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Line 26: − + − [[file:amplitude-versus-offset-avo-analysis_fig1.png|left|thumb|{{figure number|1}}Possible combinations of the acoustic and shear terms.]]+ + + + − − [[file:amplitude-versus-offset-avo-analysis_fig2.png|thumb|{{figure number|2}}Brine sand model.]] − − [[file:amplitude-versus-offset-avo-analysis_fig3.png|left|thumb|{{figure number|3}}Gas sand model.]]
Amplitude versus offset (AVO) analysis (view source)
Revision as of 12:54, 14 May 2014
, 12:54, 14 May 2014→AVO feasibility studies
==AVO feasibility studies==
==AVO feasibility studies==
<gallery mode=packed>
file:amplitude-versus-offset-avo-analysis_fig1.png|{{figure number|1}}Possible combinations of the acoustic and shear terms.
file:amplitude-versus-offset-avo-analysis_fig2.png|{{figure number|2}}Brine sand model.
file:amplitude-versus-offset-avo-analysis_fig3.png|{{figure number|3}}Gas sand model.
</gallery>
Whether or not there is an application for [[amplitude]] versus [[offset]] analysis in a given exploration setting is an often posed problem. The explorationist should ask several questions. Are the AVO phenomena that may be present large enough to overcome the various [[noise]]s in the system? Are there sufficient differences between geological conditions and seismic expressions to distinguish between them?
Whether or not there is an application for [[amplitude]] versus [[offset]] analysis in a given exploration setting is an often posed problem. The explorationist should ask several questions. Are the AVO phenomena that may be present large enough to overcome the various [[noise]]s in the system? Are there sufficient differences between geological conditions and seismic expressions to distinguish between them?
A reflection coefficient (see [[Displaying seismic data#Polarity|seismic polarity]]) can be thought of as consisting of the sum of two components—an acoustic term and a [[shear]] term. The acoustic term depends only on the [[impedance]] of the two layers and the [[angle of incidence]]. The shear term depends on [http://en.wikipedia.org/wiki/Poisson%27s_ratio Poisson's ratio] in the two layers and also on the angle of incidence.
A reflection coefficient (see [[Displaying seismic data#Polarity|seismic polarity]]) can be thought of as consisting of the sum of two components—an acoustic term and a [[shear]] term. The acoustic term depends only on the [[impedance]] of the two layers and the [[angle of incidence]]. The shear term depends on [http://en.wikipedia.org/wiki/Poisson%27s_ratio Poisson's ratio] in the two layers and also on the angle of incidence.
An AVO response not only occurs from an interface characterized by a contrast in Poisson's ratio, but also from interfaces that are entirely acoustic—that is, the measured response is more than a simple contrast in Poisson's ratio.
An AVO response not only occurs from an interface characterized by a contrast in Poisson's ratio, but also from interfaces that are entirely acoustic—that is, the measured response is more than a simple contrast in Poisson's ratio.
Consequently, four response cases are possible, as shown in [[:file:amplitude-versus-offset-avo-analysis_fig1.png|Figure 1]]. Two of these cases—(a) and (c)—represent constructive summation of the two terms, yielding a large AVO response. The other two cases—(b) and (d)—are destructive, and the total AVO response is small. A third case consisting of little shear response and strong acoustic response may produce high AVO and may not be associated with a Poisson's ratio contrast.
Consequently, four response cases are possible, as shown in [[:file:amplitude-versus-offset-avo-analysis_fig1.png|Figure 1]]. Two of these cases—(a) and (c)—represent constructive summation of the two terms, yielding a large AVO response. The other two cases—(b) and (d)—are destructive, and the total AVO response is small. A third case consisting of little shear response and strong acoustic response may produce high AVO and may not be associated with a Poisson's ratio contrast.