Creating tartan grid properties

The Tartan Grid Properties form (simulate > Hydraulic Fractures > Workflow > Tartan Grid Properties) creates the properties needed for dynamic reservoir simulation. These are properties such as porosity, permeability K (xyz), Ntg, fluid properties and any other property that you might need. The property values can be mapped from an un-fractured source grid or can be entered in a Tartan Grid Properties table as constant values. Each tartan grid must have its own set of properties; however, as you can easily copy and paste the data from one table to another, the tartan grid property mapping is really easy and flexible. In the dynamic simulation the grid properties and the fracture definition of a selected tartan grid are ‘combined’ to create the simulation grid.

The Hydraulic Fracture Modeling workflow will very likely be used to assess different well pad configurations and fracture definitions in order to find the most optimal set-up for reservoir development. In doing so you will probably create several tartan grids, based on the same 3D geological grid and its properties, the source grid. The best procedure, therefore, is to create a 3D grid which covers the relevant area involved in the hydraulic fracturing and create all required properties with the functionality provided by the application before you start this ‘Create Tartan Grid Properties’ workflow.

To create tartan grid properties

For Tartan grid, select the tartan grid for which you want to create properties.
For Folder, specify a name for the folder in which to place the properties. Do not remove or rename properties in the folder. The simulation expects and recognizes the properties in the folder by their specific names.
Select a fracture system model. If the permeability difference between matrix and fractures is very large (as in unconventional reservoirs), the result of dynamic reservoir simulation will be very much affected by the calculation of the transmissibility between cells. The simulation will produce better and more realistic results if you apply a dual permeability model. In a dual permeability model the high (fracture) and the low (matrix) permeability systems are modeled as separate systems, with transmissibility between them controlled by the actual permeability difference and simulation grid cell size.

Single permeability  Select to apply a single permeability model. Dynamic reservoir simulation treats the entire model volume as one entity as far as flow properties are concerned. In the calculations it uses one simulation grid, which describes both rock matrix and fractures. If fractures are not an overall important contributor to hydrocarbon flow, a single permeability model is sufficient to obtain reliable simulation results.

Dual permeability model  Select to model the fracture system and the matrix separately. With a dual permeability model, the simulation uses two simulation grids in the calculations, one for matrix flow and the other for fracture flow. If the difference between matrix permeability and the fracture permeability is large and fractures are an overall important, or even essential, factor of the flow characteristics, a dual permeability model, which distinguishes between a matrix system and a fracture-system, is required to achieve reliable simulation results.

More about dual permeability

Explicit fractures are hydraulic fractures or natural fractures activated by the hydraulic fracturing. They are represented in the model with an orientation, spacing and permeability. Implicit fractures are small natural, or fracturing-induced, fractures with medium permeability and a random orientation. Based on the implications for the buildup of the simulation model and the modeling of transmissibility between explicit and implicit fractures, different simulators have made different choices in how to approach the explicit fractures in dual permeability models: either as part of the matrix-system or as part of the fracture-system.

It is assumed that flow over larger distances in the SRV takes place predominantly through the small natural, implicit, fractures. Implicit fractures are always modeled in the fracture system. Explicit fractures, such as hydraulic fractures and large natural fractures, can be modeled either in the fracture system or the matrix system. If the explicit fractures are modeled in the matrix system, the hydrocarbons can relatively easy flow from a matrix cell (in the matrix system) to an explicit fracture cell (in the matrix system). If the explicit fractures are modeled in the fracture system, the transmissibility between a matrix cell (in the matrix system) and an explicit fracture cell (in the fracture system) may become very small since the cells around the fractures are very small. The disadvantage of the former approach is that to ensure a proper coupling of the implicit fractures (fracture system) and the explicit fractures (matrix system) unrealistic permeability values need be given to the explicit fractures (too low) and to the unfractured matrix cells (too high). The advantage of the latter approach is that a good coupling between implicit and explicit fractures is ensured in the SRV, provided the spacing between the implicit fractures is not too large. Theoretically, the methods should not lead to very different results.

Model explicit hydraulic and natural fractures in the fracture system  Select if you expect that hydrocarbon flow mainly goes through implicit and explicit fractures and that flow through the matrix is of minor importance.

Model explicit hydraulic and natural fractures in matrix system  Select if you expect that hydrocarbon flow for a considerable part has to go through the matrix.
If you want to calculate transmissibility directly between the fracture and the neighboring cell, without taking the matrix between the fracture and the neighboring cell into account, then check the Neglect matrix properties in fracture cell check box. If cell size is not too large as compared to the fracture width, this approach can be acceptable.
In Source 3D grid, select an existing source grid whose properties you want to map onto the tartan grid. Because the properties are taken from an un-fractured source grid, they are called 'unaffected'. They are the matrix properties.
If you want to use a least squares interpolation method to map the properties from the source grid to the tartan grid, then check the Interpolate properties check box. If you don't check this option, the cells of the tartan grid are given the value of the source grid cell in which their center occurs (the nearest neighbor interpolation method).

The properties of the source grid are mapped to the property folder that you specified in this workflow.
Specify or select the tartan grid properties. Properties can be 3D grid properties or fixed values.

Filter source by property type Select this option to restrict the property selection options in The Tartan Grid Properties View to properties of the relevant type.

Specify properties Click Specify properties to open the The Tartan Grid Properties view.
To create the properties, click Apply. Click OK to create the properties and move to the next step in hydraulic fracture modeling, Creating a simulation case.