Evaluation of the Impact of Ferrous Species on the Performance of a Poly(carboxylic acid)-Based Scale Inhibitor

This work aims to evaluate, from a static and dynamic perspective, the performance of a polycarboxylic acid-based scale inhibitor in the presence of iron ions (Fe^III). The static (jar test) and dynamic (tube blocking test) tests were performed according to NACE TM0197-2010 and NACE TM31105-2005 standards, respectively. The lowest inhibition concentration (LIC) was determined under flow conditions of oil wells. In addition, the influence of the concentration of Fe^III ions on the precipitation process was also evaluated. The scale deposits were analyzed by X-ray diffraction (XRD), infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results demonstrated that the scale inhibitor is chemically compatible and efficient with the selected brines, possessing a LIC of 30 mg L 1 in the absence of Fe^III ions. In the presence of Fe^III ions, the inhibitor proved to be inefficient and incompatible, and it was not possible to determine the LIC. The combined XRD, FTIR, and SEM analyses allowed us to identify the inhibitor’s mechanism of action as being one of complexation, poly(carboxylic acid)-Ca²⁺. Furthermore, analyses in the presence of Fe^III ions demonstrated a significant change in the morphology of the incrustation of CaCO₃ crystals. Additionally, it has been proven that Fe^III ions significantly affect the performance of the inhibitor. Finally, the results indicated that in the absence of high concentrations of Fe^III ions, the poly(carboxylic acid) scale inhibitors can be an option to mitigate operating costs resulting from the deposition of inorganic scale in oil wells.

Keywords:
scale inhibitor; polymer; poly(carboxylic acid); tube blocking tests; oil well; calcium carbonate