NMR Investigation of Viscoelastic Surfactant Compatibility with Corrosion Inhibitors
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SummaryViscoelastic surfactants (VESs) have been successfully applied as acid-diversion fluids. However, high-temperature (<200F), interaction of VES with metallic cations, alcohol-based additives, and chelating agents all interfere with the apparent viscosity of VES-based acid and reduce its efficiency. Even though corrosion inhibitors constitute one of the most essential additives in acidizing, they can interfere with VES. Many other parameters also affect the performance of corrosion inhibitors, including tabular materials, acid types, and concentrations, as well as the presence of other additives that might interfere with the corrosion inhibitors. Hence, a wide range of corrosion inhibitors is available to address corrosion issues adequately. The present study characterizes the interactions of various types of industrial corrosion inhibitors with different types of VES-based systems, including zwitterionic and nonionic surfactants.In this work, we conducted viscosity measurements on VES-based solutions combined with different concentrations of tested corrosion inhibitor formulae to characterize the rheological properties of the VES-based acids. Visual tests were done to detect any incompatibilities. To understand the nature of the VES interactions with corrosion inhibitors at a temperature range of 78 to 200F, nuclear magnetic resonance (NMR) spectroscopy was conducted. Corrosion tests were carried out to determine the effects of VES on the performances of corrosion inhibitors.The results of rheological measurements show that adding different types of corrosion inhibitors, in the industrial concentration range, leads to change in the conformation of micellar structures and rheology of the VES-based solutions. The main interactions/reactions are acid-base reactions and hydrogen bonding. The results of this study also show that the amide part of VES is the leading functional group that can interact with corrosion-inhibitor solutions and cause alternation of micellar structures because of change in the repulsion forces between surfactant headgroups. Corrosion results indicate that the addition of VES solutions would not affect the performance of corrosion inhibitors significantly. The results presented in this study can be used to select corrosion inhibitors more efficiently and optimize their effectiveness in the presence of VES-based fluids. These results can be used to predict any probable interactions and rheological changes in VES-based stimulation fluids because of the addition of corrosion inhibitors.
