Initial Geochemical Equilibrium between Minerals and Brine
I'm simulating CO2 injection into sandstone aquifer of synthetic brine, NaCl. I've read in several papers in which TOUGHREACT w/ ECO2N is used and something is mentioned like "batch geochemical modeling of water–rock interaction was performed to equilibrate the 1.0 M solution of sodium chloride with the primary minerals listed in Table 2 at a CO2 gas pressure of 0.1 bar and a temperature of 75 C".
I'd like to learn how the initial batch simulation is done using TOUGHREACT. Is it possible to send me a set of sample input files if you have done it?
Thanks a bunch,
you simply use your inputfiles of mineralogy, kinetic reactions, initial water composition, and initial pressure and temperature, which you probably have already created for your injection simulation. You remove any injection sources and you can also reduce your grid to 1 single cell. You let this simulation run for e.g. 1000 or 10000 years. The minerals will approach an equilibrium state, thereby changing the water composition.
Now you can start your injection simulation by using the final mineral and water composition from the end of your equilibration run for the input data in the chemical.inp file. Thats all.
Best regards, Lennard
Thank you very much for the reply, Lennard. I've done just what you suggested. What I found out is that the mineral assembly has completely changed after equilibrium is achieved, which is not desirable for me. I was wondering if there is way to not change the mineral composition and yet still find the brine composition that is at equilibrium with this rock?
The continuous mineral changes depend less on the brine composition, but rather on the primary mineral composition. If these are not (partially) stable against each other, they will continue to react, independently from your brine composition. You could try to reduce your minerals (e.g. represent your carbonate phases by only one carbonate mineral) to simplify the systems.
Thanks again, Lennard. The mineral assembly was measured for our rock sample, which is why I would like to stick to it. Indeed there are uncertainties associated with the measurements. I could try to simply my carbonate minerals into one, what other reasonable modifications you would also suggest?
Thanks for the sample files. The format does look slightly different from that of V2. I will try to run these and get back to you.