Hydraulic optimization of the reaction zone around an injection well during subsurface iron removal (SIR)

In subsurface iron removal (SIR), oxygen-enriched water is injected into an aquifer to create a reaction zone. Ahrns et al. (2017) simulated a doubling of the efficiency coefficient by the inactivation of well screen sections during injection for a vertical SIR pilot well penetrating an aquifer with varying dissolved iron concentrations. The optimized injection regime was adopted conceptually in a pilot SIR test. An inflatable packer was used to manipulate the outflow distribution. The packer was inflated before the injection phase then evacuated with a vacuum pump before pumping while remaining inside the casing. Cycles with conventional injection were performed first and iron breakthrough was monitored in the pumped water. Subsequently when the packer was used, iron removal increased by 25% and the efficiency coefficient by 50% for an adopted reference value of 5.0 mg/l. Although the study site was unfavorable for SIR because of the unfavorable low alkalinity (pH in the re-and infiltrate decreased down to 4.2), the injectant could have been pretreated by the addition of alkalis prior to injection. This was not considered in the simulation and iron concentrations were above the limits commonly used in practice. However, the overall use of an optimized injection will still be presented.

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