Interpretation of phase reversals in seismic reflections from attenuating targets

Abstract

Phase reversals are commonly observed during exploration seismic amplitude-versus-offset analysis, and usually modelled with the Zoeppritz equations. In practice, when multiple fluids are present we often deal with reflections from interfaces having a contrast in both elastic and anelastic properties. In this paper, we present a new phenomenological model for phase reversals in cases in which velocity dispersion and attenuation are present. We demonstrate strong qualitative differences in behaviour between the elastic and anelastic cases, influencing both the amplitude and phase of the reflection coefficient. Analysis of seismic data showing a phase reversal from a gas reservoir in the Vienna basin shows a striking agreement with the modelling. We conclude that the influence of fluid-induced dispersion on reflection data is a significant and measurable phenomenon in cases of practical interest, that recognition of the phenomena may be used as a novel fluid indicator and that frequencydependent rock physics analysis may be an important tool for both industrial geophysics and seismic monitoring of CO 2 storage.

Frequency‐ and angle‐dependent poroelastic seismic analysis for highly attenuating reservoirs

“…() have used the frequency‐dependent AVO to estimate gas saturation. The phase reversal signatures from the attenuating targets have also been reported by Wu, Chapman and Angerer (). From a more general perspective, Zhao et al .…”

“…This is also reported by Wu et al . () in which the fluid‐induced attenuation can cause Class‐II and Class‐IV AVO to exhibit a gradual continuous variation of phase with incident angle. It is also interesting to see that, for seismic data with different frequency components, the phase reversal is found to show up at different incident angles.…”

Estimating gas saturation in a thin layer by using frequency‐dependent amplitude versus offset modelling

“…Figure 2b displays the corresponding phase variation, which is determined by the ratio of the real and imaginary parts of the complex reflection coefficient. A detailed interpretation of phase variation in dispersive medium has been presented by Wu et al (2015).…”

Laboratory‐based seismic attenuation in Fontainebleau sandstone: Evidence of squirt flow

“…Nevertheless, the presence of an intricate pore structure or an inhomogeneous fluid saturation distribution in a reservoir can dramatically influence the magnitude and frequency dependence of attenuation. Once its trends are well quantified, attenuation could be employed as an attribute to aid existing inversion techniques in seismic exploration and, particularly, in reservoir characterization [ Chapman et al ., ; Li et al ., ; Lambert et al ., ; Wu et al ., ]. In the laboratory, the forced oscillation technique provides for the measurement of seismic attenuation and the corresponding modulus dispersion from a sinusoidal stress/strain procedure [ Subramaniyan et al ., ].…”