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Recirculation Wells

Bob Smith

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I am trying Xt2 to simulate a field experiment that my group conducted in the “Anderson” well gallery at the Rifle, CO site to created a bioactive zone using recirculation wells.  In the experiment, water was pumped from a production well (M-07) and amended with urea and molasses using a metering pump and an in line pipe-mixer for 12 days and reinjected (well M-02) up-gradient.  The pumping well was shut off and the reactive zone was monitored for 400+ days.  I understand how to create the recirculation cell in Xt2 (GWB12), but I am struggling with an approach to add the urea and molasses to the injected water.  Can two fluids be injected simultaneously into a single well? Or should I look for another approach such as creating a fictive solid placed in the grid block with the well with a defined, constant release rate? Any insights would be welcome.

In addition, the Goldschmidt Reactive Transport Workshop was great.


Bob Smith

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Hi Bob,

There are a couple methods you  might try. One idea is to add the urea and molasses as simple reactants. Simple reactants are field variables, meaning the mass reacted can vary spatially. You might use the node-by-node editor to set the reactant mass everywhere in the domain to 0 except for the node containing the injection well. Keep in mind that simple reactants are added continuously throughout the simulation, though, unless you specify a cutoff value. I think you’d need a cutoff to ensure the urea and molasses are added only during the first 12 days. For more information, please see 3.1 “Titration paths” in the GWB Reaction Modeling Guide, the Heterogeneity Appendix in the GWB Reactive Transport Modeling Guide, and 9.89 “react” in the GWB Command Reference.

Alternatively, you could define a new fluid for the urea and molasses solution (with negligibly small amounts of the rest of your basis entries) and add a new injection well. Beginning with GWB11, you can specify any number of wells within a single nodal block. X2t determines from the position you specify the nodal block a well would fall within, then uses the corresponding nodal point as the actual position. You could define two sources of fluid (the direct injection well and the recirculation well) where the mixed fluid is being injected. With wells, of course, you turn pumping on and off whenever you like, so the 12 day injection interval is no problem.

I’m glad to hear you enjoyed the workshop at the Goldschmidt Conference. It was nice to meet you in person.

Hope this helps,

Brian Farrell
Aqueous Solutions LLC

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