Calculating the effective overburden stress from the hydrostatic pore pressure

With the velocity input logs and the V0 and Vmax parameters defined in the previous steps of the Bowers Method workflow, the next step is to calculate the effective overburden stress using the Effective Overburden form (1D MODEL > Pore Pressure > Bowers Method). On this form, the effective overburden stress is calculated from the overburden stress and hydrostatic pore pressure. For both of these parameters you can use previously calculated logs or manually specify constants to make the calculation. Once calculated, the resulting logs and, optionally, calibration points, can be added to the Bowers Method view for further observation.

To calculate effective overburden stress

  1. For the Overburden Stress input you can use a log, such as the Overburden Stress log calculated on the Overburden form, or specify a theoretical overburden stress based on a rock density matrix constant. To specify a constant stress value, check the Calculate theoretical overburden stress box; a value of 2.31 g/cm3 is set as the default value.
  2. The Hydrostatic Pore Pressure input can be defined in the same way as the Overburden Stress Input; you can specify a log or provide a fluid density constant. The Calculate hydrostatic pore pressure box is checked by default so that you can enter a fluid density; uncheck this box if you wish to use a log instead. A value of 1.03 g/cm3 is set as the default fluid density value.
  3. To calculate the effective overburden stress, click (Re)Calculate. The name of the calculated log is then displayed in the form.
  4. In the Logs list you can select pressure measurements to add to the Bowers Method view. Check the box for each of the pressure measurement logs that you want to display.
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.

  1. Click the Show button to open the Bowers Method view with the newly calculated data. Two tracks are added to the view, the first contains the calculated effective overburden stress, the overburden stress and hydrostatic pore pressure input data and the calibration points. The second track contains the effective overburden stress and the input data in terms of equivalent mud weight.

  2. Click OK to move to the next form, Bowers EQ Depth.