Click on the Exp. Solubility tab to enter the data generated earlier for solubility of CO2 in brine. Make sure that the unit selected for entering the solubility is Mole Fraction, then enter the value predicted for the amount of CO2 in brine from the first part of this case study. For the flash at 500 psia, the amount of CO2 in the aqueous phase was calculated to be 0.47996 mole%, thus the entry in the table should be 0.0047996 as shown below. All of the other entries in the table can be left blank. They will default to a value of “-1”. A negative value indicates that a given experimental data point will not be used in the regression.
User's Guide WinProp Appendix A • 171 Click OK to return to the main form.
The flash specification with experimental data constructed above can now be copied and modified for the other pressures. Make sure that the OGW/EOS Multiphase Flash row is selected, then select Edit|Copy from the main menu (or press Control-C). Click on the first blank row underneath the OGW/EOS Multiphase Flash, then select Edit|Paste from the main menu (or press Control-V).
Double-click on the new OGW/EOS Multiphase Flash row to open the data entry form. Change the pressure to 1500 psia, then click on the Exp. Solubility tab and enter the value of CO2 solubility recorded for this pressure from the first part of this case study. This should be a mole fraction of 0.0101982.
Create flash specifications and enter the CO2 solubility data for 2500 psia (0.0121624 mole fraction CO2), 3500 psia (0.0131680 mole fraction CO2) and 4500 psia (0.0139434 mole fraction CO2).
Complete and Run the Regression Data Set
After the last flash specification, make sure the first blank row at the end of the data set is selected and then select Regression|End to enter an End Regression form into the data set. The completed regression data set should now appear as follows:
Save and run the data set.
View the output by selecting File|View output or by pressing the F3 function key. At the end of the output file, two summary tables are printed: “Summary of Regression Variables” and “Summary of Regression Results.” Looking at the before and after regression values in the regression results table in comparison to the experimental values shows that the fit has been considerably improved. Investigation of the regression variables table, however, shows that both of the regression variables have reached the default upper bound imposed. This indicates that further improvement to the fit could be obtained by increasing this limit for one or both of the parameters chosen.
172 • Appendix A User's Guide WinProp A summary of the regression iterations appears roughly in the middle of the output file. Examination of this table shows that the Henry’s constant for CO2 (indicated by the name HEN1 in the table) reached its limit first during the regression iterations. Thus, we will try increasing the upper bound for this parameter.
Modify the Regression Data Set
Close the output file, then double-click on the Regression Parameters row to bring up the data entry form. Click on the Variable bounds tab, and change the upper bound for the CO2
Henry’s constant to 5500 atm. At this point the convergence tolerance can also be tightened on the tab Regression controls. Enter a value of 0.000001 in the convergence tolerance text box. Click OK to return to the main form, then save and run the data set.
Viewing the summary tables at the end of the output file now shows that an excellent match of the CO2 solubility data has been obtained. Close the output file in preparation for the final phase of the modelling process.
Create a New Data Set
Once the process of tuning the model has been completed, a new data set can be created with all of the updated model parameters. Select File|Update component properties from the main menu. This will overwrite the first three forms in the data set with the model parameters obtained from the regression run. Use File|Save As … to save the file under a new name. This new file will be used to generate the fluid model specification for GEM. First, remove all of the calculation options below the composition form. Click on the
Regression Parameters row and drag the mouse down to the End Regression row to select
all of the calculations, then select Edit|Delete or press the Delete key to remove the calculations as shown below.
User's Guide WinProp Appendix A • 173
Add GEM Fluid Model Creation to the Data Set
Click on the first blank row underneath the Composition row, then select
SimulatorPVT|CMG GEM EOS Model from the main menu as shown below.
This will insert a CMG GEM EOS Model form into the data set. Double-click on this row to bring up the data entry form.
Under File Selection, click the check box labelled Print component properties for GEM. It is also possible to get an echo of the component properties to the output file by clicking the check box labelled Print detailed component properties to *.OUT. GEM does not need to have the water component included in the component list, therefore the checkbox labeled Include H2O in
GEM component list can be left in its default unchecked state. To output Henry’s constants
and molar volumes, the check box labelled Print aqueous phase component solubility
parameters must also be checked. Note that when the solubility parameters are defined on the Component Selection/Properties form, they are constant for a data set, and the option buttons
available under Solubility Parameters will have no effect. Selecting these options only affects the results when the internal model is used to generate Henry’s constants and other solubility parameters. The reservoir temperature must also be entered to complete the fluid model description for GEM.
174 • Appendix A User's Guide WinProp
Run the Data Set for the GEM Fluid Model
Save and run the data set, then view the output file. The table in the output file shows a listing of the properties for all of the components, including the aqueous phase solubility parameters. The GEM fluid model is saved in a file with the same root name as your data file and output file, but with the (.gem) extension (e.g. for the Case2b.dat data file, the GEM fluid model is stored in the file Case2b.gem). The file can be viewed by selecting File|View GEM EOS
Model from the main menu. This file contains the same information as shown in tabular form
in the output file, but written out in the keyword format required for GEM.
The GEM fluid model file can be referenced in a GEM data set using an “include” statement, or it can be imported into a data set using CMG’s ModelBuilder program.