This quick look will provide you with a good overview of GridSTAT in a minimum amount of time. In making a Vsh grid, we assume that we have put the Vshale log data in a data file TESTVSH.LOG and that the formation top(s) have been chosen and put in a marker file TESTMRK.DAT. These files come with the installation.
Project Panel: Click the Next button on the lower left.
Import Panel:
Click the pull down list at the top (initially Not Defined) then select To MarkerHeader
Check the box in front of TESTMRK.DAT
Click the Preview button, then select As Text
Click the Convert button
Click the pull down list at the top then select From Log Data
Click the pull down list at the top right then select Match Keyword
Check the box in front of TESTVSH.LOG
Click the Preview button, and then As Data
Click the Convert button
Click the Next button on the lower left.
DataQC Panel: Click the Next button on the lower left.
Variogram Panel:
Click the Points button on the left of the panel
Click the Curve button then select Spherical
Click the Next button on the lower left.
Click the Next button on the lower left.
Click the Start button on the upper right
Click the Next button on the lower left.
Click Graph button on the upper left of the panel then select 3D View
Open a new project. Click on the File pull down menu. Then click on New. The new project will be UNTITLED and initially it is empty. From the Project panel, you should see that none of the files (data, marker, etc.) have a check mark next to them.
If you have been working on the UNTITLED project and want to save the results before starting another project, use Save As from the File pull down menu then type in the name you want to save the results to.
If you have been working on a project, that project will be the current project when you restart GridSTAT. Then you may not need to do anything in this panel. To change to another existing project, click on the File pull down menu and select that project from the project history listing. You may also click Open or Find File to find additional listings.
At the bottom line first field on the left, check if you are in the correct project. If the bottom line is outside the open screen area, move it to the open.
At the bottom line, check if you are in the correct working directory.
If you expect to have data file available, there should be a check mark in the box to the right of Data File.
If you expect to have marker file available, there should be a check mark in the box to the right of Marker File.
If you expect to have calculated variograms, there should be a check mark in the box to the right of Variogram.
If you expect to have generated a grid, there should be a check mark in the box to the right of 3D Grid.
Go next to the import panel by either clicking on the Next button on the lower left or by clicking on Import on the right hand side of the Project panel.
If data files are already in GridSTAT format and in the correct subdirectory and of correct file name, either because you have imported them before or copied from somewhere, you do not need to import data now. In that case you may skip the Import Panel.
This example includes importing both a marker file and a log data file. The default search path is C:\GSWORK\*.DAT for marker data file and C:\GSWORK\*.LOG for log data file, where C:\GSWORK is the working directory on which GridSTAT is installed.
On the top, click on the Data Import list, then select To MarkerHeader. This tells the software that you are going to import a marker file.
Check the box in front of the marker file you want to import. In this case it is TESTMRK.DAT.
Click the Preview button, then select As Text.
If you do not want to use the default, then from the top of the previewed columns, click the arrows to pull down the selection list to modify the column definitions. The first column is Well and the well names in this column is needed to match the well names in the log data file. For those columns you do not want to use, either leave the selection blank or mark as Other. To use more formation tops, move to the right by clicking the right arrow or dragging the horizontal sliding bar.
All horizon markers are called "top" here. The last "top" will be used as a bottom. The marker depths should be in subsea (negative below sea level). If measured depth is used in the marker file, they should be converted from MD to Subsea after importing all data. The conversion option is in Tools/Marker >. Deeper markers should be to the right of shallower markers. If you have only one horizon marker, constant thickness will be assumed in subsequent calculations, and the top and bottom will be initially set based on available data.
If x-y location and kb are included in the log data file with required keywords, the only required columns in the marker file are the well name column and marker columns. Quite often, log data files contain logs while x-y location and kb are in the marker file. In this case, marker file must be imported first with selected x-y and kb. Afterwards when importing log data files, make sure the file names are the same as the well names in the marker file. Then make sure the File Type on the upper right of the panel is Las/Match Filename.
Click the Convert button to import the marker file.
On the top, select From Log Data. This tells the software that you are going to import well logs. The software will clear the panel and reset the searchpath to *.LOG. Click the pull down list at the top right then select Match Keyword. This tells the software to read x, y and kb by searching for corresponding keywords in the *.LOG file.
Check the box in front of the well log file you want to import. For this example it is TESTVSH.LOG. You may check multiple well log files to convert them into one project.
Click the Preview button, and the As Data button. To preview As Data allows skipping long text headers.
In this example, TESTVSH.LOG contains well name, x-y location, and kb with keywords. The File Type on the upper right of the panel should be Match Keyword. If the log data files contain only logs, filename will be used as well name and the File Type on the upper right of the panel should be changed to Las/Match Filename.
Sometimes the default import parameters does not meet the required need, then pull down the Options menu and select ImportPar.... The vertical spacing (DZ) minimum is used for initial read and the maximum is used for adjustment limit. If the desired data spacing is not within the specified range, the range should be changed. If the data is of variable spacing, it is best to use same minimum and maximum to fix the output spacing.
Click the Convert button to import the well logs.
In the last line of the panel, you should see how many data traces are imported and how many marker horizons are imported. GridSTAT will match the markers to the well logs by the well names. If the matched % is less than 100, some of the well markers are not available. In later calculations, these wells will automatically be ignored. In this example, the matched % should be 100.
The Vshale log is just an example here. In its place you may use porosity or other attributes.
At the bottom line, check if you are in the correct project.
At the bottom line, check if you already have data in this project.
At the bottom line, check if you have enough disk space free for adding data.
Select the correct type of import at the top of the panel.
Select the correct file to import.
For Log Data, use correct file type and correct data spacing (DZ) range.
Check or select the correct label for the data columns after preview.
Make sure the marker file has the same well names as the well log data file.
Go to the next panel by either clicking on the Next button on the lower left or by clicking on DataQC on the right hand side of the panel.
This Panel is used to quality-control (QC) the data before further analysis and gridding.
Use the Table and Graph pull down menus to open more tables or graphs to look for potential errors in the data. Click at one of the four picture areas to make it active. When you open a graph, it will be placed in the active area. Besides the Basemap that is shown as default, you may graph the surface elevation, depth range, depth of markers, data trace, fan-section, data distribution, etc. Keep in mind that your final grid will only be as good as your input data and that most input data does contain some errors.
You may select some of the wells to graph. With the basemap in display, click the Select button on the left of the panel and turn Pick Well on. Now you can pick the wells you want to graph. Data trace, traces, fan-section, etc. will follow the selected well sequence. The first two groups of the graphs in the Graph pull down menu are linked in the well selections. We may select or deselect a well in any one of those graphs and the selection will show up in other graphs of those two groups. You may need to use Redraw from the View pull down menu to renew the graphs.
If a 3D grid is available and is the current grid (see lower right of GridOutput panel), the contour from that grid will be displayed on the fansection (cross section) graph. To change how the grid is displayed, use Options pull down menu and select GridGraph panel. To change show the fansection is display, use Options pull down menu and select Fansection panel. To change color of a graph object, use Options pull down menu and select Graphpar panel.
If you find errors in the data, make correction to your data or delete bad data. There are many functions in GridSTAT for deleting bad data (Remove button on the left of the DataQC panel) and normalizing data (Change button on the left of the DataQC panel).
Check if the well locations are correct in the basemap. The numbers are in the Header table.
Look through the Data Overview table to make sure the numbers are what you expect. For an overview of possible data problems, use the Data Quality table. If there are too many wells or too many data points, some may not be read into memory. Use Tools pull down menu then Read Filter to limit the read.
For markers, make sure that all wells have corresponding markers (ideally there should be 100% match), that there is data in the corresponding zones (you may also compare graphs of Depth Range and Markers), and that the zone thickness is positive. For zone thickness and number of valid markers for each well, use the Graph button on the left of the DataQC panel.
For trace by trace details open the Statistics table from the Table pull down menu.
You may modify the Statistics table from the Tools pull down menu Table Design to display other items or output the whole table to a file.
If there is only one data point per well, the data average (Data AV) graph is the same as graphing the value of the data point.
Change to 1 Graph view from View pull down menu for better viewing.
Print with PicPrint if you want to print the picture area only.
Go to the next panel by either clicking on the Next button on the lower left or by clicking on Variogram on the right hand side of the panel.
Variograms model the spatial continuity of whatever data is being gridded (in this case, Vshale).
Click the Points button on the left of the panel to calculate the variogram points. The All Variograms graph shows the variograms for the northwest, north, northeast, and east directions as well as the vertical variogram. The vertical variogram is also shown separately for better view. The well pair variance graph shows how the variance between wells varies with the distance between them. For those well pairs that are close (small separation distance) but that still have large variances, there is usually error associated with either the data, the location, or the markers. The areal variogram graph shows how reservoir continuity varies in the different directions.
Click the Curve button to fit a variogram model to the calculated points. If you don’t know which model to choose, select Spherical first.
Make sure you have multiple wells if you want to calculate areal variogram.
You need multiple data points in each trace to calculate vertical variogram.
Make sure you already have correct markers (check in DataQC panel) if you want to honor the horizons.
If you don’t have markers, areal variograms will be calculated in the horizontal direction.
You can turn off a marker or markers from the Options pull down menu Markers panel.
Each time there should be one type of (primary) data for variogram calculation.
Calculate the variogram points first.
Curve fit the results. The fit is automatic as soon as you choose a model. To modify the fit, go to the next panel (GridOptions). Turn on Input on the top left to see your input curve fit.
Other graphs may be brought up from the Graph button on the left. Change the graphs with Options pull down menu Graphpar panel. For example you may turn off some of the curves on the All Variograms graph.
Variograms usually increases with distance.
Vertical variogram usually reaches high variance value in much shorter distance.
Well Pair Variance graph is a good indicator of data quality. For those well pairs that are in short distance but showing relatively large variance, there is usually problem in the data, well location (including adjustment for deviated wells), or marker depth.
Correlation Ratio to Vertical (CR_v) is usually larger than 10 (50, 100, 1000 depending on the data) if the vertical scale is depth. If vertical scale is layer index (when imported as layer data), it depends on the layer thickness and whether the data in different layers are correlated.
Go to the next panel by either clicking on the Next button on the lower left or by clicking on GridOption on the right hand side of the panel.
The curve fit results from variogram modeling in the previous step are automatically copied to this panel. The variogram parameters in this panel are then used in the gridding process. The variogram parameters in this panel can be modified by typing over.
Make sure the major correlation length is large enough to cover all the area you want to cover, but not too large to extrapolate into area that you do not want to extrapolate.
If areal anisotropy is not supported by geological understanding, make areal correlation ratio CR_Area 1.
Carefully modify the vertical correlation ratio CR_Vertical to confirm to geological aspect ratio. This parameter has the largest impact on the final model.
Grid Along Marker is the usual option chosen. Grids that follow the markers are called stratigraphic.
Use Brick Model Grid if your visualization tool requires that. One example would be to model faults when the visualization tool cannot model full fault models.
Make sure the major correlation length, which is the longest correlation of the correlation ellipsoid and the distance limit of data search, is reasonable. You may need to increase it to cover areas far from any wells.
Make sure Correlation Ratio to Vertical (CR_v) is reasonable. Too small a CR_v will disrupt the layer-like character while too large a CR_v will make the layering too continuous.
The areal correlation ratio (CR_a) is usually close to 1. If CR_a is larger than 1 and there is no geological trend in the corresponding direction, the result will be biased.
If you only want to see the results within zone boundaries, such as for flow simulation, and you have markers included, select Grid Along Marker. Otherwise use Brick Model Grid.
Go to the next panel by either clicking on the Next button on the lower left or by clicking on GridSize on the right hand side of the panel.
If you do not want to use the default, modify the grid size definition to suit your need. Select Kriging or Conditional Simulation.
Decide to make a three-dimensional grid (default) or a fan-section only (check the box at top right).
Click the big Start button on the top right to start the gridding process.
The initial grid dimension is designed to cover all the data and have 10 cells in each horizon direction. Make a small grid first. You can redefine the cell sizes to make a finer grid or covering more area later.
Make sure the grid definition is consistent with the data coverage.
From Table pull down menu you can open DataView or Statistics table to check available information.
Make sure Log-Normal Data option is on if the data is resistivity or permeability.
Do Kriging first even when your final goal is conditional simulation. This will give you a baseline case.
If you don’t have any data, conditional simulation will become unconditional simulation and a grid can be generated (simulated heterogeneity).
If you have changed some parameters and want to reset to the defaults (for example changing from fan-section to 3D grid), use File pull down menu Reset then Gridding Input and not to use the saved parameters.
To generate a two-dimensional grid along a fan section or cross section, turn on the FanSection option. A more detailed fan section grid can be generated in shorter time than a 3D grid.
Go to the next panel by either clicking on the Next button on the lower left or by clicking on GridOutput on the right hand side of the panel.
From the Graph button on the upper left of the panel, you can select 3D View to show the 3D grid, or graph one of the directions.
Click the Range button on the left of the panel to slice the 3D grid.
Modify the pictures from Option button on the left or from the Options pull down menu Graphpar or GridGraph panel.
Use the Export button to export the grid for other software.
Graph FanSection from the Graph pull down menu to view a fan section. For a 3D grid, different cross sections may be picked from DataQC panel and the cross section drawn with contours from the grid. For a fan section grid, only the original sequence can be used and picking a new section will disable the contouring from the grid.
For most data, the graphed grid should show lateral continuity but not complete continuity.
Be aware of the aspect ratio. Typically the vertical scale is exaggerated for better viewing, this may cause the result to appear less continuous in the horizontal direction.
If the grid has been made to follow markers, you should be able to show the result in structure for attribute option.
If NZ is 1 or the Data Type is Depth (select from Options pull down menu Data&Units panel), you should be able to show the result in Structure for Depth grid option.
If grid does not show the layering as you expected, check the following:
Have you included the correct marker(s), checking from DataQC Panel.
Is the variogram showing enough lateral continuity (CR_v >40), checking from Variogram Panel and GridOption Panel.
If you don’t see the whole grid in display, check if grid dimension is consistent with data coverage and, if markers are used, there is data within the zones, checking from DataQC Panel and GridSize Panel.
When a graph involving a grid is opened, the active grid is used. If multiple grids are available, select the desired grid from the bottom right hand side pull down list.
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