Attenuation and anisotropy; the effect of extra fine layering

Layering that is finer than that typically resolved by sonic logging will contribute to apparent attenuation and anisotropy in the sonic-to-seismic frequency range. The significance of this contribution can be discerned through resolution enhancement of sonic and density logs. In this study a borehole compensated sonic and density log recorded in a cyclical sedimentary sequence have been enhanced by response matching with a high-resolution microresistivity log. The additional resolved layering increases the layer-induced dispersion by 50%, with the additional attenuation showing a peak with a Q of 135 at 1.2 kHz. The increase in average anisotropy is frequency dependent with a minimum increase of 50% at zero frequency. In the absence of high-resolution data, the effects of layering can be severely underestimated, resulting in poor estimates of the intrinsic properties of rocks and their pore fluids.