Measurement of electrolyte resistance fluctuations generated by oil-brine mixtures in a flow-loop cell

Measurements of current and electrolyte-resistance fluctuations between two working electrodes in a flow-loop cell have been carried out with the objective to assess and/or monitor corrosion and characterize hydrodynamic flows in pipelines. Linear flow 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 confirmed. The current fluctuations present a very complex and nonmonotonic behavior with the VOC, which yields corrosion monitoring virtually impossible in these conditions. Conversely, the electrolyte-resistance fluctuations appeared to be a reliable and very sensitive tool for the real-time analysis of hydrodynamic conditions and flow 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 identification 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%).