GS File Examples
5.2 Estimating Grid Properties with Kriging Algorithms
There are several types of kriging offered in the Geostatistics menu:
• "Estimating Properties with Kriging," page 5-6
• "Estimating Properties with Kriging with Trend," page 5-8
• "Estimating Properties with Kriging with External Drift," page 5-10
• "Estimating Properties with Bayesian Kriging," page 5-12
• "Estimating Properties with Collocated Cokriging," page 5-14
• "Estimating Properties with Indicator Kriging," page 5-16
Kriging processes are more sophisticated than traditional interpolation processes in that they enable you to specify statistical anisotropy in terms of variogram parameters. If you also want to model heterogeneity in the property, you can do this by using various types of stochastic simulation processes (see "Running Geostatistical Simulations" on
page 5-18).
5.2.1 Estimating Properties with Kriging
The kriging algorithm provides a minimum error-variance estimate at any unsampled location.
You should have an ASCII file containing the variogram data and an object that can serve as the property source ("hard data" should lie at least partially inside the SGrid or Voxet).
To run kriging to create SGrid or Voxet properties
1 Display the SGrid or Voxet and the property object in the 3D Viewer.
2 Select Voxet, SGrid, or General commands > Geostatistics > Kriging to open the Kriging dialog box.
3 In the Grid Object box, enter one or more Voxets or SGrids.
5.2 Estimating Grid Properties with Kriging Algorithms 5-7 User Guide
4 In the Region name box, enter the grid object region where the kriging will be performed.
Note By default, kriging will be performed for all points (everywhere) on the grid.
5 In the Discrete property server by box, enter the object that carries the existing property values.
6 In the By region box, enter the input data region.
7 In the Property box, select the object property to be used in the operation.
8 In the New property prefix box, type the prefix for the created properties. (For example, if you type Kriging_, the two new created properties will be named Kriging_estimate and Kriging_variance.)
9 To specify the ASCII file that contains the variogram data (see "GS File" on page 5-2), do either of these:
• Enter the path to the file in the GS file box.
• Click , find and select the file, and then click OK.
10 If you want to set options for the variogram and associated parameters, click Advanced to expand the dialog box.
a In the Kriging Type box, select one the following kriging options:
• Simple. Residuals are computed from the mean of the data and kriged.
• Ordinary. Input data values are used directly for the kriging.
• Use_variogram_file_setting. Use the type set in the variogram file.
b To allow for the possibility that the result at a cell containing data points is not kriged, but rather directly assigned from input data in that cell, select one of the following data value assignment options:
• No data assignment. All cells are kriged.
• Assign data to nearest cells. In any particular cell, the data point closest to the cell center is assigned as the estimation at the cell.
• Assign mean at cell center. The mean of all the data points in a particular cell is assigned as the cell value.
If you choose this option, also select a method of computing the mean in the Mean computation type box, and type the value for the exponent (in the standard mean power equation) in the Power mean power box.
11 Click OK or Apply.
5.2.2 Estimating Properties with Kriging with Trend
In kriging with trend (also known as universal kriging), the modeled property is assumed to follow a trend that is only a function of the location coordinates.
You should have an ASCII file containing the variogram data and an object that can serve as the property source (it should lie at least partially inside the SGrid or Voxet).
To run kriging with trend to create SGrid or Voxet Properties
1 Display the SGrid or Voxet and the property object in the 3D Viewer.
2 Select Voxet, SGrid, or General commands > Geostatistics > Kriging with Trend to open the Kriging With Trend dialog box.
3 In the Grid Object box, enter one or more Voxets or SGrids.
4 In the Region name box, enter the grid object region in which the kriging will be performed.
Note By default, kriging will be performed for all points (everywhere) on the grid.
5 In the Discrete property server by box, enter the object that carries the existing property values.
6 In the By region box, enter the input data region.
7 In the Property box, select the object property to be used in the operation.
8 In the New property prefix box, type the prefix for the created properties. (For example, if you type Kriging_, the two new created properties will be named Kriging_estimate and Kriging_variance.)
5.2 Estimating Grid Properties with Kriging Algorithms 5-9 User Guide
9 To specify the ASCII file that contains the variogram data (see "GS File" on page 5-2), do either:
• In the GS file box, enter the path to the file.
• Click to open the Select Text File dialog box, find and select the file, and then click OK.
10 In the Kriging Type box, select one the following kriging options:
• Simple. Residuals are computed from the mean of the data and kriged.
• Ordinary. Input data values are used directly for the kriging.
• Use_variogram_file_setting. Use the type set in the variogram file.
11 To allow for the possibility that the result at a cell containing data points is not kriged, but rather directly assigned from input data in that cell, do one of the following to assign data values to cells:
• Select the Assign data to nearest cells check box. In any particular cell, the data point closest to the cell center is assigned as the estimation at the cell.
• Clear the Assign data to nearest cells check box. All cells are kriged.
12 In the Trend Model area, select the check boxes representing the trend components you want.
• a, u, a5v2, or a9vw. The trend is a function of a, u+a5v2+a9vw.
• a, a5, or a9. These are unknown weights that will be estimated during the kriging process.
13 Click OK or Apply.
5.2.3 Estimating Properties with Kriging with External Drift
In kriging with external drift, the trend is a linear function of a secondary property (drift) that does not have to be in the same units as the data.
You should have an ASCII file containing the variogram data and an object that can serve as the property source (it should lie at least partially inside the SGrid or Voxet).
To run kriging with external drift to create SGrid or Voxet properties
1 Display the SGrid or Voxet and the property object in the 3D Viewer.
2 Select Voxet, SGrid, or General commands > Geostatistics > Kriging with External Drift to open the Kriging With External Drift dialog box.
3 In the Grid Object box, enter one or more Voxets or SGrids.
4 In the Region name box, enter the grid object region in which the kriging will be performed.
Note By default, kriging will be performed for all points (everywhere) on the grid.
5 In the Discrete property server by box, enter the object that carries the existing property values.
6 In the By region box, enter the input data region.
7 In the Property box, select the object property to be used in the operation.
8 In the Drift Property box, enter the secondary property that exists everywhere on the Grid.
9 In the New property prefix box, type the prefix for the created properties. (For example, if you type Kriging_, the two new created properties will be named Kriging_estimate and Kriging_variance.)
5.2 Estimating Grid Properties with Kriging Algorithms 5-11 User Guide
10 To specify the ASCII file that contains the variogram data (see "GS File" on page 5-2), do either:
• In the GS file box, enter the path to the file.
• Click to open the Select Text File dialog box, find and select the file, and then click OK.
11 In the Kriging Type box, select one the following kriging options:
• Simple. Residuals are computed from the mean of the data and kriged.
• Ordinary. Input data values are used directly for the kriging.
• Use_variogram_file_setting. Use the type set in the variogram file.
12 To allow for the possibility that the result at a cell containing data points is not kriged, but rather directly assigned from input data in that cell, do one of the following to assign data values to cells:
• Select the Assign data to nearest cells check box. In any particular cell, the data point closest to the cell center is assigned as the estimation at the cell.
• Clear the Assign data to nearest cells check box. All cells are kriged.
13 Click OK or Apply.
5.2.4 Estimating Properties with Bayesian Kriging
Bayesian kriging is similar to "Estimating Properties with Kriging with External Drift" on page 5-10, except that the drift property should be in the units of the data being estimated.
You need an ASCII file containing the variogram data and an object that can serve as the property source (it should lie at least partially inside the SGrid or Voxet).
To run Bayesian kriging to create SGrid or Voxet properties
1 Display the SGrid or Voxet and the property object in the 3D Viewer.
2 Select Voxet, SGrid, or General commands > Geostatistics > Bayesian Kriging to open the Bayesian Kriging dialog box.
3 In the Grid Object box, enter one or more Voxets or SGrids.
4 In the Region name box, enter the grid object region in which the kriging will be performed.
Note By default, kriging will be performed for all points (everywhere) on the grid.
5 In the Discrete property server by box, enter the object that carries the existing property values.
6 In the By region box, enter the input data region.
7 In the Property box, select the object property to be used in the operation.
8 In the Guess Property box, enter the secondary property that exists everywhere on the Grid and has the same units as the property being estimated (selected in step 7).
5.2 Estimating Grid Properties with Kriging Algorithms 5-13 User Guide
9 In the New property prefix box, type the prefix for the created properties. (For example, if you type Kriging_, the two new created properties will be named Kriging_estimate and Kriging_variance.)
10 To specify the ASCII file that contains the variogram data (see "GS File" on page 5-2), do either:
• In the GS file box, enter the path to the file.
• Click to open the Select Text File dialog box, find and select the file, and then click OK.
11 In the Kriging Type box, select one the following kriging options:
• Simple. Residuals are computed from the mean of the data and kriged.
• Ordinary. Input data values are used directly for the kriging.
• Use_variogram_file_setting. Use the type set in the variogram file.
12 To allow for the possibility that the result at a cell containing data points is not kriged, but rather directly assigned from input data in that cell, select one of the following data value assignment options:
• No data assignment. All cells are kriged.
• Assign data to nearest cells. In any particular cell, the data point closest to the cell center is assigned as the estimation at the cell.
• Assign mean at cell center. The mean of all the data points in a particular cell is assigned as the cell value.
If you choose this option, also select a method of computing the mean in the Mean computation type box, and type the value for the exponent (in the standard mean power equation) in the Power mean power box.
13 Click OK or Apply.
5.2.5 Estimating Properties with Collocated Cokriging
Use collocated cokriging to fill the selected SGrid or Voxet with property values (to assign property values to all the nodes in the SGrid or Voxet).
You need an ASCII file containing the variogram data and an object that can serve as the property source (it should lie at least partially inside the SGrid or Voxet).
The SGrid or Voxet should have a property that will be used as the soft data (see step 9).
To run collocated cokriging to create SGrid or Voxet properties
1 Display the SGrid or Voxet and the property source object in the 3D Viewer.
2 Select Voxet, SGrid, or General commands > Geostatistics > Collocated Cokriging to open the Collocated Cokriging dialog box.
3 In the Grid Object box, enter one or more Voxets or SGrids.
4 In the Region name box, enter the grid object region in which the kriging will be performed.
Note By default, kriging will be performed for all points (everywhere) on the grid.
5 In the Discrete property server by box, enter the object that carries the existing property values.
6 In the By region box, enter the input data region.
7 In the Property box, select the object property to be used as the source for kriging.
This property is considered the hard data.
5.2 Estimating Grid Properties with Kriging Algorithms 5-15 User Guide
8 In the New property prefix box, type the prefix for the created properties. (For example, if you type Kriging_, the two new created properties will be named Kriging_estimate and Kriging_variance.)
9 In the Soft data box, enter the name of the SGrid or Voxet property that will be used as the soft data in the cokriging.
10 In the Correlation coefficient box, type a positive number between 0 and 1, specifying the scale factor of the variogram data for the soft data.
11 To specify the ASCII file that contains the variogram data (see "GS File" on page 5-2), do either:
• In the GS file box, enter the path to the file.
• Click to open the Select Text File dialog box, find and select the file, and then click OK.
Note The variogram is used by the hard data, then scaled by the factor specified in step 10 on page 5-15 and used by the soft data. If the file is not in the default directory, you need to include the proper path in the file name.
12 To allow for the possibility that the result at a cell containing data points is not kriged, but rather directly assigned from input data in that cell, select one of the following data value assignment options:
• No data assignment. All cells are kriged.
• Assign data to nearest cells. In any particular cell, the data point closest to the cell center is assigned as the estimation at the cell.
• Assign mean at cell center. The mean of all the data points in a particular cell is assigned as the cell value.
If you choose this option, also select a method of computing the mean in the Mean computation type box, and type the value for the exponent (in the standard mean power equation) in the Power mean power box.
13 Click OK or Apply.
5.2.6 Estimating Properties with Indicator Kriging
Use indicator kriging to fill the selected SGrid or Voxet with property values (to assign property values to all the Nodes in the SGrid or Voxet).
You need an ASCII file containing the variogram data and an object that can serve as the property source (it should lie at least partially inside the SGrid or Voxet).
To run indicator kriging to create SGrid or Voxet properties
1 Display the SGrid or Voxet and the property source object in the 3D Viewer. Display a SGrid or Voxet Section with the property on which you want to run kriging.
2 Select Voxet, SGrid, or General commands > Geostatistics > Indicator Kriging to open the Indicator kriging dialog box.
3 In the Grid Object box, enter one or more Voxets or SGrids.
4 In the Region name box, enter the grid object region in which the kriging will be performed.
Note By default, kriging will be performed for all points (everywhere) on the grid.
5 In the Discrete property server by box, enter the object whose property will be the source for kriging.
6 In the By region box, enter the input data region.
7 In the Property box, select the object property to be used as the source for kriging.
8 In the New property prefix box, type the prefix for the created properties. (For example, if you type CutOff_, the two new created properties will be named CutOff_1, CuttOff_2, and so on.) The number of properties is equal to the number of cutoffs specified in the variogram file.
5.2 Estimating Grid Properties with Kriging Algorithms 5-17 User Guide
9 To specify the ASCII file that contains the variogram data (see "GS File" on page 5-2), do either:
• In the GS file box, enter the path to the file.
• Click to open the Select Text File dialog box, find and select the file, and then click OK.
Note If the file is not in the default directory, you need to include the proper path in the file name.
10 In the Kriging Type box, select one the following kriging options:
• Simple. Residuals are computed from the mean of the data and kriged.
• Ordinary. Input data values are used directly for the kriging.
• Use_variogram_file_setting. Use the type set in the variogram file.
11 In the Distribution Type box, select the type of distribution function to be used.
Your selection determines how the cutoff value given in the variogram files are used to define the indicator kriging (IK) stages and how the input property values are interpreted in each stage.
• PDF (Probability Density Function). In each threshold value kriging, a data point equal to that value is considered 1 and a data point not equal to that value is considered 0. For discrete properties only.
• CDF (Cumulative Distribution function). In each interval kriging, a data point within that interval is considered 1 and a data point outside of that range is considered 0. For continuous and discrete properties.
12 To allow for the possibility that the result at a cell containing data points is not kriged, but rather directly assigned from input data in that cell, do one of the following to assign data values to cells:
• Select the Assign data to nearest cells check box. In any particular cell, the data point closest to the cell center is assigned as the estimation at the cell.
• Clear the Assign data to nearest cells check box. All cells are kriged.
13 Click OK or Apply.