Variogram model
Use the Variogram form (model > Rock Properties > Assign Variogram) to assign a variogram model to your Volume of Interest (VOI) if you assigned a variogram-based modeling method (SGS or Kriging) to your rock properties model. A VOI with a variogram-based modeling method but with no variogram assigned, will be blocked from running in the last step of the modeling workflow. Input to the variogram is the upscaled grid property.
Upon opening the Variogram Model form, the Rock Properties Variogram View is opened automatically. If you have saved an experimental variogram in the previous step, it will be visualized now. If you have not done so, the view will open with nothing on display.
To assign a variogram - overall workflow
Variogram modeling requires first to calculate an experimental variogram (data points) and then finding the parameters describing the variogram model (curve). The intended workflow on the form is as follows:
- After opening the Variogram Model form, first select the Rock Properties Model from the Model drop-down list at the top of the form. If you arrive on this form by proceeding through the workflow, the model and the VOI will already be selected for you.
- Fill in all required fields:
- Variogram Model Directions
- Azimuth - Specify the azimuth (angle with Northing direction) of the direction. By default, the azimuth of the Major direction is 0°, and the azimuth of the Minor direction always perpendicular to it. The major direction is defined as the direction of the greatest spatial continuity. For the minor and vertical directions, the table is read only.
- Dip - Specify the dip angle. By default, the dip of the Vertical direction is -90°. For the minor and vertical directions, the table is read only.
Uncertainty The Azimuth of the Major direction can be propagated as a parametric uncertainty in a probabilistic volumetric calculation with the study strip. Click the uncertainty symbol
behind the Azimuth entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling. - Curve Type - Choose the type of variogram model (Gaussian, Spherical or Exponential) that you want to auto-fit as a curve to your experimental variogram (colored datapoints).
- Parameters - Fill in values for the following parameters:
- Sill - The semi-variance where the variogram curve levels off and becomes a flat curve. The value indicates the maximum semi-variance of the data set.
- Nugget - The semi-variance when distance between data points is below the sampling resolution. The value indicates the minimum semi-variance of the model.
- Major range - The lag distance at which property values become independent (the variogram reaches its plateau) in the major direction. The major direction is the direction with the largest spatial continuity.
- Minor range - The lag distance at which property values become independent (the variogram reaches its plateau) in the minor direction. The minor direction is the direction with the least spatial continuity (by definition perpendicular to the major direction).
- Vertical range - The lag distance at which property values become independent (curve reaches its plateau) in vertical direction.
- On the right side of the form you have two options: you can either fill in all values yourself, or you can use the Autofit to Data or Autofill buttons at the bottom of the form. Once the required fields are filled in, this triggers a curve-fitting to determine an initial variogram model.
- Autofit to Data - Select this option to have the application fill in the 'Parameters' section for you. You must specify an Azimuth and Dip for the major direction and a curve type yourself.
- Autofill - Select this option to copy all the settings of an existing rock properties variogram model to the currently selected VOI. Clicking the button will open a new form where you select the rock properties model and VOI to copy the settings from.
- Assign the variogram model(s) to the selected VOI by clicking Apply at the base of the form. Click OK or Next to go the next step in the workflow.
Using the context menu options Copy and Paste, you can copy-paste settings between the VOIs which have variogram-based modeling methods (i.e. Kriging, SGS). Once you have copied settings, you can select Paste Settings Options. This will open a separate form, which allows you to paste the settings to multiple VOIs at once. Note that checkbox selection can be done in bulk by holding down SHIFT while selecting a range of VOIs (they turn blue), then checking the box of one of them. All other VOIs in the selected range will get checked simultaneously.
Uncertainty This parameter can be propagated as a parametric uncertainty in a probabilistic volumetric calculation with the study strip. Note that the variogram range impacts the Search Ellipsoid, as such the number of data points included in the grid point calculation, see 'Search Factor' in Controlling the rock property modeling method. Click the uncertainty symbol behind the 'Major range' entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling.
behind the 'Major range' entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling. Uncertainty This parameter can be propagated as a parametric uncertainty in a probabilistic volumetric calculation with the study strip. Note that the variogram range impacts the Search Ellipsoid, as such the number of data points included in the grid point calculation, see 'Search Factor' in Controlling the rock property modeling method. Click the uncertainty symbol behind the 'Minor range' entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling.
behind the 'Minor range' entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling.For uncertainty studies and other sensitivity scenarios, you can specify a Minor range value greater than the Major range value if you have assigned TGS and SIS method for the selected VOI's. A warning message is displayed on the form in such cases.
Uncertainty This parameter can be propagated as a parametric uncertainty in a probabilistic volumetric calculation with the study strip. Note that the variogram range impacts the Search Ellipsoid, as such the number of data points included in the grid point calculation, see 'Search Factor' in Controlling the rock property modeling method. Click the uncertainty symbol behind the 'Vertical range' entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling.
behind the 'Vertical range' entry field to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. For information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling.