1D Reactive Transport Model

[syed]

Dear Brain,

I want to find how the concentration of fifferent species( in water) changes as it passes through the aquifer with distance and time as it reacts with the minerals present in the aquifer. But my model is not converging. Kindlly help //..

> # X1t script, saved Tue Apr 05 2016 by Administrator

> data = "C:\Program Files\Gwb\Gtdata\thermo.tdat" verify

> time start = 0 yr, end = 20 yr

> length = 100 m

> width = .3 m

> height = .3 m

> Nx = 100

> discharge = 5 m/yr

> permeability = -5 darcy porosity = 30

> scope = initial

> H2O = 1 free kg

> HCO3- = 0 mg/l

> Cl- = 0 mg/l

> balance on Cl-

> F- = 0 mg/l

> SiO2(aq) = 0 mg/l

> Al+++ = 0 mg/l

> Ca++ = 0 mg/l

> Na+ = 0 mg/l

> K+ = 0 mg/l

> pH = 7

> scope = inlet

> H2O = 1 free kg

> HCO3- = 513 mg/l

> Cl- = 1 mg/l

> balance on Cl-

> F- = .5 mg/l

> SiO2(aq) = 34.2 mg/l

> Al+++ = .033 mg/l

> Ca++ = 56.49 mg/l

> Na+ = 63.3 mg/l

> K+ = 1.997 mg/l

> pH = 7.17

> react 34 "wt fraction" of Quartz

> react 7 "wt fraction" of Albite

> react 48 "wt fraction" of Muscovite

> react 7 "wt fraction" of Anorthite

X1t >

[Brian Farrell]

Hi syed,

The Geochemist’s Workbench is at its core a thermodynamic modeling program that solves mass balance and mass action equations. The “zero” values you’ve specified for the component concentrations don’t work with these. The program can, however, handle very small numbers (for example, 1e-9 mmol/kg) which you can use in place of the “zero” values. For more information, please see section 7.2, Equilibrium models, in the GWB Essentials Guide.

By the way, it’s a good idea to start with some simple calculations in SpecE8 or React before you set up a reactive transport model. You could start, for example, by equilibrating your inlet fluid in SpecE8 to understand its composition, then moving on to the initial fluid, or the initial fluid and rock system. You may find that it's necessary to change the charge balancing ion, as described in the section referenced above.

Hope this helps,

Brian Farrell

Aqueous Solutions LLC