Time-Resolved Fluorescence for Real-Time Monitoring of Both Scale and Corrosion Inhibitors: A Game-Changing Technique

Abstract Inhibitor products have been widely used to reduce both steel corrosion and scale deposition on pipelines, tubings and safety valves in critical offshore sites. Their simultaneous injection with brine has gradually increased the lifetime of production wells with incontestable benefits for the oil and gas industry. However, the large use of such additives has not been followed by the development of any efficient technique of dosage that considers the strict requirements of an offshore platform. In this paper, we describe a novel method of chemical dosage that takes into account all the on-site technical and practical parameters, such as the quantification thresholds or molecule specificity, the real-time monitoring, the resistance and compactness of measurement device and a user-friendly interface of measurement. Current techniques of inhibitor monitoring that use elemental analysis (ICP, MS, …) for sub-ppm quantifications appear too complex for a successful long-term on-site industrial exploitation due to the bulky dimensions of apparatus and the delay and complexity of analysis. A long-term collaboration between University of Lyon and Total EP has defined a simple and accurate method for inhibitor monitoring based on the use of lanthanide tracers and the Time-Resolved Fluorescence (TRF) technique. We exploited the fact that inhibitor chemicals (i) are good chelators for lanthanide ions and (ii) amplify the luminescence signal of rare-earths. In this way we are able to collect the photon emission signal by TRF apparatus and dosing the inhibitors. The portability of the TRF device as well as the sensitivity of detection have been engineered in order to obtain a sub-ppm quantification threshold via 1-click task. Several carboxylates, phosphonates and sulphonates additives diluted in brine solutions has been easily measured out even in presence of residual oil. More than 20 commercial inhibitor solution samples were quickly prepared and dosed with an impressive linearity of response (R2 test > 0.996) in the 10 – 100 ppm range. Any further extension of range has been possible. In addition, we were able to quantify two inhibitors (scale – scale, scale – corrosion) in the same brine water. This technique certainly opens a new conception of smart chemicals management in oil and gas production for (i) a dramatic minimization of the injected compounds (ii) a reducing delay in pipelines monitoring, and (iii) a shut down of expenses of pipeline maintenance.