Creating tartan grids

On the Tartan Grid form (simulate > Hydraulic Fractures > Workflow > Tartan Grid) you can create a tartan grid in which the grid cell size distribution is not uniform in the I and J directions, but is defined by a fracture definition and a number of additional grid cell size settings and constraints. The grid cell size in the vertical direction is defined by a source 3D grid.

To create a tartan grid

1. Specify a name for a new tartan grid or select an existing tartan grid.
2. For Fracture definition, select the fracture definition you want to use to create the tartan grid. The fracture definition contains the area for the tartan grid, and the location and orientation of the hydraulic fractures.

3. In the 3D grid cell dimensions area, review the cell size parameters as currently set in the selected fracture definition. You can edit these values. This allows you to create a number of tartan grids, with different parameter settings based on one and the same fracture definition.

   Perpendicular to the fractures  Settings that define the grid cell size (increase) in the direction perpendicular to the fractures.

   Size at the fracture  Minimum grid cell size at the fracture/well intersection in the direction perpendicular to the fracture plane. This setting applies to all fractures that contribute to the stimulation, i.e. hydraulic fractures and natural fractures.

   Max cell size  Maximum grid cell size in the direction perpendicular to the fracture plane. This setting applies to all fractures that contribute to the stimulation, i.e. hydraulic fractures and natural fractures.

   Cell coarsening factor  Multiplication factor that defines grid cell size increase

   Along the fractures  Settings that define the grid cell (increase) along the fracture plane away from the fracture/well intersection.

   Size at the well Grid cell size at the fracture/well intersection in the direction along the fracture pane. This setting applies to all fractures that contribute to the stimulation, i.e. hydraulic fractures and natural fractures.

   Max cell size Maximum grid cell size along the fracture plane. This setting applies to all fractures that contribute to the stimulation, i.e. hydraulic fractures and natural fractures.

   Cell coarsening factor Multiplication factor that defines grid cell size increase.

4. To open the Tartan view and inspect or edit the current settings (if necessary), click Preview. For a description of the Tartan view see About tartan patterns.

   When the area of the tartan grid extends beyond the selected source 3D grid the tartan grid is clipped.
5. For the Source 3D grid, specify the grid with the stratigraphic layering that you want to use. The vertical grid cell size of the tartan grid is defined by the existing grid.

6. In the Specify vertical fracture extent area, you specify at which point above the specified grid layer to ignore the fracture extent. The vertical extent of the fractures in the fracture definition is given by the Height property of the fractures. Due to layer thickness variability, however, fractures can extend in the tartan grid above or below the grid zone in which the fracturing is supposed to occur. In real life such a situation of fractures extending too far into the overlying or underlying layer is solved by adapting the hydraulic fracturing, or, depending on the brittleness of the layers, the hydraulic fracture die out anyway. In the modeling, you can realize this effect and restrict the fracture extent by ignoring that part of fractures that extends above or below a specified grid layer interval.

   Top surface  Select a top surface for the fractured interval. You can select a model surface or (the top of a) model K-layer.

   Base surface  Select a base surface for the fractured interval. You can select a model surface or (the top of a) model K-layer.

7. In the Map properties area, you map properties of the grid onto the tartan grid that you are going to create. The properties you select here can be the 3D properties that you need for dynamic reservoir simulation. The step is optional, and you might find it easier to skip it and map properties in the next workflow form.

   Important   You should do all property mapping in the next workflow form Tartan Grid Properties, where you must specify additional properties and settings for the dynamic reservoir simulation. The next form also gives you access to the Tartan Grid Properties View, where you can edit property values, and add more properties, if so required.

8. If you select properties to map on this form, you can check the Interpolate mapped properties check box to select whether the property mapping uses an interpolation. With this unchecked, the interpolation uses the Nearest Neighbor method. The tartan grid cells are given the value of the source grid cell in which the tartan grid cell’s center occurs. If it is checked, the tartan grid cells are given a value that is calculated from the value of the source grid cell in which the tartan grid cell’s center occurs and the values of the surrounding source grid cells. The calculation uses the Least Squares interpolation method.

9. To create the tartan grid, click OK.

When you create a tartan grid, a number of default properties are automatically created. In the Geometry folder under the Properties folder of the tartan grid in JewelExplorer the following properties are created:

• X Cell Dimensions
• Y Cell Dimensions

In another Properties folder, called Fracture Geometry, the following fracture related properties are created:

• Distance to Hydraulic Fracture
• Fracture Type
• Lateral Distance to Hydraulic Fracture Center
• Stimulated Reservoir Volume
• Vertical Distance to Hydraulic Fracture Center

These fracture properties allow you to inspect and assess the fracture model and the stimulation possibilities of the tartan grid.