Hydrogen-Brine-Calcite Reaction

[Zitong]

Dear all,

I am trying to model subsurface hydrogen reactions with Calcite. The following is my code:

TITLE H2-Gas_Mineral_Reaction_in_Mondarra_Gas_Reservoir
   
Selected_Output
   -file out.xls
   -temperature true
   -totals C(4) C(-4) H(0) S(6) S(-2) Na Cl
   -kinetics Calcite
   -gases CO2(g) CH4(g) H2S(g) hdg(g)
   -water
   -charge_balance true
   -ionic_strength true
      
Rates   
Calcite
-start
1 REM PARM(1) = specific surface area of calcite, cm^2/mol calcite
2 REM PARM(2) = exponent for M/M0
10 si_cc = SI("Calcite")
20 IF (M <= 0 and si_cc < 0) THEN GOTO 200
30 k1 = 10^(0.198 - 444.0 / TK )
40 k2 = 10^(2.84 - 2177.0 /TK )
50 IF TC <= 25 THEN k3 = 10^(-5.86 - 317.0 / TK)
60 IF TC > 25 THEN k3 = 10^(-1.1 - 1737.0 / TK )
80 IF M0 > 0 THEN area = PARM(1)*M0*(M/M0)^PARM(2) ELSE area = PARM(1)*M
110 rate = area * (k1 * ACT("H+") + k2 * ACT("CO2") + k3 * ACT("H2O"))
120 rate = rate * (1 - 10^(2/3*si_cc))
130 moles = rate * 0.001 * TIME # convert from mmol to mol
200 SAVE moles
-end

   
Hdg(g)
   -start
   10 if (M < 0) then goto 70
   20 rate = 2.3e-09*(TOT("C(4)")/1e-3 + TOT("C(4)")) + 9.26e-8*(TOT("S(6)")/(1.e-4 + TOT("S(6)")))
   30 moles = rate * TIME
   40 if (moles > M) then moles = M
   70 SAVE moles
   -end   
END

#================
# Mondarra Sample
#================
Solution 1
    -temperature           117.85
    -density                0.949
    -pressure               88.8231 
    -pH                     10 charge
    units ppm
    Na                     47520
    Cl                     86500
    Ca                     5840
    K                      1152
    C                      596.7   as HCO3
    S(6)                   61.5 as SO4
    Mg                     771
    -water                 0.54
REACTION_TEMPERATURE 1
   117.85
REACTION_PRESSURE 1
   88.8231
   
Save Solution 1
END

Use Solution 1
KINETICS 1
Calcite
     -M0  6.5234893                    # initial moles   
     -tol 1e-8
     -parms 10 0.3

Hdg(g)
     -M0  3.340580489                  # initial moles   
     -tol 1e-8

-time_step 365 day in 365             # 365 time steps
-cvode   true

INCREMENTAL_REACTIONS true
Save Solution 2
   
END

I expect most of the calcite will dissolve in brine due to the addition of hydrogen gas. However, the amount of calcite bearly changes during the reaction for the whole year. Am I defining something wrong for the calcite rates and kinetics? Or my overall model has some problems. Any help would be greatly appreciated. Thank you very much!

Best Wishes,
Zitong

[dlparkhurst]

You should use Hdg when you want to simulate H2 as an inert aqueous species.

If you want H2 to react with C(4), you need to use H2(g). Try adding -formula H2 1 in your KINETICS definition for Hdg(g) to see if the results are more what you expect.

And run your simulation for 2 days rather than 365 until you get the results you are expecting.
 

[Zitong]

Dear Mr. Parkhurst,

Your suggestions are very useful. Thank you very much!

Best,
Zitong