EEI (Extended Elastic Impedance)

Description Calculates Extended Elastic Impedance (EEI) curves from P-velocity, S-velocity and density logs.
Module(s) QI
Requirements
Related Elastic Properties (Isotropic)
Works with

Computes Extended Elastic Impedance (EEI) well curves from P-velocity, S-velocity, and density logs. Outputs log acoustic impedance (lnAI), log gradient impedance (lnGI), and a gather of EEI curves spanning a user-defined range of chi (χ) angles.

  1. In the Control Panel, go to View  > New Single Well View.
  2. In the Single Well window, open the Process tab.
  3. At the tab header, click the blue "+" icon.
  4. Click on EEI (Extended Elastic Impedance).
  5. Type a name for the process and click OK.

Configure EEI

  1. Input Curves:
    • Velocity type: Select whether Vp and Vs are provided as velocity or slowness curves.
    • Vp: Select a P-velocity or P-slowness curve.
    • Vs: Select a S-velocity or S-slowness curve.
    • Density: Select a bulk density curve (g/cc).
  2. Chi Scan Range: Set the range and step size of chi angles for the output EEI gather. Chi angles may range from −360° to 360°. Default: 0° to 360°, step 5°.
    • Custom chi angle: Specify a separate, exact chi value to generate a single custom-chi EEI output curve.
  3. EEI Parameters:
    • Background Velocity Ratio (K): Controls how the background Vs/Vp ratio scaling factor is determined across the calculation window.
      • Constant: Uses one user-defined scalar K value (default 0.25) for the full interval.
      • Average: Computes a single scalar K from the input logs as K = (average(Vs) / average(Vp))² and applies it uniformly.
      • Mudrock variable: Derives K from mudrock parameters A and B (Vs = (Vp − B) / A), evaluated as a single scalar using the average Vp.
    • Advanced mode: When enabled, shows the base normalisation constants:
      • Reference P-Velocity (Vp0): Default 3000 m/s.
      • Reference S-Velocity (Vs0): Default 1500 m/s.
      • Reference Density (ρ0): Default 2.5 g/cc.
  4. Output:
    • Enable custom name: Specify the name of the output curves. Each curve will be named as "[output class]_[process name]" by default, or if a custom name is supplied, "[output class]_[custom name]".
    • Extent: Specify the extents of the output curves.

Output

Output Curves:

  • EEI: lnAI: Log acoustic impedance — EEI at χ = 0°.
  • EEI: lnGI: Log gradient impedance — EEI at χ = 90°.
  • EEI: Output: A gather of EEI curves, one trace per chi angle in the configured scan range (e.g. EEI: Output [0°, 90°]).
  • EEI: Custom Chi: EEI at the exact custom chi angle entered in the Chi Scan Range section.