Determining the theoretical velocity and equivalent depth pore pressure

Before making the final pore pressure calculation you first need to calculate the theoretical velocity and equivalent depth pore pressure, also known as Pore Pressure Bowers Undercompaction, on the Bowers Eq Depth form (1D MODEL > Pore Pressure > Bowers Method). The theoretical velocity is calculated from either the velocity or acoustic converted log that you specified previously on the Input Logs and Filtering form. For the calculation of the pore pressure equivalent depth, the empirical parameters A and B can be specified or calculated here. Once the pressure is calculated you can inspect the results in the Bowers Method view and the Velocity vs Effective Stress cross plot to determine which values best match your data.

Important  Notice that changing the units for any of your velocity or stress logs will automatically affect the A parameter. However, the B parameter has no dependency on these units.

To calculate the theoretical velocity and equivalent depth pore pressure

  1. Select which log, Velocity or Acoustic, to use in the calculation of the theoretical velocity.
  2. Define the empirical parameters A and B. The values you use depend on where you are drilling. Use values taken from offset wells, if available. Use the Calculate from log option in order to automatically obtain these values from your input logs. For more information about selecting the A and B parameters, see the Bowers Method section in Pore pressure prediction methods.
  3. To calculate the theoretical velocity and equivalent depth pore pressure based on values for A and B, click (Re)Calculate. The resulting log names appear in the text fields below the (Re)Calculate button.
    4. To change the default name of the created log, double click in the log field. The background turns blue, indicating you can edit the text. When done, click the green check mark to apply the changes.
  4. The newly calculated Bowers pore pressure log can be added to the Bowers Method view by clicking Show. This adds the log, named Pore Pressure, Bowers Undercompaction to the view.
  5. In addition to reviewing the results in the Bowers Method view, they can also be observed in the Velocity vs Effective Stress cross plot. This cross plot allows you to review the behavior of V0, Vmax and the A and B empirical Bowers parameters.
  6. To move to the next step of the workflow, Bowers Unloading, click OK.