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Hi GWB Forum,


I am currently working on my thesis on corrosion and scaling in thermal waters of geothermal power stations. I hope GWB can help me analyse these reactions in geothermal brines (high pressure, high temperature). Therefore I downloaded the student version.

I have the following questions.


1) Can GWB simulate corrosion?


2) As far as I know mineral precipitation can only be calculated with the standard version of GWB. Is there a way to simulate scaling/precipitation in the student version?


3) As far as I know pressure is not included in the calculation, but how can I consider pressure? Do I have to use another database of GWB to include pressure in the calculation? Do I have to use a totally different software like PhreeqC to consider high pressure?


4) Does GWB automatically calculate the amount of CO2 contained in thermal water, if I include other parameters like HCO3-, pH etc.

For example I have an analysis of thermal water, where the brine was first degassed and content of CO2 was measured. Then the amount of ions like HCO3- was measured. Since I can only put either CO2 or HCO3- into the calculation, does GWB conclude CO2 content from the other values like HCO3- or in other words is one of both values sufficient?


For instance I'd like to simulate scaling/precipitation of calcite in a geothermal power station, that pumps the brine from a depth of about 4350 m through pumps, heat exchangers etc. and reinjects it. If I can calculate the solubility of minerals like calcite or can simulate the precipitation for the different locations/parameters in the power station, I can estimate the extent and location of scaling. The pressure is an important parameter in this example because the brine loses pressure, which leads to degasing of CO2, which leads to precipitation. That's why I need to consider it.


Thanks in advance for the answers.

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1) Yes, you can certainly apply the GWB in corrosion research.


2) You can calculate the saturation state of minerals in a fluid using SpecE8, which is included in the GWB Student Edition, but to precipitate the minerals you’ll need React, which is included in the GWB Standard package. You might also want to use X1t and X2t from the Professional package, if you’re interested in reactive transport. Finally, Act2 and Tact, included in the GWB Student Edition, can be useful for understanding the geochemical conditions under which various minerals are stable.


3) You can use a thermo dataset compiled at the pressure of interest, but hydrothermal chemists not uncommonly assume the effects of confining pressure are small compared to the uncertainty in determining log Ks and activity coefficients. Note, however, that gas partial pressures are almost invariably significant. You account for the partial pressure of a coexisting gas by setting its fugacity.


4) The HCO3- basis entry in SpecE8 most commonly (and in its default state) is set up as a bulk constraint, meaning it refers to the sum of carbon species (CO2, HCO3-, CO3--, CaHCO3+, etc.). If you select the “free” option from the units pulldown, however, you’re specifying that the concentration you entered refers only to the individual ion. You should compare your constraints with the concentrations of individual species and the thermodynamic components in SpecE8’s output to verify your calculations. For more information, please see 2.1 Configuring a calculation, 2.2 Setting and constraining the basis, 7.1 Example calculation, and 7.2 Equilibrium models in the GWB Essentials Guide.


If you’re referring to fluid produced from a wet-steam well (vapor and liquid phases), then you’ll need to use React to recombine the vapor and liquid phases to find the composition of the original fluid. For more information, see 23.3 Geothermal fields in Iceland in Craig Bethke’s Geochemical and Biogeochemical Reaction Modeling text.




Brian Farrell

Aqueous Solutions LLC

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