Modeling fracture gradients

On the Custom FG form (1D MODEL > Fracture Gradient > Custom FG), you use the interpreted pore pressure and overburden profiles to calculate fracture pressure curves for display in the Fracture Gradient EMW track.

Available methods

The Hubert Willis, Matthews Kelly, and Eaton methods are available for calculation. In addition, you can calculate the fracture gradient based on the rock type. After selecting a calculation method, you can make adjustments to the input for the calculation method. The name of the resulting Fracture Gradient log(s) appears in the text field at the lower part of the form. The logs are stored (with these names) in the JewelExplorer. For more information about the fracture gradient methods, see Fracture gradient methods.

Modeling the fracture gradient

1. At the top of the form, under 'Calculate Fracture Gradient' select the input logs for the fracture gradient calculation and up to three fracture gradients to calculate.

   Overburden Stress  Select the overburden stress log to use in the fracture gradient calculation.

   Pore Pressure  Select the pore pressure log to use in the fracture gradient calculation.

   Fracture Gradient 1 – 3  Select the fracture gradient option to activate it for calculation. For each fracture gradient calculation, you must select the calculation method. Based on the calculation method selected, you can select a Static Poisson's Ratio input or adjust the constant factor for the calculation. You can also calculate the fracture gradient per rock type. When selecting <rock type dependent>, click the Edit button to open the Rock Dependent Constants form and then select the input parameters for the rock types included in the calculation.

   (Re)Calculate  Click to calculate the fracture gradient. The resulting fracture gradient appears in the text field below the button. After you make adjustments, click (Re) Calculate again to recalculate the fracture gradient.

   If the lock is green, the (re)calculation is done automatically.
   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.

2. Show the calculated fracture gradients in the associated view.

   Show on FG View  Opens the Fracture Gradient view with the Fracture Gradient and its associated EMW log added as the last two tracks in the view.

   Show on PPP View  Opens the Pore Pressure Prediction view with the Fracture Gradient and its associated EMW log added as the last two tracks in the view.