This quick look will provide you with a good overview of GridSTAT in a minimum amount of time.
In this example, we want to make a grid of a formation top. We assume that coming into GridSTAT, the top marker(s) of the formation(s) of interest have been chosen and that this data has been put in a file TESTMRK.DAT. This example file is included in the installation.
Here is the minimum steps required to generate a map of formation top (or a map of other properties) after GridSTAT is installed.
For a more detailed step by step explanation please read on.
Open a new project. Click on the File pulldown 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 pulldown 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 pulldown menu and select that project from the listing. You may also click Open or Find File to find additional listings.
1. 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.
2. At the bottom line, check if you are in the correct working directory.
3. If you expect to have data file available, there should be a check mark in the box to the right of Data File.
4. If you expect to have calculated variograms, there should be a check mark in the box to the right of Variogram.
5. 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.
In this example we import the data in layer-based form. The default search path for the data files is C:\GSWORK\*.DAT, where C:\GSWORK is the working directory on which GridSTAT is installed. When you get to the Import panel, files are already listed from the search path.
On the top left of Import panel, select From Layer Data. This tells the software that you are going to import layer-based data.
Click to check-mark the box in front of the 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 modify the column definitions. The first column is Well and will be used as well name. You will also need X and Y columns. For those columns you do not want to use, either leave the selection blank or mark as Other. To use more data columns, move to the right by clicking the right arrow or dragging the horizontal sliding bar.
Click the Convert button to import the file.
In the last line of the panel, you should see how many wells are imported.
Formation top is used as an example data here. In its place you may use zone thickness, average porosity, pressure, etc.
1. At the bottom line, check if you are in the correct project.
2. At the bottom line, check if you already have data in this project.
3. At the bottom line, check if you have enough disk space free for adding data.
4. Select the correct type of import at the top of the panel.
5. Select the correct file to import
6. Check or select the correct label for the data columns after preview.
7. If multiple data columns are used, they should be of same data type, i.e. all depth or all thickness, but not mixed data types. Create different projects for different data types.
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 pulldown 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. 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.
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), but we don’t want to get into that in this introduction.
1. Check if the well locations are correct in the basemap. The numbers are in the Header table.
2. Look through the Data Overview table to make sure the numbers are what you expect.
3. For trace by trace details open the Statistics table from the Table pulldown menu.
4. You may modify the Statistics table from the Tools pulldown menu Table Design to display other items or output the whole table to a file.
5. If there is only one data point per well, you may graph the data average (Data AV) which in this case is the same as the value of the data point.
6. Change to 1 Graph view from View pulldown menu for better viewing.
7. 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, subsea depth of formation top).
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 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. For structure depth type of data, the spherical variogram is ususally tried first.
1. Make sure you have multiple wells if you want to calculate areal variogram.
2. You need multiple data points in each trace to calculate vertical variogram.
3. In the current version each project should contain one type of data for variogram calculation.
4. Calculate the variogram points first.
5. Curve fit the results. The fit is automatic as soon as you choose a model.
6. Other graphs may be brought up from the Graph button on the left. Change the graphs with Options pulldown menu Graphpar panel. For example you may turn off some of the curves on the All Variograms graph.
7. Variograms usually increases with distance.
8. Vertical variogram usually reaches high variance value in much shorter distance.
9. 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 or well location.
10. 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 parameters from variogram modeling are automatically copied on this panel.
Check the variogram parameters. You may change any of them here.
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.
1. Make sure the major correlation length, which is the longest correlation length 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.
2. 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.
3. 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.
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.
Click the big Start button on the top right to start the gridding process.
1. 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.
2. Make sure the grid definition is consistent with the data coverage.
3. From Table pulldown menu you can open DataView or Statistics table to check available information.
4. Do Kriging first even when your final goal is conditional simulation. This will give you a baseline case.
5. If you have changed some paratmeters and want to reset to the defaults, use View pulldown menu Reset and not to use the saved parameters.
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 pulldown menu Graphpar or GridGraph panel.
Use the Export button to export the grid for other software.
1. For most data, the graphed grid should show lateral continuity but not complete continuity.
2. 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.
3. If NZ is 1 or the Data Type is Depth (select from Options pulldown menu Data&Units panel), you should be able to show the result in Structure for Depth grid option.
4. If grid does not show the layering as you expected, check the following:
5. If the variogram showing enough lateral continuity (CR_v >40), checking from Variogram panel and GridOption panel.
6. 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.
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