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[OLD] Injection of water into an aquifer


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From: Gregg W. Jones

Subject: Injection of water into an aquifer

I'm trying to simulate the injection of potable water that is fresh out of a water treatment plant into an aquifer storage and recovery well. The storage zone is in the Suwannee Limestone in the Floridan Aquifer. I am interested in the composition of the mixed fluid. I'm assuming the treatment plant water is equilibrated with the atmosphere. I am interested in getting the sulfate/sulfide ratio at each reaction step. I am assuming the sulfide concentration is virtually zero in the water out of the treatment plant. Prior to mixing, the sulfate and sulfide concentrations in the formation water are 1,526 mg/l and 14.5 mg/l respectively. I ran the model first without swapping in HS- and it ran fine. At the pH of the formation water, sulfide is present mostly as HS-. When I swapped HS- for O2(aq), the model didn't run and the message was "initial solution is too supersaturated". Am I setting the problem up correctly and why does the model not run when I try to get sulfide into the basis? I'm using release 3.2.1 I start by characterizing the injection water from the treatment plant.


Swap O2(g) for O2(aq)

Swap CO2(g) for H+

f O2(g) = 0.2

log f CO2(g) = -3.5

T = 25.8

TDS = 325 mg/l

Ca++ = 88.9 mg/l

Mg++ = 9.5 mg/l

Na+ = 61 mg/l

HCO3- = 81.9 mg/l

S04-- = 114 mg/l

Cl- = 28.7 mg/l

Fe++ = 0.1 mg/l

K+ = 1.9 mg/l



Pickup reactants = fluid

Reactants times 5

Now I characterize the formation water.


T = 26.4

TDS = 2510 mg/l

pH = 6.99

Ca++ = 399 mg/l

Mg++ = 148.5 mg/l

Na+ = 52.7 mg/l

HCO3- = 129.5 mg/l

SO4-- = 1526 mg/l

Cl- = 97.2 mg/l

Swap HS- for O2(aq)

HS- = 14.94 mg/l

Fe++ = 0.07 mg/l

K+ = 5.2 mg/l



From: Craig Bethke

Subject: Re: Injection of water into an aquifer

Your fluid is very supersaturated with respect to pyrite, which is causing your problems. Since in reality pyrite isn't likely to form in this system, I suggest you simply suppress it. Also, I think that instead of swapping sulfide for dioxygen, you want to decouple sulfide. This way, you can create a model in redox disequilibrium.

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