Download GEMS Tutorial, A. Gysi Oct 2016 MODULE 2: REACTION PATH

GEMS Tutorial, A. Gysi
Oct 2016
MODULE 2: REACTION PATH MODELING
In this tutorial we will use the GEMS project file ”Module2” in the examples
to model the reaction path of K-feldspar in contact with a NaCl-bearing aqueous
solution and calculate the evolution of the fluid and the minerals formed as a function
of increased fluid-rock interaction. Installation instructions for GEMS can be found at
http://gems.web.psi.ch/GEMS3/techinfo.html
Compute the chemical equilibria of single chemical systems (SysEq)
1. Copy the folder Module2 to your project folder located in Library\Gems3\projects.
2. Open GEMS and choose the project in the Equilibria Calculation Mode. The
user interface is shown in Figure 1. Panel 1 permits to create new records and
run the program for calculations. Panel 2 gives you different calculation options.
3. Choose the Create New Record System from the menu in Panel 1 and fill the
parameters listed in Figure 2
4. In the Open recipe dialog, which can also be found in Panel 1, add phases,
quantity and units as shown in Figure 3; Aqua (1000 g), HCl (0.1 M), NaCl (50
g), O2(g) (1e-7) and K-feldspar (10 g).
Fig. 1: GEMS user interface
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Oct 2016
Fig. 2: New record window
5. Model the chemical equilibrium between 10 g of K-feldspar (microcline) and H2 O
at 150 ◦ C by pressing Calculate BCC followed by Calculate Equilibrium in
Panel 1. Inspect the pop up window with pH, redox and phase proportions, then
accept.
(a) Determine the pH of this system as shown in the lower right of the main
window (Figure 4).
(b) What is the pH of this system with 10, 20, 50 and 100 g K-feldspar? Change
the amount of feldspar by clicking the Open recipe dialog (Figure 3) followed by Calculate BCC and by Calculate Equilibrium.
(c) What minerals are stable with increasing pH?
6. Clone your existing Rct path 1 chemical system by selecting it and choosing
Clone a new record in Panel 1. Change the temperature to 300 ◦ C in the pop
up window.
(a) Determine the pH of this system as shown in the lower right of the main
window.
(b) What is the pH of this system with 10, 20, 50 and 100 g K-feldspar?
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GEMS Tutorial, A. Gysi
Oct 2016
(c) What minerals are stable with increasing pH?
(d) Are there differences between the modeled system at 150 and 300 ◦ C
Fig. 3: System Recipe dialog
pH
moles minerals
Fig. 4: Results of the calculations, i.e. with 10 g K-feldspar added to the fluid.
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Oct 2016
Compute processes using a titration model (Process)
1. Select the Process option in Panel 2 (Figure 1).
2. Click Creat a record from scratch in Panel 1 and select your system (SysEq)
calculated at 150 ◦ C (Figure 5).
3. Name this process simulation titration model and use the Process simulation
code (S) as shown in Figure 6.
4. In the next window, choose a model ( titration cNu linear), a mineral (
Compos, Min K-feldspar) and select the temperature (150 ◦ C), pressure (0 for
water vapor saturation P) and amount of mineral to be added (iNu: 10-250 g in
10 g steps) as shown in Figure 7.
5. Select items to be plotted (Scalars: pH; Xa: Kaolinite, Pyrophyllite, Microcline,
Muscovite, Albite and Quartz) as shown in Figure 8.
6. Accept all the following dialogues and click on Save this record to database
in Panel 1 (Figure 1). Then click on the calculator icon Re-calculate and
check record data.
7. There is a tab menu with 3 important selections: Controls, Sampling and
Results. In the Controls tab add a description of the modeling project (Figure 9). In the Sampling tab change the script as shown in Figure 10 to choose as
x-variable the amount of K-feldspar added (the process extent: cNu). Click Save
this record to database and the calculator icon (Re-calculate and check
record data) in Panel 1. Toggle to the Results tab to inspect your modeling
results.
(a) How many grams of K-feldspar need to be added to get a constant pH and
what is the value?
(b) Which mineral assemblages buffer the fluid pH, are there different ranges?
8. Clone your existing Rct path 1 chemical system by selecting it and choosing
Clone a new record in Panel 1 (Figure 1). Select your system (SysEq) calculated at 300 ◦ C (Figure 11). Accept all the following dialogues. In the Controls
tab (Figure 9) change the description of the modeling project and change the
temperature to 300 ◦ C to replace the starting and ending values of 150 ◦ C. Click
Save this record to database.
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Oct 2016
9. Switch the tab to Results and click the calculator icon (Re-calculate and
check record data) in Panel 1 (Figure 1) to see how pH and mineralogy is
changed by varying the system temperature.
10. Toggle between both calculated process simulations at 150 and 300 ◦ C on the left
pane and inspect the results.
(a) How many grams of K-feldspar need to be added to get a constant pH and
what is the value?
(b) Which mineral assemblages buffer the fluid pH, are there different ranges?
(c) What are the main difference for the simulations at 150 and 300 ◦ C?
11. Finally, we are going to fine tune the model and plot it! Choose the process
simulation at 150 ◦ C and in the Controls tab change the amount of K-feldspar to
be added (Figure 9) using 2 to 50 g in 2 g steps and save. Choose the Results tab
and click the calculator icon (Re-calculate and check record data). Click on
the small Plot data on Graph dialog in Panel 1 (Figure 1). The resulting graph
should look similar to Figure 12. The plots indicate different mineral assemblage
buffer the fluid at different pH values. You can inspect which minerals by choosing
the Customize button with values shown in Figure 13.
12. The resulting reaction path at 150 ◦ C is shown in Figure 14.
13. The resulting reaction path at 300 ◦ C is shown in Figure 15
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Oct 2016
Fig. 5: Select a chemical system (SysEq) for modeling a Process
Fig. 6: Name the Process and indicate the type (note: the process type code names are described
and changeable on the next screen as well)
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Oct 2016
P at psat
(1) titration model T at 150 ºC
(2) choose mineral
add 10-250 g of min
in 10 g steps
Fig. 7: Set the parameters for the Process simulation
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Oct 2016
Fig. 8: Choose the results to be plotted
description
pressure
temperature
amount of min
added
modeling script
Fig. 9: The Controls dialog for defining the model conditions
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Oct 2016
choose x-variable
choose y-variables
Fig. 10: The Sampling dialog for selecting the output data to plot.
single chemical
systems from SysEq
Results from
Process simulation
Fig. 11: Choosing a SysEq record when cloning a Process simulation
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Fig. 12: Results using the Plot data on Graph dialog
(1)
(2)
Fig. 13: Customize x- and y- axis in the plots (1). Note: the Fragment option (2) permits to select
an inset view in the graph by toggling the Fragment button in the graph (see Figure 12)
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Fig. 14: The resulting reaction path at 150 ◦ C
Fig. 15: The resulting reaction path at 300 ◦ C
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