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.