Effective Stress Ratio

In the Effective Stress Ratio method (1D MODEL > Horizontal Stress > Effective Stress Ratio), you calculate the maximum and minimum horizontal stress from overburden stress, pore pressure and Shmin and SHmax effective stress calibration points. If you have entered information about the stress state in the well, such as LOT/FIT points, RFTs, or lost circulation events, you can plot them in the tracks of the Horizontal Stress Model as unitless effective-stress-ratio points. The horizontal stress can be calculated from these calibration points when interpolated with a custom trend line.

The equations that define this method are:

You can determine the SHmax azimuth in the same Horizontal Stress model by combining azimuth logs with an azimuth of maximum horizontal stress curve.

Modeling horizontal stress using the effective stress ratio method

  1. On the Effective Stress Ratio form, select the input logs from the drop-down list that you want to use for modeling the horizontal stress, either the Overburden stress and/or the Pore pressure log.

  2. Specify the calibration points for minimum and maximum horizontal stress.

    Shmin calibration points  Select the Shmin calibration points. Supported calibration data are stress-based logs and Equivalent Mud Weight (EMW) logs, i.e. log types Stress, Mud Weight, Equivalent Mud Weight and EMW Stress.

    Add Shmin point  With this option you can add a known Shmin calibration point. Select and specify the MD value and the Stress value for the new point, which appears in the track.

    SHmax calibration points  Select the SHmax calibration points. Supported calibration data are stress-based logs and Equivalent Mud Weight (EMW) logs , i.e. log types Stress, Mud Weight, Equivalent Mud Weight and EMW Stress.

    Add SHmax point  With this option you can add a known SHmax calibration point. Select and specify the MD value and the Stress value for the new point, which appears in the track.

  3. In the Show ESR logs section, view the names in respective fields of Effective Stress Ratio logs for Shmin and SHmax.

    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. Click Show/Refresh to open the Horizontal Stress view. In the view, create trend lines for the Effective Stress Ratio logs with the Edit Custom Trend option from Editing Tools in order to interpolate the calibration points.
  5. Click OK to close the form and proceed to the Horizontal Stress form.