Calculate Variogram

This command takes the *.DAT file from Prepare Variogram and calculates the variogram data, outputting the Nugget, Sill and Range.

Data File:
The data file appears in the top left corner. If the file is not displayed, chose Select, or double click in the file name window. To start it with a specific file, start it as:
\path\Csvgram batch-\path\filename
 
Variogram Type:

The type of variogram to calculate can is shown in the upper left corner. If the datafile has only one variable, the Covariance option in the yellow box will not be enabled. First, select the Head Variable in the yellow box, shown here as Thk m. Then select the type, such as  Semivariogram. This should then display the head variables span from low to high. The current types of variograms to choose from is shown below. Details of each method can be found online.

• Semivariogram
• Cross Semivariogram
• Covariance
• Correlogram
• General Relative Semivariogram
• Parwise Relative Semivariogram
• Semivariogram of Logarithms
• Semirodogram
• Seminadogram
  

 

Variogram Attributes:

Trimming limits will provide a range selection to process. A value of 0 trimming will delete null values. Set the number of lags and lag separation distance. Lags are the number of intervals, the separation is the distance between the intervals. Normally the Lag Tolerance is Lag Separation Distance divided by 2. OmniDirectional will look in multiple circular groups for pairs. If it is off, then it will look just directional for the pairs. The number of directions, Angle Tolerance and Bandwidth apply to the directional.

Pressing Go will show the plot and show # of pairs in each lag.

Fitting:
Omnidirectional: Click Exponential option beside big circle on the right to begin. Hold down left mouse and drag on the plot to set Range, Sill and Nugget or enter them in the boxes.

Directional Trend: Select the Head Variable, the variogram plots redraw by clicking on the lines on the large directional circle so the 4 angles would be: 0 Azimuth, 135 Azimuth, 90 azimuth and 45 azimuth. The resulting values are displayed above for geostatistical modeling.
   
Format:

Data Files (standard to all Variogram analysis programs)
Line 1            title
Line 2            # of Data Variables (including X and Y)
Line 3            X Variable Name
Line 4            Y Variable Name
Lines 5 to 5+#-3    Other Variable Names
Remaining lines:         X Y V1 V2 … V(#-2)
            Variables separated by spaces     - pick some negative number for null
Example:
Zone A Data, Big Bean Field
8
X m                              meters east of origin
Y m                              meters north of origin
Thk m                            zone thickness in meters
Por %                            porosity in percent
Perm md                          permeability in millidarcies
LogPerm -                        base 10 log of permeability
LogPermPrd -                     LogPerm predicted by regression against Por
LogPermRsd -                     Residual from LogPerm-Por regression
12100 8300 37.1531 14.6515 2.8547 0.4556 0.1357 0.3198
5300 8700 31.4993 14.5093 -999.9999 -999.9999 -999.9999 -999.9999
3500 13900 36.9185 14.0639 -999.9999 -999.9999 -999.9999 -999.9999
5100 1900 24.0156 15.1084 1.1407 0.0572 0.2268 -0.1696
9900 13700 35.0411 13.919 -999.9999 -999.9999 -999.9999 -999.9999
2900 900 28.4249 13.1304 0.3897 -0.4093 -0.1674 -0.2419
7900 6700 33.2458 14.5724 -999.9999 -999.9999 -999.9999 -999.9999
.....

Prompts

Command: vgramun
Drop-Down Menu Location: StrataCalc in Geology
Keyboard Command: vgramdat