Determination of scaling ions in oilfield produced water by laser-induced breakdown spectroscopy

Abstract

The deposition of inorganic scale in pipelines used in the exploration of oil on marine platforms caused by the precipitation of metal ions is one of the main causes for reduction in the production process of the oil industry. Therefore, a simple and efficient method for the determination of scaling ions in oilfield produced water using laser-induced breakdown spectroscopy (LIBS) was developed. Filter paper was used as a cellulosic solid substrate for phase conversion of Mg(II), Ca(II), Sr(II) and Ba(II) ions in saline medium. Instrumental parameters such as laser pulse energy, gate delay and gate width were evaluated along with sample preparation parameters, such as the type of cellulosic, polymeric or glass substrate, sample volume deposited on the substrate and the time required for drying, use of internal standards and effect of salinity. Energy-dispersive X-ray spectroscopy (EDS) analysis showed a homogeneous distribution of the analytes on the microfibers of the filter paper. The results indicated that salinity significantly affects the emission intensities of the analytes as well as the relative standard deviations, which ranged from 5.2 to 8.1% and 9.2 to 12.9% for samples prepared in water and in a solution with a salinity of 30‰, respectively. The spectral data were normalized using the C emission line (C I 247.88 nm) to minimize the matrix effect of the highly saline waters. Under optimized conditions and considering data without and with normalization, it was possible to obtain limits of detection ranging from 1.0 to 11.4 mg L⁻¹, with a linear response range from 20 to 60 mg L⁻¹ for Mg(II), Ca(II) and Sr(II) ions and from 40 to 80 mg L⁻¹ for Ba(II) ions in aqueous solutions. The determination of scaling ions in produced water by LIBS showed that data normalization provides results that do not significantly differ from those obtained by inductively coupled plasma atomic emission spectroscopy (ICP OES) at a confidence level of 95%, demonstrating that the developed method has potential application to monitor the concentration of scaling ions in produced water, helping prevent scaling in the pipelines of oil platforms.