Accurate detection of scale inhibitor residuals from produced waters is a critical part of flow assurance. Tagged scale inhibitors have been developed to improve the detection limit. The purpose of having multiple different tags on the same inhibitor chemistry is to be able to separately detect the level of inhibitor for several subsea templates when commingled in a single flow back line to a production facility. These new tagged scale inhibitors combine the excellent scale inhibition performance of sulphonated copolymers with fluorescence technology, delivering lower detection limits of residual inhibitor concentrations.

The authors have developed a testing protocol that enables accurate detection of two tagged scale inhibitors from a produced water sample using fluorescence spectroscopy. The development of the chemistry and detection monitoring technique, and the results demonstrating the validity of the analysis method are discussed. The method has been validated and tested with real produced water samples collected from a subsea field in the North Sea. The samples were spiked with unknown concentrations of two fluorescent tagged sulphonated copolymers with concentrations between 0 and 200 ppm as product.

The tested products have specific excitation and emission wavelengths, enabling the independent detection of both products with a fluorometer without any disturbing effect. The test results clearly show that the protocol can be used for analyzing low concentrations of scale inhibitor polymers from produced waters. The final goal is to analyse residual inhibitor concentrations using a portable fluorometer delivering onsite detection, and thus enabling real-time monitoring of the scale inhibitor squeeze returns.

This fluorescence technology can be used in combination with a phosphorus tagged scale inhibitor and ICP analysis method to detect three products from the same commingled sample. The validity of the protocol has been confirmed and has generated great interest in the oil and gas industry where accurate detection will maximize safe and economic oil production.

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