Co2-acid-rock interactions

[Victor]

Dear PhreeqC Community,

I am currently working on a PhreeqC model to replicate laboratory results for CO2-brine-rock and CO2-acid-rock interactions. While the initial CO2-brine-rock simulation closely matches experimental data, I am facing challenges in simulating acid-rock interactions.

Specifically, I want to include acids such as hydrochloric acid (HCl), acetic acid (CH3COOH), and formic acid (HCOOH) in my model. However, I have been unable to find them in the default PhreeqC database.

Is it possible to define a custom database within PhreeqC that includes these specific acids?

For reference, my current code on the CO2-brine-rock interaction is added to help.

I would greatly appreciate any insights on how to create these acidic solutions within my model.

"

Code: [Select]

TITLE Geochemical Modelling of CO2-brine-Rock (Sample CS-1)

# initial solution (brine)
SOLUTION 1 NaCl brine @70g/L
    temp      60
    pH        6.65
    pe        4
    redox     pe
    units     mol/l
    density   1.043
    Cl        1.19  # NB. moles = mass/Mol mass
    Na        1.19
    -water    1 # kg

# Supercritical CO2 injection
EQUILIBRIUM_PHASES 1
    CO2(g) 0 10   

# Potential ionic exchange during CO2 dissolution
EXCHANGE 1
    X 1.0
    equilibrate with solution 1

MIX 1
    1 1.0

USE solution 1

REACTION_PRESSURE 1
    109  # Experiment conducted at 1600psi = 108.87atm

REACTION_TEMPERATURE
    60 # C

# Initial mineralogical composition based on XRD results. (%concentration)
EQUILIBRIUM_PHASES 2
    Dolomite  0 0.029
    Hematite  0 0.019
    Illite    0 0.0311
    Kaolinite 0 0.065
    Quartz    0 0.8222
    Siderite  0 0.017

# Transport properties
TRANSPORT
    -shifts                20
    -lengths               0.0781
    -dispersivities        0.0381
    -diffusion_coefficient 1e-09
    -thermal_diffusion     2   1e-09

REACTION 1
    CO2(g) 2
    0.03 moles in 120 steps

USE equilibrium_phases 2

# Output options
SELECTED_OUTPUT
    -file output.txt
    -high_precision true
    -state true
    -totals Fe Na Cl Al Ca K Si Mg
    -saturation_indices true Halite CO2(g) Dolomite Hematite Illite Siderite

# Output porosity and mineral volumes left post dissolution
USER_PUNCH
    -headings Time Porosity pH Quartz Kaolinite Illite Dolomite Hematite Siderite
    -start
10 PUNCH TIME, 0.21, -LA("H+"), EQUI("Quartz"), EQUI("Kaolinite"), EQUI("Illite"), EQUI("Dolomite"), EQUI("Hematite"), EQUI("Siderite")
    -end

END"

[dlparkhurst]

You can add hydrochloric acid with any of the databases.

Code: [Select]

REACTION
HCl 1
0.1 mol

Acetate and formate need definitions for their acid/base reactions and their capacity as ligands. Acetate is defined in llnl.dat, minteq.dat, minteq.v4.dat, and sit.dat. Formate is defined in minteq.dat and minteq.v4.dat. It is possible to take definitions from one of these databases and insert them in other databases like phreeqc.dat or wateq4f.dat, or better, include the definitions in your input file if they are not in the database you are using. The program lsp at phreeplot.org may be useful to extract the acetate or formate definitions if you want to insert them in another database or input file.

Provided SOLUTION_MASTER_SPECIES and SOLUTION_SPECIES are defined for Acetate or Formate (either in a database or input file), you can use REACTION to add them in the same way as HCl.

Code: [Select]

REACTION
HAcetate 1
0.1 mole


[Victor]

Thanks for your help, David.

I was able to get things working by using some information from the core10.dat database. (I get error anytime I change the default database).

However, I would still like to understand how to add species to the database manually. I tried including acetic acid (CH3COOH) in my input but encountered some errors. Any insights on addressing these errors and manually adding species would be greatly appreciated!

Below is what I tried doing initially by adding the species manually:

Code: [Select]

SOLUTION_MASTER_SPECIES
    CH3COOH    CH3COOH # adding acetic acid

SOLUTION_SPECIES
    CH3COOH = CH3COO- + H+   # This species was obtained from the core10.dat database
        -log_k -4.7572
        -gamma 4.5
        -analytical_expression -0.96597e2 -0.34535e-1 0.19753e4 0.38593e2 0.30850e2

######## Below are the error messages I got ###########
ERROR: Expected alkalinity for master species in master species input.
ERROR: Elements in species have not been tabulated, CH3COOH.
ERROR: Reaction for species has not been defined, CH3COOH.
ERROR: Calculations terminating due to input errors.


When I switch to using just the core10.dat database, I get the following errors

Code: [Select]

ERROR: Phase not found in database, Illite.
ERROR: Master species not in database for X, skipping element.
ERROR: Calculations terminating due to input errors.

Thank you in advance

[dlparkhurst]

Look at the manual or use PhreeqcI to enter data for SOLUTION_MASTER_SPECIES. There are more fields than you have entered.

Every phase that you use in EQUILIBRIUM_PHASES must be defined in a PHASES data block, either in the database or the input file. If a phase is not in the database, you can define it in the input file. Note that if you are using an ion-association database, you can copy PHASE definitions from other ion-association databases into your input file with a few provisions. All of the elements in the phase must be defined in the database (or input file). In addition, some databases use SiO2(aq) as the master species for Si and some use H4SiO4.  To copy from one to another, you must rewrite the reaction to use the appropriate master species using the equation H4SiO4 = SiO2 + 2H2O. Log K for the reaction is assumed to be zero

Do not define acetate with a reaction involving the element C. Acetate will never be stable in a solution relative to CO2 and CH4. Use the definitions in llnl.dat or one of the other database that define Acetate. Defining a separate element Acetate eliminates redox reactions with other carbon species or other redox elements.

I don't know how you used X, but it is used in phreeqc.dat and some other databases in defining EXCHANGE reactions. Again you need EXCHANGE_MASTER_SPECIES and EXCHANGE_SPECIES defined in the database or the input file if you want to define EXCHANGE with the exachanger X.

[Victor]

Hi David,

Thanks again for your initial help!  Your insights pointed me in the right direction.

I went through the documentation and was able to fix the errors I was encountering when adding species manually. I also realized the "MIX" component wasn't affecting my results, so I removed it for now.

It seems specifying just the chemical formula for the acids is working perfectly!

Thanks again for your assistance.