Vs or Density (from Vp)

Description Calculate S-velocity or Density from P-velocity. Use this to fill missing values or calculate new curve.
Module(s) Quantitative Interpretation, Explorationist *
Works with

* This process is made available in the Explorationist module temporarily.

Calculate a S-Velocity or Density values from P-Velocity. Use this process to fill missing values or calculate new synthetic curves.

  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 Vs or Density from Vp.
  5. Type a name for the process and click OK.

Configure Vs or Density from Vp

  1. Calculate: Choose the calculation to perform.
    • Vs
    • Density
  2. Use existing (VS/Density) curve: Enable this option to add values to an existing curve.
  3. Vp: Select a P-Velocity curve.
  4. Vs (when calculating Vs + use existing): Select an S-Velocity curve
  5. Density (when calculating Density + use existing): Select a Density curve
  6. Missing/Invalid Values:
    • Interpolate (default): Calculate missing Vp values using the class interpolator
    • Output 0: Replace missing Vp values with 0
    • Output Null: Replace missing Vp values with Null.
  1. Layers: Use layers to choose different calculations and methods over several intervals. Each layer starts at the specified top and ends at the next layer (or the end of the available data if it is the last layer).
    • By default, a single layer is used for the calculation.
    • Click the blue "+" icon to add a row and red "x" icon to remove the row.
    • Click and drag the dotted area to change the row order.
  2. For each layer:
    • Top: Enter the start of the layer
    • Depth: select the datum and enter a value
    • Marker: select a marker and an optional offset
    • Horizon: select a horizon and an optional offset
    • Method: Choose the calculation (see Calculation Methods below)
    • Velocity in km/s: Convert Vp to km/s before calculating, and convert the result back to m/s afterwards. Coefficients in publications and literature often expect Vp in km/s.
    • Calculation terms: Enter the terms for the selected method
    • Use existing ... value (if available):
      • Enabled: Use values from the existing Vs or Density curve when they are available (instead of the calculation)
      • Disabled: Always use the calculated result
  1. Enable custom name:  Allow the user to define the process output curve name.
  2. Prefix: Text appended to the name of each output curve.
  3. Extent: Output is always in TWT.
    • Enter the start, stop and step size.
    • Reset: set the start, stop and step size to match the available data in TWT

Calculation Methods

Choose the calculation to perform for each layer.

  • No Value: Output null / nothing for this layer      
  • Constant: A single value for the layer      
  • Two-Term (Ax + C) (default): Linear relationship  
    • A × Vp + Constant
  • Three-Term (Ax2 + Bx + C): 3-term polynomial relationship
    • A×Vp2+B×Vp+Constant        
  • Power-Law (AxB + C): 3-term power-law relationship
    • A×VpB+Constant