Interpolating your facies trend map

To select an interpolation method

1. Select the interpolation method from the Method drop-down list. The form will be populated with additional settings based on your selection.
2. Fill in the settings for the selected method, see below for more information.

Inverse Distance Weighting (IDW)

This method uses the inverse distance-weighted algorithm to interpolate the data. Inverse Distance Weighting (IDW) does not have a preference for direction and will only use the distance to data points as input for interpolating the surface. You can select the weighting exponent used for the weighting of the distances. In general the IDW method does not provide good results, as the algorithm is sensitive to the amount of input data. This means that especially added constraints will change the result drastically.

• Power  The power parameter controls how strongly the weight depends on the distance from each data point. Any value greater than zero is allowed. Values between 0.5 and 10 are recommended. The default value of 2 produces a smooth interpolation and is appropriate for most applications. Smaller values for the power parameter generate more equal weights and interpolations approximating a constant value with spikes at each data point. Larger values for the power parameter generate larger weights for nearby data points and interpolations approximating a nearest neighbor interpolation.
• Advanced Settings  (Only relevant when 'IDW', or 'Ordinary (legacy) Kriging' are selected under 'Method'.) Clicking the button opens the 'Advanced Settings' dialog. If you want to Apply trend analysis and data filtering, check the box at the top of the dialog. This will do the following:
  • Optimize the computation time by allowing you to specify the number of data points used to calculate the output surface.
  • The trend analysis, automatically carried out by the application, creates a relatively coarse regularly spaced grid in the specified area. The selected interpolation method is used to compute the values at these data points. A relatively fine spaced grid is then filled with the values from the coarse grid and adjusted with the local offset of the available data points. The filtering settings are then applied.
    • Use <number> data points: Shows the total number of data points of the input object (for reference only).
    • Use <number> trend analysis points: Shows the number of data points in the coarse, regularly spaced grid. You can edit this value, then click OK.
  JewelSuite Subsurface Modeling applies the following rules for trend analysis:
  • When the number of input data points is less than 250, trend analysis is never applied.
  • Trend analysis is automatically applied when the number of input data points is greater than: Kriging: 5000; Triangulation: 100000; Inverse Distance Weighting: 10000.
  • Trend analysis is automatically applied when the number of output data points is greater than 100000.

Kriging

This method uses the Kriging algorithm to interpolate the data. The Kriging method also uses input locations as constraining input, but allows more options to be specified. You can select the variogram type, and specify the direction and range of the major and minor axis. The mean is unknown and only constant over the search ellipsoid.

• Type  Select 'Ordinary', 'Ordinary (legacy)' or 'Simple':
  • Ordinary  The mean is unknown and only constant over the search ellipsoid. Good approach when there are many hard data and there is some evidence of non-stationarity. The industry standard Kriging library is used.
  • Ordinary (legacy)  This type of Ordinary Kriging does not make use of the industry standard Kriging library and is performance optimized. It is the recommended method when using constraints, especially for polyline and/or patch constraints. When you choose this option (as opposed to non-legacy Ordinary Kriging), the 'Advanced Settings' button at the base of the form becomes active and the 'Search Factor' is grayed-out.
  • Simple  The global mean is known and is held constant over the area of interpolation. Simple Kriging is the best approach when there is no or little evidence of significant non-stationarity and few hard data. The industry standard Kriging library is used.
• Variogram Type - Choose a variogram type to control how the variogram model is auto-fitted to the data:
  • Exponential
  • Exponential Power - Only available when 'Ordinary (legacy)' is selected under 'Type'. Set the value in the Power entry field, which sets the lateral extension of the kriging.
  • Gaussian
  • Spherical
A default value of 0.0001 is used for the nugget effect of the variogram model.
• Major range - Specify the distance at which the values become independent (the variogram reaches its plateau). The distance is measured in the direction with the greatest spatial continuity. By default, the azimuth of the Major direction is 0°, and the azimuth of the Minor direction always perpendicular to it.
• Minor range - Specify the distance at which the values become independent (the variogram reaches its plateau). The distance is measured in the direction with the least spatial continuity and is orthogonal to the major direction.
When your data does not have anisotropy, enter the same value for both the Major range and Minor range.
• Azimuth (GN) - Enter the azimuth (angle with Northing direction) of the axis corresponding with the major range.
• Search factor - (Not available when 'Ordinary (legacy)' is selected under 'Type'.) The variogram model ranges are multiplied with the search factor to obtain the size of the search ellipsoid, i.e. Search ellipsoid = Search factor x Variogram model range. The search factor is applied to both ranges of the variogram model so that the shape of the search ellipsoid reflects the spatial anisotropy.

Recursive Refinement

Use this method to create maps with smooth contours, extrapolation and trends. The method creates a grid around your input data and assigns values from the data points to the nodes of the grid (snapping) in order to build the map. The grid starts with a coarse resolution and it is refined iteratively in order to reach the resolution of the area you specified on the Assign Data form. For more information on this interpolation method, see the section Recursive Refinement.

• Multiplier for initial coarse resolution - The number that is multiplied by the resolution of the specified area to produce the initial grid resolution. With the default value of 0, the method will automatically determine the most suitable multiplier value based on the desired final resolution and the distribution of your input data. Enter a number greater than the default in the entry field, or use the up and down arrows at the side of the field.
• Extrapolation method - Select an extrapolation method to ensure that the final map is fully populated with values (in cases of insufficient input data or input settings).
  • None - Select this option to not extrapolate.
  • Linear (default) - Extrapolate using a linear function.
  • Quadratic - Extrapolate using a quadratic polynomial technique.
• Extrapolation area (active only when an extrapolation method is selected) - Specify the extent of the extrapolation by selecting one of the two options from the drop-down list:
  • Outside convex hull - Extrapolate outside the convex hull around the input data.
  • As needed (default) - Extrapolate in areas where grid nodes have not received a value.
• Grid nodes affected by snapping - The number of grid nodes that will be affected by each input data point. By default, the value of each input data point is assigned to the nearest 16 grid nodes. Enter a value less than the default value of 16 in the entry field, or use the up and down arrows at the side of the field.
3. Click Apply to save the settings, interpolate the selected facies trend map and keep the form open, or click OK to save the settings, interpolate the facies trend map and close the form.

To create a constraint with the Editing Tools

1. Visualize the map that you want add/edit constraints for in one of the following ways:

• Open the map in a 2D View  Facies trend maps are stored in the JewelExplorer: Maps > Facies Trend Maps > Your Facies Trend Map > 2D Grid or Property.

• Open the dedicated Thickness/Trend Map  You can open the dedicated Thickness/Trend Map via opening one of the forms in the Facies Trend Maps workflows.

• Open the Interpolate Map form  This will open the dedicated Thickness/Trend Map. On the Constraints tab, you can select the facies class to visualize its map.

2. Open the floating palette via clicking one of the following:
• Workspace > Tools > Editing Tools (Shift + F1)
• Open Editing Tools button on the Constraints tab on the Interpolate Map form

The editing tools for the constraints contains two sections. The 'Create' section allows you to create new constraints. The 'Constraint Tools' section allows you to further edit existing constraints such as by adding, moving or removing nodes.





The editing tools for the constraints are distributed in two sections.    click to enlarge

3. Select one of the tools depending on the type of constraint you want to create:

	Create Node Constraint  Create a constraint that consists of a single node.
	Create Polyline Constraint  Create a constraint that consists of a polyline.
	Create Patch Constraint  Create a patch constraint.

When you select one of the tools the Add Node tool, or the Extend Constraint tool is activated.

4. Click on the map at the location(s) where you want to add a constraint.
5. When you have finished, click on the Add Node tool or the Extend Constraint tool to deactivate the tool.
6. The constraints are stored in the JewelExplorer under the selected map you are working with (Maps > Facies Trend Maps > Your Facies Trend Map > Facies Class > Constraints).
7. A constraint entry has now been created on the Constraints tab on the Interpolate Map form. Type a value in the table that will be used as constraint. A constraint (i.e. a single node, a polyline or area) can only have a single value.
Uncertainty   You can apply uncertainty to the constraints of your Facies Trend Map, and carry this uncertainty forward in a probabilistic volumetric calculation with the study strip. To do this, click the uncertainty symbol next to the Probability column on the Constraints tab, to open the Uncertainty Parameter dialog. For how to use the controls on the dialog, see The Uncertainty Parameter dialog. Once you have made the facies constraints uncertain, make sure to assign the Facies Trend Map to the Facies Model with the model > Facies > 'Trends & Proportions' form > 'Vertical, Lateral or 3D' tab. For general information about parametric uncertainties and how to use them in JewelSuite Subsurface Modeling, see Incorporating uncertainty in static or dynamic modeling.
8. Click OK or Apply on the Interpolate Map form to interpolate the map using the constraint(s). All constraints that have their checkbox checked on the form, are used.

For more information on working with the editing tools, see Creating and editing constraints