CO2-brine-rock interaction

[sophiekristin]

Hey,
I'm pretty new to PHREEQC and want to reproduce the results in this paper: https://doi.org/10.1016/j.chemgeo.2022.120742 (Geochemical modelling of CO2 interactions with shale: Kinetics of mineral dissolution and precipitation on geological time scales, 2022)
It is modelling the interactions between brine (NaCl solution), CO2 and sediment rock (Quartz, Calcite, Dolomite, Illite, Kaolinite, Pyrite and K-Feldspar).
My code so far looks like this, however it doesn't produce the expected results:
EQUILIBRIUM_PHASES 1
    Quartz    0 0.2763
    Calcite   0 0.1798
    Dolomite  0 0.0005
    Illite    0 0.0345
    Kaolinite 0 0.0403
    Pyrite    0 0.015
    K-feldspar 0 0.0036

GAS_PHASE 1
    -fixed_pressure
    -pressure 177
    -volume 1
    -temperature 70
    CO2(g)    177

SOLUTION 1
    temp      70
    pH        7
    pe        4
    redox     pe
    units     mol/l
    density   1
    Na        1
    Cl        1
    -water    1 # kg

I assume one problem is that I'm not including surface area for each mineral, which I have given, however don't know how to include in PHREEQC.
I'm very grateful for any help I can get (also for hints if there are other things obviously missing/wrong in the code).
Thank you very much for your help!
Best regards Sophie

[dlparkhurst]

I couldn't really make sense of their paper, but maybe you can. The surface area would only be important for the kinetics calculation.

Here is the way I would calculate the pure equilibrium system. CO2(g) has a fixed partial pressure at 10^2.25 = 177 atm. Some of the minerals dissolve completely, so check the calculation of the moles:water ratios. I used the phreeqc.dat database.

Code: [Select]

EQUILIBRIUM_PHASES 1
    Quartz    0 0.2763
    Calcite   0 0.1798
    Dolomite  0 0.0005
    Illite    0 0.0345
    Kaolinite 0 0.0403
    Pyrite    0 0.015
    K-feldspar 0 0.0036
    CO2(g)    2.25 10

SOLUTION 1
    temp      70
    -pressure 177
    pH        7
    pe        4
    redox     pe
    units     mol/l
    density   1
    Na        1
    Cl        1
    -water    1 # kg


[sophiekristin]

Hello dlparkhurst,
Thanks a lot for your fast reply and your help!
Unfortunately, I don't understand the paper that well either but maybe with your tips and code, I can make sense of it.

[dlparkhurst]

If you are going to get into kinetics, you might as well get the latest version of PHREEQC or PhreeqcI, version 3.8.0 at https://github.com/usgs-coupled. Look for the Releases on the right side of the page for each program.

This version has new capabilities for calculating rates. There is a new database from Eric Oelkers and the Carbfix group called Kinec.v2.dat, which has RATES definitions for an extensive set of minerals. Another new database for rates is phreeqc_rates.dat, which has new keyword data blocks named RATE_PARAMETERS_HERMANSKA (Hermanska and others, 2023), _PK (Palandri and Kharaka, 2004), and _SVD (Sverdrup and others, 2019). New Basic functions RATE_HERMANSKA, _PK, and _SVD calculate rates (mol/m^2/s) for minerals listed in the data blocks. Note that you must define a RATES definition for each mineral using a RATE_ basic function and account for the surface area factor (see examples in phreeqc_rates.dat).