Impact of Fe (III) on the Performance of Viscoelastic Surfactant-Based Acids
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Viscoelastic surfactant (VES)-based acid systems have been used successfully in matrix and acid fracturing treatments. However, the existence of Fe (III) as a contaminant in such systems may lead to many problems, due to interactions between VES and Fe (III). Such interactions can reduce the effectiveness of VES-based acid systems and potentially lead to formation damage. In this study, two VES’s were selected and reaction mechanisms between VES and Fe (III) were studied. Rheological properties of these two surfactants were examined with various concentrations of Fe (III). An energy dispersive X-ray spectroscopy (EDS) was used to identify precipitates from reaction products. Inductively coupled plasma (ICP) was applied to measure iron concentrations, and the two-phase titration method was used to determine VES concentrations in all liquid phases of the sample. The effect of several chelating agents on the reaction of VES with Fe (III) was also examined. Experimental results indicate that the apparent viscosity of live VES-based acids (20 wt% HCl, 4 vol% VES) increased from 3 to 131 cp at a shear rate of 100 s-1 at room temperature when the Fe (III) concentration increased from 0 to 2,300 ppm, and started to decrease at higher Fe (III) concentrations. This is because of the electrostatic interactions between negative charged [FeCl4]- groups and positive charged amine groups in VES in live acids. Both surfactants interacted with Fe (III), and precipitates, which are complexes containing iron and VES, were noted at 5,000 ppm and higher concentrations of Fe (III). On the other hand, adding a chelating agent [1:1 mole ratio to Fe (III)] helped in reducing the apparent viscosity of the sample, which means that the chelating agent reacted with Fe (III) and reduced interactions between VES and Fe (III). At the same time, coreflood setup was also used. With a chelating agent, Fe (III) was recovered in 98%, which was much higher than that without any chelating agent (46%). These results provided a clue of the protection effect of a chelating agent on VES-based acid in Fe (III) containing environment. Adding a suitable chelating agent can minimize the impact of Fe (III) on VES-based acids.
Shu, Yi (2013). Impact of Fe (III) on the Performance of Viscoelastic Surfactant-Based Acids. Master's thesis, Texas A & M University. Available electronically from