Etude du comportement stochastique de systèmes diphasiques par analyse couplée du bruit électrochimique et d'images vidéo.

This work is aiming at coupling acquisitions of electrochemical noise and video images to study electrochemical systems with a strongly stochastic behaviour such as gas-evolving electrodes and hydrodynamic flows of oil-brine mixtures of various composition. The mean radius and the mean detachment rate of hydrogen bubbles evolving at a current density between 5 and 500 mA/cm2 on an horizontal platinum electrode have been estimated from the electrolyte-resistance fluctuations generated. The analysis of the video images allowed the results to be validated at current densities lower than 100 mA/cm2. The electrolyte-resistance fluctuations close to or between two iron electrode(s) at the corrosion potential in an oil-brine mixture with a volume oil content between 0 and 80 % are extremely sensitive to the oil content of the mixture and allow changes in hydrodynamic flows to be monitored in real time. The mean electrolyte resistance measured between two electrodes in a pipe for a mixture circulating at a flow rate of 2 m/s and the theoretical resistance of the Maxwell model are in good agreement.Le but de ce travail est de coupler des acquisitions de bruit électrochimique et d'images vidéo pour étudier des systèmes à caractère fortement aléatoire, le dégagement de bulles gazeuses sur électrode en milieu liquide et l'écoulement de mélanges huile-saumure de composition variée. Le rayon moyen et la fréquence moyenne de détachement de bulles d’hydrogène se dégageant à une densité de courant entre 5 et 500 mA/cm2 sur une électrode horizontale de platine ont été déterminés à partir des fluctuations de résistance d’électrolyte générées. L'analyse des images vidéo a permis de valider les résultats pour les densités de courant inférieures à 100 mA/cm2. Les fluctuations de résistance d’électrolyte près d'une ou entre deux électrode(s) de fer au potentiel de corrosion dans un mélange huile-saumure avec un pourcentage en volume d’huile entre 0 et 80 % sont extrêmement sensibles à la composition du mélange et permettent de suivre en temps réel les changements d'écoulement hydrodynamique. La résistance d’électrolyte moyenne entre deux électrodes mesurée pour un mélange circulant dans un canal à la vitesse de 2 m/s et la résistance théorique du modèle de Maxwell sont en bon accord

Measurement of Electrolyte Resistance Fluctuations Generated by Oil-Brine Mixtures in a Flow-Loop Cell

International audienceMeasurements of current and electrolyte-resistance fl uctuations between two working electrodes in a fl ow-loop cell have been carried out with the objective to assess and/or monitor corrosion and characterize hydrodynamic fl ows in pipelines. Linear fl ow velocities of 1 m/s and 2 m/s were used to ensure different hydrodynamic conditions for oil-brine mixtures with a large range of volumetric oil content (VOC) from 0% to 80% (water-cut from 100% to 20%). Previous results obtained in conventional cylindrical cells, in which the oil-brine mixture was homogenized with a rotating magnet, have been confi rmed. The current fl uctuations present a very complex and nonmonotonic behavior with the VOC, which yields corrosion monitoring virtually impossible in these conditions. Conversely, the electrolyte-resistance fl uctuations appeared to be a reliable and very sensitive tool for the real-time analysis of hydrodynamic conditions and fl ow composition that can be used for the indirect assessment of oil-brine corrosivity. The analysis of the mean electrolyte-resistance values has shown an excellent agreement with the theoretical predictions of Maxwell's model of the electrical conductivity in two-phase media over the whole VOC range investigated, provided that hydrodynamic conditions ensure the homogeneity of the mixture. Electrochemical measurements have been complemented with the analysis of video images that allowed identifi cation of the oil/brine mixture structure close to the pipe wall and the distribution function of the oil-droplet diameter, which were shown to be spherical for VOCs up to 60% (water-cut down to 40%)