations can cause substantial attenuation of seismic signal. We study this effect in the Patchawarra formation (Coper Basin, Australia), where coal seams are interbedded with relatively stiff sandstones. The apparent attenuation is estimated from zero-offset VSP data using a variant of the Centroid Frequency Shift method. The scattering component of attenuation is estimated by applying the same method to full-wave synthetic VSP seismograms computed from sonic and density well log data. The results reveal that the presence of coal seams within the Patchawarra formation causes significant seismic attenuation (Qapp~14), which is mainly caused by scattering. Such a drastic loss of seismic energy should be taken into account during surveys design. Furthermore, it might be possible to use seismic attenuation explicitly to characterize the Patchawarra formation and other coal-bearing formations.