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| ==AVO feasibility studies== | | ==AVO feasibility studies== |
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− | [[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_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> |
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| 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? |
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− | [[file:amplitude-versus-offset-avo-analysis_fig2.png|thumb|{{figure number|2}}Brine sand model.]]
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| 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. |
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| 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. |
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− | [[file:amplitude-versus-offset-avo-analysis_fig3.png|left|thumb|{{figure number|3}}Gas sand model.]]
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| 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. |