Conceptual Models > Design of conceptual models
CO2 solubility
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Ricardo Borba:
Dear Dr. David Parkhurst
I am simulating a real situation of CO2 solubility at 600 atm and 65ÂșC. Under these conditions, in the aquifer, there are no bubbles, the solution is monophasic. I tried to model this situation in Phreeqc in different ways and obtained different CO2 solubilization capacities for the same P and T conditions. For simulations 1, 3 and 4 the CO2 was completely dissolved, for the others there was only its partial dissolution. Could you help me understand why the simulations showed different results?
SOLUTION 1
temp 60
pH 7
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
REACTION 1
CO2(g) 1
90 moles in 10 steps
GAS_PHASE 1
-fixed_pressure
-pressure 600
-volume 1
-temperature 65
END
SOLUTION 1
temp 60
pH 7
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
REACTION 1
CO2(g) 1
90 moles in 10 steps
GAS_PHASE 1
-fixed_pressure
-pressure 600
-volume 1
-temperature 65
CO2(g) 0
END
SOLUTION 1
temp 60
pH 7
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
REACTION 1
CO2(g) 1
90 moles in 10 steps
EQUILIBRIUM_PHASES 1
CO2(g) 100 0
GAS_PHASE 1
-fixed_pressure
-pressure 600
-volume 1
-temperature 65
END
SOLUTION 1
temp 60
pH 7
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
REACTION 1
CO2(g) 1
90 moles in 10 steps
GAS_PHASE 1
-fixed_pressure
-pressure 600
-volume 1
-temperature 65
CO2(g) 1
END
SOLUTION 1
temp 60
pH 7
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
REACTION 1
CO2(g) 1
90 moles in 10 steps
EQUILIBRIUM_PHASES 1
CO2(g) 100 0
REACTION_PRESSURE 1
1 600 in 10 steps
END
SOLUTION 1
temp 60
pH 7
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
REACTION 1
CO2(g) 1
90 moles in 10 steps
EQUILIBRIUM_PHASES 1
CO2(g) 100 0
REACTION_PRESSURE 1
1 600 in 10 steps
GAS_PHASE 1
-fixed_pressure
-pressure 1
-volume 1
-temperature 65
CO2(g) 1
END
dlparkhurst:
I'm not going to go through all the permutations. I'll just make a few comments.
In your first simulation, you did not include CO2(g) in the GAS_PHASE definition. So all 90 moles go into solution with a calculated pH of 87. 10 to 20 moles of solute is pretty much the limit, even for pitzer.dat. Results would be reasonable if you included CO2(g) in the GAS_PHASE.
"CO2(g) 100 0" in EQUILIBRIUM_PHASES indicates a bubble would form when the partial pressure in the solution reached 10^100 atm. I think that is probably black-hole kind of pressures. For your conditions, CO2(g) 2.78 0 would represent 600 atm.
You probably do not want CO2(g) as an EQUILIBRIUM_PHASE and in a GAS_PHASE. Pick one or the other.
MichaelZ20:
Hi David!
I paid attention to a strange behavior of gas phase and pH at small addition of CO2 (1 mole) when H2O(g) is considered.
Could you please comment?
SOLUTION 1
temp 65
pH 7 charge
pe 4
redox pe
units mmol/kgw
density 1
Cl 10
Na 10
-water 1 # kg
END
USE SOLUTION 1
REACTION 1
CO2(g) 1
1 moles in 100 steps
GAS_PHASE 1
-fixed_pressure
-pressure 600
-volume 1e-9
-temperature 65
CO2(g) 0
H2O(g) 0
USER_GRAPH 1
-headings RXN Gas_volume pH
-axis_titles "CO2 addition, mol" "Gas volume, L" "pH"
10 GRAPH_X RXN
20 GRAPH_Y GAS_VM * GAS("CO2(g)")
30 GRAPH_SY -LA("H+")
END
dlparkhurst:
That is a bug. All the gas should be dissolved. I'll have to check with Tony on how to fix the problem.
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