Reflectivity and Separability

The QI Stochastic Model window calculates reflectivity and separability coefficients based on predetermined interfaces (with uncertainty), which is useful in AVO classifications. 

AVO, amplitude variation with offset, is a variation in seismic reflection amplitude with a change in distance between shot-points and the receiver. As AVO studies are being done on CMP data, the offset increases with the angle. An AVO anomaly is most commonly expressed as increasing (rising) AVO in a sedimentary section, often where the hydrocarbon reservoir is "softer" (lower acoustic impedance) than the surrounding shales. Typically amplitude decreases (falls) with offset due to geometrical spreading, attenuation, and other factors. 

Using the Reflectivities Tab

Property: Click the drop-down arrow to see the available options, and select one of the reflectivity properties to display.

Depth: Scenarios are modelled at various depths for better estimation and understanding of a set of probabilities. Select a desired depth. 

Error Curves: Select whether to show/hide the error curves. If the Show error curves option is selected, the number of errors is defined by the input of the # Std Dev field.

# Std Dev: Enter the number of standard deviations of the mean.

Plot Settings:

  • Legend: To display the legend, click the amber circle. The amber circle will turn green. Click the green circle to hide the legend, and the green circle will turn amber. Select the position of the legend from the drop-down list.
  • Zero Lines: Show/hide a line intersecting the 0 value of the vertical axis.
  • Width and Height: Customize the width and height of the reflectivity charts. 0 is assigned for the automatically selected scale.

Ranges: Set the desired ranges for the Angle and Reflectivity axes.

Using the Separability Tab

Property: Click the drop-down arrow to see the available options (Near/Far or Intercept/Gradient), and select one of the separability properties to display.

Depth: Scenarios are modelled at various depths for better estimation and understanding of a set of probabilities. Select a desired depth.

Interface Pairs: Analysis pairs from the Interfaces tab are listed here. Click Configure pairs to edit the interface pairs.

Plot Settings:

  • Legend: To display the legend, click the amber circle. The amber circle will turn green. Click the green circle to hide the legend, and the green circle will turn amber. Select the position of the legend from the drop-down list.
  • Zero Lines: Show/hide a line intersecting the 0 value of the vertical axis.
  • Width and Height: Customize the width and height of the separability charts. 0 is assigned for the automatically selected scale.

Ranges: Set the desired ranges for the Angle and Separation axes.