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Author Topic: Mineral dissolution/precipitation for CO2 injection  (Read 330 times)

261239

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  • Posts: 1
Mineral dissolution/precipitation for CO2 injection
« on: May 06, 2022, 11:09:42 AM »
Dear all,

I am a master student working with modelling the behaviour of minerals when CO2 is injected to the reservoir. I am interested to show how minerals will dissolve and precipitate due to the acidic environment created by the dissolved CO2 into the formation water. Since I am new to PHREEQC, it would be very nice to get some feedback from the more experienced users.

To model the behaviour, I have built an equilibrium model based on the inputs from Liu et. al (2018)- https://www.mdpi.com/2071-1050/11/2/317
Solution 1 is created based on a fluid analysis for the Northern Lights CCS- project in Norway.
One of my many questions, is why doesn’t magnesite and halite precipitate when both CO3 (-2) /Mg2+ and Na+/Cl- should exist in the solution once CO2 is dissolved to the water. I am also wondering what the difference between adding undersaturated CO2 in the equilibrium phases versus using the GAS_PHASE and REACTION adding X moles stepwise to the solution?
Code: [Select]
# Mineral trapping- saline aquifer
TITLE Aurora

PHASES
Magnesite
        MgCO3 = Mg+2 + CO3-2
        log_k   -8.029
        delta_h -6.169  kcal


Halite
        NaCl = Na+ + Cl-
        log_k   1.582
        delta_h 0.918   kcal

SOLUTION 1
    temp      115
    pH        6.1
    pe        4
    redox     pe
    units     mg/l
    density   1
    B         49.1
    Ba        389
    Ca        6540
    Fe        0.1
    K         5580
    Mg        636
    Na        17800
    Sr        697
    Br        250
    Cl        45600
    -water    1 # kg

   
EQUILIBRIUM_PHASES 1
    Albite    0 0.025  #NaAlSi3O8
    Anhydrite 0 0.007   #CaSo4
    Ca-Montmorillonite 0 0.005
    Calcite   0 0.133 #CaCO3
    Chlorite(14A) 0 0.001 #CiO2
    Dolomite  0 0.083 precipitate_only  #CaMg(CO3)2
    Illite    0 0.021 #
    K-feldspar 0 0.025
    Kaolinite 0 0.036
    Pyrite    0 0.011 #FeS2
    Quartz    0 0.558 #SiO2
    Magnesite 0 0 #MgCO3
    Halite 0 0 #NaCl
       
GAS_PHASE 1
    -fixed_pressure
    -pressure 78.95386
    -volume 1
    -temperature 50
    CH4(g)    0
    CO2(g)    0
    H2(g)     0
    H2O(g)    0
    H2S(g)    0
REACTION 1
    CO2(g)      1
    10 moles in 1 steps
   
Save Solution 1
Save Equilibrium_Phases 1
END
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dlparkhurst

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Re: Mineral dissolution/precipitation for CO2 injection
« Reply #1 on: May 06, 2022, 04:05:19 PM »
The initial solution is undersaturated with halite, and addition of CO2 does little to change the saturation index; so, halite does not precipitate.

Likewise, magnesite is undersaturated  (SI -1.3) after the addition of CO2 and precipitation of calcite and dolomite.

Note that the reaction occurs at 115 C rather than 50 C, which is defined in GAS_PHASE. 50 C (and 1 L) would be used to calculate the initial gas composition if components were not all zeros.

Using a fixed pressure GAS_PHASE allows the volume of the gas phase to vary. If the sum of the partial pressures of the components are less than the total pressure, the gas phase will not exist. If sum of partial pressures exceeds the total pressure a gas phase will exist and its volume will adjust to produce equilibrium between the gas phase and the solution.

If you use equilibrium phases with a specified number of moles of CO2 available to react, either all of the CO2 will dissolve, or the solution will be brought to equilibrium with the specified log10 partial pressure.


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