Characterization of Iron Interaction with Viscoelastic Surfactant VES-Based Stimulation Fluid

Viscoelastic surfactant (VES) have been successfully applied as acid-diversion fluids. However, high temperature, interaction of VES and Fe(III), addition of alcohol-based additives, and chelating agents all interfere with the apparent viscosity of the VES-based acid and reduce its efficiency. In the present study, the interactions of Fe(III) with a new type of VES-based acid system, which can be applied effectively for diversion at high temperatures, were characterized. Viscosity measurements were conducted on the VES-based acid in the presence of different concentrations of Fe(III) to characterize the rheological properties of the VES-based acid. The results showed that addition of Fe(III) in the concentration range of 2000 to 10000 ppm, lead to increase in the viscosity of the VES-based acid even at room temperature. Higher concentration of Fe(III) (more than 40000 ppm) lead to phase separation of VES out of the acid and formation of a brown gel-like material, which is considered as the main cause of formation damage by VES-based diversion fluids. IR spectroscopy was employed to understand the nature of the VES interactions with Fe(III) in live acid conditions. Also, UV-vis spectroscopy was conducted to determine stoichiometry of the reaction as well. The results show that interaction of amide part of the VES with Fe(III) that results in screening the repulsion forces between surfactant head groups and formation of wormlike micelles is the primary reason for increase in the viscosity. To the best of authors' knowledge, although Formation damage caused by VES-based system due to iron contamination were reported previously both in the laboratory studies and field applications, the present paper is the first mechanistic attempt to characterize and understand the nature of a VES-based system interaction with Fe(III) as the driving force for the occurrence of reported formation damage. The findings of the present study can be utilized to further investigation of the effects of additives on the performance of VES-based systems.