Abstract
ABSTRACTThe wedge model is commonly used to study the limits of seismic resolution where conventionally the thickness of sub‐resolution seismic layers can be determined from thin layer tuning curves. Tuning curves relate the layer temporal thickness to the wavelet frequency, but, to our knowledge, no systematic study has been done to date of the effects of velocity dispersion and attenuation on tuning. In this work, we study the tuning properties of a thin layer dispersing according to the standard linear solid model. We show that the first tuning curve is sensitive to the attenuation, relative polarity and magnitude of the two reflection coefficients at the top and base of the layer. We provide an analytic formula for the upper bound in the mismatch between the elastic and dispersive tuning curves. We conclude that highly attenuative thin layers can appear thicker or thinner than they actually are depending on polarity and relative magnitude of reflection coefficients at the layer interfaces. Our results are particularly relevant in the quantification of CO2 where knowledge of the temporal thickness of CO2 layers is reliant on their tuning curves.
Highlights
One of the goals of seismic interpretation is to relate seismic amplitude variations to rock and fluid properties from variations in acoustic impedance
When geological layers are thinner than the seismic wavelength, interference form their top and base distorts the relation between seismic amplitude and acoustic impedance
We assume a thin layer that disperses according to the standard linear solid (SLS) model (Ursin & Toverud, 2002), and calculate the shift induced by attenuation in its tuning curves as well as the upper bound in this shift
Summary
One of the goals of seismic interpretation is to relate seismic amplitude variations to rock and fluid properties from variations in acoustic impedance. We assume a thin layer that disperses according to the standard linear solid (SLS) model (Ursin & Toverud, 2002), and calculate the shift induced by attenuation in its tuning curves as well as the upper bound in this shift. It should be noted, that we do not consider different dissipation mechanisms i.e. due to solid-solid friction or contact-line movement (Rozhko, 2020; Winkler & Nur, 1982) in which dispersion depends on wave amplitude rather than frequency, but postpone such considerations for future work. The wedge model we discuss here is assumed homoegeneous this is not always the case, in the context of CO2 monitoring (Glubokovskikh et al, 2020)
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