newbie help with pH plot

[Ken]

Hey

 

I have just opened GWB-standard (v7) for the first time and wondered if anyone could help me with what is probably a very simple exercise (I apologize in advance for ignorance).

 

I am trying to make plots of the change in pH of a model CO2 bearing aqueous hydrothermal fluid as it cools at different pressures. I am interested to see if there are any "cliffs" in pH. The details on the fluid and the system are as follows

 

aqueous fluid cooling from 300C to 150C

pressure could have been anywhere from 200 - 700 bars

CO2 = 2 - 4 mol%

CH4 = 0.2 - 2.3 mol%

H2S = 0.01 - 0.2 mol%

NaCl = 2 - 4 wt%

the fluid also contained He and the following trace elements Sb, Hg, As, Au, Ag, Te, Tl, Rb, W, Cu,

There was also Si (enough to become saturated in quartz as it cools below 200C), Ca, K in the fluid

 

Could give me pointers on how to produce plots of T vs pH for my model fluid as it cools (for a range of pressures and CO2 contents)?

 

Thanks

Ken

[Ken]

oops... Actually I just realized it is not pH that I should be interested in but calcite solubility

[Tom Meuzelaar]

Hi Ken:

 

I'd start by taking a look at polythermal reaction path models in the Reaction Modeling User's Guide. You should be able to view the pH vs. temperature trends in Gtplot. Dealing with variable pressures is going to be a bit trickier, given that the database is compiled for a single confining pressure (1 atm). For most aqueous species and minerals, the equilibrium constant data does not change significantly, but for gases it is a different story altogether, and you may need to make some database modifications.

 

Hope that helps get you started,

 

Tom Meuzelaar

RockWare, Inc.