Mineral Precipitation

[serhatttt]

Hi,

I want to simulate a geothermal well in which we observed mineral precipitation. The well is approximately 550 meters, and the outlet temperature of the geothermal water is 168.6 °C. The reservoir temperature is 180 °C.
I prepared the code. Here is the code. However, when I run the code, I get the following error. I tried to increase the step, but it didn't work.
Thank you for helping.

ERROR: gas moles Total moles in gas phase has not converged.
Residual: -2.288531e-01

ERROR: Numerical method failed on all combinations of convergence parameters, cell/soln/mix 1
Stopping.

CODE:

DATABASE c:\phreeqc\database\pitzer.dat

SOLUTION 1
         temp           25
         pH             5.6
    units mg/L
    Ca             3020
    Mg             111
    Na             17700
    K              1925
    Cl             35300
    Alkalinity     85.8965 as HCO3 #104.8?
    S(6)           204 as SO4      #206.6  #also 83.3 S measured
    Si             189 as SiO2        #between 160-200
    Ba             6.82               #6.01
    Sr             142.5
    Li             22.6
    Fe             6.2               #added LW
END

# Raise temperature and pressure
# Equilibrate selected minerals if undersaturated
USE solution 1
REACTION_TEMPERATURE
180
REACTION_PRESSURE
50
EQUILIBRIUM_PHASES 1
    Anhydrite 0 10
    Barite    0 10
    Calcite   0 CO2(g)    10
    Chalcedony 0 10
SAVE solution 1
END

# Lower temperature and pressure
# Allow gas phase to form
# Precipitate minerals
INCREMENTAL_REACTIONS
USE SOLUTION 1
EQUILIBRIUM_PHASES 1
   Gypsum 0 0
   Anhydrite 0 0
   Barite 0 0
   Celestite 0 0
   Chalcedony 0 0
   #Quartz 0 0
   #SiO2(a) 0 0
   Calcite 0 0
   #Dolomite 0 0
   #Magnesite 0 0
   #Halite 0 0
   #Diopside 0 0
GAS_PHASE 1
    -fixed_pressure
    -pressure         3.56             #average wellhead pressure
    -volume           0.0542
    -temperature      168.6            #average wellhead temperature
        CO2(g)    0.             #0.472 #NCG=50% of steam (NCG analyses: 0.944)
        H2O(g)    0.             #0.5   #water is 50% of steam flow
REACTION_TEMPERATURE 1
         180.0 168.6 in 188 steps
REACTION_PRESSURE 1
         50.0 4.0 in 188    steps # minimum pressure 4 atm to allow convergence
   
SELECTED_OUTPUT
         -file Well.sel
         -reset false
   
USER_PUNCH
         -headings Depth_m CO2 H2O(g) Calcite Chalcedony Barite
    10 PUNCH -(TC-168.6)/((180-168.6)/550)
         20 PUNCH LOG10[GAS("CO2(g)")]
         30 PUNCH LOG10[GAS("H2O(g)")]
         40 PUNCH EQUI("Calcite")
    50 PUNCH EQUI("Chalcedony")
    60 PUNCH EQUI("Barite")

   
USER_GRAPH 1
    -headings               Depth Calcite Chalcedony Barite CO2(g) H2O(g) TC Pressure
    -axis_titles            "Depth, m" "Log10 Cumulative Moles" " Celsius or atm"
    -axis_scale x_axis      -600 0 auto auto
    -axis_scale y_axis      -8 auto auto auto
    -axis_scale sy_axis      -10 auto auto auto
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 a = (180 - 168.6)/550
20 b = 168.6
30 depth = (TC - b)/a
40 GRAPH_X -depth
50 GRAPH_Y LOG10[EQUI("Calcite")], LOG10[EQUI("Chalcedony")], LOG10[EQUI("Barite")]
60 GRAPH_Y LOG10[GAS("CO2(g)")], LOG10[GAS("H2O(g)")]
70 GRAPH_SY TC, PRESSURE
  -end
END

[dlparkhurst]

I think you more or less evaporated all of the water, resulting in high concentrations for the liquid phase. PHREEQC will have convergence problems at high concentrations and (or) low water volumes.

You have specified a fixed-pressure gas, which will use the pressure calculated for each depth. The gas volume will expand to be in equilibrium with the solution. The calculation at a pressure of 4.5 atm was successful, at which point the gas volume was about 400 liters. Given your initial GAS_PHASE definition, this is probably a much larger gas volume than you expect.

[serhatttt]

Dear David,

Thank you so much. Now it works.